572183
research-article2015
WMR0010.1177/0734242X15572183Waste Management & ResearchTriantou et al.
Original Article
Melt processing and property testing of a model system of plastics contained in waste from electrical and electronic equipment
Waste Management & Research 1–7 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X15572183 wmr.sagepub.com
Marianna I Triantou, Petroula A Tarantili and Andreas G Andreopoulos
Abstract In the present research, blending of polymers used in electrical and electronic equipment, i.e. acrylonitrile–butadiene–styrene terpolymer, polycarbonate and polypropylene, was performed in a twin-screw extruder, in order to explore the effect process parameters on the mixture properties, in an attempt to determine some characteristics of a fast and economical procedure for waste management. The addition of polycarbonate in acrylonitrile–butadiene–styrene terpolymer seemed to increase its thermal stability. Also, the addition of polypropylene in acrylonitrile–butadiene–styrene terpolymer facilitates its melt processing, whereas the addition of acrylonitrile–butadiene–styrene terpolymer in polypropylene improves its mechanical performance. Moreover, the upgrading of the above blends by incorporating 2 phr organically modified montmorillonite was investigated. The prepared nanocomposites exhibit greater tensile strength, elastic modulus and storage modulus, as well as higher melt viscosity, compared with the unreinforced blends. The incorporation of montmorillonite nanoplatelets in polycarbonate-rich acrylonitrile–butadiene–styrene terpolymer/polycarbonate blends turns the thermal degradation mechanism into a two-stage process. Alternatively to mechanical recycling, the energy recovery from the combustion of acrylonitrile–butadiene–styrene terpolymer/polycarbonate and acrylonitrile–butadiene–styrene terpolymer/ polypropylene blends was recorded by measuring the gross calorific value. Comparing the investigated polymers, polypropylene presents the higher gross calorific value, followed by acrylonitrile–butadiene–styrene terpolymer and then polycarbonate. The above study allows a rough comparative evaluation of various methodologies for treating plastics from waste from electrical and electronic equipment. Keywords Acrylonitrile–butadiene–styrene terpolymer, blending, calorific value, extrusion, organoclay, polycarbonate, polypropylene, waste from electrical and electronic equipment
Introduction With continuous growth for more than 50 years, global production of plastics in 2012 rose to 288million tonnes (mt), showing a 2.8% increase compared with 2011. However in Europe, plastics’ production decreased by 3% from 2011 to 2012, reaching 57m t. In 2012, the demand in Europe decreased by 2.5% and reached 45.9m t. The electrical and electronic equipment sector covered 5.5% of the European plastics demand in 2012. Furthermore, 25.2m t of plastics ended up in the waste stream in 2012. That year, the landfill disposal of plastics was 38.1% (9.6m t), the plastics’ recycling was 26.3% (6.6m t) and energy recovery reached 35.6% (8.9m t). The total recovery of plastics increased by 4% and at the same time, there was a reduction of 5.5% of landfilled plastics. Collection for mechanical recycling showed a growth of 4.7%, while feedstock recycling increased by 19.4%. Energy recovery also increased by 3.3% (Plasticseurope, 2013). As reported, waste from electrical and electronic equipment (WEEE) represents about 8% of the total municipal waste internationally (The Economist, 2005). In the European Union, 12–20 kg WEEE/habitant is produced each year and their
overall, annual production varies between 6.5–7.5m t according to Hellenic Solid Waste Management Association (HSWMA; www.eedsa.gr); whereas in Greece, 170,000 t WEEE is produced per year. In Greece, in 2012, 36,021 t of WEEE, was collected from the domestic sector and, from them, 33,411 t was further processed (EOAN, 2013). During 2005–2013 (1st semester), 87.73% of WEEE was treated, whereas 12.27% was led to landfill in Greece (www.electrocycle.gr). The polymers hold the second position in the composition of WEEE, as they are met at 20%–21% (www.eedsa.gr). The polymers and plastic technical components used by the involved
Laboratory of Polymer Technology, National Technical University of Athens, Athens, Greece Corresponding author: Marianna I Triantou, Laboratory of Polymer Technology, School of Chemical Engineering, National Technical University of Athens, Heroon Polytechneiou 9, Zografou, 15780 Athens, Greece. Email: [email protected]
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industries are estimated to amount to some 15%–20% of the total value of plastics used in Europe, or about 60–80 billion € (www. plasticsconverters.eu/markets/electrical). The materials used for technical parts in the above industries are very numerous, and often very advanced. The most common plastics are polystyrene, acrylonitrile–butadiene–styrene terpolymer (ABS), polycarbonate (PC) as well as blends of the above. These are widely used for equipment housings and enclosures and, in the case of PC, for optical storage media (CDs). Poly(butylene terephthalate) (PBT) is growing fast, especially for connectors. Low and High-Density Polyethylene (PE-LD and PE-HD) and crosslinked polyethylene are used increasingly in applications, such as cable sheathing as an alternative to poly(vinyl chloride) (PVC). Thermosetting resins also play a major part in electrical and electronic products (www.plasticsconverters.eu/markets/electrical). There are several researches dealing with the recycling of ABS/PC blends. Eguiazábal and Nazábal (1990) concluded that recycling of PC/ABS blends produces a change in the rubbery phase of ABS as it becomes crosslinked/oxidised. The effect of reprocessing on the properties shows two stages. After one or two processing cycles all the high-strain mechanical properties show only a slight change in the usual condition, however, after more than two processing cycles, the decrease in these properties is very significant. Also, Balart et al. (2005) investigated the effect of previous degradation and partial miscibility of ABS/PC blends to their mechanical performance. Liang and Gupta (2002) mixed virgin ABS with virgin and recycled PC and examined the rheological and mechanical behaviour of the blends. Khan et al. (2007) concluded that recycled PC can be used as an additive for virgin or recycled ABS, as a means of giving flame resistance to ABS in high-value applications. Elmaghor et al. (2004) toughened waste PC by maleic anhydride (MAH) grafted ABS (ABS-g-MAH) and considered that the grafting of MAH onto ABS is a key factor, which resulted in a special morphology of ABS domains dispersed in PC matrix, partially eliminating the repulsion between the two polymers. Farzadfar et al. (2013) compatibilised recycled PC and ABS using ABS-g-MAH and ethylene-vinyl-acetate-grafted-maleic anhydride (EVA-g-MAH) and observed that EVA-g-MAH increases the impact strength in comparison with ABS-g-MAH. Liu and Bertlsson (1999) blended recycled ABS and PC/ABS (70/30) with a small amount of methyl-methacrylate-butadienestyrene core-shell impact modifiers and observed better impact properties for the mixture than any of its individual components. Mahanta et al. (2012) studied the effect of the addition of two compatibilisers (maleic anhydride-grafted polypropylene (PP-g-MAH) and solid epoxy resin) and the effect of incorporating organically modified nanoclays to the thermomechanical properties of recycled ABS/PC blends. On the other hand, the literature is limited in the topic of the recycling of ABS/PP blends, maybe owing to the lack of miscibility which characterises the components. Lazzaro et al. (2008) investigated the degree of sorting required based on contamination levels of one of the plastics in ABS/PP blends.
The thermal, mechanical and rheological properties of the blends prepared for this investigation lead to the conclusion that ABS and PP are not compatible and that substantial sorting would be required to obtain a useful material. Lee et al. (2012) studied the effects of maleic anhydride-grafted styrene– ethylene–butylene–styrene copolymer (SEBS-g-MAH) on the mechanical and morphological properties of the PP/ABS 70/30 blends during accelerated aging. The tensile and impact strength of compatibilised blends are decreased less than 10% after five cycles, whereas the corresponding non-compatibilised blends are reduced as much as 37%. As it can be concluded from the mentioned literature search, recycling and reuse of the polymers used in electrical and electronic equipment is a critical step in plastics waste management, mainly owing to their high added value, since the related waste stream contains engineering plastics. The full recycling of engineering plastics is of great importance today, even in the case of non-reinforced matrices. In fact, the study of a model glass fiber, GF-free system might be an interesting first step towards the final target of recycling the actual WEEE. The aim of this research, a part of which was presented at 2nd International Conference on Sustainable Solid Waste Management, 12–14 June 2014, Athens, Greece, was to study blends of model polymers of the same type with those found in WEEE, in an attempt to explore some parameters of a possible recycling process based on direct mixing of the asreceived stream of plastics. In the same context, the incorporation of reinforcing fillers, such as organically modified montmorillonite, might be a means of upgrading the properties of the recycled plastics as a compensation of the expected deterioration owing to their thermomechanical aging. An evaluation of the amount of energy that could be obtained from these mixtures was also within the scope of the present work, in order to allow comparison between the most beneficial recycling methodologies.
Materials and methods Materials The terpolymer ABS was supplied by BASF, under the trade name Terluran® GP-35 and PC by Bayer under the trade name Makrolon® 2805. The density of ABS and PC was 1.04 and 1.20 g cm-3, respectively, and their melt flow rate (MFR) was 35 g/10 min for ABS at 220 °C with 10 kg load and 10 g/10 min for PC at 300 °C with 1.20 kg load. According to Galvan et al. (2012), this type of ABS consists of 44% acrylonitrile, 42% styrene and 14% butadiene. The PP (Εcolen® HZ40Ρ) with density equal to 0.9 g cm-3 and MFR (230 °C, 2.160 kg) equal to 12 g/10 min was donated by Hellenic Petroleum. The tensile strength at yield of virgin ABS, PC and PP are 44, 65 and 34 MPa, respectively. Commercial montmorillonite clay, Cloisite® 30B was purchased by Rockwood Clay Additives GmbH. The organic modifier is a methyl, tallow, bis-2hydroxyethyl, quaternary ammonium.
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Preparation of blends ABS/PC and ABS/PP blends with compositions 100/0, 70/30, 50/50, 30/70 and 0/100 w/w were prepared by melt mixing, in a co-rotating twin-screw extruder, with length/diameter, L/D = 25 and 16 mm diameter (Haake PTW 16), operating at screw speed of 200 r min-1, with a temperature profile ranging from 190 °C to 290 °C for ABS/PC blends and from 180 °C to 210 °C for ABS/ PP blends, depending on the mixture composition. All materials were dried before processing, in order to avoid hydrolytical degradation. After melt mixing, the obtained material in the form of continuous strands was granulated using a Brabender knife pelletiser.
Characterisation The melt flow index (MFI) was determined in a Kayeness Co. model 4004 capillary rheometer at 260 °C with 2.16 kg load for ABS/PC blends and at 230 °C with 2.160 kg load for ABS/PP blends. Mechanical testing of the injection moulded specimens was run according to ASTM D 638, in an Instron tensometer (4466 model), operating at grip separation speed of 50 mm min-1. Injection moulding was performed with an ARBURG 221K ALLROUNDER machine. Dynamic mechanical analysis (DMA) measurements were performed in an Anton Paar analyser, MCR 301, at a frequency of 1 Hz, with a heating rate of 5 °C min-1 between −120 °C to 200 °C for ABS/PC blends and between −120 °C to 160 °C for ABS/PP blends, in an N2 atmosphere. Samples prepared by injection moulding were studied by this technique. Thermogravimetric analysis (TGA) measurements were accomplished in a thermal gravimetric analyser (Mettler Toledo, TGA-DTA) from 25 °C to 800 °C for ABS/PC blends and from 25 °C to 600 °C for ABS/PP blends, at a rate of 10 °C min-1, in an N2 atmosphere. Gross calorific value (GCV) measurements were performed according to ASTM D 5865 in a bomb calorimeter (Parr 6400).
Results and discussion It is well known that the MFI of a material is a measure of its viscosity. From Figure 1(a), it is observed that the ABS/PC blends exhibit higher MFI than that of their components, maybe owing to the partial miscibility between the PC and the styrene– acrylonitrile (SAN) phase of ABS. Furthermore, it can be seen that the incorporation of organoclay into ABS/PC blends results in a decrease of MFI, which implies an increase of the mixture’s viscosity. Confinement of polymer chains motion, caused by the organoclay platelets and tactoids in the ABS/PC matrix and the interactions between the polar groups of ABS and oxygencontaining groups of Cloisite 30B (Aalaie and Rahmatpour, 2007), as well as the hydrogen bonding between the carbonyl groups in PC and the hydroxyl groups in the organoclay (Lee and Han, 2003), may be responsible for this behaviour. According to the bars shown in Figure 1(b), ABS exhibits
Figure 1. MFI of (a) ABS/PC blends and their nanocomposites at 260 °C, with a load of 2.160 kg and (b) ABS/PP blends and their nanocomposites at 230 °C, with a load of 2.160 kg. ABS: acrylonitrile–butadiene–styrene terpolymer; PC: polycarbonate; PP:polypropylene.
higher viscosity than PP and ABS/PP blends present melt behaviour closer to that of PP. Moreover, the melt viscosity of ABS/PP blend drops by increasing PP content and tends to increase when organically modified montmorillonite is added to the mixture. Regarding the mechanical properties, PC displays higher tensile strength (64.72 MPa) in comparison with that of ABS (46.77 MPa). The tensile strength of ABS is improved by the addition of PC and the related increase seems to follow the rule of mixture. Similar results can be found in the literature (Khan et al., 2005; Nigam et al., 2005; Rimdusit et al., 2012; Wong, 2003). On the other hand, the tensile strength of ABS is higher than that of PP (35.36 MPa) and, thus, the mixture’s strength significantly decreases by the addition of PP. The tensile strength of ABS/PP blends is closer to that of PP and presents negative deviation from the additive rule, maybe owing to the lack of miscibility between their components. As far as the Young’s modulus is concerned (Figure 2), a synergic action between ABS and PC is observed. A significant enhancement of modulus is clear, since the contribution of PC leads to an increase of the rigidity of ABS and limits the plasticising effect of the rubber phase. The highest improvement of Young’s modulus is recorded for composition 50/50 w/w. This behaviour is attributed to the diffusion of polymeric chains from one phase to another, which brings about partial miscibility between the components. In ABS/PP blends, the Young’s modulus decreases as the PP content is increased following the additive rule. The incorporation of nanofillers in ABS/PC blends seems to cause a slight increase in their tensile strength. Thus, the addition of organoclay tends to increase the tensile strength in ABS-rich blends, whereas in PP-rich blends a slight decrease of the strength can be recorded. On the other hand, the addition of nanofiller significantly improves the Young’s modulus of the examined blends.
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Figure 2. Young’s modulus of ABS/PC and ABS/PP blends and their nanocomposites.
ABS: acrylonitrile-butadiene-styrene terpolymer; PC: polycarbonate; PP: polypropylene.
The increase of tensile strength can be attributed to the high aspect ratio of clay, to its efficient dispersion in the polymer matrix and to the strong adhesive bonding at the filler-matrix interface, which facilitates the stress transfer from the matrix to clay. The improvement of elastic modulus might be attributed to the high stiffness of organically modified clay (Guo et al., 2004; Lim et al., 2010), to the difference in elastic modulus between the organoclay and polymer matrix (Basurto et al., 2012), to the high aspect ratio of clay (Basurto et al., 2012) and/or to the low deformability of polymeric chains penetrating the silicate galleries (Lim et al., 2010). Xiang-Fang et al. (2009) prepared PP/ABS/organically modified montmorillonite (OMMT) nanocomposites and recorded a small decrease of their tensile strength and an increase of the tensile strain and modulus, in comparison with unreinforced blends. The van der Waals forces seemed to play a large role on the overall interaction between OMMT particles and PP/ABS matrix, as they can form an interface layer owing to physical entanglement. Thus, the faint effects between layers hardly resisted the load, resulting in cracks in the matrix and decreased strength. The storage modulus, Gʹ, is one of the most important parameters determined by DMA, relevant to the elastic response during the sample’s deformation. From Figure 3(a) it can be seen that the storage modulus of ABS, PC and their blends decreases gradually with the increase of temperature. At the various heating ranges, the decrease rates are different, which suggests different material states, such as glassy, viscoelastic, rubber states, etc. The Gʹ curve of net PC and ABS resin intersect at 70 °C. PC has a smaller value of storage modulus than ABS when the temperature is lower than 70 °C and PC has a higher value of storage modulus than ABS when the temperature is higher than 70 °C. Moreover, it is observed that the Gʹ of ABS drops sharply from ~70 °C and is close to zero at 110 °C, while PC drops sharply at ~130 °C and approaches zero at 150 °C. A synergistic effect is observed for ABS/PC blends and the highest value is recorded for 50/50 w/w composition, which also corresponds to maximum of Young’s modulus.
Figure 3. Storage modulus versus temperature of (a) ABS/PC and (b) ABS/PP blends. ABS: acrylonitrile–butadiene–styrene terpolymer; PC: polycarbonate; PP: polypropylene.
The storage modulus, Gʹ, of PP starts to drop at ~(–20) °C and then sharply decreases approaching zero at 150 °C (Figure 3(b)). A change in the behaviour of storage modulus of ABS/PP blends is recorded at about 10 °C. In particular, below 10 °C, the ABS/PP blends present a higher storage modulus than that of neat ABS and lower than, or equal to, that of neat PP. On the contrary, over 10 °C, the Gʹ of ABS/PP blends is higher than that of neat PP and lower than that of neat ABS. A return to the initial behaviour can be observed at 110 °C. From Figure 4, it can be seen that the incorporation of nanoparticles leads to an impressive increase of storage modulus, in comparison with this corresponding to unreinforced blends. This behaviour can be attributed to the high aspect ratio and to the stiffness of clay. Also, the confinement of polymer chains motion, owing to their interactions with the nanoparticles and owing to the dispersion of filler, causes an increase of the storage modulus. An improvement of storage modulus by adding clay particles is also reported by Cai et al. (2010), Modesti et al. (2008), Patiño-Soto et al. (2008) and Choi et al. (2005) for ABS matrix and by Nayak et al.(2010) and Chow and Neoh (2010) for
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Figure 4. Storage modulus versus temperature of ABS/PC and ABS/PP blends and their nanocomposites at 30/70 w/w.
ABS: acrylonitrile–butadiene–styrene terpolymer; PC: polycarbonate; PP: polypropylene.
PC matrix. It should be mentioned that the above analysis might also provide data for the calculation of Tg and, further, for an assessment of the miscibility of the blend components. This work has already been made in an earlier, already published article (Triantou and Tarantili, 2014). Regarding the thermal stability, it increases with the following order: ABS
research-article2015
WMR0010.1177/0734242X15572183Waste Management & ResearchTriantou et al.
Original Article
Melt processing and property testing of a model system of plastics contained in waste from electrical and electronic equipment
Waste Management & Research 1–7 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X15572183 wmr.sagepub.com
Marianna I Triantou, Petroula A Tarantili and Andreas G Andreopoulos
Abstract In the present research, blending of polymers used in electrical and electronic equipment, i.e. acrylonitrile–butadiene–styrene terpolymer, polycarbonate and polypropylene, was performed in a twin-screw extruder, in order to explore the effect process parameters on the mixture properties, in an attempt to determine some characteristics of a fast and economical procedure for waste management. The addition of polycarbonate in acrylonitrile–butadiene–styrene terpolymer seemed to increase its thermal stability. Also, the addition of polypropylene in acrylonitrile–butadiene–styrene terpolymer facilitates its melt processing, whereas the addition of acrylonitrile–butadiene–styrene terpolymer in polypropylene improves its mechanical performance. Moreover, the upgrading of the above blends by incorporating 2 phr organically modified montmorillonite was investigated. The prepared nanocomposites exhibit greater tensile strength, elastic modulus and storage modulus, as well as higher melt viscosity, compared with the unreinforced blends. The incorporation of montmorillonite nanoplatelets in polycarbonate-rich acrylonitrile–butadiene–styrene terpolymer/polycarbonate blends turns the thermal degradation mechanism into a two-stage process. Alternatively to mechanical recycling, the energy recovery from the combustion of acrylonitrile–butadiene–styrene terpolymer/polycarbonate and acrylonitrile–butadiene–styrene terpolymer/ polypropylene blends was recorded by measuring the gross calorific value. Comparing the investigated polymers, polypropylene presents the higher gross calorific value, followed by acrylonitrile–butadiene–styrene terpolymer and then polycarbonate. The above study allows a rough comparative evaluation of various methodologies for treating plastics from waste from electrical and electronic equipment. Keywords Acrylonitrile–butadiene–styrene terpolymer, blending, calorific value, extrusion, organoclay, polycarbonate, polypropylene, waste from electrical and electronic equipment
Introduction With continuous growth for more than 50 years, global production of plastics in 2012 rose to 288million tonnes (mt), showing a 2.8% increase compared with 2011. However in Europe, plastics’ production decreased by 3% from 2011 to 2012, reaching 57m t. In 2012, the demand in Europe decreased by 2.5% and reached 45.9m t. The electrical and electronic equipment sector covered 5.5% of the European plastics demand in 2012. Furthermore, 25.2m t of plastics ended up in the waste stream in 2012. That year, the landfill disposal of plastics was 38.1% (9.6m t), the plastics’ recycling was 26.3% (6.6m t) and energy recovery reached 35.6% (8.9m t). The total recovery of plastics increased by 4% and at the same time, there was a reduction of 5.5% of landfilled plastics. Collection for mechanical recycling showed a growth of 4.7%, while feedstock recycling increased by 19.4%. Energy recovery also increased by 3.3% (Plasticseurope, 2013). As reported, waste from electrical and electronic equipment (WEEE) represents about 8% of the total municipal waste internationally (The Economist, 2005). In the European Union, 12–20 kg WEEE/habitant is produced each year and their
overall, annual production varies between 6.5–7.5m t according to Hellenic Solid Waste Management Association (HSWMA; www.eedsa.gr); whereas in Greece, 170,000 t WEEE is produced per year. In Greece, in 2012, 36,021 t of WEEE, was collected from the domestic sector and, from them, 33,411 t was further processed (EOAN, 2013). During 2005–2013 (1st semester), 87.73% of WEEE was treated, whereas 12.27% was led to landfill in Greece (www.electrocycle.gr). The polymers hold the second position in the composition of WEEE, as they are met at 20%–21% (www.eedsa.gr). The polymers and plastic technical components used by the involved
Laboratory of Polymer Technology, National Technical University of Athens, Athens, Greece Corresponding author: Marianna I Triantou, Laboratory of Polymer Technology, School of Chemical Engineering, National Technical University of Athens, Heroon Polytechneiou 9, Zografou, 15780 Athens, Greece. Email: [email protected]
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industries are estimated to amount to some 15%–20% of the total value of plastics used in Europe, or about 60–80 billion € (www. plasticsconverters.eu/markets/electrical). The materials used for technical parts in the above industries are very numerous, and often very advanced. The most common plastics are polystyrene, acrylonitrile–butadiene–styrene terpolymer (ABS), polycarbonate (PC) as well as blends of the above. These are widely used for equipment housings and enclosures and, in the case of PC, for optical storage media (CDs). Poly(butylene terephthalate) (PBT) is growing fast, especially for connectors. Low and High-Density Polyethylene (PE-LD and PE-HD) and crosslinked polyethylene are used increasingly in applications, such as cable sheathing as an alternative to poly(vinyl chloride) (PVC). Thermosetting resins also play a major part in electrical and electronic products (www.plasticsconverters.eu/markets/electrical). There are several researches dealing with the recycling of ABS/PC blends. Eguiazábal and Nazábal (1990) concluded that recycling of PC/ABS blends produces a change in the rubbery phase of ABS as it becomes crosslinked/oxidised. The effect of reprocessing on the properties shows two stages. After one or two processing cycles all the high-strain mechanical properties show only a slight change in the usual condition, however, after more than two processing cycles, the decrease in these properties is very significant. Also, Balart et al. (2005) investigated the effect of previous degradation and partial miscibility of ABS/PC blends to their mechanical performance. Liang and Gupta (2002) mixed virgin ABS with virgin and recycled PC and examined the rheological and mechanical behaviour of the blends. Khan et al. (2007) concluded that recycled PC can be used as an additive for virgin or recycled ABS, as a means of giving flame resistance to ABS in high-value applications. Elmaghor et al. (2004) toughened waste PC by maleic anhydride (MAH) grafted ABS (ABS-g-MAH) and considered that the grafting of MAH onto ABS is a key factor, which resulted in a special morphology of ABS domains dispersed in PC matrix, partially eliminating the repulsion between the two polymers. Farzadfar et al. (2013) compatibilised recycled PC and ABS using ABS-g-MAH and ethylene-vinyl-acetate-grafted-maleic anhydride (EVA-g-MAH) and observed that EVA-g-MAH increases the impact strength in comparison with ABS-g-MAH. Liu and Bertlsson (1999) blended recycled ABS and PC/ABS (70/30) with a small amount of methyl-methacrylate-butadienestyrene core-shell impact modifiers and observed better impact properties for the mixture than any of its individual components. Mahanta et al. (2012) studied the effect of the addition of two compatibilisers (maleic anhydride-grafted polypropylene (PP-g-MAH) and solid epoxy resin) and the effect of incorporating organically modified nanoclays to the thermomechanical properties of recycled ABS/PC blends. On the other hand, the literature is limited in the topic of the recycling of ABS/PP blends, maybe owing to the lack of miscibility which characterises the components. Lazzaro et al. (2008) investigated the degree of sorting required based on contamination levels of one of the plastics in ABS/PP blends.
The thermal, mechanical and rheological properties of the blends prepared for this investigation lead to the conclusion that ABS and PP are not compatible and that substantial sorting would be required to obtain a useful material. Lee et al. (2012) studied the effects of maleic anhydride-grafted styrene– ethylene–butylene–styrene copolymer (SEBS-g-MAH) on the mechanical and morphological properties of the PP/ABS 70/30 blends during accelerated aging. The tensile and impact strength of compatibilised blends are decreased less than 10% after five cycles, whereas the corresponding non-compatibilised blends are reduced as much as 37%. As it can be concluded from the mentioned literature search, recycling and reuse of the polymers used in electrical and electronic equipment is a critical step in plastics waste management, mainly owing to their high added value, since the related waste stream contains engineering plastics. The full recycling of engineering plastics is of great importance today, even in the case of non-reinforced matrices. In fact, the study of a model glass fiber, GF-free system might be an interesting first step towards the final target of recycling the actual WEEE. The aim of this research, a part of which was presented at 2nd International Conference on Sustainable Solid Waste Management, 12–14 June 2014, Athens, Greece, was to study blends of model polymers of the same type with those found in WEEE, in an attempt to explore some parameters of a possible recycling process based on direct mixing of the asreceived stream of plastics. In the same context, the incorporation of reinforcing fillers, such as organically modified montmorillonite, might be a means of upgrading the properties of the recycled plastics as a compensation of the expected deterioration owing to their thermomechanical aging. An evaluation of the amount of energy that could be obtained from these mixtures was also within the scope of the present work, in order to allow comparison between the most beneficial recycling methodologies.
Materials and methods Materials The terpolymer ABS was supplied by BASF, under the trade name Terluran® GP-35 and PC by Bayer under the trade name Makrolon® 2805. The density of ABS and PC was 1.04 and 1.20 g cm-3, respectively, and their melt flow rate (MFR) was 35 g/10 min for ABS at 220 °C with 10 kg load and 10 g/10 min for PC at 300 °C with 1.20 kg load. According to Galvan et al. (2012), this type of ABS consists of 44% acrylonitrile, 42% styrene and 14% butadiene. The PP (Εcolen® HZ40Ρ) with density equal to 0.9 g cm-3 and MFR (230 °C, 2.160 kg) equal to 12 g/10 min was donated by Hellenic Petroleum. The tensile strength at yield of virgin ABS, PC and PP are 44, 65 and 34 MPa, respectively. Commercial montmorillonite clay, Cloisite® 30B was purchased by Rockwood Clay Additives GmbH. The organic modifier is a methyl, tallow, bis-2hydroxyethyl, quaternary ammonium.
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Preparation of blends ABS/PC and ABS/PP blends with compositions 100/0, 70/30, 50/50, 30/70 and 0/100 w/w were prepared by melt mixing, in a co-rotating twin-screw extruder, with length/diameter, L/D = 25 and 16 mm diameter (Haake PTW 16), operating at screw speed of 200 r min-1, with a temperature profile ranging from 190 °C to 290 °C for ABS/PC blends and from 180 °C to 210 °C for ABS/ PP blends, depending on the mixture composition. All materials were dried before processing, in order to avoid hydrolytical degradation. After melt mixing, the obtained material in the form of continuous strands was granulated using a Brabender knife pelletiser.
Characterisation The melt flow index (MFI) was determined in a Kayeness Co. model 4004 capillary rheometer at 260 °C with 2.16 kg load for ABS/PC blends and at 230 °C with 2.160 kg load for ABS/PP blends. Mechanical testing of the injection moulded specimens was run according to ASTM D 638, in an Instron tensometer (4466 model), operating at grip separation speed of 50 mm min-1. Injection moulding was performed with an ARBURG 221K ALLROUNDER machine. Dynamic mechanical analysis (DMA) measurements were performed in an Anton Paar analyser, MCR 301, at a frequency of 1 Hz, with a heating rate of 5 °C min-1 between −120 °C to 200 °C for ABS/PC blends and between −120 °C to 160 °C for ABS/PP blends, in an N2 atmosphere. Samples prepared by injection moulding were studied by this technique. Thermogravimetric analysis (TGA) measurements were accomplished in a thermal gravimetric analyser (Mettler Toledo, TGA-DTA) from 25 °C to 800 °C for ABS/PC blends and from 25 °C to 600 °C for ABS/PP blends, at a rate of 10 °C min-1, in an N2 atmosphere. Gross calorific value (GCV) measurements were performed according to ASTM D 5865 in a bomb calorimeter (Parr 6400).
Results and discussion It is well known that the MFI of a material is a measure of its viscosity. From Figure 1(a), it is observed that the ABS/PC blends exhibit higher MFI than that of their components, maybe owing to the partial miscibility between the PC and the styrene– acrylonitrile (SAN) phase of ABS. Furthermore, it can be seen that the incorporation of organoclay into ABS/PC blends results in a decrease of MFI, which implies an increase of the mixture’s viscosity. Confinement of polymer chains motion, caused by the organoclay platelets and tactoids in the ABS/PC matrix and the interactions between the polar groups of ABS and oxygencontaining groups of Cloisite 30B (Aalaie and Rahmatpour, 2007), as well as the hydrogen bonding between the carbonyl groups in PC and the hydroxyl groups in the organoclay (Lee and Han, 2003), may be responsible for this behaviour. According to the bars shown in Figure 1(b), ABS exhibits
Figure 1. MFI of (a) ABS/PC blends and their nanocomposites at 260 °C, with a load of 2.160 kg and (b) ABS/PP blends and their nanocomposites at 230 °C, with a load of 2.160 kg. ABS: acrylonitrile–butadiene–styrene terpolymer; PC: polycarbonate; PP:polypropylene.
higher viscosity than PP and ABS/PP blends present melt behaviour closer to that of PP. Moreover, the melt viscosity of ABS/PP blend drops by increasing PP content and tends to increase when organically modified montmorillonite is added to the mixture. Regarding the mechanical properties, PC displays higher tensile strength (64.72 MPa) in comparison with that of ABS (46.77 MPa). The tensile strength of ABS is improved by the addition of PC and the related increase seems to follow the rule of mixture. Similar results can be found in the literature (Khan et al., 2005; Nigam et al., 2005; Rimdusit et al., 2012; Wong, 2003). On the other hand, the tensile strength of ABS is higher than that of PP (35.36 MPa) and, thus, the mixture’s strength significantly decreases by the addition of PP. The tensile strength of ABS/PP blends is closer to that of PP and presents negative deviation from the additive rule, maybe owing to the lack of miscibility between their components. As far as the Young’s modulus is concerned (Figure 2), a synergic action between ABS and PC is observed. A significant enhancement of modulus is clear, since the contribution of PC leads to an increase of the rigidity of ABS and limits the plasticising effect of the rubber phase. The highest improvement of Young’s modulus is recorded for composition 50/50 w/w. This behaviour is attributed to the diffusion of polymeric chains from one phase to another, which brings about partial miscibility between the components. In ABS/PP blends, the Young’s modulus decreases as the PP content is increased following the additive rule. The incorporation of nanofillers in ABS/PC blends seems to cause a slight increase in their tensile strength. Thus, the addition of organoclay tends to increase the tensile strength in ABS-rich blends, whereas in PP-rich blends a slight decrease of the strength can be recorded. On the other hand, the addition of nanofiller significantly improves the Young’s modulus of the examined blends.
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Waste Management & Research
Figure 2. Young’s modulus of ABS/PC and ABS/PP blends and their nanocomposites.
ABS: acrylonitrile-butadiene-styrene terpolymer; PC: polycarbonate; PP: polypropylene.
The increase of tensile strength can be attributed to the high aspect ratio of clay, to its efficient dispersion in the polymer matrix and to the strong adhesive bonding at the filler-matrix interface, which facilitates the stress transfer from the matrix to clay. The improvement of elastic modulus might be attributed to the high stiffness of organically modified clay (Guo et al., 2004; Lim et al., 2010), to the difference in elastic modulus between the organoclay and polymer matrix (Basurto et al., 2012), to the high aspect ratio of clay (Basurto et al., 2012) and/or to the low deformability of polymeric chains penetrating the silicate galleries (Lim et al., 2010). Xiang-Fang et al. (2009) prepared PP/ABS/organically modified montmorillonite (OMMT) nanocomposites and recorded a small decrease of their tensile strength and an increase of the tensile strain and modulus, in comparison with unreinforced blends. The van der Waals forces seemed to play a large role on the overall interaction between OMMT particles and PP/ABS matrix, as they can form an interface layer owing to physical entanglement. Thus, the faint effects between layers hardly resisted the load, resulting in cracks in the matrix and decreased strength. The storage modulus, Gʹ, is one of the most important parameters determined by DMA, relevant to the elastic response during the sample’s deformation. From Figure 3(a) it can be seen that the storage modulus of ABS, PC and their blends decreases gradually with the increase of temperature. At the various heating ranges, the decrease rates are different, which suggests different material states, such as glassy, viscoelastic, rubber states, etc. The Gʹ curve of net PC and ABS resin intersect at 70 °C. PC has a smaller value of storage modulus than ABS when the temperature is lower than 70 °C and PC has a higher value of storage modulus than ABS when the temperature is higher than 70 °C. Moreover, it is observed that the Gʹ of ABS drops sharply from ~70 °C and is close to zero at 110 °C, while PC drops sharply at ~130 °C and approaches zero at 150 °C. A synergistic effect is observed for ABS/PC blends and the highest value is recorded for 50/50 w/w composition, which also corresponds to maximum of Young’s modulus.
Figure 3. Storage modulus versus temperature of (a) ABS/PC and (b) ABS/PP blends. ABS: acrylonitrile–butadiene–styrene terpolymer; PC: polycarbonate; PP: polypropylene.
The storage modulus, Gʹ, of PP starts to drop at ~(–20) °C and then sharply decreases approaching zero at 150 °C (Figure 3(b)). A change in the behaviour of storage modulus of ABS/PP blends is recorded at about 10 °C. In particular, below 10 °C, the ABS/PP blends present a higher storage modulus than that of neat ABS and lower than, or equal to, that of neat PP. On the contrary, over 10 °C, the Gʹ of ABS/PP blends is higher than that of neat PP and lower than that of neat ABS. A return to the initial behaviour can be observed at 110 °C. From Figure 4, it can be seen that the incorporation of nanoparticles leads to an impressive increase of storage modulus, in comparison with this corresponding to unreinforced blends. This behaviour can be attributed to the high aspect ratio and to the stiffness of clay. Also, the confinement of polymer chains motion, owing to their interactions with the nanoparticles and owing to the dispersion of filler, causes an increase of the storage modulus. An improvement of storage modulus by adding clay particles is also reported by Cai et al. (2010), Modesti et al. (2008), Patiño-Soto et al. (2008) and Choi et al. (2005) for ABS matrix and by Nayak et al.(2010) and Chow and Neoh (2010) for
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Figure 4. Storage modulus versus temperature of ABS/PC and ABS/PP blends and their nanocomposites at 30/70 w/w.
ABS: acrylonitrile–butadiene–styrene terpolymer; PC: polycarbonate; PP: polypropylene.
PC matrix. It should be mentioned that the above analysis might also provide data for the calculation of Tg and, further, for an assessment of the miscibility of the blend components. This work has already been made in an earlier, already published article (Triantou and Tarantili, 2014). Regarding the thermal stability, it increases with the following order: ABS
