Journal of Metals, Materials and Minerals. Vol.18 No.2 pp.207-211, 2008

Characterization of Short Glass Fiber-Reinforced PC/ABS Blends Nattapon SAMAKRUT1, Satida KRAILAS2 and Sarawut RIMDUSIT1* 1

Polymer Engineering Laboratory, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand. 2 PTT Phenol Company Limited, Chatuchak, Bangkok 10900, Thailand Abstract

Received Jan. 28, 2008 Accepted Feb. 11, 2009

Blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) of a high flow ability grade were reinforced with short glass fibers vary from 0 to 30 wt% by used a fixed fiber length of 3 mm. From rheological studies, the viscosity of the filled systems increases with an increasing content of the short glass fiber. Shear thinning behavior was also observed in those filled and unfilled polymers. From the DSC and DMA thermograms, the results revealed that the values of the glass transition temperature (Tg) slightly increased with enhancement content of the short glass fiber. From thermogravimetric analysis, the degradation temperature of the composite specimen was found to be negligibly affected by the presence of the glass fiber. Scanning electron micrographs exhibited that the glass fiber was surrounded by the PC phase rather than by the ABS phase. The presence of the glass fiber predominantly in the PC phase was also confirmed by base and acid etching techniques to dissolve the PC and the ABS phase, respectively. The adhesion at the interface between glass fibers and polymer matrix was attributed to increase the glass transition temperature in the composites and crucial to the effective reinforcement of the fiber. Key words : PC/ABS Blends, Short Glass Fiber, Reinforcement.

Introduction One of the alternatives for cost reduction of producing polymer was adding mineral fillers. Moreover, nowadays fillers increasingly play a functional role, such as improving the stiffness or surface finish of a polymer product. Especially, the reinforcement of thermoplastic compounds by short fibres has received special attention because of their properties, that can be used in various applications i.e. engineering field, both the chemical and automotive industries.(1) For some specific applications that require substantially high mechanical properties (such as a case of notebook etc.), one effective method to improve the properties and maintain its processability by traditional extrusion or injection is by compositing with short glass fiber. From this point induce the interesting applied of short glass fiber in the system of Polycarbonate (PC) / Acrylonitrile-butadiene-styrene (ABS), blends due to they are well-known commercial products. The cause of their success on the market is due to complementary properties of the components. PC contributes mainly to good mechanical and thermal properties whereas ABS provides ease of processability and reliable notched impact

resistance.(2-4) Therefore, the major purpose of this study is to investigate the effect of short glass fiber (i.e. 3 mm in length) on thermomechanical properties of these result of the composite. The interfacial morphology between the polymer matrix and the glass fiber is also studied.

Materials and Experimental Procedures Materials In this research, the commercial grade of PC and ABS were selected as the polymer matrix of the blends and the short glass fiber was purchased from Chongqing Polycomp. International Corp., China. Preparation of PC/ABS Composites Both PC and ABS pellets were dried to constant weight in an air-circulated oven to remove some moisture, which could cause PC degradation and defection in this sample.(5) Compounding of PC, ABS and glass fiber was carried out by a twin screw extruder (Thermo

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208 SAMAKRUT, N. et al. Haake Reomex, HAAKE PolyLab Co., Ltd., Germany). The fiber content added to this blend varied from 0, 10, 20 and 30 wt%. The extruded strands were cut into pellets (lengths of > 3 mm.) and dried before use.

20°C/min. The temperature was scanned from 50 to 700°C under air atmosphere. The purge air flow rate was 50 ml/min.

Experimental Procedures

Rheological Properties

Rheological Property Measurement

From Figure 1, the viscosity of PC/ABS blend reinforced with short glass fibers was increased with increasing the content of the glass fiber. The plots also indicate the decrease in viscosity with increasing shear-rate, the characteristic of shear thinning fluid. The viscosity value of 30wt% glass fiber filled compound was about one order of magnitude higher than that of the neat PC/ABS used.

DMA was used to characterize the viscoelastic properties of the studied material. The dimension of tested specimens is 55mm x 10mm x 2mm. The DMA tests were carried out at 1 a frequency of 1 Hz in the three-point bending mode using NETZSCH DMA242 equipment. Nitrogen was used as a purge gas. The thermograms were obtained in the temperature range of 50 to 170°C at 15oC/min. The storage modulus (E’), loss modulus (E”), and loss tangent (tanδ) were recorded in the thermograms. The glass transition temperature was determined by the maximum point of loss modulus curve. Differential Scanning Calorimeter (DSC) Thermal characteristics of each specimen were determined by Perkin-Elmer Differential Scanning Calorimeter, Diamond DSC. Approximately 5-9 mg of samples was sealed in aluminum pans and was tested using the temperature ramp rate of 10°C/min from room temperature to 180°C under nitrogen atmosphere. Glass transition temperature of samples was determined as the midpoint temperature of the change in specific heat in the transition region. Thermogravimetrix Analysis The degradation temperature (Td) and residual weight of the PC/ABS blends at various glass fiber contents were studied by using a Perkin Elmer Instrument Technology (SII Diamond TGA/DTA) thermo gravimetric analyzer at a heating rate of

1000

3

Dynamic Mechanical Analysis

Complex Viscosity ( x 10 Pa.s)

The melt viscosities of PC/ABS blends have glass fiber loadings of 0 to 30 wt% at a constant shear rate (1 sec-1) were determined using a parallel plate rheometer, Haake Rheo Stress 600, from Thermoelectron Cooperation. The diameter of each plate is 20 mm and the gap between the plates was fixed at 1 mm.

Results and Discussion

0.1

0.1

1

10

100

Frequency (Hz)

Figure 1. Viscosity of PC/ABS blend at various glass fiber contents (●) 0%, (■) 10%, (♦) 20% and (▲) 30%

Dynamic Mechanical Analysis In Figure 2, the storage modulus of PC/ABS blend reinforced with short glass fibers was observed to systematically increase with increasing short glass fiber mass fraction. The behavior implies the reinforcing effect of the glass fiber on the PC/ABS matrix. The Tg’s or αrelaxation of the composites can be roughly estimated from the drastic decrease of the storage modulus (about one order of magnitude in this case) at the temperature above 135°C. The glass transition temperature of the composites was found to shift to higher temperature with the amount of the glass fiber. As a consequence, the presence of the glass fiber in the composites resulted in the more rigid polymer hybrids as seen from a higher storage modulus at room temperature.

209 Characterization of Short Glass Fiber-Reinforced PC/ABS Blends

Storage modulus

from the loss tangent was in agreement with those determined from loss modulus.

S t or a ge mo du lus o f P C /AB S bl e nd o

C)

0

5

10

15

20

25

Tan δ

Storage modulus

a t v a rio d g la s s fib e r c o nte nt (5 0

30

G las s fiber c on ten t (w t% )

40

T emperarure ( oC )

180

Figure 2. Storage modulus of PC/ABS blend at various glass fiber contents (●) 0%, (■) 10%, (♦) 20% and (▲) 30%

Loss modulus

Figure 3. Shows the temperature dependence of loss modulus of the composites at various glass fiber contents. Obviously, the two glass transition temperatures of both the PC-rich and the ABS-rich phases are slightly increased with the contents of glass fiber because the interfacial adhesion between the short glass fiber and the PC/ABS matrix can hinder the molecular movement in composites.

Temperature ( oC)

40

Figure 4. Loss tangent of PC/ABS blend at various glass fiber contents (●) 0%, (■) 10%, (♦) 20% and (▲) 30%

Differential Scanning Calorimetry The DSC measurements (Figure 6) revealed similar Tg results of DMA. The two glass transition temperatures are observed for each composite and slightly increased with the short glass fiber loadings. The shifts in the glass transition temperatures are found to be dependent on glass fiber wt%. Maximum shifts of the Tgs were expectedly found at 30 wt% of glass fiber loading in the PC/ABS. P C /A B S : 60/40 P C /A B S /G F : 54/36/10 P C /A B S /G F : 48/32/20 P C /A B S /G F : 42/28/30

Temperature ( oC)

180

Heat Flow

exo

40

180

Figure 3. Loss modulus of PC/ABS blend at various glass fiber contents (●) 0%, (■) 10%, (♦)

20% and (▲) 30% 0

Figure 4. Exhibits the α-relaxation peaks of the loss tangent (tan δ) of the short glass fiber reinforced PC/ABS. It was also found that the peak maxima were shifted to high temperature with the fiber loadings. The trend in glass transition temperatures

50

100

150

200

250

o

Tem perature ( C )

Figure 6. DSC thermograms of PC/ABS blend at various glass fiber contents (●) 0%, (■) 10%, (♦) 20% and (▲) 30%

210 SAMAKRUT, N. et al. Thermogravimetric Analysis The thermal degradation of glass fiberreinforced PC/ABS blend is presented in Figure 6. The TGA thermograms of all composites were found to decrease in two steps. The first step was between 360 and 460°C and the second step was approximately 520°C. From the figure, it can be seen that the degradation temperature at 5% weight loss was ranging from 371 to 380°C. Moreover, the residual solid of all composites were found to be consistent with the composition in the molding compounds suggesting good dispersion of the fiber in the PC/ABS matrix.

a

b

c

d

120

% Residual Weight

100

Figure 7. Fracture surface of PC/ABS/GF 10% (a), (b) unetched sample (c) aqueous acid solution treated (d) aqueous NaOH solution treated.

80 60 40 20 0

0

100

200

300

400

500

600

700

In Figure 7c, the fracture surface of the reinforced PC/ABS composite was etched by aqueous acid solution. This treatment was used to eliminate the ABS phase in the compound.(6) The figure revealed that the glass fiber embedded mainly in the PC phase (the remained component after acid etching) rather than in the ABS phase.

o

Temperature ( C) Figure 6. TGA thermograms of PC/ABS blend at various glass fiber contents (●) 0%, (■) 10%, (♦) 20% and (▲) 30%

Fiber Dispersion and Composite Interface from Microscopy The SEM micrographs of the fracture surface of PC/ABS blend filled with 10 wt% of short glass fiber are shown in Figure 7a and 7b. Figure 7a reveals the relatively good dispersion of the short glass fiber in the PC/ABS matrix. The uniform dispersion is one key feature to yield a good composite property. Figure 7b illustrates also the glass fibers to substantially adhere to the PC/ABS matrix which is essential for its mechanical property enhancement by the reinforcing fiber.

The SEM micrograph of fracture surface after etching with NaOH solution is presented in Figure 7d. It can be observed that there was a clear gap at the interface between the matrix and the glass fiber from the etched PC phase. This experiment suggested that glass fiber was likely to be surrounded predominately by the PC phase rather than by the ABS phase. This phenomenon may be attributed to the more polar nature of the PC that is likely to show more affinity to the polar glass fiber than the less polar ABS phase. The adhesion between the fiber and the matrix possibly hindered the movement of PC/ABS molecules and had an effect on the increase of the glass transition temperature and the modulus of the composites.

Conclusions The viscosity of PC/ABS reinforced with short glass fiber increased with increasing the glass

211 Characterization of Short Glass Fiber-Reinforced PC/ABS Blends fiber content whereas substantial bonding between the glass fiber and the PC/ABS was observed. The processing condition used can provide a specimen with relatively uniform fiber dispersion. The storage modulus of composite increased with enhancement content of the short glass fiber. The glass transition temperatures of PC/ABS reinforced with short glass fiber (both PC-rich phase and ABS rich phase) slightly shifted to higher values than those of pure PC/ABS. It was also observed from the micrographs of the fracture surface of the composite that the glass fibers were likely to be surrounded by the PC phase rather than the by the ABS phase.

Acknowledgment This research is financially supported by PTT Phenol Company Limited.

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