Research Article ABS MODIFIED BMI RESINS-EFFECT OF ABS ... I/JERS VOL... · Research Article ABS...

Journal of Engineering Research and Studies E-ISSN 0976-7916

JERS/Vol.I/ Issue II/Oct.-Dec., 2010/221-229

Research Article

ABS MODIFIED BMI RESINS-EFFECT OF ABS

CONTENT ON THE PERFORMANCE OF THE RESIN

AND COMPOSITES Salini K

1*, Krishna M

1, K S Rai

2 and Satheesh chandran M

1

Address for Correspondence 1 Research and Development, Dept. of Mech. Engg., R V College of Engineering, Bangalore-

560 059, India. 2 Sir M V PG Centre, Dept. of Polymer Science, University of Mysore, Mandya,

*Email. [email protected] [email protected]

ABSTRACT This paper reports an experimental study on the effect of addition of Acrylonitrile Butadiene Styrene (ABS)

in weight percentages (2-10wt %) to Bismaleimide resin (BMI) on thermal, morphological and mechanical

properties. The bismaleimide resin was composed of 4,4’-bismaleimidediphenyl methane (BMI) and o,o’-

diallyl bisphenol A (DABA). The ABS incorporated BMI resin system have showed decreased Tg with

increase of ABS wt%. Modified and unmodified BMI/ carbon composites were prepared and tested for

Tensile, flexural and impact properties and were found to be highest at 8% weight of ABS loading. SEM

analysis has shown homogeneous blends of BMI/ABS system.

KEYWORDS BMI, DABA, ABS, Carbon composite, Mechanical properties, SEM

1.0 INTRODUCTION

Bismaleimide (BMI) resins are a kind of

high performance resin systems which is

now a days the most important choice in

both aerospace and electronic industries

owing outstanding properties [1-3].

The unique properties of BMI resins, such as

low moisture absorption, excellent fire

resistance , good mechanical performance

excellent chemical and corrosion resistance,

high thermal stability and excellent hot-wet

performance etc. make BMI widely

applicable in laminating resins, prepregs,

adhesives, electrical packaging and other

composite applications[4-8]. However,

cured BMI resin exhibits significant

brittleness, low resistance to crack initiation

and propagation and poor processing

characterization because of its high cross-

link density, poor solubility in ordinary

solvents, and high crystalline melting point

of BMI monomers. [9-12].Various attempts

have been made to improve the impact and

fracture toughness of BMI resins [13]. One

excellent modification method for reducing

the brittleness of the BMI systems is the

use of thermoplastics [14-15].As a result,

much work has been made to toughen them

with high performing, temperature

withstanding thermoplastics. Some of

reported thermoplastics include

polyetherimide (PEI), and poly (arylene-

ether ketone) s [14-15]. This article reports

the modification approach of the two

component BMI resin system with the high

performance engineering thermoplastic

Acrylonitrile Butadiene Styrene (ABS)

which has not been reported in the open

literature abundantly. In this work an

attempt has been made to evaluate the effect



of addition of ABS in different weight

percentages (2-10 wt %) in to BMI system.

The properties under consideration were the

effect of ABS on the temperature

performance of the resin system and the

mechanical performance of the

thermoplastic modified BMI/carbon

composites. The properties of the modified

BMI resin system are compared with those

of unmodified BMI.

2.0 EXPERIMENTAL STUDIES

2.1 MATERIALS

The BMI resin system consists of

bismaleimidodiphenylmethane (BMPM) and

reactive diluent oo’-diallyl bisphenol A

(DABA) (Figure1) (supplied by ABR

Organics, Hyderabad). The engineering

thermoplastic, ABS (Figure 2) was supplied

by Shah Polymers, Bangalore. Dimethyl

formamide (DMF) was used as solvent for

the BMI system. The carbon fabrics (204

gsm, plain weave), supplied by M/s CD

Interglass Germany was used as the

reinforcement for the composites.

N C H2

C

C

O

O

N

C

C

O

O

4, 4’- bismaleimidodiphenylmethane (BMPM)

CH3

CH3

OHOH

CH2

CH2

CH CH2CHCH

2

O-O’ diallyl bisphenol A (DABA).

Figure1.Chemical structure of BMPM and DABA

Figure 2. Chemical structure of ABS



2.2 BMI MODIIFICATION WITH

THERMOPLASTICS

BMI was chosen as the thermoset network

to be modified with the engineering

thermoplastics. This two-part systems

comprised 4, 4 bismaleimidodiphenyl-

methane and oo’-diallyl bisphenol A in all

formulation containing various

thermoplastic modifiers, the ratio of

BMPM/DABA was kept at 57:43 parts by

weight (1:0.85 mole ratio). A major reason

for the choice of this resin system was the

ability of component two to dissolve the

thermoplastic modifiers to form a hot melt

solution and then to co-react in to the

network through the allyl groups without

producing any volatiles. In the current work

modification BMPM/DABA resin system

with the thermoplastic was done by blending

with ABS (from 2 to 10 wt %). Initially 57g

of BMPM was dissolved in 25g of DMF.

The required wt % s of ABS was dissolved

in DMF and was added in to 43g of DABA.

In to this solution the dissolved BMPM in

DMF was added.

The mixture was stirred well until a

homogeneous single solution was formed.

The ABS blended BMI resin system was

used as a matrix to impregnate the carbon

fabric using hand lay-up technique and

dried at hot air oven at 160ºC for 10 minutes

for removing the solvent DMF form the B

stage pre-pregs. Before prepregging, carbon

fabrics were exposed to 400 ºC in air for

removing the coated epoxide sizing, which

would otherwise chemically degrade during

high temperature post cure condition.

Laminate was fabricated by placing fifteen

plies of B stage prepreg in a metal mould

240 X 120 X 3 mm with the application of

vacuum pressure (4 Mpa) in a hydraulic hot

press. The mould was placed in a hot press

at 120 ºC and the following curing schedule

was adopted (i) Cure at 180 o C for 1 hour

and 220 o C for 2 hours (ii)Post cure at 250 º

C for 6 hours in the oven. It was observed

that the processability of the resin became

difficult due to higher viscosity at higher

percentage of ABS (>10wt %).

2.3 CHARACTERIZATION

Thermal characterization of the modified

resin was studied using Mettler 823,

Differential Scanning Calorimeter (DSC)

calibrated with an Indium standard. A

stream of Nitrogen at a flow rate of 20

mL/min was used to purge the DSC cell.

The DSC measurement was done at a

heating rate of 10 º C/ min and on line DSC

thermograms were obtained. BMI / carbon

fibre and modified BMPM/DABA /ABS /

carbon fibre composites were tested for

ultimate tensile strength as per ASTM D-

3039 (dimension 208X12.7X3mm ) standard

using Universal Testing Machine (UTM)

with a cross head speed of 5 mm/min. Five

samples were tested and average values was

reported. The flexural strength of both

unmodified and modified BMI composites



was determined using the three-point bend

method as per ASTM-D790 (dimension

80X10X3mm) standard. Five specimens

with span length of 50mm and cross-head

speed of 2 mm/min were tested and average

values were reported. The Izod impact

strength of both unmodified and modified

composites was measured as per ASTM D-

256, (dimension 64 x12.7 x 3mm) using

Izod impact testing machine. The

morphology of the resin and the tensile

fracture analysis of the composites were

studied using JEOL JSM840A-(Japan)

Scanning Electron Microscope (SEM).

3 RESULTS AND DISCUSSION

3.1 DSC STUDIES

DSC study of the cured resins of different

weight percentage of ABS was performed

using Mettler made DSC. From the DSC

analysis it was found that with the

increasing percentages of ABS the glass

transition temperature (Tg) of the BMI

system reduces ascertaining that the

thermoplastic content is the determinant of

the high temperature performance of the

BMI system after modification. Fig. 3 shows

the DSC thermograms of the cured BMI

with different weight percentages of ABS.

From the DSC graphs the Tg of the resin

was determined at different weight

percentages of the ABS and is shown in

table 1. It was found that from the DSC

analysis, Tg was found to be fairly constant

up to 8 weight% of the inclusion of ABS

and after which it started decreasing rapidly.

The decrease in Tg is expected to be due to

the effect of thermoplastic addition by which

the matrix have got plasticized by the

embodiment of the thermoplastic between

the highly cross-linked aromatic

bismaleimide chain structures.

Figure 3. DSC thermograms of BMPM/DABA at different weight percentage loading of ABS. (a) Pure BMI(b)2 wt% (c)4wt% (d) 6wt% (e) 8wt% and (f) 10wt %



Table 1: Glass transition temperature of modified Bismaleimide specimens obtained

from DSC thermogram

3.2 MORPHOLOGY OF THE

COMPOSITE

The SEM micrographs of the tensile

fractured surface of modified and

unmodified resins are shown in the Figure 4

.Generally SEM provides evidence of the

bonding between the matrices and in the

present case it shows the effect of addition

of ABS in to BMI and the modified

BMI/Carbon system. Fiber breaking was the

dominant failure mode in both unmodified

and 2 wt% ABS modified BMI/ carbon

specimens shown by Fig 4 (a and b). As the

percentage of addition of the ABS increases,

the matrix became smoother, and it is due to

the effect of ABS which plasticizes the

matrix effectively and the degree of

plasticization/ toughening increased as a

function of increase of the wt % of ABS up

to 6 wt%. It is evidenced by the SEM

morphohraph Fig. 4(c) , that as the wt%

loading (up to 8wt%) increases, the BMI

matrix become more homogeneous, smooth

and the adhesion between the matrix and the

fibre seem to be more strong which means

the effective toughening by the blending of

ABS and BMI systems.

The composites have shown a change in the

morphology pattern at the higher weight

percentage of addition of the engineering

thermoplastic ABS. For higher loading

(greater than 8 wt% ABS), the samples

showed delamination as shown in Fig 4 (d)

which corresponds to 10 wt % ABS. Even

though the fiber breaking is the dominant

mode of failure in these specimens, due to

the poor ABS-BMI interaction at higher

loading of ABS, some area have showed

matrix cracking and fiber pull-out. It is

expected that the increase in the percentage

loading of ABS have made the resin highly

viscous in nature and resulted in reduced

wetting of the fabric and thereby the

laminate.

3.3 MECHANICAL PROPERTIES

(UTS, FS AND IMPACT STRENGTH)

Fig. 5, 6, & 7 shows the Ultimate Tensile

Strength (UTS), Flexural Strength (FS) and

Impact strength respectively for the

Bismaleimide /Carbon composites modified

with different wt % of ABS. The mechanical

properties showed varying tendencies with

different weight percentages of ABS. The

tensile strength and Impact strength attained

ABS wt% Tg (0C)

a 0 324

b 2 292

c 4 284

d 6 268

e 8 253

f 10 248



the greatest values at 8wt % ABS addition in

the composites. Above the 8 wt % loaded

specimens , the mechanical strength was

found to be low due to the high wt %

content of ABS which decreased the rigidity

of the cross-linked systems of BMI leading

to high extend of plasticization and hence

low mechanical performance.

UTS, flexural and impact strength were

increased by 14 % ,27 % and 36.9 %

respectively in modified specimens at 8 wt

% ABS addition compared to that of BMI

composites. The improvements are

attributed to the decrease in voids which act

as defect sites and initiate cracks leading to

premature failure. The thermoplastic have

improved the matrix / fibre compatibility.

The flexible butadiene group in ABS is

expected to reduce the cross linking density

and helped in softening of the matrix which

helped to absorb fracture energy. The

addition of more than 10 wt % ABS

increased the viscosity of the BMI resin

leading to processing difficulties which

limited the further wt % loading of ABS.

Figure 4. SEM pictures of the tensile fractures specimens: (a) BMPM/DABA,

(b)2 wt % of ABS,(c) 8 wt % of ABS, and(d) 10 wt% of ABS.



Figure 5: Tensile performance of the modified Bismaleimide/ Carbon Composites

Figure 6. Flexural strength of modified Bismaleimide/ Carbon composites.

Figure7: Impact strength of modified Bismaleimide/ Carbon composites



4. CONCLUSION

BMI was modified with engineering

thermoplastic ABS by loading with different

weight percentage (2-10%). Carbon

composites were prepared by ABS modified

BMI resin system. The ABS modified BMI

resin was characterized for thermal stability

by DSC and BMI/ABS/Carbon composite

specimens were evaluated for mechanical

performance before and after modification.

Again the morphological characterization

was carried out by SEM. From the DSC

thermograms , it was found that with %

increase in weight of ABS Tg was found to

be decreasing to a minimum extend up to 8

wt% loading and marginally after 8 wt%

loading of ABS. Tensile and Impact

performance of the composites showed that

8 wt. % of ABS have the maximum values

while maintaining high thermal stability. A

homogeneous structure of the blends was

confirmed by SEM. From the results it can

be concluded that incorporation of ABS in

to the BMI resin is an effective way of

toughening BMI with minimal reduction in

the high temperature performance while

maintaining the mechanical strength.

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Research Article ABS MODIFIED BMI RESINS-EFFECT OF ABS ... I/JERS VOL... · Research Article ABS...

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