584845 research-article2015
WMR0010.1177/0734242X15584845Waste Management & ResearchHirayama and Saron
Original Article
Characterisation of recycled acrylonitrilebutadiene-styrene and high-impact polystyrene from waste computer equipment in Brazil
Waste Management & Research 1–7 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X15584845 wmr.sagepub.com
Denise Hirayama and Clodoaldo Saron
Abstract Polymeric materials constitute a considerable fraction of waste computer equipment and polymers acrylonitrile-butadiene-styrene and high-impact polystyrene are the main thermoplastic polymeric components found in waste computer equipment. Identification, separation and characterisation of additives present in acrylonitrile-butadiene-styrene and high-impact polystyrene are fundamental procedures to mechanical recycling of these polymers. The aim of this study was to evaluate the methods for identification of acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment in Brazil, as well as their potential for mechanical recycling. The imprecise utilisation of symbols for identification of the polymers and the presence of additives containing toxic elements in determinate computer devices are some of the difficulties found for recycling of acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment. However, the considerable performance of mechanical properties of the recycled acrylonitrile-butadiene-styrene and high-impact polystyrene when compared with the virgin materials confirms the potential for mechanical recycling of these polymers. Keywords Mechanical recycling, polymers, acrylonitrile-butadiene-styrene, high-impact polystyrene, waste electrical and electronic equipment, computer equipment
Introduction Waste electrical and electronic equipment (WEEE) has recently gained importance owing to its high production and environment impacts caused by improper disposal (Barthes et al., 2012; Buekens and Yang, 2014; Colesca et al, 2014; He and Xu, 2014; Li et al., 2014; Ortuño et al., 2014; Wang and Xu, 2014; Yu et al., 2014). It is estimated that worldwide 20–50 million tonnes of WEEE are generated per year and this figure is growing at each year (Wang and Xu, 2014). WEEE contains not only toxic and hazardous contaminants, but also valuable materials if treated in a proper way (Wang and Xu, 2014). Some countries have actively issued a series of laws and regulations to standardise WEEE management (European Union, 2002a, 2002b, 2008, 2012). In Brazil, the Federal Law 12.305/2010 regulates the management of solid waste and assigns responsibility for the generators and to the State (República Federativa do Brasil, 2010). Among the political aims of solid waste are the minimisation of the generation, reuse, recycling and environmentally adequate disposal of these wastes. Waste computer equipment (WCE) from desktop PCs represents an important fraction of WEEE, which is basically composed by glass, metals and polymers, as well as others compounds, some of which are toxics, such as lead, mercury and cadmium
(Buekens and Yang, 2014, Ongondo et al., 2011, Taurino et al., 2010). Polymers constitute 15–20 wt% of WEEE (Wang and Xu, 2014), however, if the low density of polymers is considered, the volumetric representation of polymers in WEEE is more significant (Wang and Xu, 2014). High-impact polystyrene (HIPS) and acrylonitrile-butadiene-styrene (ABS) are the main thermoplastic polymer constituents of the WEEE, representing around 65% of the total weight of the WCE (Brennan et al., 2002; Kasper et al., 2011). Adequate identification and separation of the polymeric components from WCE are fundamental procedures for successful mechanical recycling of these materials. The mixture of several polymers and contaminants often produces materials with depreciated thermal and mechanical properties. Consequently, the
Department of Materials Engineering, University of São Paulo, Lorena, Brazil Corresponding author: Clodoaldo Saron, Department of Materials Engineering, Engineering School of Lorena, University of São Paulo, LOM-EEL/USP, Polo Urbo Industrial, Gleba AI-6, s/n, CEP: 12602-810 Lorena, SP, Brazil. Email: [email protected]
Downloaded from wmr.sagepub.com at Bobst Library, New York University on July 16, 2015
2
Waste Management & Research
performance of the recycled polymers is affected, invalidating their application as engineering polymers (Barthes et al., 2012; Li et al., 2014; Taurino et al., 2010). In Brazil, the identification of polymers from WEEE can be performed by symbol codes printed on polymeric devices, according to recommendations of standard practice ABNT – NBR13230 (2006). This standard distinguishes the polymers in six groups of thermoplastics: polyethylene terephtalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS). However, it is not possible to distinguish ABS, HIPS and PS. Brand codes are also used for identification of the thermoplastics polymers in WCE, however, the injudicious use of symbols hinders the reliability of identification (Coltro et al., 2008). Another problem verified for recycling of thermoplastics polymers from WCE is the presence of halogenated flame retardants, which are represented mainly by brominated organic compounds (Peeters et al., 2014, Schlummer et al., 2007, Taurino et al., 2010). Owing to the presence of an electrical power source in electric and electronic equipment (EEE) and to the inherent potential ignition of this thermoplastic, flame retardants are necessary in several polymeric components in EEE. On average 26 wt% of all WEEE plastics contain flame retardants (Peeters et al., 2014). The thermal treatment of halogenated flame retardants can produce extremely toxic halogenated dioxins and furans. Moreover, the presence flame retardants can make operations of thermo-mechanical processing of the polymer difficult owing to the liberation of gases, as well as interfering in the compatibility of the polymer with others components (Li et al., 2014; Taurino et al., 2010). Aromatic brominated compounds are the main kinds of halogenated flame retardants. Among brominated flame retardants, the tetrabromobisphenol alone represents around 50% of the consume (Zang and Sahajwalla, 2014). The aims of this study were to evaluate difficulties and potential for mechanical recycling of thermoplastic ABS and HIPS from computer equipment waste in Brazil, considering procedures to identify the polymers, the presence toxic additives and performance of mechanical and rheological properties compared with virgin resins.
Materials and methods Materials Obsolete informatics equipment such as central processing units (CPUs), printers, monitors, keyboards, microphones and mice were disassembled, and polymeric thermoplastic components separated, according to identification by Fourier transform infrared (FTIR) as well as symbols (ABNT – NBR13230) printed on the components. Co-polymer ABS and HIPS obtained from informatics equipment were used as recycled polymers (ABSr) and (HIPSr), while virgin resins Terluran®GP-35 (ABSv) and HIPS825® (HIPSv) were kindly supplied by BASF Ltda, Brazil and Video Lar S/A, Brazil, respectively.
Methods FTIR analyses were performed in transmittance mode after dilution of the recycled and virgin polymers in KBr pellets, using a spectrometer Shimadzu IR Prestige-21 at 64 scans and resolution at 4 cm-1. For X-ray fluorescence (XRF) analyses, virgin and recycled polymers were grounded and pressed with boric acid in pneumatic equipment (SPEX, model 3628 Bench-press) at 20 t by 20 s to produce pellets with a 4-cm diameter. Then, the pellets were analysed with an XRF spectrometer (Panalytical, model AXIOS max). X-ray diffractograms were obtained using a Panalytical Empyrean diffractometer with copper Kα radiation and a diffraction angle 2θ, range 7–90º. Thermogravimetric analyses (TGA) were carried out in a simultaneous thermal analyser (NETZSCH model STA 449 F3 Jupiter) at a heating rate of 10 ºC min-1 and a nitrogen flow at 100 mL min-1 as protective and purge gas. Tensile and impact testing were performed according to standard practices ASTM D 256 and ASTM D 638, respectively. For preparation of specimens, initially polymeric thermoplastic components from informatics equipment were grounded in a knife mill to generate a particle size around 5 mm of length. Then, recycled and virgin polymers were processed by extrusion in an Imacon with a temperature profile at 190/200/200/210 °C from the alimentation zone to matrix in the presence of a thermal stabilizer (SONGNOX 21B) at 0.15 wt%. After extrusion moulding, specimens for tensile and impact testing were simultaneously prepared by injection moulding in a Spazio DW-130. Tensile testing were carried out in an universal testing machine (EMIC DL 3000) with a load cell of 5 kN at speed of 10 mm min-1, while impact resistance was performed in mode Izod with notched samples in a Time Group XJU-2.75, using a hammer of 2.75 J. The melting flow index (MFI) of the polymers was determined using specimens for mechanical testing after being analysed. For this, specimens were again grounded in a knife mill to generate a particle size of around 5 mm in length. The material was then analysed in an extruder plastometer (Ceast 7021) at 230 ºC with 3.8 kg of load.
Results and discussion Identification of polymeric components by symbol codes The reading of printed brands or symbol codes on polymeric devices has been shown to be insufficient for precise identification of the polymeric components of ABS and HIPS in WEEE. Table 1 shows the symbols used for identification of ABS and HIPS present in WCE. The ambiguity and small flexibility of the symbol code, according to recommendations of standard practice ABNT – NBR13230, which have only the options of category 6 or 7 to classify HIPS and ABS, make a doubtful identification mainly
Downloaded from wmr.sagepub.com at Bobst Library, New York University on July 16, 2015
3
Hirayama and Saron Table 1. Symbols used for identification of polymers in WCE. Acrylonitrile-butadiene-styrene (ABS)
High impact polystyrene (HIPS)
>ABS
PS
WMR0010.1177/0734242X15584845Waste Management & ResearchHirayama and Saron
Original Article
Characterisation of recycled acrylonitrilebutadiene-styrene and high-impact polystyrene from waste computer equipment in Brazil
Waste Management & Research 1–7 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X15584845 wmr.sagepub.com
Denise Hirayama and Clodoaldo Saron
Abstract Polymeric materials constitute a considerable fraction of waste computer equipment and polymers acrylonitrile-butadiene-styrene and high-impact polystyrene are the main thermoplastic polymeric components found in waste computer equipment. Identification, separation and characterisation of additives present in acrylonitrile-butadiene-styrene and high-impact polystyrene are fundamental procedures to mechanical recycling of these polymers. The aim of this study was to evaluate the methods for identification of acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment in Brazil, as well as their potential for mechanical recycling. The imprecise utilisation of symbols for identification of the polymers and the presence of additives containing toxic elements in determinate computer devices are some of the difficulties found for recycling of acrylonitrile-butadiene-styrene and high-impact polystyrene from waste computer equipment. However, the considerable performance of mechanical properties of the recycled acrylonitrile-butadiene-styrene and high-impact polystyrene when compared with the virgin materials confirms the potential for mechanical recycling of these polymers. Keywords Mechanical recycling, polymers, acrylonitrile-butadiene-styrene, high-impact polystyrene, waste electrical and electronic equipment, computer equipment
Introduction Waste electrical and electronic equipment (WEEE) has recently gained importance owing to its high production and environment impacts caused by improper disposal (Barthes et al., 2012; Buekens and Yang, 2014; Colesca et al, 2014; He and Xu, 2014; Li et al., 2014; Ortuño et al., 2014; Wang and Xu, 2014; Yu et al., 2014). It is estimated that worldwide 20–50 million tonnes of WEEE are generated per year and this figure is growing at each year (Wang and Xu, 2014). WEEE contains not only toxic and hazardous contaminants, but also valuable materials if treated in a proper way (Wang and Xu, 2014). Some countries have actively issued a series of laws and regulations to standardise WEEE management (European Union, 2002a, 2002b, 2008, 2012). In Brazil, the Federal Law 12.305/2010 regulates the management of solid waste and assigns responsibility for the generators and to the State (República Federativa do Brasil, 2010). Among the political aims of solid waste are the minimisation of the generation, reuse, recycling and environmentally adequate disposal of these wastes. Waste computer equipment (WCE) from desktop PCs represents an important fraction of WEEE, which is basically composed by glass, metals and polymers, as well as others compounds, some of which are toxics, such as lead, mercury and cadmium
(Buekens and Yang, 2014, Ongondo et al., 2011, Taurino et al., 2010). Polymers constitute 15–20 wt% of WEEE (Wang and Xu, 2014), however, if the low density of polymers is considered, the volumetric representation of polymers in WEEE is more significant (Wang and Xu, 2014). High-impact polystyrene (HIPS) and acrylonitrile-butadiene-styrene (ABS) are the main thermoplastic polymer constituents of the WEEE, representing around 65% of the total weight of the WCE (Brennan et al., 2002; Kasper et al., 2011). Adequate identification and separation of the polymeric components from WCE are fundamental procedures for successful mechanical recycling of these materials. The mixture of several polymers and contaminants often produces materials with depreciated thermal and mechanical properties. Consequently, the
Department of Materials Engineering, University of São Paulo, Lorena, Brazil Corresponding author: Clodoaldo Saron, Department of Materials Engineering, Engineering School of Lorena, University of São Paulo, LOM-EEL/USP, Polo Urbo Industrial, Gleba AI-6, s/n, CEP: 12602-810 Lorena, SP, Brazil. Email: [email protected]
Downloaded from wmr.sagepub.com at Bobst Library, New York University on July 16, 2015
2
Waste Management & Research
performance of the recycled polymers is affected, invalidating their application as engineering polymers (Barthes et al., 2012; Li et al., 2014; Taurino et al., 2010). In Brazil, the identification of polymers from WEEE can be performed by symbol codes printed on polymeric devices, according to recommendations of standard practice ABNT – NBR13230 (2006). This standard distinguishes the polymers in six groups of thermoplastics: polyethylene terephtalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS). However, it is not possible to distinguish ABS, HIPS and PS. Brand codes are also used for identification of the thermoplastics polymers in WCE, however, the injudicious use of symbols hinders the reliability of identification (Coltro et al., 2008). Another problem verified for recycling of thermoplastics polymers from WCE is the presence of halogenated flame retardants, which are represented mainly by brominated organic compounds (Peeters et al., 2014, Schlummer et al., 2007, Taurino et al., 2010). Owing to the presence of an electrical power source in electric and electronic equipment (EEE) and to the inherent potential ignition of this thermoplastic, flame retardants are necessary in several polymeric components in EEE. On average 26 wt% of all WEEE plastics contain flame retardants (Peeters et al., 2014). The thermal treatment of halogenated flame retardants can produce extremely toxic halogenated dioxins and furans. Moreover, the presence flame retardants can make operations of thermo-mechanical processing of the polymer difficult owing to the liberation of gases, as well as interfering in the compatibility of the polymer with others components (Li et al., 2014; Taurino et al., 2010). Aromatic brominated compounds are the main kinds of halogenated flame retardants. Among brominated flame retardants, the tetrabromobisphenol alone represents around 50% of the consume (Zang and Sahajwalla, 2014). The aims of this study were to evaluate difficulties and potential for mechanical recycling of thermoplastic ABS and HIPS from computer equipment waste in Brazil, considering procedures to identify the polymers, the presence toxic additives and performance of mechanical and rheological properties compared with virgin resins.
Materials and methods Materials Obsolete informatics equipment such as central processing units (CPUs), printers, monitors, keyboards, microphones and mice were disassembled, and polymeric thermoplastic components separated, according to identification by Fourier transform infrared (FTIR) as well as symbols (ABNT – NBR13230) printed on the components. Co-polymer ABS and HIPS obtained from informatics equipment were used as recycled polymers (ABSr) and (HIPSr), while virgin resins Terluran®GP-35 (ABSv) and HIPS825® (HIPSv) were kindly supplied by BASF Ltda, Brazil and Video Lar S/A, Brazil, respectively.
Methods FTIR analyses were performed in transmittance mode after dilution of the recycled and virgin polymers in KBr pellets, using a spectrometer Shimadzu IR Prestige-21 at 64 scans and resolution at 4 cm-1. For X-ray fluorescence (XRF) analyses, virgin and recycled polymers were grounded and pressed with boric acid in pneumatic equipment (SPEX, model 3628 Bench-press) at 20 t by 20 s to produce pellets with a 4-cm diameter. Then, the pellets were analysed with an XRF spectrometer (Panalytical, model AXIOS max). X-ray diffractograms were obtained using a Panalytical Empyrean diffractometer with copper Kα radiation and a diffraction angle 2θ, range 7–90º. Thermogravimetric analyses (TGA) were carried out in a simultaneous thermal analyser (NETZSCH model STA 449 F3 Jupiter) at a heating rate of 10 ºC min-1 and a nitrogen flow at 100 mL min-1 as protective and purge gas. Tensile and impact testing were performed according to standard practices ASTM D 256 and ASTM D 638, respectively. For preparation of specimens, initially polymeric thermoplastic components from informatics equipment were grounded in a knife mill to generate a particle size around 5 mm of length. Then, recycled and virgin polymers were processed by extrusion in an Imacon with a temperature profile at 190/200/200/210 °C from the alimentation zone to matrix in the presence of a thermal stabilizer (SONGNOX 21B) at 0.15 wt%. After extrusion moulding, specimens for tensile and impact testing were simultaneously prepared by injection moulding in a Spazio DW-130. Tensile testing were carried out in an universal testing machine (EMIC DL 3000) with a load cell of 5 kN at speed of 10 mm min-1, while impact resistance was performed in mode Izod with notched samples in a Time Group XJU-2.75, using a hammer of 2.75 J. The melting flow index (MFI) of the polymers was determined using specimens for mechanical testing after being analysed. For this, specimens were again grounded in a knife mill to generate a particle size of around 5 mm in length. The material was then analysed in an extruder plastometer (Ceast 7021) at 230 ºC with 3.8 kg of load.
Results and discussion Identification of polymeric components by symbol codes The reading of printed brands or symbol codes on polymeric devices has been shown to be insufficient for precise identification of the polymeric components of ABS and HIPS in WEEE. Table 1 shows the symbols used for identification of ABS and HIPS present in WCE. The ambiguity and small flexibility of the symbol code, according to recommendations of standard practice ABNT – NBR13230, which have only the options of category 6 or 7 to classify HIPS and ABS, make a doubtful identification mainly
Downloaded from wmr.sagepub.com at Bobst Library, New York University on July 16, 2015
3
Hirayama and Saron Table 1. Symbols used for identification of polymers in WCE. Acrylonitrile-butadiene-styrene (ABS)
High impact polystyrene (HIPS)
>ABS
PS
