Recycled Polypropylene Improved with Thermoplastic...

Research ArticleRecycled Polypropylene Improved withThermoplastic Elastomers

Ecaterina Matei,1 Maria Râps,2 Árpád Andor Andras,2 Andra Mihaela Predescu,1

Cristian Pantilimon,1 Alexandra Pica,3 and Cristian Predescu1

1Faculty of Materials Science and Engineering, University Politehnica of Bucharest, 313 Splaiul Independentei,060042 Bucharest, Romania2Research Institute of Auxiliary and Organic Products S. A., ICPAO, 8 Carpati St., Medias, 551022 Sibiu, Romania3Research Institute for Advanced Coatings S. A., ICAA, 49 ATheodor Pallady Blv., 032258 Bucharest, Romania

Correspondence should be addressed to Maria Rapa; [email protected] andAndra Mihaela Predescu; [email protected]

Received 9 January 2017; Revised 7 March 2017; Accepted 12 March 2017; Published 30 March 2017

Academic Editor: De-Yi Wang

Copyright © 2017 Ecaterina Matei et al.This is an open access article distributed under the Creative CommonsAttribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The use of recycled polypropylene (RPP) as raw material for various industries has been known. However, the mechanical andthermal properties of recycled products are lower than those of raw material. The objective of this study was to obtain andinvestigate the modified recycled polypropylene (RPP) with commercial elastomers for possible applications. The compoundedRPP-based thermoplastic elastomers were investigated in order to determine their thermal properties (melt flow index (MFI),differential scanning calorimetry (DSC), VICAT softening temperature (VST), and heat deflection temperature (HDT)), structuralcharacteristics (optical microscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD)), and mechanical properties(tensile properties, density, and IZOD impact). The RPP compounded with 10% elastomer recorded higher tensile properties thanthe unmodified RPP. Also, IZOD impact strength increased from 4.3 ± 0.2 kJ/m2 (registered for RPP) to 21.7 ± 2.5 kJ/m2 forthe PPR/SIS30 compound, while the degree of crystallinity decreased for all compounds. The obtained results recommend theRPP/elastomers compounds both for environmental remediation from postconsumer PP wastes and to realize new goods withhigh performance for various applications.

1. Introduction

It is known that most polypropylene (PP) materials show lowresistance to impact especially at low temperatures, whichlimits its applications in engineering fields. The technicalrequirements for automobiles, appliances, and other com-mercial products applications of PP materials envisage goodmechanical properties, easy processing, good aesthetics, andlow weight and cost. In order to obtain these properties,usually PP is compounding with elastomer, resulting inpolypropylene composites with improved properties [1].Generally, the elongation, impact strength, and brittle/toughtransition temperature represent the most important prop-erties improved when PP is compounded with elastomer

[2–8]. For example, [7] investigated the compatibilizedPP/poly(ethylene glycol-co-cyclohexane-1,4-dimethanol ter-ephthalate) blend with styrene-ethylene/butylene-styrene(SEBS), styrene-butadiene-styrene (SBS), and styrene-iso-prene-styrene (SIS) and reported a remarkable increase inimpact strength due to the addition of SIS, about 5 timesas that of the uncompatibilized blends; the yield strengthof the blends with SBS and SIS is enhanced from 33.6 to39.6 and 37.6MPa, respectively. A significant improvement onelongation at break from 35.9% to 91.2% and notched IZODimpact from 3.5 kJ/m2 to 7.1 kJ/m2 was obtained when PPwascompounded with 10% SEBS [3].

However, the widespread use of PP in various domainsresults in a significant amount of plastic waste. Different

HindawiInternational Journal of Polymer ScienceVolume 2017, Article ID 7525923, 10 pageshttps://doi.org/10.1155/2017/7525923

https://doi.org/10.1155/2017/7525923

2 International Journal of Polymer Science

recycling methods have been used for PP wastes includingland filling (causing a negative impact on the environment),mechanical [9, 10] including dissolution/reprecipitationmethod [11], chemical method [12, 13], and incineration[14, 15]. By mechanical recycling, the PP wastes are sepa-rated from other resin types, washed to remove dirt andcontaminants, and grinded and crushed to reduce theplastics’ particle size, followed by extrusion by heat andreprocessing into new plastic goods. Chemical recyclingleads to the conversion of plastic wastes to originalmonomersor other valuable chemicals, while, by incineration, energyis obtained. Among all recycling methods, mechanicaland chemical recycling are the most used for PP wastesmanagement.

The reuse and recovery rate of recycled PP materials areof great importance for the plastic industry, which dependson oil and has consequences on the environment and theeconomy.Therefore, the amount of energy and raw materials(such as propylene) required for the manufacturing of newproducts is reduced, large quantities of raw materials arereturned to the economic circuit, and the amount of PP wastedeposited at the landfill or incinerators is also diminished.

A large number of papers describe the modificationof recycled polypropylene with different additives, fillers,or processing reinforcements for obtaining of wood plasticcomposites (WPC) with high added value [9, 16–21], con-crete [22], and a novel coupling agent for fibrous cellu-lose/polypropylene composite [23].

It is known that themechanical properties of virginmate-rials are different from those of the corresponding recycledmaterials [10, 24]. For example, it showed that the tensilestrength of the highly recycled polypropylene decreased byabout 15% when it is compared to neat polypropylene [10].In another paper, by investigating the mechanical propertiesof recycled PP/nylon compounded with SEBS elastomer,it was found that the impact strength was improved withthe increase of SEBS content, while the tensile strength ofPP/nylon blend was not enhanced by the addition of SEBS[25]. The same results were obtained by Jose and coworkers[26] that modified the PP wastes with rubber in a BrabenderPlastograph. The effect of recycling on the molecular weight,rheological properties and the mechanical properties ofthe PP-based composites, and the deformation mechanismswere also investigated [24, 27]. The obtained results showedthat thermomechanical recycling process led to decreaseof the molecular weight, failure stress, and impact energy.Instead, the yield stress and the Young modulus increaseduntil the fifth cycle of reprocessing due to increase of thecrystallization rate taking place during the recycling process.Previous researches of our team indicated the incorporationof 10% elastomer as the optimum amount that leads to theimprovement of the recycled polypropylene properties [28–31].

The aim of this work is to investigate the modifiedrecycled polypropylene with commercial elastomers by ther-mal properties (MFI, DSC, VICAT, and HDT), structuralcharacteristics (XRD, optical microscopy, and AFM), andmechanical properties (tensile properties, density, and IZODimpact) for possible applications.

2. Experimental

2.1. Materials andMethods. Polymeric matrix, recycled poly-propylene (RPP) (in the granule form), comes from industrialpostconsumer boxes processed by injection moulding tech-nology. It is characterized by a density of 0.96–0.99 g/cm3, amelt flow index (190∘C, 5 kg) of 6 g/10min, tensile strengthbreak of 2.06MPa, elongation at break of 2.83%, and IZODimpact strength at 23∘C of 6 kJ/m2. Three elastomers typeswith different contents of styrene were used:

(1) Styrene-ethylene/butylene-styrene block-copolymer,Calprene H 6144 (SEBS), was acquired fromDynasol,Spain. It contains 31% styrene and is characterized byviscosity in 5.23% toluene, 30 cSt, Brookfield viscosity(10%, 25∘C), 400 cP, volatile matter, max. 0.5%, andshore hardness, 75∘ShA.

(2) Styrene-isoprene-styrene block-copolymer, D1165P(SIS30), purchased from Kraton, USA, is character-ized by tensile strength at break, 32MPa, elongation atbreak, 1300%, shore A hardness, 48∘ShA, and density,0.93 g/cm3. SIS 30 contains 28.2–31.8% styrene.

(3) Styrene-isoprene-styrene block-copolymer, D1160BT(SIS20) provided byKraton,USA, contains 17.4–20.5%styrene and similar characteristics as SIS30.

Besides these materials, polyethylene grafted with maleicanhydride (PE-g-MA), 0.5 wt.% of maleic anhydride, pro-vided by Sigma-Aldrich, was used as the compatibilizerbetween RPP and thermoplastic elastomers. It shows aviscosity at 140∘C 500 cP, density at 25∘C 0.92 g/mL, melt-ing enthalpy (Δ𝐻𝑚) 51.8 J/g, and melting temperature (𝑇𝑚)113∘C. Also, 2,6-ditert-butyl-4-methylphenol (Topanol OC)was used as an antioxidant for compounds containing SISelastomer. It is characterized by a density of 1.03 g/cm3,melting temperature 70∘C, and water solubility at 25∘C0.00006 g/100mL.

2.2. Preparation of Polypropylene Compounds. Three kindsof compounds coded RPP/SEBS, RPP/SIS30, and RPP/SIS20were prepared by compounding of RPP with each elastomertype in content of 10 wt.% by using of a SHJ-35 corotatingtwin-screw extruder (ø 35.6mm, L/D 32, nine zones oftemperature, and speed of screw 60–600 rpm) providedwith pelletizing line. The RPP, PE-g-MA, and thermoplasticelastomers were premixed in appropriate ratios prior tocompounding according to the formulations listed in Table 1.

PE-g-MA was introduced to RPP compounds prepara-tion in order to improve the interfacial adhesion betweenRPP matrix and elastomer phase which signifies the increaseof mechanical properties (tensile strength at break) of com-pounds. Other authors have also reported the use of compat-ibilizers containing maleic anhydride in order to increase theadhesion between phases of the polypropylene componentsof mixture [8, 32, 33]. The proposed mechanism that showsthe compatibilizing action of PE-g-MA in RPP compounds isshown in Figure 1.

Bymelting the components it is assumed that interactionsbetween PE-g-MA with elastomer and thermoplastic matrix

International Journal of Polymer Science 3

Table 1: Composition of RPP compounds.

Compound code RPP, wt.% PE-g-MA, wt.% Elastomer, wt.% Topanol OC, wt.%RPP/SEBS 85 5 10 —RPP/SIS30 84 5 10 1RPP/SIS20 84 5 10 1

O OO

O OO

RPP PE-g-MA SEBS

CH3

CH3

CH3

CH3CH

m

m

n

n

CH

CH

CH

CH

CH2

CH2

CH

CH2 CH2 CH2

CH2 CH2 CH2

+ + (CH2 (CH2 (CH2 (CH2

(CH2(CH2(CH2(CH2

)×1

)×1

)×2

)×2

)×3

)×3

)×1

)×1

(a)

O OO

O OO

SIS

CH3

CH3

CH3

CH3

CH3

CH3CH

m

m

n

n

CH

CH

CH

CH

CH2

CH2

CH

CH C

C

C

CH C

CH2

CH2

+ +

RPP PE-g-MA

(CH2

(CH2

)×1

)×1

(CH2

(CH2

(CH2

(CH2

(CH2

(CH2

)×2

)×2

)×1

)×1

)×3

)×3

(b)

Figure 1: Proposedmechanism for compatibilizing action of PE-gMA in RPP compounds. (a) RPP/SEBS compound; (b) RPP/SIS compound.

and also between elastomer and RPP exist. The interactionscould take place through van der Waals bonding betweenthe RPP chain and the olefinic segments of PE-g-MA. Also,dipolar interactions between PE-g-MA and elastomer phaseprobably could occur (Figure 1).

In order to avoid the degradation of RPP/SIS compounds,1 wt.% antioxidant was premixed with RPP, PE-g-MA, andSIS. Each pellet mixture was then fed into the feed throat andthematerials weremelted, blended, and compatibilized in theextruder.

Compounding process was performed by using a mixingspeed in the range 425–500 rot/min, a melt temperature atthe die of 150∘C, a pressure at the die of 13MPa, and a feedrate of 250 rot/min. The temperature profile is summarizedin Table 2.

The molten blend was then forced through a stranddie, cooled in water at room temperature, and followed bythe granulation process. Black pellets with cylindrical shape

were obtained and dried at 105∘C. The specimens for furthercharacterizations are taken from sheets and films prepared bycompression moulding of compounded samples by means ofa laboratory press (FONTUNE) at 200∘C, for 5min, and at amaximum compressive load of 8 tons. RPP unmodified waspressed in the same conditions like RPP compounds and usedas the control sample.

2.3. Microscopic Characterization. Thin cross-microtomesections of the 1mm thick sheets were examined with a LeicaDM 2500Mmicroscope with a digital camera at 200x.

A 4000SPM MultiView/NSOM atomic force microscopesystem (AFM) (Nanonics Imaging, Ltd.) was used to inves-tigate the surface morphology of the compounded recycledpolypropylene. SPM images were acquired in air, noncontactmode (at a distance between 0.1 and 10 nm of sample). Ana-lyzed surface area was 80𝜇m2 and the measurement speedused was 12ms/point. The needle used for surface analysis


Table 2: Preset/achieved temperature [∘C] for the compounding of recycled polypropylene with thermoplastic elastomers.

Zone I Zone II Zone III Zone IV Zone V Zone VI Zone VII Zone VIII Zone IX140/136 147/147 158/174 165/162 175/166 175/169 171/158 171/169 165/169

showed a peak of Cr. Interpretation of the analysis wasperformed using the WSxM 4.0 software. Surface roughnessof the RPP compounds and unmodifiedRPPwas expressed asroot mean square (RMS) of the vertical 𝑍-dimension valueswithin the examined areas, which were calculated using (1)according to Selli and coworkers [34]:

RMS𝑥,𝑦 = √ 𝑁∑𝑥,𝑦=1

(𝑍𝑥,𝑦 − 𝑍average)2𝑁2 , (1)

where 𝑍average is the average 𝑍 value within the examinedarea, 𝑍𝑥,𝑦 is the local 𝑍 value, and𝑁 is the number of pointswithin the area.

2.4. Density and Melt Flow Index Measurements. The mea-surement of the melt flow rate was performed on theMeltflixer 2000 (Thermo Haake) equipment according tostandard ISO 1133 at 175∘C, with a load of 5 kg, 6 g of granules,preheating time of 4min, and cutting time of 15 sec. Thedensity was measured according to the standard ISO 1183,using the materials extruded during the melt flow rate test.

2.5. Differential Scanning Calorimetry (DSC). A differentialscanning calorimetry, DSC 823e (Mettler Toledo), was con-ducted to analyze the melting temperatures and the coolingprocess within the temperature range of 40–200∘C. A heatingrate of 10 K/min was used. The degree of crystallinity (𝜒𝑐) ofblends was evaluated from the endothermic melting peaksusing

𝜒𝑐 = Δ𝐻𝑚Δ𝐻0𝑚 × 𝑤 × 100,%, (2)

where Δ𝐻𝑚 is the melting enthalpy of sample; Δ𝐻0𝑚 isthe melting enthalpy corresponding to 100% crystalline PP(190 J/g); 𝑤 is the weight fraction of RPP used.

2.6. X-Ray Diffraction Analysis. The X-ray diffractograms ofblends were investigated by X’Pert PROMPD diffractometerwith high-intensity Cu-K𝛼 radiation (𝜆 = 1.54065A) and2𝜃 range from 10 to 90∘ was used to obtain XRD patterns.The diameter of crystallites was calculated from the Debye-Scherrer equation (3) as is cited byMatei and coworkers [35]:

𝐷 = 𝐾 × 𝜆Cu-K𝛼cos 𝜃 × FWHM

, (3)

where 𝐷 is the crystallite dimension, 𝐾 is coefficient (0.89),𝜆Cu-K𝛼 is wavelength of the radiation from the diffractiontube, FWHM is full width at half maximum of diffraction inthe 2𝜃 scale (rad), and 𝜃 is diffraction Bragg angle.

Table 3: Roughness values for the samples calculated from AFManalysis.

Sample code RMS [nm]RPP 77.2RPP/SEBS 189.5RPP/SIS30 32.4RPP/SIS20 33.2

2.7. Tensile Tests. The tensile tests were measured in accor-dance with ISO 527 using at least five rectangular testspecimens with a thickness of 1mm. The speed rate was of50mm/min.

2.8. IZOD Impact Test. Notched impact test was carriedout using a IZOD-CHARPY Impact Tester (CEAST, Italy).The tests were performed for all specimens at 23∘C. Therectangular shaped test specimens with 80 × 10 × 4mmdimensions and a 2mm notch with an angle of 45∘ weretested in accordance with ISO 179. A hammer of 2 J was usedfor all measurements.

2.9. VICAT Softening Temperature (VST) and Heat DeflectionTemperature (HDT). The VST and HDT tests were per-formed by means of a HDT/VICAT equipment (CEAST,Italy), as follows: VST test was conducted according to ISO306, Method A50, load 10N, and heating rate of 50∘C/h andHDT test was carried out according to EN ISO 75, using aload of 0.45MPa and a heating rate of 120∘C/h. Specimenswith thickness of 4mm were used for both tests.

3. Results and Discussion

The optical microscopic images of RPP and RPP/elastomersblends are shown in Figures 2(a), 2(b), 2(c), and 2(d).

Optical microscopic images from Figure 2 reveal aninhomogeneous surface for RPP (Figure 2(a)) while theintroduction of elastomers into RPP matrix led to a gooddispersion of those within a continuous phase of the thermo-plastic matrix, especially for RPP/SIS20 (Figure 2(d)).

The morphology images for the RPP compounds andunmodified RPP surfaces are presented in Figures 3(a)–3(d)and the root mean square (RMS) roughness is reported inTable 3.

AFM analysis reveals the rough surface of the RPP/SEBS(Figure 3(a)) with many voids and relatively large depths(200 nm deep approximately) and peaks ranged from 150 to200 nm (Figure 3(b)), while by incorporation of SIS into RPPmatrix a relatively smooth surface can be noticed (Figures3(c) and 3(d)) having fewest voids in material but also morepronounced peaks ranged from 20 to 170 nm.


50 �휇m

(a)

50 �휇m

(b)

50 �휇m

(c)

50 �휇m

(d)

Figure 2: SEMmicrograph of the fractured surface of the RPP compounds and unmodified RPP. (a) RPP; (b) RPP/SEBS; (c) RPP/SIS30; (d)RPP/SIS20.

Table 4: Density and MFI values for RPP/elastomer compoundsand unmodified RPP.

Sample code Density [g/cm3] MFI [g/10min]RPP 0.9948 ± 0.0026 8.74 ± 0.17RPP/SEBS 0.9642 ± 0.0006 3.14 ± 0.09RPP/SIS30 0.9622 ± 0.0018 4.91 ± 0.20RPP/SIS20 0.9577 ± 0.0018 4.81 ± 0.14

From Table 3, it can see that the surface roughness valuesincrease with introduction of SEBS into mixture (189.5 nm)which proved that the interface between the elastomer andRPP matrix is weaker due to the poor dispersion andcompatibility and decreases for SIS elastomers (∼32 nm) incomparison with RPP. This indicated a good compatibilitybetween SIS elastomers and the RPP matrix. Also, it isassumed that the introduction of PE-g-MA improved thecompatibility between SIS elastomers and RPP and increasedthe surface smoothness. From Table 3 it can also be observedthat the surface roughness of RPP/SIS 30 slightly decreasedwhen compared to that of RPP/SIS20, due to the increase ofPS content.

The values for the densitymeasured at 23∘C andmelt flowindex (MFI) of granules samples are presented in Table 4.

The obtained compounds show the density and melt flowindex values lower than unmodified RPP. RPP/SIS samples

recorded high MFI values (∼5 g/10min) in comparison withRPP/SEBS compound (∼3 g/10min) indicating the decreaseofmelt viscosity.The easier flowbehavior of theRPP/SIS sam-ples is in correlation with their roughness values (reported inTable 3). Analyzing the roughness values fromTable 3 and themelt flow index from Table 4 in the case of unmodified RPPand RPP/SIS compound it is observed that RPP possesseshigh RMS, but its melt viscosity is less than RPP/SIS. It isknown that the viscosity depends on interfacial adhesionbetween the individual blend components [26]. In the case ofthe elastomer introduced in the RPP matrix, the interfacialadhesion increases. This is attributed to the immisciblestyrene block from the elastomer introduced to the PPmatrixmaking it difficult to flow resulting in an increase in viscosity.Due to the good compatibility of SIS with polymeric matrix,the surface roughness decreased compared with unmodifiedRPP.

Figure 4 shows the DSC curves recorded by RPP com-pounds and RPP. The thermal parameters, heat melting,Δ𝐻𝑚, melting temperature,𝑇𝑚, and the degree of crystallinityfor PP, (𝜒𝑐), have been determined fromDSC curves and theyare reported in Table 5.

From Figure 4 and Table 5 two endothermic meltingpeaks are observed for investigated samples, the first beingassociated with polyethylene (PE) melting (∼128∘C) and thesecond with 𝛼 crystals melting from RPP (∼166∘C). Thissuggests that the recycled polymers represent a mixture


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Figure 3: AFM topography images showing the surface and microhole profiles. (a) RPP; (b) RPP/SEBS; (c) RPP/SIS20; (d) RPP/SIS30.

of different polymers as was reported by Martın-Alfonsoand coworkers [36]. The obtained results indicate that thecrystalline phase of PE remains separated in PP domains atmicrostructural level; these results validating the observa-tions from other papers [37, 38]. From the first endothermicpeak assigned to PE 𝑇𝑚, Δ𝐻𝑚, and 𝜒𝑐 (Table 5) wereevaluated. The degree of crystallinity for PE was calculatedusing the melting enthalpy of a 100% crystalline PE of 290 J/g

[38]. If it is assumed that the crystalline phases from PE arethe same with the amorphous ones as Brachet and coworkersdemonstrated [39], then the total amount of PE from recycledPP is ∼25%.

Introducing of elastomer into RPP matrix led to minorchanges of the melting temperature (𝑇𝑚) in comparison withRPP, while the degree of crystallinity (𝜒𝑐) recorded a decreasecompared to the RPP. Among all investigated elastomers,


Table 5: Thermal parameters for RPP samples evaluated from DSC thermograms, first heating scan.

Sample code Δ𝐻𝑚, PE[J/g] 𝑇𝑚, PE[∘C] Δ𝐻𝑚, PP[J/g] 𝑇𝑚, PP[∘C] 𝜒𝑐, PP[%] 𝜒𝑐, PE[%]RPP 36.81 129.8 34.8 166.6 18.3 12.7RPP/SEBS 22.7 129.1 28.9 165.9 17.9 7.8RPP/SIS30 21.8 128.7 25.1 166.1 15.7 7.5RPP/SIS20 25.1 128.3 25.8 166.0 16.1 8.6

RPPPRR/SEBS

RPP/SIS30RPP/SIS20

up exo

−6

−5

−4

−3

−2

−1

0

1

2

Hea

t flow

(mW

)

Heating rate 10∘C/min

60 80 100 120 140 160 18040 200Temperature (∘C)

Figure 4: DSC curves for RPP and RPP/elastomer compoundscontaining 10% elastomers.

Table 6: Average crystallite sizes (nm) for RPP compounds andunmodified RPP.

Code sample Average crystallite size [nm]RPP 37.58RPP/SEBS 48.55RPP/SIS30 41.80RPP/SIS20 46.41

SEBS elastomer shows the smallest change in the degreeof crystallinity (17.9%) with respect to RPP (18.3%). Thisbehavior in the crystallinity is assigned to the compatibil-ity between the continuous phase of RPP matrix and theethylene-butylene phase from SEBS that does not disturb thelattice structure of RPP. Compounds based on RPP and SISelastomers recorded a decreased degree of crystallinity due tothe good compatibility with the matrix in comparison withSEBS elastomer. In the case of RPP/SIS compounds, due tothe decreased degree of crystallinity and smooth surfaces(Table 2) it is expected to show an improvement on the tensileproperties and IZOD impact.

Figure 5 shows the X-ray diffraction patterns of theRPP reference and RPP/elastomer samples. The average ofcrystallite sizes for RPP compounds and unmodified RPP isgiven in Table 6.

RPP

RPP/SEBS

RPP/SIS30

RPP/SIS20

10 20 30 40 50 60 70 80 90Position (∘2 Theta (copper))

Figure 5: Representative XRD patterns for RPP and RPP/elastomersamples.

The elastomers influence on the crystallite sizes of RPPcompounds is higher than those of RPP. It is expected thathigh dispersed particles of elastomers were made at RPPcompounding. The increase of the crystallite sizes causeddisturbances of the microcrystalline network formation, itseffect being recorded by DSC analysis (Table 5). However, theincorporation of SEBS elastomer into RPP matrix exhibitedthe highest increase of the crystallite sizes in comparisonwith compounds containing SIS.This can be explained by thehigh viscosity of SEBS and poor compatibility with polymericmatrix (Table 4) that leads to increasing the tendency for theagglomeration of the crystallite size.

Influence of the elastomer type on the tensile strength atbreak and elongation at break of RPP compounds comparedwith RPP is shown in Table 7.

Tensile strength of RPP/elastomer compounds increasedwith the introduction of the elastomer in RPP polymermatrix, Table 7.This increase is due to the effect of PE-g-MA,which increases interaction between RPP matrix and elas-tomer. RPP/SIS30 sample recorded the highest value of tensilestrength at break (11.7 ± 0.77MPa), followed by RPP/SIS20sample (8.9 ± 2.2MPa) and RPP/SEBS (7.33 ± 0.7MPa).These values of tensile strength are in good agreement withthe degree of crystallinity (Table 5). The smooth surface forRPP/SIS compounds (Table 2) is also responsible for theincreased tensile strength at break. From Table 7 it is alsoobserved that the elongation at break increased by about 5times for all RPP compounds compared to RPP, due to the


Table 7: Tensile properties for RPP/elastomer compounds and RPP.

Code compound Tensile strength at break [MPa] Elongation at break [%]RPP 2.06 ± 0.20 2.83 ± 0.11RPP/SEBS 7.33 ± 0.70 12.89 ± 4.20RPP/SIS30 11.70 ± 0.77 10.96 ± 2.25RPP/SIS20 8.90 ± 2.20 11.03 ± 4.08

Table 8: IZOD impact strength of RPP blends.

Code sample Izod impact [kJ/m2]RPP 4.35 ± 0.23RPP/SEBS 8.55 ± 2.14RPP/SIS30 21.78 ± 2.58RPP/SIS20 16.91 ± 2.52Table 9: VST andHDT properties for the unmodified RPP and RPPblends.

Code sample VST [∘C] HDT [∘C]RPP 162.0 ± 1.0 87.0 ± 6.5RPP/SEBS 162.3 ± 2.3 73.0 ± 2.0RPP/SIS30 160.0 ± 4.3 64.6 ± 3.5RPP/SIS20 157.6 ± 2.5 67.5 ± 0.7elastomer component that favors the flow and mobility ofRPP. There is no noted difference on elongation at breakbetween all used elastomers.

IZOD impact strength for the RPP and RPP/elastomercompounds performed on notched specimens is shown inTable 8.

As is shown in Table 8, the IZOD impact strengthincreased for all compounds compared to that for RPP(4.35 ± 0.23 kJ/m2) with a spectacular increase in the case ofRPP/SIS30 (21.78 ± 2.58 kJ/m2). This increase is attributedto the elastomeric phase that absorbs and transfers theforce at impact from the continuous phase of RPP matrix[26]. In addition, the flexible interface between elastomerand RPP prevents the development of cracks. Consequently,the impact resistance of RPP compounds is significantlyimproved, in good agreement with the decrease of the degreeof crystallinity reported in Table 5.

The influence of the used elastomers on the VICATsoftening temperature (VST) and heat deflection temperature(HDT) properties of the RPP blends is shown in Table 9.

As compared with control sample (unmodified RPP),the VST and HDT values show almost the same value forRPP/SEBS and a slow decrease for RPP/SIS30 compound (adecrease ∼2∘C) and RPP/SIS20 compound (a decrease ∼5∘C).The HDT values recorded the same trend as VST values. Thedecrease in VST and HDT values is in good accordance withthe increase of elongation at break.

From three elastomers types used to improve the RPPproperties it can be remarked that the SIS with 30% styrenecontent is a better impact modifier for RPP, reflecting the

better properties (smooth surface, melt flow, tensile strength,and impact resistance).

4. Conclusions

The postconsumer polypropylene (RPP) was compoundedwith SEBS, SIS30, and SIS20, respectively, and characterizedin terms of mechanical and thermal properties and structuralcharacteristics in order to establish the best elastomer forimprovement of RPP properties.

Generally all prepared compounds showed good proper-ties compared with unmodified RPP, suitable for obtainingnew goods for various applications, which proves that themechanical recycling of polypropylene wastes is also a goodstrategy for management of waste.

DSC analysis revealed that the degree of crystallinity (𝜒𝑐)registered a decrease for all compounds compared with RPPcontrol, while the melting temperature (𝑇𝑚) showed onlyminor changes.

The tensile strength at break of compounds increased byabout 5 times compared to RPP due to incorporation of PE-g-MA in mixture. A significant increase for elongation at breakand IZOD resistance was recorded for all compounds.

However the investigated elastomers had a quite differenteffect on the RPP properties due to their structures.

The RPP compatibilized with SEBS revealed high rootsurface and melt viscosity while those compounded with SISshowed a smooth surface and low melt viscosity.

Although by incorporation of SEBS elastomer into RPPmatrix the lattice network of polymeric matrix is not muchdisrupted, its crystallite sizes increased in comparison withcompounds containing SIS.

Based on the obtained results it can be concluded thatSIS30 was the best modifier for RPP properties leading to thehighest increase of mechanical properties of RPP compound,by about 5 times for tensile strength and IZOD impact,respectively.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

Thisworkwas supported by a grant of the RomanianNationalAuthority for Scientific Research, CNDI-UEFISCDI, Projectno. 67/2012. The authors wish to thank Dr. L. Alexandrescu(The National Research & Development Institute for Textiles


and Leather, Romania) for their kind help with the com-pounding of the materials.

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