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Keywords:

  • PC;
  • ABS;
  • recycle;
  • blend;
  • compatibilizer;
  • mechanical properties

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References

Blends of recycled polycarbonate (PC) and acrylonitrile–butadiene–styrene (ABS) were prepared and some mechanical and morphological properties were investigated. To compatibilize these blends, ABS-g-(maleic anhydride) (ABS-g-MA) and (ethylene–vinyl acetate)-g-(maleic anhydride) (EVA-g-MA) with similar degree of grafting of 1.5% were used. To compare the effect of the type of compatibilizer on mechanical properties, blends were prepared using 3, 5 and 10 phr of each compatibilizer. A co-rotating twin-screw extruder was used for blending. The results showed that ABS-g-MA had no significant effect on the tensile strength of the blends while EVA-g-MA decreased the tensile strength, the maximum decrease being about 9.6% when using 10 phr of this compatibilizer. The results of notched Charpy impact strength tests showed that EVA-g-MA increased the impact strength of blends more than ABS-g-MA. The maximum value of this increase occurred when using 5 phr of each compatibilizer, it being about 54% for ABS-g-MA and 165% for EVA-g-MA. Scanning electron microscopy micrographs showed that the particle size of the dispersed phase was decreased in the continuous phase of PC by using the compatibilizers. Moreover, a blend without compatibilizer showed brittle behaviour while the blends containing compatibilizer showed ductile behaviour in fracture. © 2013 Society of Chemical Industry


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References

Polycarbonate (PC)/acrylonitrile–butadiene–styrene (ABS) is one of the most-applied engineering blends in industry.[1] The main markets for this blend are the automotive industry, domestic appliances and electrical and electronic equipment. So, large amounts of this engineering blend are used in industry annually. Many researchers have investigated this blend from different points of view, such as processing conditions and morphological and mechanical properties.[2-11] Yin and Wang investigated the effects of strain rate and ABS fraction on the tensile deformation behaviour of PC, ABS and PC/ABS alloys.[2] They also studied the deformation of PC/ABS alloys at elevated temperatures and high strain rates.[5] Fang et al. investigated rate-dependent large deformation behaviour of PC/ABS blends over a crosshead speed range of 1–3000 mm min−1.[3] In other research, Fang et al. studied the effect of cyclic loading on the tensile properties of PC and PC/ABS and fatigue crack propagation of PC/ABS alloy.[4, 8] Hausnerova et al. demonstrated the effect of geometrical parameters of screw melt mixing on the viscoelastic properties of PC/ABS blends.[6] O-Charoen et al. studied different morphological structures in PC/ABS open-spiral injection mouldings.[7] Tan et al. studied the effect of rubber content in ABS over a wide range on the mechanical properties and morphology of PC/ABS blends with various compositions.[9] Chaudhry et al. investigated the effects of various processing conditions such as mixing time and temperature on the phase morphology of PC/ABS blends.[10] Kuczynski and Snyder studied the retention of physical properties of PC/ABS blends during repeated injection moulding cycles.[11]

As many polymeric blends are not completely miscible, compatibilizers are needed during blending. Their primary mechanism is to reduce the interfacial tension between incompatible polymeric components of a blend which will in turn lead to a finer dispersion with more regular and stable equilibrium morphologies. Generally, three main types of compatibilizer can be considered. These types vare: block or graft copolymers, nonreactive polymers containing polar groups and reactive functional polymers (shown schematically in Fig. 1). Since PC/ABS is a partially miscible blend,[12] many researchers have studied the effect of using various compatibilizers such as poly[(alkyl acrylate)-g-caprolactone], amine-functionalized styrene/n-phenyl maleimide/maleic anhydride terpolymer (amine-SPMIMA), styrene–butadiene–styrene (SBS) block copolymer and ABS-g-(maleic anhydride) (ABS-g-MA) on mechanical properties.[13-21] Lim et al. studied the effect of amine-SPMIMA and its reactive compatibilizing by grafting it to the PC phase of PC/ABS blend during melt blending.[13] Tasdemir studied the effect of SBS copolymer as a compatibilizer on the mechanical and thermal properties of PC/ABS blends.[14] Zhang et al. investigated the effect of ABS-g-MA as a compatibilizer on the mechanical properties of ABS/PC blend. They showed that a small amount of ABS-g-MA as a compatibilizer had a considerable effect on the notched Izod impact strength of the blend and little effect on tensile strength.[15] Balakrishnan and co-workers studied the mechanical properties of PC blended with ABS and ABS-g-MA. They showed that reactive blending improved the interfacial interaction in blends containing ABS-g-MA, and thus improved the mechanical properties. In other research they demonstrated that the morphology of unmodified blends showed coarse dispersion, whereas that of modified blends showed fine and lamellar dispersion.[16, 19] Jin et al. studied the compatibilizing effect of poly(methyl methacrylate) (PMMA) for ABS/PC blends. They showed that the improved adhesion of the ABS/PC interface caused by the PMMA changed the fracture mechanism and reduced the notch sensitivity of blends.[18] Yang et al. investigated the effect of PMMA, methyl methacrylate–butadiene–styrene (MBS) and acrylonitrile styrene acrylate (ASA) as different compatibilizers for PC/ABS blends. They showed that PMMA exhibited the greatest ABS domain size reduction, and annealed samples showed that it suppressed coalescence.[21]

image

Figure 1. Schematic of three main types of compatibilizer: (a) block or graft copolymers; (b) nonreactive polymers containing polar groups; (c) reactive functional polymers.

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Whereas PC and ABS are in the category of engineering plastics and are used in various industries in large amounts, it is important to find a solution to reduce their waste. For this reason, recycling such materials has been noteworthy in recent years. Nowadays, recycling of waste polymeric materials is used to reduce urban solid waste materials.[22] Therefore, recycling of polymers has an important role in everyday life. The recycling methods are related to the type of polymer. There are three main procedures for recycling of polymers:

  1. The direct method, in which the used polymer is blended with the virgin polymer.
  2. Blending the used polymer with other polymers or using it in wood–plastic composites.
  3. Depolymerization or pyrolysis of waste polymer.[22]

Various properties of recycled materials after blending have been investigated by a number of researchers. Tarantili et al. showed that blends of PC and ABS can be easily processed and display appropriate mechanical properties. So, they concluded that blends of PC and ABS can be directly prepared using the mixed engineering plastics from waste of electrical and electronic equipment without sorting.[23] Balart et al. demonstrated that due to the partial miscibility between PC and ABS, and the small degradation of the butadiene of ABS during processing, there is a worsening of the mechanical properties of PC/ABS blends.[24] Elmaghor et al. showed that the toughness of recycled PC could be improved with the use of ABS-g-MA because of the special morphology of ABS domains dispersed in PC matrix due to MA groups grafted on ABS chains.[25] Liu and Bertilsson blended recycled ABS and PC/ABS with a small amount of MBS as an impact modifier. They showed that using MBS improves the impact properties of the mixture in comparison with its individual components, although it has no significant effect on tensile strength and elongation at break. Also, they showed that the use of antioxidants and metal deactivators does not lead to the recycled materials having better mechanical properties.[26]

Production of PC/ABS blend with enhanced properties using fully recycled materials has both economic and environmental importance. So, as the main goal of the research reported here, recycled PC and ABS were blended in the presence of two different compatibilizers and the effects of each compatibilizer on the mechanical and morphological properties were investigated. Both compatibilizers used in this study were the same in type and degree of grafting so as to investigate the effect of the polymeric base of each compatibilizer on the mechanical properties of the blends. Also, MA-grafted compatibilizers were selected because of the potential of the reaction between MA groups of the compatibilizers and hydroxyl end groups of PC that can decrease the interfacial tension between the two main components of the blends by producing a graft copolymer at the interface. Many researchers have used various compatibilizers for PC/ABS blends, but none used (ethylene–vinyl acetate)-g-(maleic anhydride) (EVA-g-MA) as a compatibilizer which is investigated in the present paper. This compatibilizer (EVA-g-MA) was selected because of its rubbery nature so that it also can play the role of impact modifier for the blends to enhance their mechanical properties, especially impact strength and elongation at break, which is important because of the poorer mechanical properties of recycled raw materials.

Experimental

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References

Materials

The source of PC was recycled compact discs and the source of ABS was recycled domestic appliances. The mechanical properties of the recycled materials were tested and the results are given in Table 1. Virgin PC (Makrolon 2858) was from Bayer Material Science Co. (Germany) and virgin ABS (ABS 50) was from Ghaed Bassir Petrochemical Co. (Iran). The mechanical properties of virgin raw materials are given in Table 2. ABS-g-MA (PO-GM-20) with degree of grafting of 1.5% was supplied by Zhuhai Macau Holy Polymers Material Co. (China) with melt flow index (MFI) (200 °C, 5 kg) of 4 g (10 min)−1 and EVA-g-MA (Kimcross 1124) with degree of grafting of 1.5% was supplied by Kimia Javid Co. (Iran) with MFI (190 °C, 5 kg) of 5 g (10 min)−1.

Table 1. Physical and mechanical properties of recycled PC and ABS
PropertyRecycled PCRecycled ABS
MFI (260 °C, 5kg) (g (10 min)−1)53.8 ± 3.221.5 ± 1.5
Density (g cm−3)1.2 ± 0.021.05 ± 0.02
Filler content (%)2.0 ± 0.11.5 ± 0.1
Tensile strength at yield (MPa)58.7 ± 1.942.4 ± 1.4
Elongation at yield (%)5.9 ± 0.13.4 ± 0.1
Elongation at break (%)7.8 ± 1.411.0 ± 3.2
Charpy impact strength (unnotched) (kJ m−2)Not Broken52.9 ± 3.5
Charpy impact strength (notched) (kJ m−2)8.4 ± 1.1
Table 2. Mechanical properties of virgin PC and ABS
PropertyVirgin PCVirgin ABS
Tensile strength at yield (MPa)65.2 ± 3.044.3 ± 1.9
Elongation at yield (%)6.1 ± 0.12.8 ± 0.1
Elongation at break (%)55 ± 424.0 ± 2.0
Charpy impact strength (unnotched) (kJ m−2)Not BrokenNot Broken
Charpy impact strength (notched) (kJ m−2)45.6 ± 2.427.2 ± 0.8

Blend preparation

First, recycled PC and ABS were dried for 4 h at 100 and 80 °C, respectively. Then, the mixes were melt-blended according to the formulations given in Table 3 using a co-rotating twin-screw extruder (SHJ-20) with L/D ratio of 40. The screw speed was 400 rpm and the temperatures of the extruder zones were adjusted from 240 to 260 °C. Pellets were prepared.

Table 3. Formulation of blends
 Component (phr)
ABCDEFGAAEEFFGG
Recycled PC70707070707070
Recycled ABS30303030303030
Virgin PC70707070
Virgin ABS30303030
ABS-g-MA3510
EVA-g-MA35103510

Mechanical testing

Extruded pellets of the blends were dried at 90 °C for 8 h and then injection-moulded to yield samples for mechanical tests such as tensile and impact tests. The tensile behaviour of the specimens was determined using a Zwick/Roell tensile testing machine (model Z020) according to ISO 527 at room temperature. Eight specimens of each composition were tested and the average values were recorded. Notched Charpy impact specimens were prepared using an injection moulding machine. Six specimens of each blend were tested and the average values were recorded. Impact strength tests were carried out using a Zwick/Roell impact tester (model HIT5.5P) according to ISO179.

Scanning electron microscopy

The morphology of fractured surfaces of specimens from impact tests was examined using SEM (SERON AIS 2300). To observe the phase morphology at fractured surfaces and the phase deformation state after fracture, broken samples were etched using an aqueous solution of NaOH (30% w/v) at a temperature of 105 °C. By this method, the PC was hydrolysed leaving the ABS domains.[27]

Fourier transform infrared (FTIR) spectroscopy

FTIR spectra were obtained with a Shimadzu IRPrestige-21 to compare the blends with and without compatibilizer and to investigate the effect of compatibilizer on the chemical structure of the blends according to a published report.[28]

Results And Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References

Blends with various concentrations of compatibilizer from 0 to 10 phr (Table 3) were prepared to investigate the effect of using two different compatibilizers on mechanical properties such as tensile and impact strength. The results are given in Table 4. Also, as control samples, blends without compatibilizer and with EVA-g-MA were produced with virgin raw materials to compare the mechanical properties.

Table 4. Tensile and impact tests results of PC/ABS blends
FormulationTensile strength (MPa)Elongation at break (%)Notched Charpy impact strength (kJ m−2)
A55.1 ± 0.811 ± 111.2 ± 1.4
B56.6 ± 0.621 ± 215.7 ± 1.2
C56.2 ± 0.716 ± 217.3 ± 2.0
D56.0 ± 0.515 ± 116.6 ± 1.6
E53.6 ± 0.626 ± 225.2 ± 3.9
F51.5 ± 0.535 ± 329.7 ± 4.7
G49.8 ± 0.628 ± 229.5 ± 4.5
AA61.2 ± 2.238 ± 336.3 ± 1.5
EE57.1 ± 2.148 ± 252.2 ± 2.1
FF55.8 ± 2.559 ± 461.7 ± 2.0
GG53.4 ± 2.027 ± 365.1 ± 2.7

The results show that the mechanical properties of blends containing recycled raw materials are poorer in comparison with similar blends based on virgin raw materials. This deterioration in mechanical properties could be due to partial degradation of recycled raw materials during their previous lifetimes. Moreover, the presence of fillers in these materials can be considered as another reason for poorer mechanical properties because fillers in polymers often cause a decrease especially in elongation at break and impact strength. From the results in Table 4, it can be seen that the impact strength of the blends initially increases with increasing amount of compatibilizer (ABS-g-MA or EVA-g-MA) up to 5 phr and, after that, the impact strength decreases or shows no significant change. These results are in agreement with other work involving different compatibilizers.[15, 25] Moreover, according to the results in Table 4, the increase of impact strength when using EVA-g-MA is more than when using the same amount of ABS-g-MA as compatibilizer. However, there are no considerable differences between tensile strength results of unmodified and modified blends when using ABS-g-MA. This result is in agreement with previous work by Zhang et al.[15] The tensile strength of blends modified with EVA-g-MA decreases a little when increasing the amount of this compatibilizer. This is because of the rubbery nature of EVA copolymer. So, the value of tensile strength is lowest when using 10 phr of EVA-g-MA. Tensile elongation at break values reveal that modified PC/ABS blends are ductile while unmodified blends show brittle behaviour, which is in agreement with previous research.[16] This could be due to the chemical reaction between MA groups of the compatibilizers and hydroxyl end groups in PC (Fig. 2).[29, 30] Furthermore, processing of ABS can cause thermo-oxidative degradation in the rubber phase.[28] Also, excess MA and dicumyl peroxide in the compatibilizers may remain during the grafting reaction that produces these compatibilizers. So, MA can react with the butadiene of ABS to produce a block or graft copolymer during melt blending in the extruder, these two copolymers being able to increase the interfacial strength.[31]

image

Figure 2. Reaction between MA group and hydroxyl end group of PC.[29]

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As the SEM photomicrographs in Figs 3 and 4 show, for samples with 5 phr of each compatibilizer that have the maximum values of impact strength, the dispersed domains of ABS in the non-compatibilized blend are greater than in the compatibilized ones. This could be because of the reaction that occurs between MA groups of the compatibilizers and hydroxyl end groups of PC that improves the interfacial interactions between the blend components. This is in accordance with previous work.[15, 16] Also, according to the SEM photomicrographs, the blend without any compatibilizer shows brittle fracture behaviour while the blends containing compatibilizer (especially with EVA-g-MA) show ductile fracture behaviour. This phenomenon is in agreement with the impact strength data.

image

Figure 3. SEM photomicrographs (×1000) of PC/ABS blend: (a) without compatibilizer; (b) with 5 phr ABS-g-MA; (c) with 5 phr EVA-g-MA.

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image

Figure 4. SEM photomicrographs (×3500) of PC/ABS blend: (a) without compatibilizer; (b) with 5 phr ABS-g-MA; (c) with 5 phr EVA-g-MA.

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According to the FTIR spectra of blends without compatibilizer and with EVA-g-MA as compatibilizer (Fig. 5), a change can be seen with a peak at a wavenumber of 2851 cm−1. This peak is assigned to C–H stretch of ethylene groups of EVA-g-MA in the compatibilized blend.

image

Figure 5. FTIR spectra of PC/ABS blends without compatibilizer and with 5 phr of EVA-g-MA.

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Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References

Blends of recycled PC and ABS were prepared with two different compatibilizers and some properties such as morphology and mechanical properties were investigated. The results show that using ABS-g-MA as compatibilizer had no significant effect on the tensile strength of the blends. The tensile strength of the blends decreased gradually with increasing amount of EVA-g-MA as compatibilizer, and the lowest value of tensile strength occurred when using 10 phr of this compatibilizer. Moreover, the results show that using either of the compatibilizers increases the impact strength of the blends compared to blends without compatibilizer. The maximum amount of this increase occurred when using 5 phr for both compatibilizers, with values of 17.3 kJ m−2 for ABS-g-MA and 29.7 kJ m−2 for EVA-g-MA, while that for non-compatibilized blend was 11.2 kJ m−2. Also, SEM photomicrographs of samples with 5 phr of each compatibilizer, which have the maximum values of impact strength, show better dispersion of ABS as dispersed phase in compatibilized blends compared to the non-compatibilized one. Moreover, the blend without compatibilizer showed brittle behaviour while the blends containing compatibilizer showed ductile behaviour in fracture. Finally, the results of mechanical tests indicated that the use of the modifiers did not restore the properties of the blend of recycled polymers to those of the un-modified blend made from virgin materials.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References

The authors thank the R&D manager of Kimia Javid Sepahan Co., Mr Abbas Moayed, for permission to use test instruments. Also they thank Mr Francis Chan from Zhuhai Macau Holy Polymers Material Co. for providing ABS-g-MA.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Experimental
  5. Results And Discussion
  6. Conclusions
  7. Acknowledgements
  8. References