1. Introduction 1.1 Polymer...

1. Introduction

1.1 Polymer blends

Polymer blend (PB) - A mixture of at least two polymers or copolymers.

Polymer blends are physical mixtures of two or more polymers with/without any

chemical bonding between them. The objective of polymer blending is a practical one of

achieving commercially viable products through either unique properties or lower cost than some

other means might provide. The subject is vast and has been the focus of much work, both

theoretical and experimental. Property of polymer blends is superior to those of component

homopolymers. Blending technology also provides attractive opportunities for reuse and

recycling of polymer wastes. The various economic and property advantages accomplished by

blending are:

The opportunity to develop or improve on properties to meet specific customer needs

• The capability to reduce material cost with or without little sacrifice in properties

• Permit the much more rapid development of modified polymeric materials to meet

emerging needs by by-passing the polymerization step

• Extended service temperature range

• Light weight

• The ability to improve the processability of materials which are otherwise limited in

their ability to be transformed into finished products

• Increased toughening

• Enhanced ozone resistance

• Improved modulus and hardness

• Improved barrier property and flame retardant property

• Improved impact and environmental stress cracking resistance, etc.

In short, unique materials are generated through blending as far as its processability and

or performance are concerned. When two or more polymers are mixed, the phase structure of the

resulting material can be either miscible or immiscible. Due to their high molar mass, the entropy

of mixing of polymers is relatively low and consequently specific interactions are needed to

obtain blends, which are miscible or homogeneous on a molecular scale [1]. In the case of

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immiscible systems the overall physicomechanical behaviour depends critically on two

demanding structural parameters [2]: a proper interfacial tension leading to a phase size small

enough to allow the material to be considered as macroscopically homogeneous and an

interphase adhesion strong enough to assimilate stresses and strains without disruption of the

established morphology. Rubber –plastic blends are commercialised as rubber –toughened

plastics or as thermoplastics elastomers (TPEs). They bridge the gap between thermoplastics and

elastomers [3-9].

1.2 Types of Polymer Blends

1.2.1 On the basis of miscibility

Basically there are three different types of blends depending on the miscibility.

1. Completely miscible blends has got ΔH m <0 due to specific interactions.

Homogeneity is observed at least on a nanometer scale, if not on the molecular level.

This type of blends exhibits only one glass transition temperature (Tg), which is in

between the glass transition temperatures of the blend components in a close relation

to the blend composition. A well-known example of a blend, which is miscible over a

very wide temperature range and in all compositions is PS/PPO

2. In partially miscible blends a small part of one of the blend component is dissolved in

the other part. This type of blend, which exhibits a fine phase morphology and

satisfactory properties, is referred to as compatible. Both blend phases are

homogeneous, and have their own Tg. Both Tg s are shifted from the values for the

pure blend components towards the Tg of the blend component. An example is the

PC/ABS blends. In these blends, PC and the SAN phase of ABS partially dissolve in

one another. In this case interface is wide and the interfacial adhesion is good.

3. Fully immiscible blends have a coarse morphology, sharp interface and poor adhesion

between the blend phases. So these blends are of no use without compatibilisation.

Thee blends will exhibit different Tgs corresponding to the Tg of the component

polymers. Examples of fully immiscible blends are PA/ABS, PA/PPO, PA/EPDM

and PA/PP. Now these blends have become commercially successful, after being

efficiently compatibilised using suitable compatibilisers.

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Figure 1.1. Polymer blend phase diagram

1.2.2 Thermodynamics of Miscibility

Majority of polymers are immiscible at molecular level as given by the laws of

thermodynamics. Given enough time, the internal disorder of the polymer system will eventually

result in phase separation on a macroscopic scale. The relative miscibility of polymers controls

their phase behaviour, which is of crucial importance for final properties. The rules governing

miscible behaviour of polymer blends are understood in a thermodynamic sense through the

Gibbs free energy of mixing, Δ Gm. The free energy of mixing can be described in terms of

enthalpic and entropic contributions as

ΔGm=ΔΗm−ΤΔ S m (1.1)

where, ΔGm is the free energy of mixing per unit volume and φ2 is the volume fraction of

component 2, ΔH m and ΔS m are enthalpy and entropy of mixing respectively. ΔH m is

independent of molecular weight and is a measure of energy change associated with

intermolecular interactions. As seen in Figure 1.2, ΔG m for a binary mixture can vary with

composition.

Figure 1.2. Gibbs free energy of mixing for binary mixtures

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For a binary blend to be miscible, the following conditions should be satisfied: (i) The free

energy of mixing should be negative or zero and (ii) the second derivative of free energy

function with respect to volume fraction of major component should be positive.

ΔGm0 (1.2)

δ φ22

δ 2 ΔGm ¿

¿¿¿¿¿

> 0 (1.3)

These criteria are met by curve B for all compositions. Blends described by curve A violate

equation 1.2 and are completely immiscible. A system described by curve C is partially miscible,

in which a single amorphous phase can be formed at compositions to the left and right of the

minima of curve C. In miscible polymer blends, molecular level mixing of the components is

obtained and is characterized by a single- phase morphology. Immiscible blends do not satisfy

the conditions proposed in equations (1.2) and (1.3), and show a two-phase morphology. In the

case of partially miscible blends, the second criterion is not satisfied and will show either two

phase or single-phase morphology. However, the manifestation of superior properties depends on

the miscibility behaviour of homopolymers.

The term immiscible means that the Gibb’s free energy of mixing, ΔGm is positive

whereas “incompatible” is defined with respect to properties and means that the properties of the

blend are inferior to those of pure polymers. But, most pairs of high molecular weight polymers

are immiscible or incompatible. Polymer-polymer miscibility depends on a variety of

independent variables, viz., composition, molecular weight, temperature, pressure etc. Another

generic term found often in blend literature is compatibility. Components, which resist gross

phase segregation and show desirable blend properties, are considered to have a good of

compatibility, even though they are immiscible in a thermodynamic sense.

1.3 Compatibilisation strategy

Compatibilisation is very useful for improving the dispersity in polymer blends. It

reduces interfacial tension, facilitate dispersion, stabilize the morphology against abusive stresses

and strains (arising out of processing), enhance adhesion between phases and improve the overall

mechanical properties [10] of the products. The driving forces for the phase segregation of blend

components are gravity and interfacial tension. The rate of demixing depends on interfacial

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tension, viscosity and density differences [11-12]. Compatibilised blends are not necessarily

miscible blends, but blends that satisfy certain industrial criteria for usefulness, such as

satisfactory mechanical properties.

The key to solve problems of coarse morphology is to reduce interfacial tension in the

melt and to enhance adhesion between the immiscible phases in the solid state. One solution is to

select the most suitable blending technique so that a co-continuous or interpenetrating phase

morphology can be obtained, which results in direct load sharing. The second solution is the

addition of a third homopolymer or block or graft copolymer or low molecular reactive

compounds, which is miscible with either of the two phases. This can be considered as non–

reactive compatibilisation. The third way is to blend suitably functionalized [13] polymers,

which are capable for specific interactions or chemical reactions (reactive compatibilisation).

1.3.1. Physical Compatibilisation

In physical blending, the compatibilising agent is chemically synthesized prior to the

blending operation, and subsequently added to the blend components as a non-reactive

component. Owing to its chemical and molecular characteristics, the added agent is able to locate

at the interface, reducing the interfacial tension between the blend components (emulsification

effect) and promoting adhesion between the phases [14,15].

1.3.2 Reactive Compatibilisation

Although numerous chemical reactions are encountered in reactive processing, it is

possible to distinguish major classes such as bulk polymerization, reactive compatibilisation,

controlled degradation, coupling, grafting and functionalisation. All these types of reactions can

be classified under reactive processing. In reactive compatibilisation, copolymers can be formed

in-situ through covalent or ironic bonding duration melt blending. In this kind of reactive

compatibilisation, generally one phase contains reactive groups inherent in the polymer, while

the other has no inherent functionality. Reactive groups can be incorporated into the second

phase by adding to it a functionalized polymer, which is miscible. In some cases, both polymers

have to be functionalised.

1.4 Blends based on TPU and PP

Thermoplastic polyurethane and polypropylene form a highly incompatible blend due to

their large differences in polarity and high interfacial tensions. However, TPU/PP blends have

been prepared with an aim to reduce costs and improve the processability of polyurethane. The

mechanical, thermal and chemical properties of polyurethane are improved by blending it with

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the polyolefin. Polyurethane, in turn, increases the impact strength, adhesion, printability and

paintability characteristics of polypropylene.

Potschke et al. [16, 17] have studied the surface tension and interfacial tension of

different PU and PP polymers. The reported experimental values indicated that low interfacial

tension between polyether based TPU soft segment and PP results in better dispersion. Potschke

et al. [18-20] have also carried out PP/TPU blend study without compatibilisers. They reported

that, at similar viscosity ratios (µd/µm), blends with polyether based TPU produced a finer

morphology than blends with polyester based TPU, due to low interfacial tension between their

polyether based TPU soft segments and PP.

Lu et al. have studied TPU / PP based blends in the ratio of 70 / 30 with compatibilisers

like maleic anhydride- g- PP and primary / secondary amine –g-PP [21, 22]. Song et al.

investigated the phase morphology of nanoclay-polyurethane nanocomposite by small angle x-

ray scattering (SAXS) and atomic force microscopy (AFM) [23]. It was observed that with

increase in clay content, the surface energy of the polyurethane hard segments decreased from 45

dyne-cm /cm to 32 dyne-cm/cm for 3% wt nanoclay loading. This result suggested that organic

modification of nanoclay had a surface activation function to some extent. Compatibilisation can

be further improved by introducing functionalised PP (MA-g-PP) in the nanoclay containing

blends.

1.5 Scope and Objectives of the work

The aim of this work was to develop TPU-based blend nanocomposites with best overall

performance, using both blending and nanocomposite technologies. Thermoplastic polyurethane

is attractive because of its high abrasion resistance, tensile and tear strength, flexibility and shock

absorbing capabilities. However, it has certain disadvantages like high cost, moderate thermal

stability and mechanical strength, limitations in chemical resistance and processability. Maleic

anhyride -graft- polypropylene is well known as a compatibiliser for blends of polypropylene

and more polar polymers like nylon and polyurethane. The effect of MA-g-PP on the

dispersibility of organoclay was studied by determining the physical, mechanical and thermal

properties of the TPU/organoclay/PP blend nanocomposites. Cloisite® 10A, a more hydrophobic

organoclay, when pre-mixed with TPU, is also thought to function as a compatibiliser for

TPU/PP blends because of its affinity for the non-polar PP. The probable mechanism is that it

brings down the surface energy of the TPU hard segments to reduce the interfacial tension due to

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the large differences in polarity between TPU and PP. 70/30 TPU / PP blend ratio was chosen

for these studies so that the main properties of TPUs like elastomeric property, abrasion

resistance, damping and low temperature flexibility are retained. The study mainly focused on

the effect of nanocaly (sequence of addition) and the role of compatibiliser (MA-g-PP) in ester-

TPU/PP and ether-TPU/PP blend systems.

The main objectives of the work can be summarized as follows:

(a) Preparation of ester- and ether-TPU/C10A nanocomposites by direct melt blending.

(b) Melt-blending of the prepared nanocomposites with PP using MA-g-PP as the compatibiliser.

(c) Preparation of test specimens by injection molding.

(d) Characterization by X-ray diffraction (XRD), fourier transform infrared

spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron

microscope (TEM), differential scanning calorimetry(DSC) and dynamic mechanical

analysis (DMA).

(e) Evaluation of tensile, abrasion and water absorption properties of the blends and

blend nanocomposites.

(f) Evaluation of electrical properties like volume resistivity, dielectric constant, loss

factor and dissipation factor.

(g) Comparison of dispersion characteristics and properties of ester- and ether-TPU

based blend nanocomposites.

(h) Comparison of the experimental results with the theoretical models.

(i) Investigation of the water diffusion of the TPU/PP blends and the effect of

compatibilisation, nanoclay addition and temperature on the diffusion behaviour.

(j) Investigation of the blend ratio, compatibilisation and nanoclay addition on the flame

retardant properties.

2.1 Materials

Ester-TPU (385 S) and ether-TPU (KU2-8600) were supplied by Bayer (TPU) India Ltd.,

Chennai. The MFI value of 385 S and KU2-8600E is 10 g /10 minute and 11g/minute

respectively (190 0C / 2.16 Kg). The hardness value of 385S and KU2-8600E is Shore A 85 and

84 respectively. PP (MA 1100) was supplied by Reliance Industries Ltd., Jamnagar, India. The

MFI value of PP (MA 1100) is 11 g / 10 minute (230 0C / 2.16 Kg ). MA-g-PP compatibiliser

was purchased from Pluss Polymers, New Delhi. The compatibiliser is a maleic anhydride

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functionalised polypropylene (MA-g – PP), containing 1 wt% of maleic anhydride. The MFI

value of MA-g – PP compatibiliser is 12 g / 10 minute (190 0C / 2.16 Kg).The organoclay used in

this study (Cloisite 10 A) was obtained from Southern Clay Products, USA. It is a Na +

montmorillonite, chemically modified with dimethyl benzyl hydrogenated tallow quaternary

ammonium ions (N + 2MBHT), where N + denotes quaternary ammonium ions, HT denotes

hydrogenated tallow. HT is made of approximately 65 % C 18 H37, 30 % C 16 H33, and 5 % C 14 H29.

Cation exchange capacity is 125 meq / 100 g clay.

2.2 Preparation of nanoclay filled TPU / PP blends

Ester-TPU/C10A nanocomposites were prepared by melt blending TPU and nanoclay

using twin screw extruder. 3 wt% of the nanoclay was used. The ester-TPU pellets were dried at

100 0C for 4 h. The nanoclay was dried at 100 0C for 12 h in vacuum oven. The dried pellets

were fed into a co-rotating twin screw extruder (Berstrof ZE 25) and the temperature of the die

zone was maintained at 190 oC. The extrudate was received as strands and cut into small

granules for melt blending with PP.

Later, the granules of nanocomposites, along with pellets of PP and MA-g-PP were pre-

dried at 100 oC for 4 h in a vacuum oven. Blending was done in the co-rotating twin screw

extruder at a die zone temperature of 190 oC and the extrudate was again obtained in the form of

strands. Blends of different compositions shown in Table 2.1 were prepared by the method

described above. Neat ester -TPU / PP blends were prepared in the ratio of 70/30.

Sequence I: TPU/C10A nanocomposites were prepared and subsequently blended with PP

using MA-g-PP as compatibiliser. 3 wt% of the nanoclay was used. The ester- TPU pellets were

dried at 1000C for 4 h. The nanoclay was dried at 1000C for 12 h in a vacuum oven. The dried

pellets were fed into a co- rotating twin screw extruder and the temperature of the die zone was

maintained at 190oC. The extrudate was received as strands, which were cut into small granules

for melt blending with PP. The granules of nanocomposites, along with pellets of PP and MA-g-

PP were pre-dried at 100oC for 4 h in a vacuum oven. Blending was done in the same co-

rotating twin screw extruder with a die zone temperature of 190oC and the extrudate was again

obtained in the form of strands. Neat TPU / PP blends were prepared in the ratio of 70 / 30.

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Sequence II: Nanoclay was added to PP by similar extruder melt blending and

subsequently melt blended with TPU using MA-g-PP as compatibiliser (Table 2.1). Ether-TPU

based samples were also prepared by similar method.

Table 2.1. Sequence I and II of Blend compositionsSequence I

BlendTPU(nano)*

(wt %)PP

(wt %)MA-g-PP

(wt %)

Ester-TPU(nano)/PP 70 30 -

Ester-TPU(nano)/PP/MA-g-PP 70 25 5

Ether-TPU(nano)/PP 70 30 -

Ether-TPU(nano)/PP/MA-g-PP 70 25 5

[TPU(nano)* = 3% nano content]

Sequence II

BlendTPU

(wt %)PP

(wt %)PP-nano(wt %)

MA-g-PP(wt %)

Ester-TPU/PP/MA-g-PP 70 25 - 5

Ester-TPU/PP-nano 70 30* -

Ester-TPU/PP-nano/MA-g-PP 70 25** 5

Ether-TPU/PP/MA-g-PP 70 25 - 5

Ether-TPU/PP-nano 70 30* -

Ether-TPU/PP-nano/MA-g-PP 70 25** 5

[PP-nano* *= 8.4 % nano content, PP-nano* = 7.0 % nanocontent]2.3 Experimental Techniques

2.3.1 Phase morphology

The phase morphology was studied using cryogenically fractured samples. By immersing

the samples in liquid nitrogen, a brittle fracture is obtained avoiding large deformations in the

surface to be examined. These samples are immersed in xylene solutions to remove the PP from

TPU base. This setup kept in oil bath at 80°C for 3 hours. Then the sample is taken out and dried

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in oven at 100°C in order to remove excess of xylene. Thus chemical etching of the sample is

obtained. Morphological studies were performed on the chemically etched and gold sputtered

samples using JOEL (JSM-5800) scanning electron microscope.

2.3.2 Transmission electron microscopy (TEM)

The samples for TEM analysis were prepared by ultra-cryomicrotomy with a Leica

Ultracut UCT (Leica Mikrosystems GmbH, Vienna, Austria). Freshly sharpened glass knives

with cutting edges of 45°C were used to obtain cryosections of 100-120 nm thickness. Because

these samples were elastomeric in nature, the sample and glass knife temperatures during

ultracryomicrotomy were kept constant at -75 and -85°C, respectively [these temperatures were

well below the glass transition temperature (Tg' s) of PUs]. The cryosections were collected

individually in a sucrose solution and directly supported on a copper grid of 300 meshes in size.

Microscopy was performed with a JEOL JEM 2000 TEM instrument (Japan), operating at an

accelerating voltage of 120 kV.

2.3.3 Mechanical Properties

Tensile testing

Tensile tests were carried out as per ASTM D 638 on a universal testing machine

(International Equipments, Mumbai) at a crosshead speed of 200 mm/min. The dumbbell

specimen sizes are: 165 x 12.8 x 3.2 mm. A slip between the specimen and grip occurred at very

high strain levels (≥1100%) and the specimens could not be broken. Hence the large strain data

is not considered to be very reliable and is not discussed here. Stress at 20%, 100% and 200%

strain was recorded to avoid tensile strength variation at break. Injection molded specimens were

used for this test.

2.3.4 X-ray diffraction (XRD)

The change in gallery spacing of silicate layers in the blend nanocomposites was

determined on an X-ray diffractometer (Panalytical X-pert PRO, Netherlands) using Cu

(λ=1.5406Å) as the radiation source. The samples were scanned at a rate of 3o /min (the

increment step was 0.01 o and the step time was 0.2 s) at room temperature for 2-theta values

starting from 1o to 10 o.

2.3.5 Fourier transform infra-red spectroscopy (FTIR)

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Fourier transform infra-red spectroscopy (FTIR) has numerous applications in qualitative

and quantitative analysis. Atoms or atomic groups in molecules are in continuous motion with respect

to one another. They vibrate about some mean position. IR spectrum of a compound is the superposition

of absorption bands of specific functional groups. FTIR spectroscopy was performed for the prepared

nanocomposites and blend nanocomposites in the ATR mode for convenience of measurement. A

Thermo Nicolet (Avatar 370) spectrometer was used. Measurements were done in the spectral

range 4000-400 cm-1 at a resolution of 0.9 cm-1.

2.3.6 Differential scanning calorimetry (DSC)

The thermal properties of the blend nanocomposites were measured by a differential

scanning calorimeter (Mettler Toledo, DSC 822e). Sample weight of 3 to 5 mg was scanned in

nitrogen atmosphere at a heating rate of 10 0C/min. Thermograms were taken by heating the

samples in the temperature range from –100 0C to 300 0C.

2.3.7 Dynamic mechanical analysis (DMA)

Dynamic mechanical measurements were performed for the prepared blend

nanocomposites (60 mm Χ 13 mm Χ 3.5 mm) using a Netzsch DMA 242 instrument provided

with a dual cantilever. Analysis was done in the temperature range -100 0C to 200 0C at a

frequency of 1,10,20 Hz and a heating rate of 5 0C/min.

2.3.8 Thermogravimetric analysis (TGA)

The thermal degradation studies of the blends were carried out in Netzsch analyzer. The

samples (10mg) were degraded under nitrogen flow (30cm3 min-1 ) in the thermo balance under

dynamic condition at the heating rate of 10 0C/min. The samples were scanned from room

temperature to 800 0C. From the TG curves, the thermal degradation characteristics such as onset

degradation (Ton), temperature at maximum rate of degradation (Tmax), temperatures at different

weight losses and were calculated

2.3.9 Rheological properties

The melt rheology of the individual polymers and their blends was studied using a

dynamic rheometer (Haake RT 10), employing a parallel plate sensor with a diameter of 35 mm

at 190°C over a frequency range 100 - 1 rad s-1.

2.3.10 Electrical property measurements

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The electrical measurements were carried out using circular samples of diameter 10mm

and thickness of 3.2mm at room temperature using Novo control, Germany-Alpha ATP. The test

samples were coated with conductive graphite paint on either side and copper wires were fixed

on both sides of the samples as electrodes. All measurements were done at the frequencies

ranging from 100HZ to 1MHz. The capacitance, impedance and dielectric loss factor were

measured directly. Electrical properties such as volume resistivity, dielectric permittivity, loss

factor and dissipation factor were studied.

2.3.11 Flame retardant propertiesThe flame retardant properties of blends were investigated by limited oxygen index

(LOI), underwriters’ laboratories-94 (UL-94), rate of burning and ignition response test. LOI

test, UL-94 test, rate of burning test and ignition response test were carried as per ASTM D

2863, UL-94, ASTM D 635 and ASTM D 8713 respectively.

2.3.12 Optical contact angle measurementDifferent samples surface energy was calculated from this test using Dataphysics OCAH

230 instrument.

2.3.13 Sorption experiments

Circular samples for diffusion experiments were punched our form the injection moulded

sample specimen using sharp steel, disc (diameter 1.9cm). The samples were vacuum dried for

24 hrs at 800C and then kept in a vacuum desiccator for 2 hrs. The thickness was measured using

a dial gauge. Previously weighed samples were immersed in water taken in sorption bottles kept

at constant temperature in an air oven. At regular intervals the samples were taken out and the

swollen samples were blotted of carefully with soft tissue paper and weighed in an electronic

balance immediately in airtight bottles.

3. Results and discussion

3.1 Phase Morphology

3.1.1 Phase morphology of uncompatibilised blends by SEM

The SEM images of ester -TPU/PP and ether -TPU/PP 70/30 blends are shown in Figure

3.1(a) and 3.2(a). The micrographs demonstrate two-phase morphology. From the figure it is

clear that, PP is dispersed as spherical domains in a continuous TPU matrix. The dispersion of

PP was slightly finer in ether-TPU blends than the corresponding ester-TPU blends. This is

accounted for by the fact that the surface energy of the polyether soft segment is lower than that

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of the polyester soft segment and, consequently, closer to that of the nonpolar PP.

3.1.2 Phase morphology of compatibilised blends

The effects of MA-g-PP as compatibiliser on the morphology of ester-and ether-TPU

(70/30) blends are given in Figures 3.1 and 3.2 respectively. From the SEM micrographs it is

clear that the size of dispersed PP domains is reduced by the addition of compatibilisers. A

similar behaviour was observed for ether-TPU blend compositions also. This reduction in

domain size of dispersed PP on the addition of MA-g-PP is due to the reduction in interfacial

tension between the dispersed PP phase and TPU matrix and suppression of coalescence, which

result in the stabilization of blend morphology.

In addition, the presence of the graft copolymer at blend interface broadens the interfacial

region through the penetration of the copolymer chain segments into the corresponding adjacent

phases [24]. The average domain size of the compatibilised blends as a function of

compatibiliser concentration is given in Figure 3.3. The average domain diameter of the

uncompatibilised ester-TPU (70/30) blend is 3.53 µ m . In the case of compatibilised blends

addition of 5% MA-g-PP compatibiliser reduces the domain size to 1.10 µ m thereby causing a

reduction in size upto 70%. Beyond 5% concentration, increase of size of dispersed particle is

due to inefficiency of compatibiliser to suppress coalescence beyond CMC, it cause miscelle.

The values of D n, D w, D vs and interfacial area / unit volume of MA-g-PP compatibilised

blends are given in Table 3.1. On adding 5% of MA-g-PP the dispersed size is reduced to the

maximum extent and attained maximum interfacial area / unit volume.

(a) (b)

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(c) (d)

Figure 3.1. Scanning electron micrographs of 70/30 ester-TPU/PP blends with addition of (a) 0 (b) 3 (c) 5 (d) 7 weight % MA-g-PP

(a) (b)

(c) (d)

Figure 3.2. Scanning electron micrographs of 70/30 ether-TPU/PP blends with addition of (a) 0 (b) 3 (c) 5 (d) 7 weight % MA-g-PP

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00.5

11.5

22.5

33.5

4

0 1 2 3 4 5 6 7 8

Weight % of compatibiliser

Dn(

μm)

Ether-TPU based blends

Ester-TPU based blends

Figure 3.3. Effect of compatibiliser concentration on the dispersed domain diameter of TPU/PP (70/30) blends

Figure 3.4. Chemical reaction between urethane linkage and maleic anhydride (Reproduced from Q.W.Lu, T. R. Hoye and C.W. Macosko, J.Polym. Sci. Part A: Polym. Chem., 40, 2310 (2002) [ Ref. 25 ]

Table 3.1. Effect of compatibilisation on dispersed domain diameter, interfacial area / unit volume and inter particle distance of ester-TPU/PP (70/30) blends

Sample D n

(µm)

D w,

(µm)

D vs

(µm)

Interfacial area/ unit

volume (µm-1)Inter Particle Distance(µm)

TPU/PP (70/30) 3.53 3.79 4.23 0.56 0.74

3% MA-g-PP 1.30 1.61 1.90 1.31 0.25

5% MA-g-PP 1.10 1.36 1.70 1.52 0.20

7% MA-g-PP 1.22 1.44 1.73 1.39 0.23

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Figure 3.5. Schematic of hydrogen bonding and chemical reaction among PP, MA-g- PP, nanoclay and TPU( Reproduced from M.Kannan, S.S. Bhagawan, Tomlal Jose, Sabu Thomas, Kuruvilla Joseph,

Polym.Eng. Sci., 2010, 50(9), 1878-1886) [ Ref.26]

The equilibrium concentration at which the domain size levels off can be considered as

the so-called critical micelle concentration (CMC) ie; the concentration at which micelles are

formed. The CMC has been estimated by the intersection of the straight lines at the low and high

concentration regions [27-29], the CMC value for MA-g-PP is 5%. The CMC value indicates the

critical amount of compatibiliser required to saturate the unit volume of the interface. Generally,

CMC is estimated form the plot of interfacial tension versus copolymer concentration. As the

interfacial tension is directly proportional to domain size, CMC can be estimated from the plot of

domain size versus co-polymer concentration [30]. Several studies have been reported on the

interfacial saturation by the addition of compatibilisers [31-35]. Our present study and almost all

the reported studies on physical and reactive compatibilisation of immiscible polymer blends and

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the theoretical prediction of Noolandi and Hong [36-38] suggest that a critical concentration of

the compatibiliser is required to saturate the interface of binary polymer blends.

Table 3.2. Effect of compatibilisation on dispersed domain diameter, interfacial area / unit volume and inter particle distance of ether-TPU/PP blends

Sample D n

(µm)

D w,

(µm)

D vs

(µm)

Interfacial area/unit

volume (µm-1)

Inter Particle Distance

(µm)

TPU/PP(70/30) 3.51 3.69 4.19 0.59 0.71

3% MA-g-PP 1.47 1.67 1.99 1.27 0.29

5% MA-g-PP 1.26 1.41 1.76 1.47 0.24

7% MA-g-PP 1.41 1.5 1.79 1.35 0.27

3.1.3 Influence of nanoclay addition on compatibilised blend phase morphology

The effect of nanoclay concentration on the morphology of dispersed phase in

TPU(nano)/PP/MA-g-PP (70/30) blends can be evaluated from the SEM micrographs of

cryogenically fractured and xylene extracted surfaces of the specimen demonstrated in Figure

3.6(a).It should be noted that in both blends (ester and ether based),after the initial sharp decline

in particle size, a quasi equilibrium state is obtained at 3wt% of nanoclay in TPU component.

The nanoclay emulsification curve for the both the blend is shown in Figure 3.6(b).

SEM micrographs of chemically etched surfaces of the ester –TPU / PP, ester –TPU / PP/

MA-g-PP and ester –TPU (nano) / PP/ MA-g-PP are shown in Figure 3.7. It is observed that the

size of dispersed PP particle is considerably reduced in the ester –TPU (nano) / PP / MA-g-PP

(Figure 3.7 b) system. For nanocomposite SEM sample preparation, the PP portion was removed

by chemical etching method which gives very fine holes. In non –clay polymer blends also PP

was removed by etching ; however, the PP domains are not as fine as clay nanocomposites due

to high interfacial tension between TPU and PP and hence fine holes are not evident in SEM

micrographs.

20

(a) (b) (c )

(d) (e) (f) Figure 3.6(a). Ester TPU blend TPU (nano)/PP/MA-g-PP (70/25/5)(a) 1% nano (b) 3% nano

(c) 5% nano: Ether TPU blend TPU (nano)/PP/MA-g-PP (70/25/5)(d) 1% nano (e) 3% nano (f)

5% nano (Nano content in TPU)

Figure 3.6(b). Nanoclay emulsification curve- TPU(nano)/PP/MA-g-PP (70-nano/25/5)

3.1.4 Influence of sequence of nanocaly addition on phase morphology

SEM micrographs of chemically etched surfaces of the ester- and ether-based TPU/PP,

TPU/PP/MA-g-PP , TPU / PP(nano)/MA-g-PP , and TPU(nano)/PP/MA-g-PP blend systems are

shown in Figure 3.1,3.2 and 3.7 respectively. It is observed that the size of dispersed PP particle

21

is considerably reduced in TPU(nano)/PP/MA-g-PP. Compared to the sequence II blend

nanocomposites, the sequence I blends show better miscibility as confirmed by SEM analysis.

The clear difference between sequence I and sequence II is that the case of sequence I the effect

of nanoclay is fully utilized by changing the surface tension of the TPU hard segment from

around 45 dynes/cm to around 30 dynes/cm[23]. This change in surface tension favours for

better dispersion of PP in TPU material, and also hydroxyl group of silicate layers forms

hydrogen bonding with the carbonyl group of TPU and maleic anhydride

Compared to the ether-TPU based blend nanocomposites, the ester-TPU blends show

better compatibility as confirmed by SEM analysis. The clear difference between ester-TPU and

ether-TPU is that ester-TPU has carbonyl groups both in the polyol segements as well as the

TPU hard segments. This may lead to more extensive hydrogen bonding in the blend system thus

improving the compatibility.

(a) (b)

(c) (d)

Figure 3.7. Effect of sequence of nanoclay addition in compatibilised TPU/PP blends(a) Ester-TPU/PP (nano)/MA-g-PP (b) Ester-TPU (nano)/PP/MA-g-PP (c) Ether-TPU/PP (nano)/MA-g-PP (d) Ether-TPU (nano)/PP/MA-g-PP

22

3.1.5 XRD Studies

X-ray diffraction (XRD) is an extremely useful tool to study the structure and

morphology of polymer nanocomposites. Since the layer spacing increases due to intercalation of

polymer chains between the layers, the process can be monitored by X-ray diffraction [23,39-44 ].

The interlayer spacing of Cloisite 10A is 1.92 nm before compounding. For the uncompatibilised

system, the XRD patterns exhibits no significant increase in interlayer spacing. This indicates

that the polymer material does not intercalate into the interlayer, even in the organically modified

nanoclay. In contrast, for compatibilised systems, the XRD peaks are shifted to lower angles,

indicating the increase in interlayer spacing by the intercalation of polymer.

Figure 3.8 (a). Influence of nanoclay addition on ester-TPU based blends XRD pattern

23

Figure 3.8 (b). Influence of nanoclay addition on ether-TPU based blends XRD pattern

3.1.6 Compatibiliser effect on nanoclay dispersion in TPU/PP (70/30) blendsThe diffraction characteristics of nanoclay filled compatibilised ester-

TPU(nano)/PP/MA-g-PP blend are shown in Figure 3.8. The peak is absent in ester-

TPU(nano)/PP/MA indicating good dispersion, it appears that the compatibiliser MA-g-PP aids

the dispersion of nanoclay in the blend.

Thus, it is confirmed that the compatibiliser makes the nanoclay better dispersed with the

polymers [44-47]. This is because maleic anhydride undergoes chemical reaction with the

urethane groups in the TPU hard segments and also forms hydrogen bonds with the silicate

layers of nanoclay (C10A). XRD results are often reported to be misleading in terms of clay

dispersion [47]. Therefore, only with the XRD analysis of these nanocomposites blends, it cannot

be concluded that these nanocomposites show the intercalated or the exfoliated clay structures. In

this regard, TEM pictures were taken and the results are reflecting similar trend as XRD results.

3.1.7 Influence of sequence of nanoclay addition in compatibilised blend morphology

The diffraction characteristics of compatibilised TPU (nano)/PP blends are shown in

Figure 3.8. In TPU/PP (nano)/ MA, a peak appears at 2Ө~4.80 with reduced intensity as

compared to neat nanoclay. This is an indication that the non-polar PP chains have been

incorporated in the gallery space because of their affinity for the nanoclay. The peak is much

weakened in ester-TPU(nano)/PP/MA indicating nearly exfoliation dispersion, it appears that

24

the compatibiliser MA-g-PP aids the dispersion of nanoclay in the blend . As mentioned in the

previous section, TEM images were taken and the results showed similar trend as XRD results.

In the section on TEM analysis, effects of nanoclay dispersion are discussed with blend

morphology of these blends. Compared to the ether-TPU based blend nanocomposites, the ester-

TPU blends show better compatibility as confirmed by XRD analysis. As discussed earlier, this

observation may be due to the formation of more hydrogen bonding in ester-TPU based

nanocomposites.

3.1.8 TEM Investigation

It is well known that the difficulty in studying the nanocomposites is that no single

characterization method can adequately describe the state of clay dispersion in the

nanocomposites. The combined analyses are necessary and especially TEM is proved to be

quite effective [47-51].

(a) (b)

Figure 3.9. TEM images of ester- TPU (a) 3% , (b) 5% nanoclay loading

(a) (b)

Figure 3.10. TEM images of ether- TPU (a) 3%, (b) 5% nanoclay loading

25

(a) Ester- TPU(3%nano)/PP (b) Ester-TPU(3%nano)/PP/MA-g-PP

Figure 3.11. TEM images

(a) Ether –TPU(3%nano)/PP (b) Ether-TPU(3%nano)/PP/MA-g-PP


(a) Ester-TPU/PP(nano)/MA-g-PP (b) Ester-TPU(nano)/PP/MA-g-PP


26

(a) Ether-TPU/PP(nano)/MA-g-PP (b) Ether-TPU(nano)/PP/MA-g-PP


3.1.9 Influence of nanoclay addition on uncompatibilised blend morphology

To confirm the XRD results and clearly see the dispersion state of clays in the

nanocomposites, TEM pictures were taken and discussed. The TEM images of the ester-

TPU/nano, ester-TPU (nano)/PP, ether-TPU/nano and ether-TPU (nano)/PP are shown in

figures 3.9, 3.10, 3.11(a) and 3.12(a). The TEM images presented in those figures, present

evidence that efficient dispersion and exfoliation of clay particles did not occur in this

composition. The dispersion of nanoclay particles was found to be poor in this composition. In

the TEM images for the ester-TPU/nanoclay/PP nanocomposites (Figure 3.11a), thick

agglomerated clay particles are observed indicating poor dispersion of clay. Figure 3.12a

shows clay dispersion in the ether-TPU/nanoclay/PP nanocomposites.

3.1.10 Influence of nanoclay addition on compatibilised blend morphology

Kawasumi et al.[52], Kato et al.[53], Hasegawa et al .[54] and other authors [55-58]

showed that there are two important factors to achieve the exfoliation of the clay layer silicates

(1) the compatibiliser should be miscible with polypropylene matrix, and (2) it should include a

certain amount of polar functional groups in a molecule to react with TPU. Generally, the maleic

anhydride grafted polypropylene (MA-g-PP) fulfills the two requirements and are used as

compatibiliser for this blend system. When MA-g-PP is not introduced into the system, only

intercalated structure is obtained, and many larger aggregates exist in the matrix (Figure 3.11a

and 3.12a). When the compatibiliser is introduced in the system, the nanoclay dispersion

improves.

27

The TEM image in Figure 3.11b shows exfoliated and well dispersed nanoclay particles.

In view of this, a true nanocomposites was produced in the case of ester-TPU(nano)/PP/MA-g-

PP and 3 wt% nanoclay loading. The TEM image of the composite supports this and shows that

individual clay layers were well dispersed in the polymer. These results are well correlated with

the XRD results where almost no peaks were observed for ester-TPU(nano)/PP/MA-g-PP

nanocomposites. TEM images of nanocomposite of ether-TPU shown in Figure 3.12b, where

the degree of dispersion of clay is observed to be poorer than ester-TPU nanocomposites. This

is in agreement with the XRD result that some changes in clay layers were expected.

3.1.11 Influence of sequence of nanocaly addition on phase morphology

In sequence I, nanoclay was first added to TPU and this nanocomposite was blended

with PP, using MA-g-PP as compatibiliser. In the case of sequence II, nanoclay was added first

to PP and blended with TPU, using MA-g-PP as compatibiliser. Compared to the sequence II

blend nanocomposites, the sequence I blends of TEM images (Figures 3.13 and 3.14) shows

better nanoclay dispersion for both ester- and ether- based TPU nanocomposites. The clear

difference between sequence I and sequence II is that the effect of nanoclay is fully utilized for

changing the surface tension of TPU hard segment in sequence I. The hydroxyl group of silicate

layers forms hydrogen bonding with the carbonyl group of TPU and maleic anhydride moieties

leading to reduction in surface tension of TPU hard segment. This change in surface tension

favors for better dispersion of PP in TPU material.

3.1.12 Comparison of the experimental data with theory

According to Noolandi [37], the effect of copolymer on surface tension between the two

phases is mainly influenced by the contributions from a series of factors such as lowering of

interaction energy between the immiscible homopolymers, the entropy reduction in the system,

decrease in energy of interaction of the two blocks with each other and a large decrease in the

interaction energy of the oriented blocks with homopolymers. Based on these facts and by

neglecting the loss of conformational entropy, Noolandi derived and equation for the interfacial

tension reduction as

ΔΓ=dφc [1/ 2χ 1/Z c − 1/Z c exp [ Z c χ /2 ] ] (3.1)

where d is the width at half height of the copolymer profile reduced by the Kuhn

statistical segment length, φc the bulk copolymer volume fraction of the copolymer in the

system, ZC the degree of polymerization of the copolymer and χ the Flory-Huggins interaction

28

parameter between A and B segments.Although Noolandi’s theory was developed for the action

of a symmetrical diblock copolymer, A-b-B, in incompatible binary blends (A/B), it can be

applied to other systems too where the compatibilising action is not strictly by the addition of

block copolymers [36-38]. As the interfacial tension reduction is directly proportional to the

particle size reduction at low volume fraction of the dispersed phase, as suggested by Wu, it can

be argued that

δD=Kd φc [1 /2 χϕ 1Zc exp Z c χ /2 ]

(3.2)

where K is proportionality constant. The plot of domain size reduction as a function of the

volume fraction of the MA-g-PP for the TPU/PP(70/30) blend is shown in Figure 3.15(a). It can

be seen that at low MA-g-PP concentration (below CMC), there is a drastic decrease in domain

diameter with the increase in volume fraction of the graft copolymer whereas at higher

concentration (above CMC) a leveling off is observed in agreement with the predictions of

Noolandi and Hong.

Figure 3.15(a). Variation of particle size reduction as a function of volume % of compatibiliser

Leibler examined the emulsifying effect of an A-B copolymer in an immiscible blend of

polymers A and B and predicted a reduction of interfacial tension caused by equilibrium

adsorption of the copolymer at the interface. According to the author, the interfacial tension

reduction is given by the relation.

ΔΓ=−kT /a23/ 41/3 Σ /a2

−5 /3

ZCA ZA−2/3Z CB Z

B−2/3 (3.3)

29

where ZCA and ZCB are the number of A and B units in the copolymer, respectively, ZA and ZB

the degree of polymerisation of A and B, respectively, a the monomer’s unit length, Σ the

interfacial area per copolymer. Based on the assumption that the reaction between reactive

compatibiliser and the polymer with a different functional group occurs near the interface, one

can use the following equation for the interfacial tension reduction ( ΔΓ ) obtained by the brush

limit which is independent of the homopolymer molecular weights

ΔΓΓ 0

= 489 μ

32 χN

−12 (3.4)

where Γ 0 is the interfacial tension of polymer blend without a compatibiliser and μ is the

chemical potential which is given by the equation

μ=ln φ fχN (3.5)

where f is the volume fraction of the component in copolymer which is miscible to homopolymer

forming the dispersed phase and

φ=φ0

[φmφd exp { χ N A−N B } ] (3.6)

where φ0, φm and φd represent the volume fraction of the copolymer, matrix and dispersed

phase, respectively, NA and NB are the number of segments of the component in the copolymer

miscible to the homopolymer forming the dispersed phase and that miscible to homopolymer

forming the matrix phase, respectively. Since the value of exp { χ N A−N B } is negligible

compared to φm , φ is expressed by φ0 /φm . Since the dispersed particle reduction is directly

proportional to the interfacial tension reduction, the following equation can be used:

ΔΓΓ 0

= Γ 0−Γ

Γ 0

=ΔDD

=D0−D

D0 (3.7)

The variation in values of χ as a function of MA-g-PP in TPU/PP (70/30) blend is given

in Figure.3.15(b). As the amount of PP-g-MA increases, χ values diminish indicating enhanced

interaction between the phases at interface in presence of compatibiliser. However, note that the

theoretically calculated χ values from Libeler’s theory show apparent conflict with the

experimental observation, which shows a decrease in particle size followed by a quasi –

equilibrium state beyond CMC state owing to interfacial saturation. In the calculation process,

the reference segment size is equal to 100 g mo1-1. The total numbers of chain segments N values

are obtained by the assumption that the total number of chain segments of copolymer is just the

30

summation of two number averaged molecular weights of PP and MA-g-PP divided by the

reference segment size.

0.008

0.018

0.028

0.038

0.048

0.058

0 1 2 3 4 5 6 7 8

Weight % of MA-g-PP

Inte

ract

ion

para

met

er (χ)

Ether-TPU based blendsEster-TPU based blends

Figure 3.15(b). Effect on MA-g-PP on the χ values by Leibler's theory

3.2 Mechanical Properties

3.2.1 Mechanical properties of uncompatibilised blends

Plots showing the stress-strain behavior of TPU/PP blend of different composition and

virgin components are presented in Figure 3.16. Stress to break and strain to break could not be

measured since most specimens did not break at even at the maximum strain the machine could

impose. Also, possibilities of sample slippage from grip increase at large strains. A slip between

the specimen and grip occurred at very high strain levels (≥1100%) and the specimens could not

be broken. Hence the large strain data is not considered to be very reliable and is not discussed

here. Stress at 20%, 100% and 200% strain was recorded to avoid tensile strength variation at

break. The differences in the deformation characteristics of the blends under an applied load are

evident from the figure. In general, the stress-strain curves of PP and PP rich blends show linear

elastic region followed by yielding and necking in the inelastic region, which is typical of

plastics. The addition of more TPU considerably reduces the modulus and eliminates the necking

tendency of PP. The phase change in morphology is also reflected in the nature of the stress-

strain curves. The experimental results for uncompatibilised blends are given in Table 3.3 & 3.4.

31

Table 3.3 Mechanical properties of uncompatibilised ester-TPU based blends

Blend composition

Impact

Strength

Izod J/M

Hardness

Shore D

Tensile Modulus

(MPa)

Stress at % strain (MPa)

20% 100% 200%

TPU/PP (100/0) NF 42 90±5 3.0±0.05 3.9±0.05 4.3±0.05

TPU/PP (70/30) NF 52 253±5 5.3±0.05 5.7±0.05 6.4±0.05

TPU/PP (50/50) NF 56 613±5 12.9±0.05 14.8±0.05 15.9±0.05

TPU/PP (30/70) 38 58 1020±5 22.9±0.05 24.8±0.05 25.2±0.05

TPU/PP (0/100) 29 62 1450±5 32.6±0.05 (at break)

NF – No failure

05

101520253035

0 50 100 150 200 250 300

Strain %

Str

ess

(MP

a)

TPU/PP(100/0) TPU/PP(70/30)TPU/PP (50/50) TPU/PP(30/70)TPU/PP (0/100)

05

101520253035

0 50 100 150 200 250 300Strain %

Str

ess (

MP

a)

TPU/PP (100/0) TPU/PP (70/30)

TPU/PP (50/50) TPU/PP (30/70)TPU/PP (0/100)

Figure 3.16(a). Stress-strain curves for Figure 3.16(b). Stress-strain curves for

uncompatibilised ester-TPU/PP blends uncompatibilised ether-TPU/PP blends

32

Table 3.4. Mechanical properties of uncompatibilised ether-TPU based blends

Blend composition

Impact

Strength Izod J/M

Hardness

Shore D

Tensile Modulus

(MPa)


20% 100% 200%

TPU/PP (100/0) NF 42 90±5 3.4±0.05 4.0±0.05 4.3±0.05

TPU/PP (70/30) NF 53 274±5 5.7±0.05 6.6±0.05 6.7±0.05

TPU/PP (50/50) NF 57 643±5 15.1±0.05 16.2±0.05 16.3±0.05

TPU/PP (30/70) 40 59 1055±5 25.1±0.05 27.6±0.05 27.2±0.05

TPU/PP (0/100) 29 62 1450±5 32.6 ±0.05 (at break)

NF – No failure

Materials, which undergo strain hardening during stretching, have higher strength at

break than materials that do not undergo strain hardening [59].

3.2.2. Modeling of Tensile Moduli

Mechanical properties are widely suited for analysis of multicomponent composites,

through a comparison of experimental results and prediction based on various models. The

application of various composite models gives insight into the properties of individual

components. It also helps to check the assumptions regarding structure, mechanism and

properties of the interface. Several theories have been proposed to predict the tensile properties

in terms of various parameters. These theories can be classified into two categories: (i) based on

composition and (ii) based on morphology [60].Most of these theories assume perfect adhesion

between the phases and a macroscopically homogenous and isotropic sample. The different

models examined to predict the mechanical behaviour of the blends include the parallel, series,

Halpin-Tsai, Takayanagi, Kerner, and Kunori models. The highest upper bound parallel model

(Voight prediction) is given by the rule of mixtures. The application of these models requires the

knowledge of the experimental mechanical behaviour of the pure component polymers TPU and

PP. The two simple models are the so-called parallel and series models, which should represent

the upper and lower bounds of the tensile strength predictions

33

Figures 3.17 and 3.18 show comparison of the variation in theoretical and experimental

curves of the tensile strength and tensile moduli of ester and ether TPU/PP blends as functions of

volume fractions of PP. The predictions of these theories have been made with E1= 3.9 for

ester,E1= 4.0 for ether at 100% strain and E2 =32.6 MPa for the tensile strength for TPU and PP

respectively. The predictions of these theories also have been made with E1=90 (both ester and

ether) and E2 =1450 for the tensile modulus for TPU and PP respectively. In the experimental

curve, that there is only marginal increase in tensile strength with the addition of up to 30wt. %

of PP to TPU. In immiscible blends, the tensile strength usually depends on the particle size of

the dispersed phase. Smaller and more uniformly distributed particles are more effective in

initiating crazes and terminating it before they develop into catastrophic sizes. The lower values

for the tensile strength in this blend system upto 30% PP may be due to poor interfacial adhesion

between the dispersed PP phase and the continuous TPU matrix.

0

5

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1

Volume fraction of PP

Tens

ile S

treng

th(M

Pa)

CoranExperimentKernerParallelSeriesHalpin Tsai

0

5

10

15

20

25

30

35

0 0.2 0.4 0.6 0.8 1


Ten

sile

Str

engt

h(M

Pa)


(a) (b)

Figure 3.17. Theoretical model for uncompatibilised (a) ester (b) ether-TPU blends (Tensile

strength)

34

0

200

400

600

800

1000

1200

1400

1600

0 0.2 0.4 0.6 0.8 1


Tens

ile M

odul

us (M

Pa)


0

200

400

600

800

1000

1200

1400

1600

0 0.2 0.4 0.6 0.8 1


Tens

ile M

odul

us (M

Pa)


(a) (b)

Figure 3.18. Theoretical model for uncompatibilised (a) ester (b) ether-TPU blends (Tensile

Modulus)

3.2.3 Mechanical properties of compatibilised blends with nanoclay addition

The addition of compatibilisers affects the mechanical properties of immiscible polymer

blends are shown in Figures 3.19 & 3.20. The uncompatibilised TPU/PP(70/30) blend has low

tensile strength and exhibits considerable improvement by the addition of compatibiliser. With

increase in compatibiliser concentration, the tensile strength is found to increase upto 5 wt.%

continuously and then levels off or decrease. This increase in tensile strength is due to the

increase in interfacial adhesion between TPU and PP. This observation complements the other

studies discussed in other chapters. Figure 3.19 & 3.20 shows the variation of tensile strength of

70/30 TPU/PP blends with weight 5% of the compatibiliser, MA-g-PP. Similar results have been

reported for Nylon /PP [61] and NBR/PP systems [62]. The experimental results for

compatibilised blends are given in Table 3.5 & 3.6. The stress required for 20,100 & 200% strain

is improved with compatibilisation, which are also attributed to improved interfacial interactions.

35

0

2

4

6

8

10

12

0 50 100 150 200 250 300Strain %

Str

ess

(MP

a)

Uncompatibilised 3% MA-g-PP

7% MA-g-PP 5% MA-g-PP

0

2

4

6

8

10

12

0 50 100 150 200 250 300Strain %

Str

ess

(MP

a)

Uncompatibilised 3% MA-g-PP

7% MA-g-PP 5% MA-g-PP

Figure 3.19. Effect of compatibiliser on Figure 3.20. Effect of compatibiliser on ester-TPU blends ether-TPU blends

0

2

4

6

8

10

12

0 50 100 150 200 250 300Strain %

Str

ess (

MP

a)

TPU(nano)/PP/MA-g-PPTPU/PP(nano)/MA-g-PPTPU/PP/MA-g-PPTPU/PP

0

2

4

6

8

10

12

0 50 100 150 200 250 300

Strain %

Str

ess (

MP

a)


Figure 3.21. Stress-strain curves for Figure 3.22. Stress-strain curves for ester-TPU blends (compatibilised) ether-TPU blends (compatibilised)

36

Table 3.5. Mechanical properties of compatibilised ester-TPU based blends

Blend composition

Impact Strength Izod J/M

Hardness Shore D

Tensile Modulus

(MPa)


20% 100% 200%

TPU/PP (70/30) NF 52 253±5 5.3±0.05 5.7±0.05 6.4±0.05

TPU/PP/MA (70/25/5)

NF 53 298±5 5.7±0.05 6.7±0.05 6.9±0.05

TPU/PP(nano)/MA (70/25/5)

NF 53 356±5 7.7±0.05 8.0±0.05 8.4±0.05

TPU(nano)/PP/MA(70/25/5)

NF 55 430±5 7.9±0.05 10.1±0.05 10.3±0.05

Table 3.6. Mechanical properties of compatibilised ether-TPU based blends

Blend composition

ImpactStrengthIzod J/M

HardnessShore D

Tensile Modulus

(MPa)


20% 100% 200%

TPU/PP(70/30)

NF 52 274±5 5.7±0.05 6.6±0.05 6.7±0.05

TPU/PP/MA (70/25/5)

NF 53 310±5 6.1±0.05 6.9±0.05 7.2±0.05

TPU/PP(nano)/MA (70/25/5)

NF 53 367±5 7.1±0.05 7.8±0.05 8.3±0.05

TPU(nano)/PP/MA(70/25/5)

NF 54 436±5 7.5±0.05 9.5±0.05 9.8±0.05

Tensile test indicates that ester-TPU materials have better tensile properties than ether-

TPU materials. Compatibilised ester- and ether-TPU blend nanocomposites exhibited higher

stresses at the respective elongations than the uncompatibilised blends. The tensile test results

substantiate the compatibilisation offered by MA-g-PP as seen earlier in the other results. Ester-

TPU(nano)/PP/MA exhibited the best tensile properties as shown in the Table 3.5 & 3.6.

Nanoclay filled thermoplastic polyurethane (TPU) / polypropylene (PP) blends

compatibilised with maleic anhydride grafted polypropylene (MA-g-PP) have been studied with

emphasis on sequence of nanoclay addition. In sequence I [TPU(nano) / PP/ MA-g-PP],

nanoclay was first added to TPU and this nano composite was blended with PP, using MA-g-PP

as compatibiliser. In the case of sequence II [TPU/ PP(nano)/MA-g-PP], nanoclay was added

first to PP and blended with TPU, using MA-g-PP as compatibiliser. The results indicated that

37

sequence I imparted greater compatibility to the polymers and better nanoclay dispersion than

sequence II. Overall the TPU (nano) / PP/ MA-g-PP blend system shows better dispersion than

TPU/ PP(nano)/MA-g-PP. Nanoclay was used to reduce the surface energy of the TPU hard

segments and makes them more compatible with the non-polar PP. More miscible blends have

been obtained by using MA-g-PP as the compatibiliser. Better dispersion of organoclay may be

attributed to two reasons. Firstly, maleic anhydride forms hydrogen bonds with the hydroxyl

groups of the silicate layers. Secondly, there is a possible chemical reaction between maleic

anhydride and the urethane linkages in the TPU hard segments. Compared to the sequence II

blend nanocomposites, the sequence I blends show better miscibility as confirmed by tensile test.

3.3 Thermal Properties

3.3.1 Thermal degradation 3.3.1.1 Neat polymers

Polymers are useful in certain range of temperature- a low temperature limit below which

they are brittle and a high temperature limit above which they soften, melt degrade and ultimately

decompose. The TGA and DTG thermograms of TPU and PP in nitrogen atmosphere at a heating

rate of 10°C/min are shown in the Figure 3.23 & 3.24. TPU major degradation starts at 290°C and

gets completed at 460° C.The peak of the DTG curves gives the temperature corresponding to

maximum degradation (Tmax). In the DTG curve of ester-TPU, the peak appeared at 370.3°C.

Thermal decomposition of TPU has been studied by various researchers [63-71].

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Temperature,°C

Wei

ght

loss

(%

)

Neat PPNeat ether TPUNeat ester TPU

Figure 3.23. Neat polymers TGA analysis

38

-16

-14

-12

-10

-8

-6

-4

-2

0

0 100 200 300 400 500 600 700 800

Temperature,°C

DT

G (

%/m

in)

Neat PP

Neat ether TPU

Neat ester TPU

Figure 3.24. Neat polymers DTG analysis

The degradation of PP (Figure 3.23) starts around 390°C and almost completed at 490°C.

PP has got greater thermal stability in nitrogen atmosphere than TPU, which is evident from the

displacement of the weight loss curve to much higher temperature. DTG curve , also supports the

thermal stability of PP (Tmax 474.1°C) when compared to TPU (Tmax 370.3°C).

3.3.1.2 Uncompatibilised blends

The TGA and DTG thermograms of the blends are presented in Figure 3.25 & 3.26

respectively. Compared to the degradation pattern of the individual components, the degradation

behaviour of the blends is slightly different. The weight loss of neat polymers and their blends at

different temperatures is given in the Table 3.7. It can be seen from Table 3.7 that degradation

temperature corresponding to different percentage weight loss decreases gradually by the

addition of PP in blends. TPU (nano)/PP/MA-g-PP possesses highest Tmax values, which indicate

that high thermal stability than other blend system. As the weight percentage of the PP in the

blend increases, a gradual decrease in weight loss can be noticed indicating an increase in

thermal stability. This indicates improved thermal stability upon the incorporation of PP.

Thermal stability of the polymer blends depends mainly on the morphology and miscibility of

the system. It should be noted that in TPU/PP (30/70) blends, the thermally more stable PP forms

the matrix where as in TPU/PP (70/30) blends TPU is the continuous phase. A thermal

degradation result suggests that even though the TPU/PP blends are immiscible, the thermal

stability of TPU can be improved by the addition of PP.

39

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Temperature,°C

Weig

ht lo

ss %

TPU/PP (0/100)TPU/PP (30/70)TPU/PP (50/50)TPU/PP (70/30)TPU/PP (100/0)

(a)

-16

-14

-12

-10

-8

-6

-4

-2

0

2

0 100 200 300 400 500 600 700 800

Temperature,°C

DT

G (

%/m

in)


(b)Figure 3.25. Effect of blend ratio on the thermograms of TPU/PP blends

(a) Ester-TPU based thermograms (b) Ester-TPU based derivative thermograms

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Temperature,°C

Weig

ht lo

ss %


(a)

-16

-14

-12

-10

-8

-6

-4

-2

0

2

0 100 200 300 400 500 600 700 800

Temperature,°C

DT

G (

%/m

in)


(b)Figure 3.26. Effect of blend ratio on the thermograms of TPU/PP blends

(a) Ether-TPU based thermograms (b) Ether-TPU based derivative thermogramsTable 3.7(a). Weight losses at different temperatures of ester-TPU/PP blend

40

Sample Tonset( °C) T50Weight loss at

400°C (%)Tmax ( °C)

TPU/PP (100/0) 275 370.5 75.5 370.3

TPU/PP (70/30) 283.2 386.5 55.2 392.1,442.2

TPU/PP (50/50) 307.2 406.5 48.1 401.2,452.1

TPU/PP (30/70) 322.5 417.8 41.9 412.7,462.1

TPU/PP (0/100) 390 470.5 2.3 474.1

Table 3.7(b). Weight losses at different temperatures of ether-TPU/PP blend

Sample Tonset( °C) T50Weight loss at

400°C (%)Tmax ( °C)

TPU/PP (100/0) 277 371.9 73.2 372.3

TPU/PP (70/30) 283.7 389.1 53.2 393.3,443.6

TPU/PP (50/50) 307.9 409.7 46.1 401.8,454.2

TPU/PP (30/70) 323.7 421.5 38.1 414.2,464.3

TPU/PP (0/100) 390 470.5 2.3 474.1

3.3.1.3 Compatibilised blends

The TGA and DTG curves of TPU/PP blends compatibilised with MA-g-PP are shown in

Figures.3.27&3.28 respectively. Compatibiliser has substantial influence on the thermal

properties of the blends. The thermal stability of the blends was found to be increased by the

incorporation of MA-g-PP. In Figure 3.27, the peak corresponding to the major weight loss is

shifted to higher temperatures upon compatibilisation. Table 3.8 shows the degradation

temperature and weight loss at different temperature for the compatibilised blends.

The addition of 5 % of MA-g-PP resulted in the improvement of the onset temperature

for degradation. Further addition of the nanoclay showed again improvement in degradation

temperature of the blend. The addition of nanoclay in TPU (nano)/PP/MA-g-PP sequence has got

the maximum degradation temperature. .It also be seen from the table that the Tmax to the major

weight loss (DTG peak value) increased upon compatibilisation. The percentage weight loss at

different temperatures decreased upon compatibilisation.

Table. 3.8(a). Degradation temperatures and weight loss at different temperature of nanoclay filled 70/30 ester-TPU/PP blend compatibilised with MA-g-PP

41

Sample Tonset T50Weight loss at

400°C (%)Tmax ( °C)

TPU/PP (70/30) 283.2 386.5 55.2 392.1,442.2

TPU/PP/MA-g-PP (70/25/5)

285.2 394.1 53.3 431.9

TPU/PP(nano)/MA-g-PP (70/25/5)

290.3 399.3 50.5 442.1

TPU(nano)/PP/MA-g-PP (70/25/5)

295.2 403.3 49.2 453.1

Table. 3.8(b). Degradation temperatures and weight loss at different temperature of nanoclay filled 70/30 ether-TPU/PP blend compatibilised with MA-g-PP

Sample Tonset T50Weight loss at400°C (%)

Tmax ( °C)

TPU/PP (70/30)283.7 389.1 53.2 393.3,443.6


284.3 393.3 52.4 428.9


288.3 397.7 51.1 434.1


292.2 401.9 48.9 443.1

The increase in degradation temperature of compatibilised blends is due to the improved

interfacial adhesion between the two components as the result of compatibilisation, which is

having a direct influence on the thermal properties. MA-g-PP can increase compatibility of

TPU/PP blends through interfacial chemical reaction between its anhydride groups and the

urethane groups of TPU. The resulting copolymer will locate at the interface and decreases

interfacial tension thus provides a good interfacial adhesion between the TPU and PP phases.

This in turn will contribute towards the improvement of thermal stability. Therefore the

enhanced thermal stability of TPU/PP (70/30) blends upon compatibilisation addition can be

attributed to the compatibilising efficiency of MA-g-PP.

It is important to not that there is a strong link between the thermal properties and

morphology of the blends. The compatibilising efficiency of MA-g-PP is well evident from the

finely dispersed uniform morphology compared to uncompatibilised blend. The morphological

parameters of TPU/PP blends derived from SEM micrographs are shown in the Figure 3.6. From

the micrograph it was clear that the domain size of the dispersed PP in the compatibilised system

42

is decreased considerably. It has been revealed from this study stabilization of morphology

through chemical reaction has profound effect on the thermal properties of the blends.

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800 900

Temperature,°C

Wei

ght l

oss

%

TPU/PP (70/30) TPU/PP/MA-g-PP (70/25/5)

TPU/PP(nano)/MA-g-PP (70/25/5) TPU(nano)PP/MA-g-PP (70/25/5)

(a)

-14

-12

-10

-8

-6

-4

-2

0

2

0 100 200 300 400 500 600 700 800 900

Temperature,°C

DT

G (

%/m

in)


TPU/PP(nano)/MA-g-PP (70/25/5) TPU(nano)/PP/MA-g-PP (70/25/5)

(b)

Figure 3.27. Effect of blend ratio on the thermograms of compatibilised TPU/PP blends

(a) Ester-TPU based thermograms (b) Ester-TPU based derivative thermograms

43

0

20

40

60

80

100

120

250 300 350 400 450 500

Temperature,°C

Weig

ht lo

ss %

TPU/PP (70/30)


TPU/PP(nano)/PP (70/25/5)


(a)

-14

-12

-10

-8

-6

-4

-2

0

0 100 200 300 400 500 600 700 800 900Temperature,°C

DT

G (

%/m

in)

TPU/PP (70/30)


TPU/PP(nano)/MA-g-PP(70/25/5)TPU(nano)/PP/MA-g-PP(70/25/5)

(b)

Figure 3.28. Effect of blend ratio on the thermograms of compatibilised TPU/PP blends

(a) Ether-TPU based thermograms (b) Ether-TPU based derivative thermograms

3.3.2 Melting and crystallisation behaviour

3.3.2.1 Uncompatibilised blends

The DSC heating and cooling scans can be used to determine a number of parameters

signifying the melting and non-isothermal crystallization behaviour of the components in the

blends. The melting peak temperature (Tm), crystallisation temperature (Tc), heat of fusion (

ΔH f ) and heat crystallization ( ΔH c ) were directly obtained from these graphs. The TPU

used in this study is a –ester and –ether based TPU. It shows a wider melting range compared to

the other semicrystalline.The melting point (Tm) of the TPU which we used in this study depends

44

on both composition and the susceptibility of the mixed components. The Tm of the crystalline

component in a blend is dependent on both morphological and thermodynamic factors [72]. This

is related to crystallization condition like temperature, time, blend composition and scanning

rate. These factors can cause increase or decrease in Tm. Figure 3.29(b) represents the second

heating endotherms of TPU and some of its selected blends with PP.

Table 3.9. Melting behaviour of uncompatibilised ester-TPU/PP blends

Sample Tg (°C ) Tm(°C )ΔHf ( J/g)

NormalisedXc %

Crystallinity

TPU/PP (0/100) ------- 168.2 85.05 41

TPU/PP (30/70) -50.1 167.9 83.9 40

TPU/PP (50/50) -54.3 168.0 82.5 40

TPU/PP (70/30) -61.2 167.7 81.3 39

TPU/PP (100/0) -63.1 ------ ----- -------

-1.6

-1.1

-0.6

-0.1

0.4

-100 0 100 200 300

Temperature,° C

Heatf

low

(m

W)

Figure 3.29 (a). Neat PP DSC thermogram

Table 3.10. Melting behaviour of uncompatibilised ether-TPU/PP blends

Sample Tg (°C ) Tm (°C )ΔHf ( J/g)

NormalisedXc %

Crystallinity

TPU/PP (0/100) ------- 168.2 85.05 41

TPU/PP (30/70) -51.2 167.7 82.1 40

TPU/PP (50/50) -58.2 167.3 81.6 39

TPU/PP (70/30) -61.6 167.9 80.1 39

TPU/PP (100/0) -65.3 ------ ------ -----

45

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

-100 -80 -60 -40 -20 0 20 40

Temperature,° C

He

atfl

ow

(m

W)

TPU/PP (100/0)

TPU/PP (70/30)

TPU/PP (50/50)

TPU/PP (30/70)

Figure 3.29 (b). Effect of blend ratio on the Tg of ester-TPU/PP blends

0 50 100 150 200

Temperature,° C

Exo

-he

atf

low

(m

W) a - TPU/PP (0/100)

b - TPU/PP (30/70)c - TPU/PP (50/50)d - TPU/PP (70/30)

b

c

d

a

(a)

46

0 50 100 150 200

Temperature,° C

En

do

-he

atfl

ow

(m

W)

d - TPU/PP (0/100)

c - TPU/PP (30/70)

b - TPU/PP (50/50)

a - TPU/PP (70/30)

a

b

c

d

(b)

Figure 3.30. a) Effect of blend ratio on PP crystallization behaviour of ester –TPU/PP blends.

(b) Effect of blend ratio on the PPs (ΔHf ) enthalpy of fusion in the heating curves of ester-

TPU/PP blends

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

-100 -50 0 50

Temperature,° C

He

atflo

w (

mW

)

TPU/PP (50/50)

TPU/PP (30/70)

TPU/PP (100/0)

TPU/PP (70/30)

Figure 3.31. Effect of blend ratio on the TPUs Tg in the heating curves of ether-TPU/PP blends

47

0 50 100 150 200

Temperature,° C

Exo

-hea

tflow

(m

W)

a - TPU/PP (0/100)b - TPU/PP (30/70)c - TPU/PP (50/50)d - TPU/PP (70/30)

a

b

c

d

(a)

0 50 100 150 200Temperature,° C

En

do

-he

atflo

w (

mW

)

d - TPU/PP (0/100)c - TPU/PP (30/70)b - TPU/PP (50/50)a - TPU/PP (70/30)

a

b

c

d

(b)

Figure 3.32. (a) Effect of blend ratio on PP crystallization behaviour of ether –TPU/PP blends.

(b) Effect of blend ratio on the PPs (ΔHf ) enthalpy of fusion in the heating curves of ether-

TPU/PP blends

The crystalline melting point (Tm ) is almost same in all blends during second heating.

This reveals that blending has no effect on the melting point of the TPU and PP. This also

indicates that the two polymers are highly immiscible and the blends are incompatible.

The onset of Tm and the melting temperature (Tm ) of PP appeared at 130.6 and 168.2°C

respectively. On adding TPU, the thermogram exhibits a different behaviour. The normalized

48

value of enthalpy of fusion, ΔH f decreased to 81.3 for TPU rich blends (TPU/PP 70/30) in

ester-TPU and to 80.1 in ether-TPU. The % crystallinity and enthalpies of fusion of the blends

are significantly depending on the blend composition. The glass transition values of the TPU are

also increased (12°C). This can be attributed due to the encroachment of PP into the TPU

structure. This causes considerable increase of chain rigidity, which increases the Tg of TPU due

to the restricted mobility of TPU chains. The glass transition temperature (Tg) of the sample were

obtained from the inflexion of the thermograms in the DSC trace. The Tg of pure ester and ether

TPU are found to be -63.1 and – 65.3 °C respectively. The effect of blend ratio on the %

crystallinity is given in the Figure 3.22.

3.3.2.2 Compatibilised blends

The heating and cooling curves of TPU/PP (70/30) blend are shown in the Figure 3.34

and 3.35 respectively. The obtained from DSC thermogrames are tabulated in Table 3.11 and

3.12. The observed value indicates that compatibilisation does not show appreciable effect on

the melting and crystallization behaviour of the TPU/PP (70/30) blends. It is well evident from

the figure and table that compatibilisation does not have much contribution towards melting and

crystallisation parameter.

Table 3.11. Melting and crystallization behaviour of compatibilised ester- TPU/PP (70/30)

blends

Sample Tg (°C)Tm

(°C)Tc

(°C)

ΔHf ( J/g)

Enthalpy of fusion

ΔHc ( J/g)

Enthalpy of

Crystallisation

Xc %

Crystallinity

TPU/PP (70/30) -61.2 167.9 118.1 81.3 -82.9 39

TPU/PP/MA-g-PP

(70/25/5)-58.3 168.0 116.5 80.9 -82.1 39

TPU/PP(nano)/

MA-g-PP (70/25/5)-53.1 167.7 116.5 80.1 -81.7 38

TPU(nano)/PP/

MA-g-PP (70/25/5)-47.1 167.7 116.0 79.6 -81.2 38

49

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

-100 -50 0 50 100

Temperature,°C

He

atfl

ow

(m

W)

TPU(nano)/PP/MA-g-PP

TPU/PP(nano)/MA-g-PP

TPU/PP/MA-g-PP

TPU/PP

Figure 3.33. Effect of nanoclay on compatibilised ester TPU blends Tg

0 50 100 150 200

Temperature,° C

En

do

-he

atf

low

(m

W)

a - TPU(nano)/PP/MA-g-PPb - TPU/PPc - TPU/PP/MA-g-PPd - TPU/PP(nano)/MA-g-PP

a

b

c

d

Figure 3.34. Effect of compatibiliser and nanoclay on melting behaviour of ester 70/30 TPU/PP

blends

50

0 50 100 150 200Temperature,° C

Exo

-he

atflo

w (

mW

)

a - TPU/PP (0/100)

b - TPU/PP (70/30)

c - TPU/PP/MA-g-PP (70/25/5)

d - TPU(nano)/PP/MA-g-PP (70-nano/25/5)

a

bc

d

Figure 3.35. Effect of compatibiliser and nanoclay on crystallization behaviour on ester 70/30

TPU/PP blends

Table 3.12. Melting and crystallization behavior of compatibilised ether- TPU/PP (70/30) blends

51

SampleTg

(°C)

Tm

(°C )

Tc

(°C )

ΔHf ( J/g)

Enthalpy of fusion

ΔHc ( J/g)

Enthalpy of

Crystallisation

Xc %

Crystallinity

TPU/PP (70/30) -62.5 167.9 118.1 80.1 -81.4 39

TPU/PP/MA-g-PP

(70/25/5)-60.1 168.0 116.1 79.7 -80.9 39

TPU/PP(nano)/

MA-g-PP (70/25/5)-57.2 167.6 115.9 79.1 -80.3 38

TPU(nano)/PP/

MA-g-PP (70/25/5)-54.3 167.4 115.7 78.7 -79.8 38

-1.5

-1

-0.5

0

0.5

1

1.5

-100 -50 0 50 100

Temperature,° C

He

atflo

w (

mW

)TPU/PP

TPU/PP/MA-g-PP



Figure 3.36 (a). Effect of compatibiliser and nanoclay on Tg of ether 70/30 TPU/PP blends

0 50 100 150 200Temperature, ° C

Endo-h

eatflo

w (

mW

)

a - TPU(nano)/PP/MA-g-PP b - TPU/PPc - TPU/PP/MA-g-PPd - TPU/PP(nano)/MA-g-PP

a

b

c

d

Figure 3.36(b). Effect of compatibiliser and nanoclay on melting behaviour of ether 70/30 TPU/PP blends

52

0 50 100 150 200

Temperature,°C

Exo

-he

atfl

ow

(m

W)

a - TPU/PP (0/100)

b - TPU/PP (70/30)

c - TPU/PP/MA-g-PP (70/25/5)

d - TPU(nano)/PP/MA-g-PP (70-nano/25/5)

a

b

c

d

Figure 3.36(c). Effect of compatibiliser and nanoclay on crystallization behaviour on ether 70/30

TPU/PP blends

3.3.3 Rheological properties

For the design and development of multiphase polymer blend systems, a thorough

knowledge of the relationship between molecular characteristics of the component polymers,

their rheological and interfacial properties, the melt processing conditions and the flow induced

microstructure is essential. Melt flow studies give us valuable viscosity of polymers which are

highly important for optimizing the processing conditions and in designing processing

equipments.

The plot of complex viscosity (η*) vs frequency (ω) and the plot of storage modulus(G')

vs frequency (ω) and loss modulus (G") vs frequency (ω) for the ester TPU based blends with

nanoclay and compatibiliser are shown in Figures 3.37 and 3.38. Neat TPU had a much higher

viscosity than neat PP in all range of the frequencies carried out in this experiment. The greater

the content of TPU was, the higher was the viscosity. The introduction of PP into TPU resulted

in a reduction of the viscosity and thus the processability of the blends was improved. Very often

compatibilisation affects flow properties of the blends. Interactions occurring between blend

components generally increase the viscosity of the system. In Figures showing η* vs ω , G' vs

ω, and G" vs ω, where they showed change in complex viscosity at varying frequency, while

53

those with nanoclay and compatibiliser blend system exhibited higher complex viscosity. Higher

complex viscosity was attributed to the enhanced better dispersion in nanoclay and

compatibiliser containing blend system. Similar trend with ether-TPU based blend

nanocomposites were observed again indicating better dispersion in nanoclay and compatibiliser

added blend system. High increase of complex viscosity was observed in ester based blend

system.

1.E+02

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

η* (

Pa.

s)

TPU/PP (100/0) TPU/PP (70/30)TPU/PP (50/50) TPU/PP (30/70)TPU/PP (0/100)

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

G' (

Pa)


(a) (b)

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

G"

(Pa)


1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

η* (

Pa.

s)



TPU/PP/MA-g-PP

TPU/PP

( c ) (d)

54

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

G' (

Pa)


1.E+04

1.E+05

1.E+00 1.E+01 1.E+02

ω (rad/s)

G"

(Pa)



TPU/PP/MA-g-PP

TPU/PP

(e) (f)

Figure 3.37. Uncompatibilised-ester TPU (a) η* vs ω, (b) G' vs ω, (c ) G" vs ω

compatibilised-ester TPU (d) η* vs ω, (e) G' vs ω, (f ) G" vs ω

1.E+02

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

η* (

Pa.

s)


1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

G' (

Pa)


(a) (b)

55

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

G"

(Pa)

TPU/PP (100/0) TPU/PP (70/30)

TPU/PP (50/50) TPU/PP (30/70)

TPU/PP (0/100)

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

η* (

Pa.

s)


( c) (d)

1.E+03

1.E+04

1.E+05

1.E+00 1.E+01 1.E+02ω (rad/s)

G' (

Pa)


1.E+04

1.E+05

1.E+00 1.E+01 1.E+02

ω (rad/s)

G"

(Pa)


(e) (f)

Figure 3.38. Uncompatibilised-ether TPU (a) η* vs ω, (b) G' vs ω, (c ) G" vs ω

compatibilised-ether TPU (d) η* vs ω, (e) G' vs ω, (f ) G" vs ω

56

3.4 Dynamic Mechanical Analysis

3.4.1 Uncompatibilised BlendsFigures 3.39(a), (b), (c) and (d) show the wide temperature range DMA measurements

[storage modulus, log storage modulus, loss modulus and loss tangent factor (tan δ)] for TPU/PP

blends at 10 Hz. TPU records the minimum and intermediate values for the compatibilised

blends. At low temperature, since the polymers are in the glassy state, effect of temperature on

modulus improvement could not be observed for all compositions. The highest damping value is

seen for TPU. Damp value decreases upon incorporation of PP, as seen in the figure and have

higher loss tangent values.

The damping is low below Tg because the chain segments are frozen in. Below Tg the

deformations are thus mainly elastic and molecular slip resulting in viscous flow is low. As

temperature increases, damping goes through a maximum near Tg, in the transition region and

then a minimum in the rubbery region. Above Tg where rubbery region exists, the damping is

also low because molecular segments are very free to move about and there is very little

resistance for flow. Thus, when the segments are either frozen in or are free to move, damping is

low. The Tg due to TPU is seen at -60°C. There is change in Tg value due to TPU phase, on the

addition of PP into TPU. The Tg due to TPU transitions obtained from E "max and tan δ max are

given in Table 3.13 for ester – and ether- based TPU blends. There is considerable change in Tg

value due to TPU phase, on the addition of PP into TPU.

McGrum and colleagues have demonstrated that the tan δ curve of PP exhibits three

relaxations localized in the vicinity of -80 (γ), 10 (β) and 108 °C (α). However DMA analysis

[Figure 3.39(d) and 3.40(d)] do not show any clear separate tan δ peak corresponding to the β

relaxation [glass transition temperature of PP (Tg)], but more definite tanδ peak was observed

corresponding to Tα at approximately at 108 °C. The tanδ value at around 108°C, corresponding

to the α transition (Tα), is believed to be the result of molecular motions which resist the

softening effect of the applied heat. While Tg reflects mobility within the amorphous regions, Tα

dictates the onset of segmental motion within the crystalline regions. Clear tan δ peak was

observed corresponding to the α relaxation for the TPU/PP blend composition of 0/100 and

30/70, but not in the case of 50/50, 70/30 and 0/100. The tanδ peak corresponding Tα for TPU/PP

(0/100) and (30/70) blend composition are given in Table 3.13. Increase of TPU portion

eliminates the β relaxation in the blend system.

Table 3.13. Uncompatibilised (a) Ester- (b) Ether- TPU/PP blend57

(a) (b)

MaterialTg fromE "(°C)

Tg fromTan δ (°C)

TPU/PP 100/0 -36 -24

TPU/PP 70/30 -34 -22

TPU/PP 50/50 -24 -16

TPU/PP 30/70 -20 -7& 103 (Tα)

TPU/PP 0/100 -11 3& 108 (Tα)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

-100 0 100 200

Temperature,ºC

Sto

rag

e M

od

ulu

s (M

Pa

)

TPU/PP (0/100)

TPU/PP (30/70)

TPU/PP (50/50)

TPU/PP (70/30)

TPU/PP (100/0)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-100 0 100 200Temperature,°C

Log

Sto

rage

Mod

ulus

(M

Pa)


(a) (b)Figure 3.39 (a). Storage modulus (b). Log storage modulus of ester-TPU based

uncompatibilised blends

0

100

200

300

400

500

600

700

800

900

1000

-100 0 100 200

Temperature,ºC

Loss

Mod

ulus

(MP

a)


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

-100 -50 0 50 100 150 200

Temperature, ºC

Tan

del

ta

TPU/PP (100/0)

TPU/PP (70/30)

TPU/PP (50/50)

TPU/PP (30/70)

TPU/PP (0/100)

( c) (d)Figure 3.39 . ( c). Loss modulus (d). Tanδ of ester- TPU based uncompatibilised blends

58

MaterialTg fromE "(°C)

Tg fromTanδ (°C)

TPU/PP 100/0 -44 -30

TPU/PP 70/30 -39 -25

TPU/PP 50/50 -32 -21

TPU/PP 30/70 -28 -14& 101 (Tα)

TPU/PP 0/100 -11 3& 108 (Tα)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

-100 0 100 200

Temperature,°C

Sto

rag

e M

od

ulu

s (M

Pa

) TPU/PP (0/100)

TPU/PP (30/70)

TPU/PP (50/50)

TPU/PP (70/30)

TPU/PP (100/0)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5


Log

Sto

rage

Mod

ulus

(M

Pa)


(a) (b)

Figure 3.40(a). Storage modulus (b). Log storage modulus of ether-TPU based

uncompatibilised blends

0

100

200

300

400

500

600

700

800

900

1000

-100 -50 0 50 100 150 200Temperature,ºC

Lo

ss M

od

ulu

s(M

Pa

)

TPU/PP (0/100)

TPU/PP (30/70)

TPU/PP (50/50)

TPU/PP (70/30)

TPU/PP (100/0)

00.020.040.060.080.1

0.120.140.160.180.2

-100 0 100 200

Temperature,ºC

Tan

del

ta


Figure 3.40. (c). Loss modulus (d). tanδ of ether-TPU based uncompatibilised blends

Figures 3.39(a), 3.39(c), 3.40(a)and 3.40(c)upper and lower curves show the temperature

dependence on the storage and loss modulus of the uncompatibilised samples from -100 to 200° C.

The effects of temperature on tan δ values of the blends are seen in Figures 3.39(d) and 3.40(d). At

very low temperature modulus of the blends are high. The modulus decreased with increase in

temperature and finally levels off at high temperature. The storage and loss moduli values of TPU are

high at low temperature and decreased sharply around-60 °C indicating distinct transition from

59

glassy to rubbery region. TPU rich blend (TPU/PP 70/30) also shows same trend. At low

temperature, the molecules are frozen in and exhibit very high modulus. Some secondary relaxations

occur after the glassy transitions.TPU is having very low modulus in the rubbery plateau. The

modulus values finally levels off as temperature increases. The decrease in modulus above PP Tg is

more pronounced in PP rich blends. Around the glass transition temperature of TPU the blends are in

the glassy state and the modulus is high.

The E' intensity follows nearly the composition. Thus it can be concluded that the stiffness of

the samples decreases with TPU content. A high modulus observed in TPU/PP 30/70 is mainly due

to major contribution from PP. A sharp increase in damping value in TPU/PP 70/30 blend is due to

the major contribution of TPU phase. It is observed that at room temperature, the storage and loss

moduli of PP are greater than TPU due to the high brittleness of PP because of its high Tg. Thus the

unmodified TPU/PP shows typical behavior for immiscible blends. The above results are very much

in agreement with that of systems based on blends of polypropylene and ethylene propylene diene

monomer (PP)/EPDM studied by Papke and Karger-Kocsis[73-74]

The chain mobility of the polymer can be understood from the area under the loss modulus

versus temperature curve [75]. As expected, loss modulus increases up to transition zone, until they

reach a maximum and then decreases with temperature. The damping behaviour of the blends

increases with increase in concentration of TPU.

3.4.1.1. Modulus –Composition ModelsVarious models exist for predicting elastic properties of polymeric materials. Different

models like parallel, series, Halpin- Tsai, Kerner, Davies and Budiansky were used to predict the

mechanical behavior of the blends. The two simple models are the so-called parallel and series

models, which could represent the upper and lower bounds of the tensile strength predictions.. This

model is applicable to materials in which the components are connected parallel to one another so

that the applied stress elongates each component to the same extent. Figure 3.41(a) and (b) gives a

comparison of theoretical and experimental values of storage modulus of the ester- and ether-TPU

based blends at 10°C and frequency of 10 Hz. The experimental values are in between series and

parallel models. Experimental and theoretical curves of storage modulus of TPU/PP blend as a

function of volume fraction of PP. Poisson ratio for homopolymers was assumed to be 0.48 for TPU

and 0.40 for PP.

60

0

1000

2000

3000

4000

5000

6000

7000

0 0.2 0.4 0.6 0.8 1Volume fraction of PP

Sto

rage

Mod

ulus

(MP

a)ExperimentParallel

SeriesHalpin Tsai

CoranKerner

0

1000

2000

3000

4000

5000

6000

7000

0 0.2 0.4 0.6 0.8 1


Sto

rage

Mod

ulus

(M

Pa)

Experiment

ParallelSeries

Halpin TsaiCoran

Kerner

(a) (b)

Figure 3.41. TPU based blends theoretical model (a) Ester based blends (b) Ether based blends

The predictions of these theories have been made with E1 =293 for ester, E1= 331 for

ether and E2= 6028 MPa for the storage modulus for TPU and PP respectively.

3.4.2. Effect of Compatibilisation with nanoclay

Preparation of ester- and ether- TPU/C10A nanocomposites by direct melt blending [23, 39-44],

using 3 wt% Cloisite 10A (organically modified montmorillonite clay) as the nanoscale reinforcement.

Nanocomposites with PP using MA-g-PP as the compatibiliser were prepared by melt blending.

Low temperature DMA measurements on few selected samples of the compatibilised blends

carried out at a frequency of 10 Hz. gave the following reports. The effect of temperature on storage

modulus, loss modulus and tan δ of MA-g-PP compatibilised blends are seen in Figure 3.42.(a), (c),(d)

and 3.43 (a),(c),(d)respectively. Indication of miscibility; while two separate Tg s indicate immiscibility of

the system. Experimental evidence of miscibility is often found when a single and a sharp glass transition

temperature, Tg, is observed in between the Tg s of the individual components. In the glass transition

region of linear polymers, the storage modulus usually decreases by three to four orders of magnitude

over a temperature range of 20-30°C. Also, in the glass transition region, E" and tan δ go through

maxima. The quantities E " and tan δ can be utilized in mechanical damping applications to reduce

mechanical vibrations and noise emission. Tg from E "max and tan δ max are given in Table 3.14.The

dynamic mechanical parameters (storage modulus) for the various blend nanocomposites are plotted as a

function of temperature, at a constant frequency of 10 Hz (Figure 3.42(a)and 3.43(a). The storage moduli

at -50 0C, 0 0C, 20 0C and 30 0C are shown in Table 3.14 and 3.15.The storage modulus at -40 0C of

61

ester-TPU/PP blends, without nanoclay and compatibilised with the same wt% of MA-g-PP, prepared

under identical conditions, is reported to be 7.23 GPa. Thus, a 3 wt% C10A reinforcement increased the

storage modulus of the blend by ~ 40%. At room temperature, the storage modulus value of the ester-

TPU (nano)/ PP/ MA blend nanocomposite is more than that of the other blends. It is possible that well-

dispersed clay platelets resulted in an increase of storage modulus. The dissipation factor (tanδ) of the

materials is presented as a function of temperature in Figure 3.42(d) and 3.43(d). The tanδ peak is

associated with the soft segment glass transition temperature and the peak positions are given in Table

3.14. The temperature corresponding to the tanδ peak increases in the order- ester-TPU/PP< ester-

TPU/PP/MA-g-PP < ester-TPU(nano)/PP/MA. This is attributed to the increasing order of dispersion for

the blends. In DMA testing, one way of calculating Tg is based on tan delta. Each tan delta peak

temperature indicates the Tg of TPU soft segment for that particular composition. A shift in this peak

indicates an effect on the dispersion level of blend system. The temperature corresponding to the tan delta

peak increases in the order: TPU / PP < TPU / PP / MA-g-PP < TPU / PP(nano) / MA-g-PP < TPU

(nano) / PP / MA-g-PP (-22 0C < -15 0C< -11 0C < -7 0C for ester and -25 0C < -18 0C< -14 0C < -10 0C

for ether). The same order was observed in DSC experiment also (-61.5 0C < -59.3 0C < - 53.5 0C). The

Tg may have different numerical values but it follows the same order. DMA and DSC experiments are

based on different concepts and hence the numerical values may not match. Ether based blends also

shows same type of trend with less shift in Tg values.

Table 3.14 Tg of compatibilised (a) Ester- and (b) Ether- TPU/PP (70/30) blends (a) (b)

62

Material CompositionTg

(E")Tg

(tanδ)

TPU/PP 70/30 -34 -22

TPU/PP/MA-g-pp -26 -15

TPU/PP(nano)/MA-g-PP -24 -11

TPU(nano)/PP/MA-g-PP -19 -7

Material CompositionTg

(E")Tg

(tanδ)

TPU/PP 70/30 -39 -25

TPU/PP/MA-g-pp -34 -18

TPU/PP(nano)/MA-g-PP -32 -14

TPU(nano)/PP/MA-g-PP -27 -10

Table 3.15. Storage modulus of compatibilised ester-TPU based blends

0

2000

4000

6000

8000

10000

12000

14000


Sto

rag

e M

od

ulu

s (M

Pa

)

TPU(nano)/PP/MA

TPU/PP(nano)/MA

TPU/PP/MA

TPU/PP

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-100 0 100 200

Temperature,° C

Log

Sto

rage

Mod

ulus

(M

Pa)

TPU(nano)/PP/MA TPU/PP(nano)/MA TPU/PP/MA TPU/PP

(a) (b)

Figure 3.42(a). Storage modulus (b). Log storage modulus of compatibilised ester-TPU based

blends

0

100

200

300

400

500

600

700

800

900

-100 0 100 200Temperature,ºC

Loss

Mod

ulus

(MP

a)

TPU(nano)/PP/MATPU/PP(nano)/MATPU/PP/MATPU/PP

0

0.05

0.1

0.15

0.2

0.25

0.3


Tan

delta

TPU(nano)/PP/MA

TPU/PP(nano)/MA

TPU/PP/MA

TPU/PP

Figure 3.42(c). Loss modulus (d). Tanδ of compatibilised ester-TPU based blends

63

Blend composition

Storage modulus, E’ (MPa)

-50°C 0°C 20°C 30°C

TPU/PP 7101 1434 721 348

TPU/PP/MA-g-PP 7605 2656 1763 1361

TPU/PP(nano)/MA-g-PP 8206 2701 1804 1411

TPU(nano)/PP/MA-g-PP 10173 3612 2230 1760

Table 3.16. Storage modulus of compatibilised ether-TPU based blends

0

2000

4000

6000

8000

10000

12000

14000

-100 0 100 200

Temperature,°C

Sto

rag

e M

od

ulu

s (M

Pa

)

TPU(nano)/PP/MA

TPU/PP(nano)/MA

TPU/PP/MA

TPU/PP

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

-100 0 100 200Temperature,° C

Log

Sto

rage

Mod

ulus

(M

Pa)

TPU(nano)/PP/MA

TPU/PP(nano)/MA

TPU/PP/MA

TPU/PP

(a) (b)Figure 3.43(a). Storage modulus (b). Log storage modulus of compatibilised ether-TPU based

blends

0

100

200

300

400

500

600

700

800

900

-100 0 100 200

Temperature,ºC

Loss M

odulu

s(M

Pa)

TPU(nano)/PP/MA

TPU/PP(nano)/MA

TPU/PP/MA

TPU/PP

0

0.05

0.1

0.15

0.2

0.25

-100 0 100 200

Temperature,ºC

Tan

del

ta

TPU(nano)/PP/MA

TPU/PP(nano)/MA

TPU/PP/MA

TPU/PP

Figure 3.43(c ). Loss modulus (d). Tanδ of compatibilised ether-TPU based blends

64

Blend compositionStorage modulus, E’ (MPa)

-50°C 0°C 20°C 30°C

TPU/PP 5489 763 523 431

TPU/PP/MA-g-PP 6116 902 578 464

TPU/PP(nano)/MA-g-PP 6613 1159 760 598

TPU(nano)/PP/MA-g-PP 7763 1921 1144 917

There is change in Tg values due to TPU on adding MA-g-PP to the blend system. The

two–step curves in the figure for the blends, is due to two-phase morphology indicating

immiscibility. Thus the transitions due to TPU and PP phases indicate that addition of

compatibilisers do not make the system single phase. Or compatibiliser addition could not

promote molecular level miscibility. This observation is in agreement with conclusions made by

Paul[76] that if two polymers are far from being miscible, then no compatibiliser is likely to

make the system single phase.

The Tg corresponding to TPU transition is shifted to higher temperature upon

compatibilisation. MA-g-PP with nanoclay compatibilised blends showed maximum shift.

Nanoclay reinforcement, besides giving substantial increase in modulus and tensile strength, also

functions as a surface modifier for TPU hard segments.. The reduced interfacial tension between

the thermoplastic polyurethane and the polypropylene due to the incorporation of nanoclay gives

better compatible blends. Compatibilisation effect is further improved by introducing

functionalised PP (MA-g-PP) in the nanoclay containing blends. At room temperature, the

storage modulus value of the ester-TPU blend nanocomposite is more than that of the ether-TPU

blend nanocomposite.As mentioned in the introductory chapter, the high polarity difference

between thermoplastic polyurethane and polypropylene limits the miscibility of their blends.

Nanoclay was used to reduce the surface energy of the TPU hard segments and makes them more

compatible with the non-polar PP. More miscible blends have been obtained by using MA-g-PP

as the compatibiliser. Better dispersion of organoclay may be attributed to two reasons. Firstly,

maleic anhydride forms hydrogen bonds with the hydroxyl groups of the silicate layers.

Secondly, there is a possible chemical reaction between maleic anhydride and the urethane

linkages in the TPU hard segments. Compared to the ether-TPU based blend nanocomposites,

the ester-TPU blends show better miscibility as confirmed by DMA analysis. The clear

difference between ester-TPU and ether-TPU is that ester-TPU has carbonyl groups both in the

polyol segments as well as the TPU hard segments. This may lead to more extensive hydrogen

bonding in the blend system thus improving the miscibility.

65

3.4.3. Effect of sequence of nanoclay addition on TPU/PP blend

In sequence I, TPU/nano nanocomposites were prepared and subsequently blended

with PP using MA-g-PP as compatibiliser. In sequence II, nanoclay was added to PP by similar

extruder melt blending and subsequently melt blended with TPU using MA-g-PP as

compatibiliser

Compared to sequence II blend nanocomposites, the sequence I shows better

miscibility. The clear difference between sequence I and sequence II is that the effect of

nanoclay is fully utilized for changing the surface tension of TPU hard segment in sequence I. In

the case of sequence II, the dispersion and the reaction of nanoclay with TPU was reduced since

nanoclay is first added to PP.

Table 3.17. Effect of sequence of nanoclay addition on Tg

MaterialTg (0C) from

E”Tg (0C) from

Tan δ

TPU/PP(nano)/MA-g-PP (Ester) -22 -9.0

TPU(nano)/PP/MA-g-PP (Ester) -19 -7.0

TPU/PP(nano)/MA-g-PP (Ether) -29 -12.0

TPU(nano)/PP/MA-g-PP (Ether) -27 -10.0

0

2000

4000

6000

8000

10000

12000

14000

16000

-100 -50 0 50 100 150 200Temperature,°C

Sto

rage M

odulu

s (

MP

a) TPU(nano)/PP/MA

TPU/PP(nano)/MA

0100200300400500600700800900

-100 -50 0 50 100 150 200Temperature, ° C

Loss

mod

ulus

(M

Pa)

TPU/PP(C10A)/MA

TPU(C10A)/PP/MA

(a) Ester-TPU storage modulus (b) Ester-TPU loss modulus

66

0

0.05

0.1

0.15

0.2

0.25

0.3


Tan d

elta

TPU(nano)/PP/MA

TPU/PP(nano)/MA

0

2000

4000

6000

8000

10000

12000

-100 -50 0 50 100 150 200

Temperature,ºC

Sto

rage

mod

ulus

(M

Pa)

TPU(nano)/PP/MATPU/PP(nano)/MA

( c) Ester-TPU Tanδ (d) Ether-TPU storage modulus

0

100200

300400

500

600700

800

-100 -50 0 50 100 150 200

Temperature,ºC

Loss

mod

ulus

(M

Pa)

TPU(nano)/PP/MATPU/PP(nano)/MA

0

0.05

0.1

0.15

0.2

0.25


Tan

delta

TPU(nano)/PP/MA

TPU/PP(nano)/MA

(e) Ether-TPU loss modulus (f) Ether-TPU Tanδ

Figure 3.44. Effect sequence of nanoclay addition on compatibilised TPU/PP blends

3.5 Flame-Retardant Properties

Table 3.18 shows the flame-retardant properties of the neat and flame-retardant TPU/PP

blends with different compositions. The limited oxygen index (LOI) value of the neat and

TPU/PP blend were 18%, and those of the flame-retardant PP/TPU blends and nanoclay filled

TPU/PP blends were increased about 9–10 units as compared with that of the neat TPU/PP

blend, which showed the studied flame retardants and nanoclay could greatly increase the LOI

value of the system. However reduction of mechanical properties is observed for conventional

flame retardant based compositions.

Table 3.18. LOI test and UL 94 test values for nanoclay based 70/30 TPU/PP blends

67

Material UL-94LOI values

(ASTM D 2863)PP V2 18

Ester-TPU V2 17Ether-TPU V2 17

Ester-TPU/PP and Ether-TPU(70/30)

V2 17

Ester-TPU(nano)/PP/MA-g-PP(3%nanoclay) (70/25/5)

V1 23

Ester-TPU(nano)/PP/MA-g-PP(5%nanoclay) (70/25/5)

V0 28.5

Ether-TPU(nano)/PP/MA-g-PP(3%nanoclay) (70/25/5)

V1 22

Ether-TPU(nano)/PP/MA-g-PP(5%nanoclay) (70/25/5)

V0 27.5

The results of the vertical burning test (UL-94) of the studied samples are also shown in

Table 3.18. The pure TPU/PP blend and the nanoclay filled TPU/PP blend containing 3%

nanoclay could not pass the UL-94 test, dripping occurs. However, the vertical burning

behaviour of the PP/TPU blends was improved and no dripping occurred with the incorporation

of the 5% nanoclay and reached a V0 rating.

Nanocomposites are a new class of polymer systems. Modified layered silicates as fillers

are dispersed at a nm-level within a polymer matrix. For nanocomposites new extraordinary

properties are observed. The thermal stability and the flame retardancy of polymers forming

nanocomposites are improved. The flame retardancy mechanism of layered silicate

nanocomposites is based on the char formation and its structure; the char insulates the polymer

from heat and acts as a barrier, reducing the escape of volatile gases from the polymer

combustion. The suggested mechanism by which clay nanocomposites function involves the

formation of a char and accumulation of minerals at the surface that serves as a potential barrier

to both mass and energy transport [77-82]. Visually a smooth char layer is formed at the surface

of the nanocomposite leaving a black char residue at the end of the experiment.

68

Table 3.19. LOI test and UL 94 test values for flame retardant based 70/30 TPU/PP blends

Material UL-94 LOI values

Ester-TPU/PP

(20% DECA)V0 32

Ether-TPU/PP

(20% DECA)V0 31

DECA –Decabromodiphenyl oxide (Flame retardant)

In summary, the flame retardant composed of 5% nanoclay and MA-g-PP compatibiliser

showed a good flame-retardant effect on the TPU/PP (70:30) blend, having the highest LOI

value (28.5%) and a UL-94 V-0 rating.

3.5.1. Mechanical Properties

Table 3.20 provides the mechanical properties of the neat and the flame-retardant

PP/TPU blends. A slip between the specimen and grip occurred at a very high strain levels (≥

600 to 800) and the specimens could not be broken. The ultimate elongations for these samples

were thus unavailable. As shown in Table 3.20, the tensile stress at 200 % strain and flexural

modulus of the ester-TPU/PP (70/30) blend are 6.4 MPa and 350 MPa, respectively. The

introduction of the nanoclay as the flame retardant to the TPU/PP blend system increased the

mechanical properties. The tensile stress at 200 % strain of the flame-retardant TPU/PP blend

was increased by 120% for 5% nanoclay loading; the increase of which was the largest; the

flexural modulus was increased by 80%–90%. Sample ester-TPU(nano)/PP/MA-g-PP(5%

nanoclay loading) had the best integrated mechanical properties among the flame-retardant

PP/TPU blends; its tensile stress at 200 % strain, and flexural modulus are 14.2 MPa, and 710

MPa, respectively.

69

Table 3.20. Mechanical properties of nanoclay based TPU/PP blends

MaterialsTensile stress at 200% strain

(MPa)Flexural

modulus (MPa)

Neat PP 32.6 ( at break) 1650± 1

Neat ester-TPU 4.3± 0.05 61± 1

Neat ether-TPU 4.3± 0.05 60± 1

Ester-TPU/PP (70/30) 6.4± 0.05 350± 1

Ether-TPU/PP (70/30) 6.7 ± 0.05 365± 1

Ester-TPU(3%nano)/PP/MA-g-PP (70/25/5) 10.3± 0.05 605± 1

Ester-TPU(5%nano)/PP/MA-g-PP (70/25/5) 14.2± 0.05 710± 1

Ether-TPU(3%nano)/PP/MA-g- PP(70/25/5) 9.8± 0.05 565± 1

Ether-TPU(5%nano)/PP/MA-g-PP(70/25/5) 13.7± 0.05 673± 1

Table 3.21. Mechanical properties of flame retardant based TPU/PP blends

MaterialsTensile

strength (MPa)

Elongation

(%)

Flexural modulus (MPa)

Ester-TPU/PP

(20% DECA)31.1± 0.1 200±1 1205±1

Ether-TPU/PP

(20% DECA)30.6± 0.1 210±1 1158±1

70

Table 3.22. Rate of burning and ignition response test

MaterialRate of burning

(mm/min)

Ignition response time

(seconds)

Neat PP 17.54 5-10

Neat ester-TPU 20.93 5-10

Neat ether-TPU 20.9 5-10

Ester-TPU/PP 18.3 5-10

Ether-TPU/PP 18.2 5-10

Ester-TPU (3%nano) / PP/MA-g-PP

16.3 15-20

Ester-TPU (5%nano) / PP/MA-g-PP

15.0 20-25

Ether-TPU (3%nano) / PP/MA-g-PP

16.4 15-20

Ether-TPU (5%nano) / PP/MA-g-PP

15.5 20-25

3.6. Electrical Properties

3.6.1. Uncompatibilised blends electrical properties

3.6.1.1. Effect of blend ratio on volume resistivity

Basically, polymers have high value of resistivity, owing to the non-availability of free

electrons for conduction. Resistivity studies are important for insulating materials, because the

most desirable characteristic of an insulator is its ability to resist the leakage of electrical current.

Volume resistivity is numerically equal to the direct current resistance between opposite faces of

a one centimeter cube of a material, expressed in ohm centimeters. Figure 3.45 shows the

variation of volume resistivity ρv of TPU/PP blends as a function of TPU concentration. Polar

polymers have lower resistivity than non-polar polymers due to the polarization of polar

polymers under the influence of electrical field, which promote the conducting process.

From the Figure 3.45 it is clear that PP is a good insulator with very high value of volume

resistivity where as the volume resistivity of TPU is very low. In the case of blends the volume

71

resistivity values are in between that that of TPU and PP. As the concentration of TPU increases

the volume resistivity values decreases.

6.2

6.3

6.4

6.5

6.6

6.76.8

6.9

7

7.1

7.2

7.3

0 20 40 60 80 100 120

Weight % of TPU

Log

volu

me

resi

sitiv

ity (

Ohm

-cm

)Ether - TPU

Ester - TPU

Frequency: 1 MHz

Figure 3.45. Variation of volume resistivity of TPU/PP blends with TPU content at 30° C

Volume resistivity of TPU, PP and their blends as a function of frequency is given in the

Figure 3.46. It can be seen from the Figure 3.46 that, with the incorporation of TPU, which is

comparatively a less insulating material reduces the volume resistivity.

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7

Log frequency (Hz)

Log

volu

me

resi

stiv

ity (

Ohm

-cm

)


Figure 3.46 (a). Volume resistivity of ester-TPU, PP and their blends as a function of frequency at 30° C

In TPU/PP (30/70) blend where PP forms the matrix, the curve is very close to PP curve

and in TPU/PP (30/70) the curve is very close to TPU. In all cases reduction in volume

resistivity is observed with increase in frequency. This can be attributed to the increase in

molecular mobility at high frequencies.

72

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7Log frequency (Hz)

Log

volu

me

resi

stiv

ity (

Ohm

-cm

)

TPU/PP (0/100)

TPU/PP (30/70)TPU/PP (50/50)

TPU/PP (70/30)TPU/PP (100/0)

Figure 3.46(b). Volume resistivity of ether-TPU, PP and their blends as a function of frequency at 30° C

3.6.1.2. Dielectric constant (ε')

The dielectric constant (ε') is an important parameter in the case of an insulating material.

It is an expression of the extent to which a material concentrates electric flux. The dielectric

material is a substance that is a poor conductor of electricity, but an efficient supporter of

electrostatic fields. Materials with high dielectric constants are useful in the manufacture of high

value capacitors. The variation of dielectric constants of TPU, PP and their blends as a function

of frequency is shown in the Figure 3.47. It is evident from the figure that ε' values of neat

TPU and their blends decrease with increasing the applied frequency. Generally the dielectric

constant of a polymer arises from various polarization phenomena that come into play when the

polymer is subjected to an electric field. The dielectric constant increases with increase in

polarizability. The different types of polarization possible in a material are (1) electronic

polarization (2) atomic polarization and (3) orientation polarization [83]. The orientation

polarization contributes a major part of the total polarization for polar polymers. In

heterogeneous materials, there is a possibility for interfacial polarization, which arises due to the

difference in conductivities of the two phases [84]. Therefore in the case of TPU, which is a

polar polymer, all the three types of polarization contribute towards the dielectric constant. As a

result, TPU exhibits high dielectric constant, especially at low frequencies.73

0

1

2

3

4

5

6

7

8


Die

lect

ric c

onst

ant (

ε')

a - TPU/PP (100/0)b - TPU/PP (70/30)c - TPU/PP (50/50)d - TPU/PP (30/70)e - TPU/PP (0/100)

a

b

c

d

e

Figure 3.47(a). Variation of dielectric constant of ester-TPU /PP blends with frequency at 30° C

0

1

2

3

4

5

6

7

8


Die

lect

ric c

onst

ant (

ε')

a - TPU/PP (100/0)b - TPU/PP (70/30)c - TPU/PP (50/50)d - TPU/PP (30/70)e - TPU/PP (0/100)

a

b

c

d

e

Figure 3.47(b). Variation of dielectric constant of ether-TPU /PP blends with frequency at 30° C

74

3.6.1.3. Dissipation factor and loss factor (ε")

The tangent of the dielectric phase angle or the tangent of the dielectric loss angle is

represented by the tan δ. The measurement of dissipation factor (tan δ) and loss factor (ε") of an

insulating material is important. In electrical applications, it is desirable to keep the electrical

losses to a minimum. Electrical loss indicates the inefficiency of an insulator. The loss tangent is

a measure of the alternating current electrical energy, which is converted into heat in an insulator

[85-86]. This heat raises the temperature, leading to deterioration of the polymeric materials. The

variation of tan δ and loss factor with frequency for TPU, PP and their blends is depicted in the

Figure 3.48 and 3.49. Addition of TPU into PP increases dissipation and loss factor. The increase

in the value is due to orientation polarization of polar TPU followed by oscillation under electric

fields.

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4 5 6 7

Log frequency (Hz)

Dis

sipa

tion

fact

or (

tanδ

) TPU/PP (0/100) TPU/PP (30/70)TPU/PP (50/50) TPU/PP (70/30)TPU/PP (100/0)

Figure 3.48(a).Variation of dissipation factor of ester-TPU /PP blends with frequency at 30° C

0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3 4 5 6 7

Log frequency (Hz)

Loss

fac

tor

(ε")

TPU/PP (100/0) TPU/PP (70/30)

TPU/PP (50/50) TPU/PP (30/70)

TPU/PP (0/100)

Figure 3.48(b). Variation of loss factor of ester-TPU /PP blends with frequency at 30° C

75

0

0.1

0.2

0.3

0.4

0.5

0 1 2 3 4 5 6 7

Log frequency (Hz)

Dis

sipa

tion

fact

or (

tanδ

)


Figure 3.49(a).Variation of dissipation factor of ether-TPU /PP blends with frequency at 30° C

0

0.5

1

1.5

2

2.5

3

3.5

4


Los

s fa

ctor

(ε"

)

TPU/PP (100/0) TPU/PP (70/30)

TPU/PP (50/50) TPU/PP (30/70)

TPU/PP (0/100)

Figure 3.9(b). Variation of loss factor of ether-TPU /PP blends with frequency at 30° C

3.6.2 Compatibilised blends electrical properties

The two polymers TPU and PP are incompatible. The immiscible blends have got

unfavorable interactions which lead to unstable morphology and poor interfacial adhesion, which

leads to the inferior properties of the blends. These limitations can be overcome by

compatibilisation. Hence a reactive route was employed to compatibles the system using MA-g-

PP as the compatibiliser. The urethane group of the TPU can react with the anhydride group of

the compatibiliser to form a graft polymer, which can locate at the interface. Analysis of phase

morphology, mechanical, DMA and thermal properties proved that MA-g-PP could act as an

effective compatibiliser in TPU/PP blend system. In this context we, analyze the effect of

compatibilisation on the dielectric properties of 70/30 (TPU/PP) blends. Both ester- and ether-

based TPU was used for these studies because soft segment of ester and ether TPU has different

76

surface tension values. Further to that nanoclay was incorporated in the system to reduce the

surface tension of TPU hard segment to make the blend more compatible.

3.6.2.1.Volume Resistivity

0

2

4

6

8

10

12

14

2 3 4 5 6 7Log frequency (Hz)

Log

volu

me

resi

stiv

ity (

Ohm

-cm

)

TPU/PP (70/30)TPU/PP/MA-g-PP (70/27/3)TPU/PP/MA-g-PP (70/25/5)TPU/PP/MA-g-PP (70/23/7)

0

2

4

6

8

10

12

14


Log

volu

me

resi

stiv

ity (

Ohm

-cm

)


(a) (b)Figure 3.50 (a). Effect of compatibiliser concentration on the volume resistivity as a function of frequency at 30°C for ester based TPU blends

Figure 3.50(b). Effect of compatibiliser concentration on the volume resistivity as a function of frequency at 30°C for ether based TPU blends

The effect of compatibilisation on the volume resistivity of the TPU/PP (70/30) blends is

given in the Figure 3.50.It is well evident from the figure that compatibilisation resulted in the

increase of volume resistivity. The highest value of volume resistivity is observed at 5% of

compatibiliser concentration. With the incorporation of 3 wt% of MA-g-PP, the resistivity

becomes almost close to that of the uncompatibilised blends. During the 3% addition of the

compatibiliser, the anhydride group will react with the urethane groups of TPU, contributing

towards the reduction in overall polarity of the system. When the concentration of the

compatibiliser increases above level, the amount of polar groups in the system increases. This is

reflected in the volume resistivity at high compatibiliser loading. The morphology of the

compatibilised blends suggests that, by the incorporation of 5 wt% of the compatibiliser, CMC is

reached. Therefore further addition of the compatibiliser will leads to the formation of micelles.

It is expected that, the micellar aggregates of the compatibiliser will result in the increase of the

polarity.

77

0

2

4

6

8

10

12

14


Log v

olu

me r

esis

tivity (

Ohm

-cm

)

TPU/PP (70/30)TPU/PP/MA-g-PP (70/25/5)TPU/PP(nano)/MA-g-PP (70/25/5)TPU(nano)/PP/MA-g-PP (70/25/5)

0

2

4

6

8

10

12

14


Log

volu

me

resi

stiv

ity (

Ohm

-cm

)


(a) (b)Figure 3.51 (a). Effect of nanoclay addition on the volume resistivity as a function of frequency at 30°C for compatibilised ester based TPU blends

Figure 3.51(b). Effect of nanoclay addition on the volume resistivity as a function of frequency at 30°C for compatibilised ether based TPU blends3.6.2.2. Dielectric constant

The results of the effect of compatibilisation on the dielectric constant of TPU/PP (70/30)

blends are given in the Figure 3.52. It can be observed from the figure that compatibilisation

resulted in a substantial decrease of dielectric constant. The lowest value of dielectric constant

was observed at 5% of compatibiliser addition. Further addition of the compatibiliser increased

the dielectric constant. As discussed earlier, this observation may be due to the formation of

aggregates of the compatibiliser beyond CMC. Nanoclay addition to the compatibilised blends

resulted in decrease of dielectric constant values. Compared to sequence II blend

nanocomposites, the sequence I shows high volume resistivity and low dielectric constant values.

78

3

3.5

4

4.5

5

5.5

6

6.5

7


Die

lect

ric c

onst

ant (

ε')

TPU/PP (70/30)TPU/PP/MA-g-PP (70/23/7)

TPU/PP/MA-g-PP (70/27/3)TPU/PP/MA-g-PP (70/25/5)

3

3.5

4

4.5

5

5.5

6

6.5

7


Die

lect

ric c

onst

ant (

ε')


(a) (b)

Figure 3.52. Effect of compatibiliser concentration on the dielectric constant as a function of frequency at 30°C (a) Ester –TPU based (b) Ether –TPU based

0

1

2

3

4

5

6

7


Die

lect

ric c

onst

ant (

ε')



TPU/PP (70/30)


0

1

2

3

4

5

6

7


Die

lect

ric c

onst

ant (

ε')



TPU/PP (70/30)


(a) (b)

Figure 3.53. Effect of nanoclay addition on the dielectric constant as a function of frequency at 30°C for compatibilised (a) Ester -TPU based (b) Ether-TPU based

3.6.2.3. Dissipation factor and loss factor

Figures 3.54 to 3.57 show the variation of dissipation factor (tanδ ) and loss factor (ε")

on compatibilisation. As the frequency increases tanδ and loss factor decreases and then levels

off. The loss factor and dissipation factor reaches a minimum at 5% loading of the

compatibiliser. Increase in loss factor and dissipation factor at high concentration of MA-g-PP

can be attributed to the increase in the polarity of the systems at high loadings The lower values

79

of tan δ and ε" at the TPU(nano)/PP/MA-g-PP (compatibiliser loading of 5%,nanoclay loading

of 3%) implies that insulating property can be improved by using optimum concentration of the

compatibiliser and nanoclay.

0

0.05

0.1

0.15

0.2

0.25

0.3


Dis

sipa

tion

fact

or (

tanδ

)


0

0.05

0.1

0.15

0.2

0.25

0.3


Dis

sipa

tion

fact

or (

tanδ

)


Figure 3.54 Figure 3.55

Figure 3.54. Effect of compatibiliser concentration on the dissipation factor as a function of frequency at 30° for ester-TPU based blends

Figure 3.55. Effect of compatibiliser concentration on the dissipation factor as a function of frequency at 30° for ether-TPU based blends

0

0.05

0.1

0.15

0.2

0.25

0.3


Dis

sipa

tion

fact

or (

tanδ

)


0

0.05

0.1

0.15

0.2

0.25

0.3

0 1 2 3 4 5 6 7

Log frequency (Hz)

Dis

sip

atio

n f

act

or

(ta

nδ)


(a) (b)

Figure 3.56. Effect of nanoclay addition on the dissipation factor as a function of frequency at 30°C for compatibilised (a) Ester -TPU based (b) Ether-TPU based

80

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5 6 7

Log frequency (Hz)

Loss

fact

or (

ε")

TPU/PP (70/30)


TPU/PP(nano)/MA-g-PP (70/25/5)TPU(nano)/PP/MA-g-PP (70/25/5)

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5 6 7

Log frequency (Hz)

Loss f

acto

r (ε

")

TPU/PP (70/30)




(a) (b)Figure 3.57. Effect of nanoclay addition on the loss factor as a function of frequency at 30°C for compatibilised (a) Ester -TPU based (b) Ether-TPU based3.7.FTIR Analysis

3.7.1. Neat Polymer FTIR Analysis

0

20

40

60

80

100

120

600110016002100260031003600

Wavenumber (1/cm)

Tra

nsm

itta

nce %

Hydrogen bonded - NH

Hydrogen bonded C=O

Free C=O

Figure 3.58 (a). Neat ester-TPU FTIR

0

20

40

60

80

100

120

600110016002100260031003600

Wavenumber (1/cm)

Tra

nsm

itta

nce %

Hydrogen bonded -NH

Hydrogen bonded C=O

Free C=O

Figure 3.58(b). Neat Ether-TPU FTIR

81

0

20

40

60

80

100

120

60012001800240030003600

Wavenumber (1/cm)

Tra

nsm

ittance %

(a)

(b)

Figure

3.59.

(a)

Polypropylene FTIR (b) MA-g-PP FTIR

Figure 3.58(a) and 3.58(b) show the FTIR spectra of neat ester- and ether –polyol soft

segment based TPUs respectively. As reported in the literature, the hard segments of TPU

contains NH and C=O groups, which can interact and form intermolecular hydrogen bonding.

Two infrared regions are of interest in this study on TPU/PP blends,i.e. N-H (3500-3000 cm -1)

and C=O (1800-1640 cm-1) stretching vibration absorption regions. Both the NH and C=O

absorption peaks are contributions of overlapping bands of their free and hydrogen –bonded

group respectively.

In figure 3.58 , the – NH absorption peak is observed at 3340 cm-1 which is due to the

hydrogen bonded –NH in the urethane linkage. Similar behaviour is exhibited in FTIR spectra at

82

0

20

40

60

80

100

120

60012001800240030003600

Wavenumber ( 1/cm )

Tra

nsm

ittance %

the regions of 1780-1640 cm-1 as shown in Figure 3.58 for C=O groups. Two peaks of carbonyl

absorption for pure TPU could be seen, which were attributable to a free carbonyl stretching

vibration at 1730 cm-1 and hydrogen –bonded one at 1710 cm-1. For ether-TPU sample, the peak

at 3340 cm−1 due to the N-H stretching(H-bonded to carbonyl), the peak at 2956-2850 cm−1 due

to the asym and sym CH2 stretching, the peak at 1728 cm−1 due to the free C=O stretching and

the peak at 1704 cm−1 due to hydrogen bonded C=O stretching. There was no distinct peak

assigned to NCO group at about 2230 cm−1 for all samples, suggesting that the NCO group failed

to reach a detectable level. In the case of carbonyl peak, difference is observed between ester and

ether based TPU. The intensity of free carbonyl group is more for ester category, but in ether

category hydrogen bonded carbonyl group is more.

3.7.2 Uncompatibilised and compatibilised TPU/PP blends FTIR analysis

600110016002100260031003600

Wavenumber (1/cm)

Rela

tive T

ransm

ittance %

( a ) TPU/PP ( b ) TPU/PP/MA

( c ) TPU/PP(nano)/MA ( d ) TPU(nano)/PP/MA

1

23

a

b

c

d

Figure 3.60. Ester-TPU based compatibilised blends FTIR

Parts a, b,c and d of Figure 3.60 show the FTIR spectra of ester based TPU/PP,

TPU/PP/MA-g-PP, TPU/PP(C10A)/MA-g-PP and TPU(C10A)/PP/MA-g-PP blend systems

83

respectively. Three significant peaks are considered for discussion. Peak at 3340 cm -1 wave

number represents the hydrogen bonded– NH group. Peak at 1730 cm -1 and peak at 1700 cm -1

wave number represents free – C= O ( carbonyl ) and hydrogen bonded – C= O respectively.

The –NH groups in the urethane linkage of TPU/PP composition form hydrogen bonds

with carbonyls of other urethanes in TPU hard segments and with carbonyl group in the soft

segments of TPU[39-43]. In the case of TPU/PP/MA-g-PP composition –NH groups form

additional hydrogen bonding with maleic anhydride group of compatibiliser. In the case of TPU

(nano)/PP/MA-g-PP and TPU/PP (nano)/MA-g-PP composition –NH groups form further

hydrogen bonding with oxygen group of silicate layers of nanoclay. The increase of hydrogen

bonding is reflected in the FTIR spectra by increase of 3340 cm -1 peak intensity. The peak

intensity of hydrogen bonded – NH group increases in the order: TPU/PP< TPU/PP/MA-g-PP <

TPU/PP(nano)/MA-g-PP < TPU(nano)/PP/MA. The intensity of 1730 cm -1 peak decreases and

intensity of 1700 cm -1 peak increases from a to d of Figure 3.60. The – C= O of ester-TPU

hard and soft segments form hydrogen bonds with – NH group of urethane linkage leading to

free – C= O peak and hydrogen bonded – C= O peak corresponding to 1730 cm -1 peak and

1700 cm -1 of Figure 3.60a. In the case of Figure 3.60b, – C= O forms additional hydrogen

bonding with maleic anhydride group and in Figure 3.60c and Figure 3.60d, – C= O forms

further hydrogen bonding with hydroxyl groups of nanoclay silicate layer. Hence, the intensity

of 1730 cm -1 peak decreases and intensity of 1700 cm -1 peak increases from Figure 3.60a to

Figure 3.60d.

Table 3.23. Ratio of the areas under the specific peaks

MaterialEster-TPU Based blends Ether-TPU Based blends

ANH/ACH AHCO/ AFCO ANH/ACH AHCO/ AFCO

TPU/PP 0.21 0.56 0.12 3.12

TPU/PP/MA 0.23 0.61 0.15 3.32

TPU/PP(nano)/M

A

0.29 0.73 0.18 3.48

TPU(nano)/PP/M

A

0.35 overlap 0.28 3.96

ANH: area under the hydrogen bonded –NH peak; ACH: area under the -CH peak stretching

peak; AHCO: area under the hydrogen bonded –C=O peak; AFCO : area under the free –C=O peak.

84

0

50

100

150

200

250

300

350

400

450

600110016002100260031003600

Wavenumber (1/cm)

Re

lativ

e T

ran

smitt

an

ce %

( a ) TPU/PP ( b ) TPU/PP/MA

( c ) TPU/PP(nano)/MA ( d ) TPU(nano)/PP/MA

a

b

c

d

12

3

Figure 3.61 Ether-TPU based compatibilised blends FTIR

Parts a, b,c and d of Figure 3.61 show the FTIR spectra of ether based TPU/PP,

TPU/PP/MA-g-PP, TPU/PP(nano)/MA-g-PP and TPU(nano)/PP/MA-g-PP blend systems

respectively. Ether based blend system also reflects the same trend of ester which is discussed in

earlier.

The intensity of free carbonyl group is more for ester category, but in ether category

hydrogen bonded carbonyl group is more. Typically the –NH groups in the urethane linkage

form hydrogen bonds with carbonyls of the urethane linkage in the hard segment in both cases of

ether-TPU and ester-TPU. The –NH groups are also able to form hydrogen bonds with ether

oxygen of ether-polyol in the soft segment in case of ether –TPU and with carbonyl of ester-

polyol in the soft segment in case of ester-TPU. Ester based blends has totally (inclusive of free

and hydrogen bonded) more –C=O groups than ether based blends as confirmed by FTIR

analysis. The FTIR results indicate that the ester-TPU exhibited better compatibility than ether-

TPU. The clear difference between ester-TPU and ether-TPU is that ester-TPU has carbonyl 85

groups both in the polyol segments as well as the TPU hard segments. This may lead to more

extensive hydrogen bonding in the blend system thus improving the compatibility.

Cloisite 10A, a more hydrophobic nanoclay, when pre-mixed with TPU, is also thought

to function as a compatibiliser for TPU/PP blends because of its affinity for the non-polar PP.

Compared to the other blend system, the ester-TPU(nano)/ PP/MA-g-PP blends show better

dispersion as confirmed by FTIR analysis. Presence of nanoclay in ester –TPU(nano)/PP/MA-g-

PP may lead to more extensive hydrogen bonding in the blend system ,thus improving the

dispersion.

3.7.3. Effect of sequence of nanoclay addition on TPU/PP blends by FTIR analysis

In this work, studies were made on nanoclay filled MA-g-PP compatibilised TPU/PP

blends by considering the sequence of nanoclay addition. Figure 3.60 and 3.61 indicates that,

compared to sequence II (TPU/PP(nano)/MA-g-PP) blend nanocomposites, the sequence I

(TPU(nano)/PP/MA-g-PP) shows better compatibility for both ester- and ether-based blends. The

effect of nanoclay is fully utilized for changing the surface tension of TPU hard segment in

sequence I. The areas under hydrogen –bonded (AHCO) and free carbonyl peaks (AFCO) were

calculated and presented Table 3.23. In addition, the area under –CH stretching (2860-2940 cm -1) was also calculated and used as internal standard. Table 3.23 indicates that, the ratio of

ANH/ACH and AHCO/ AFCO value increases in the order: TPU/PP< TPU/PP/MA-g-PP <

TPU/PP(C10A)/MA-g-PP < TPU(C10A)/PP/MA for ester- and ether-based blends.

3.8. Transport Properties

3.8.1. Effect of blend composition

The amount of water uptake by neat TPU, PP and their blends at room temperature (30°

C) is given in the Figure 3.62. It is clear from the Figure 3.62 that water uptake percentage

varies with blend composition at 30°C (RT). Neat TPU exhibits the highest water uptake value.

This indicates that TPU is highly prone to water absorption due to the presence of carbony1,

ester/ether groups in TPU, which can form hydrogen bonds with water. In addition to this, since

TPU is hygroscopic in nature, diffused water molecule can form hydrogen bonding with already

bonded water molecules. A very interesting observation of the neat TPU curve is that, it exhibits

an overshoot effect in which a maximum uptake occurs followed by a decrease. This over shoot

effect is caused by penetrant rejection during chain relaxation. The chain relaxation is attributed

to chain rearrangement after maximum penetrant uptake, and change in morphology due to the

86

presence of swollen molecule and also due to sample thickness [87-91]. The degree of the over

shoots effect decreases as the PP content increased and is absent at 30, 50 and 100% PP.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 50 100 150 200 250 300 350

(t)1/2 (min)1/2

Qt (

mol%

)


(a)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 50 100 150 200 250 300 350

(t)1/2(min)1/2

Qt (

mol

%)

TPU/PP (100/0) TPU/PP (70/30)

TPU/PP (50/50) TPU/PP (30/70)

TPU/PP (0/100)

(b)

Figure 3.62. Sorption curves showing % uptake of water for polymers and their blends at

room temperature. (a) Ester- TPU based (b) Ether-TPU based

In the case of PP, water absorption is almost negligible. All the blends show a significant

initial increase in water uptake with time and reaches equilibrium after a few days. The Q t values

systematically increases with increase in the TPU content. The higher percentage water uptake

for the 50, and 70% of TPU can be explained on the basis of the morphology of the blends. In 87

TPU/PP (70/30) blend PP is dispersed as domains in the continuous TPU matrix. So with

increase in the TPU content, the hydrophilic TPU forms the continuous phase and facilitates the

entry of the water, thus increases the water sorption of the blends.

3.8.2. Effect of compatibilisation

As discussed in the previous sections, owing to the lack of favourable interfacial

interactions, TPU and PP are highly immiscible. We employed compatibilisation strategy to

improve the compatibility between the polymers. The compatibiliser used is MA-g-PP, which

ensures compatibility through hydrogen bonding and chemical reaction between urethane linkage

and maleic anhydride moiety. There are several examples in the literature for the urethane-

anhydride reactive compatibilisation [21,22,25]. We have investigated the effect of addition of

different levels of compatibiliser, MA-g-PP on the water sorption behaviour of TPU/PP (70/30)

blends. The influence of addition of MA-g-PP on the water uptake of TPU/PP (70/30) blends is

shown in the Figure 3.63. It is evident from the figure that water sorption decreases with

compatibiliser addition. This is due to the compatibilising action of the copolymer.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 50 100 150 200 250 300 350

(t)1/2(min)1/2

Qt (

mol%

)


TPU/PP/MA-g-PP (70/23/7) TPU/PP/MA-g-PP (70/25/5)

(a)

88

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 50 100 150 200 250 300 350(t)1/2(min)1/2

Qt (

mol

%)


TPU/PP/MA-g-PP (70/23/7) TPU/PP/MA-g-PP (70/25/5)

(b)

Figure 3.63. Effect of compatibilisation using MA-g-PP on the water sorption of TPU/PP

(70/30) blends at RT (30°C) (a) Ester-TPU based blends (b) Ether –TPU based blends

A detailed analysis of the action of the compatibiliser molecules in reducing the water up

take indicates that, prior to compatibilisation, the blends is characterized by a sharp interface due

to the high interfacial tension and poor adhesion between the components. Upon the addition of

the compatibiliser the situation undergoes a drastic change. The maximum uptake reduction is

observed for 5% of the compatibiliser loading. This is because interfacial saturation has occurred

at around 5% of MA-g-PP and further addition of the compatibiliser could not modify the

interface any more.

3.8.3 Effect of nanoclay addition

The sorption curves of TPU/PP (70/30) blends compatibilised with 5% of MA-g-PP and

two different sequence of nanoclay addition is shown in the Figure 3.64.

89

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 50 100 150 200 250 300 350

(t)1/2(min)1/2

Qt (

mol

%)

TPU/PP (70/30)




(a)

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350

(t)1/2(min)1/2

Qt (m

ol%

)

TPU/PP (70/30)TPU/PP(nano)/MA-g-PP (70/25/5)TPU(nano)/PP/MA-g-PP (70/25/5)TPU/PP/MA-g-PP (70/25/5)

(b)

Figure 3.64. Effect of compatibilisation using 5% of MA-g-PP with different sequence of

nanoclay addition on the water sorption of TPU/PP (70/30) blends

(a) Ester-TPU based blends (b) Ether –TPU based blends

The equilibrium uptake is highest for TPU/PP (70/30) and lowest for TPU

(nano)/PP/MA-g-PP. The other systems show intermediate values. The transport of the water

through the nanoclay filled compatibilised system is in the order: TPU (nano)/PP/MA-g-

PP(70/25/5)< TPU/PP(nano)/MA-g-PP (70/25/5)< TPU/PP/MA-g-PP(70/25/5) < TPU/PP(70/30).

90

These observations can be also explained on the basis of surface tension values which were

explained in earlier. Ether based TPU blends uptake of water is less compare to ester based

systems.

4. Conclusion

Nanoclay reinforcement, besides giving substantial increase in modulus and

tensile strength also function as a surface modifier for TPU hard segments. The reduced

interfacial tensions between the thermoplastic polyurethane and the polypropylene due to the

incorporation of nanoclay gives better compatible blends. Cloisite 10A, a more hydrophobic

nanoclay, when pre-mixed with TPU, is also thought to function as a compatibiliser for TPU/PP

blends because of its affinity for the non-polar PP. Compatibilisation can be further improved by

introducing functionalised PP (MA-g-PP) in the nanoclay containing blends. The strategy of

compatibilisation is supposed to be hydrogen bonding between carbonyl functional groups of

TPU, hydroxyl group of nanoclay silicate layers and anhydride moiety of MA. Different

characterisation techniques such as XRD, DSC, TGA, SEM, TEM and DMA studies were

carried out to characterize the prepared samples. Evaluation of tensile, abrasion and water

absorption properties of the blends and blend nanocomposites were carried out for analyses

purpose. Comparison of dispersion characteristics and properties of ester- and ether-TPU blend

nanocomposites and effect of sequence of nanoclay addition were evaluated. The melt blending

technique that we have adopted offers an advantage of introducing no foreign materials (like

solvents) into the blend. For this reason and because of the simplicity and speed of melt mixing it

has an economic advantage, which makes it a commercially acceptable blending method.

Most of the polymer products have to undergo cyclic stressing during their service

period. This cyclic stressing will generate heat, which can cause failure of the material. Hence

the study of the dynamic mechanical thermal properties is of crucial importance. The storage

modulus for the blends was between the E'/T curves of the pure TPU and PP, which also

suggested that the TPU and PP are partially miscible. Variation of the storage modulus (E') as a

function of the temperature was studied for the pure TPU and PP, as well as for the TPU/PP

blends. The values of storage modulus decreased monotonically with increasing temperature.

The E' curve of TPU shows a typical behaviour of an elastomer.The storage modulus curves of

the blends around the glass transition zone were intermediate between the E'/T curves of the pure

TPU and PP. The value of storage modulus of blends steady increases with increasing PP content

in blends. The damping factor, tanδ, of the pure TPU, PP, and TPU/PP blends were discussed. A

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very good correlation was found between morphology and dynamic mechanical properties.

Various composite models were used to predict the behaviour of the blends. Compatabilisation

of the blends and nanoclay addition showed significant increase in storage modulus because of

the enhanced interfacial interaction.

Mechanical properties of polymeric material are of crucial importance in designing a product.

The results obtained from mechanical property measurements and SEM analyses were

complementary. The mechanical properties of pure TPU, PP, and TPU/PP blends were measured by

stress–strain tests and obtained results are discussed. Pure TPU is ductile elastomer, while pure PP is

a rigid material. Simultaneously, the TPU had higher elongation at break in comparison to pure PP. It

is generally expected that an increase in the amount of stiff material in elastomeric material results in

an increase in tensile strength of blends. Compatibilisation improved the mechanical properties. The

increase in mechanical properties can be assigned to the increase in interfacial adhesion between

TPU and PP phases. Compatibilisation led to a fine morphology and made the interface stronger,

where effective stress transfer is possible. MA-g-PP was found to be a good compatibiliser for this

blend system. Nanoclay addition led to a further fine morphology in the blend system. Effect of

sequence of nanoclay addition in the blend system also studied.

The analysis of thermal stability of polymeric materials is necessary for the development of

durable products. The thermal degradation of TPU/PP blends was investigated using

thermogravimetric method. The thermogravimetric (TGA) studies revealed that the addition of PP to

TPU improved the thermal stability of the blends significantly. All the blends showed improved

initial decomposition temperature up on the addition of PP to TPU. Phase morphology was found to

be one of the decisive factors that affected the thermal stability since the thermal stability depended

on the stability of the matrix phase. The effect of compatibilisation of TPU/PP blend using MA-g-PP

on thermal degradation was also investigated. It was observed that the compatibiliser improved the

thermal stability of the blends considerably, by providing improvement in the interfacial interaction

between TPU and PP. The compatibiliser increased the decomposition temperature of these systems

especially at a critical value of its concentration in the blends. Nanoclay addition in the

compatibilised TPU/PP blends was also found to provide improvement in the decomposition

temperature. Nanoclay filled compatibilised blend showed the highest decomposition temperature.

Among the different composition systems used, sequence I nanoclay filled ester-TPU based system

showed higher activation energy values.

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XRD studies of the uncompatibilised blends revealed a slight reduction in crystallinity and

increase in interplanar distance of the PP as the incorporation of TPU. Compatibilisations did not

show much appreciable change in the crystallization pattern. In the case of nanoclay addition

marginally reduced the crystallinity of the system.

The transport properties of blends were studied to get an idea about the barrier properties of

the material. The transport properties are mainly depending on blend ratio, solvent polarity and

temperature. Since TPU is a hygroscopic thermoplastic, there is a good practical importance in

investigating water sorption behaviour of TPU based blends. The electrical properties such as

volume resisitivity, dielectric constant, loss and dissipation factors were measured over a wide range

of frequencies. Compared to polar TPU, PP exhibited good insulating properties. Among the neat

polymers, PP possessed the maximum volume resistivity and minimum dielectric constant. The

volume resistivity values of the blends fell in between those of TPU and PP. Ester-TPU has got high

dielectric constant. With the addition of PP, the dielectric constant decreased due to the decrease in

the overall polarity of the system. Among the different composition based systems used, the

nanoclay filled compatibilised ester-TPU based system, showed the lowest dielectric constant value.

The mixed system showed an intermediate value. Finally it can be concluded that thermoplastic

elastomer from compatibilised nanoclay filled TPU/PP system could be utilized for many

applications such as electrical, automotive etc.

SCOPE OF FUTURE WORK

1. Interfacial thickness can be measured using small angle X-ray scattering (SAXS), small

angle neutron scattering (SANS) ellipsometry

2. Computer software could be developed to predict the miscibility and phase behaviour of binary

polymer blends. Computational modeling of the behaviour of these blends can be done.

3. The effect of fillers on morphology and properties is an area to be explored. The effect of

other nanofillers like carbon nanotube (CNT), nanoclaciumcarbonate, etc, can be studied.

4. NMR spectroscopy can be utilized to assess the extent of compatibility of these blends.

5. The studies can be extended to free volume measurements by positron annihilation technique.

6. Variation in maleic anhydride content of MA-g-PP can change the properties of the blends

under discussion to a great extent. This could be future programme.

REFERENCES

1. D.J. Walsh, S. Rostami, Adv. Polym. Sci., 70, 119 (1985)93

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