塑料回收外文文献英文

Plastic waste from recycling centres Characterisation and evaluation of plastic recyclability Giorgia Faraca Thomas Astrup Technical University of Denmark Department of Environmental Engineering Bygningstorvet 2800 Kgs Lyngby Denmark a r t i c l ei n f o Article history Received 17 January 2019 Revised 11 June 2019 Accepted 21 June 2019 Available online 25 June 2019 Keywords Contamination Quality Circular economy Material fl ow analysis Recycling effi ciency Sampling a b s t r a c t While recycling has been recognised as the preferred plastic waste management solution little is known about the detailed characteristics of plastic waste and how these may affect its recycling In this study hard plastic plastic fi lm and PVC waste collected at three Danish recycling centres were sampled and characterised according to product applications legislative requirements quality expected product life time polymer types and presence of potential impurities such as coloured plastics non plastic materials and multi polymer products The obtained information was applied for estimation of overall recycling potentials for selected archetype recycling process chains based on material fl ow analysis In addition to providing detailed data for the composition of the plastic waste products the results showed that impurities represented 28 wet weight of the plastic waste and that about 75 of the plastic waste was characterised as Low Quality applications indicating some legislative recovery restrictions By accounting for the level type of impurities the overall recycling potential was found to be 52 for hard plastics 59 for plastic fi lms and 79 for PVC waste The results showed that while varying according to polymer type the recyclability of High Quality plastic waste was 12 35 higher than Low Quality applications While actual results are representative of Danish conditions the study demonstrates that detailed characteristics of plastic waste are needed to identify potential challenges to recycling and thereby potentially improving the design and recovery effi ciency of recycling facilities 2019 Elsevier Ltd All rights reserved 1 Introduction For more than 50 years plastics have played an important role in a wide range of product applications e g packaging automotive constructions and telecommunications In 2016 the world pro duction of plastics was 280 million Mg Plastics Europe 2018 Also in 2016 about 27 million Mg of plastics were collected in Europe as waste of these 31 was collected for recycling 42 incinerated and 27 landfi lled Plastics Europe 2018 Separate collection of plastic waste for recycling includes in house bin systems kerb side collection drop off containers and recycling centres Recycling centres are large drop off points where private citizens free of charge bring and source separate household waste into a large number of waste fractions residual household waste is not received at Danish recycling centres and represent an important yet often overlooked collection method in some European coun tries e g UK Denmark Sweden and Norway In Denmark about 44 50 of the plastic waste is currently collected through such recycling centres while plastic bottles are collected through a deposit refund system DRS 2015 Milj styrelsen 2017 More over separate collection of hard plastic waste was recently intro duced in the urban areas but no separate collection exists for other plastic packaging waste Sweco Danmark 2015 Despite plastic waste recovery is recognized as a priority both at European and Danish levels e g EC 2018a very little information is avail able about the composition and characteristics of plastic waste col lected from recycling centres which is expected to differ from the composition of plastic waste collected via in house bin systems This lack of information considerably limits our abilities to identify potential challenges to recycling and thereby improve the design of recovery facilities and the overall waste management system https doi org 10 1016 j wasman 2019 06 038 0956 053X 2019 Elsevier Ltd All rights reserved Abbreviations 1D one dimensional ABS acrylonitrile butadiene styrene CPH Copenhagen sampling site eng polym engineered polymers EPDM ethylene propylene diene monomer EU European Union LDPE low density polyethylene MFA material fl ow analysis MRF material recovery facility NIR near infra red PBT Polybutylene terephthalate PC polycarbonate PET polyethylene terephtha late PMMA poly methyl methacrylate PP polypropylene PS polystyrene PUR polyurethane PVC polyvinyl chloride RKE Roskilde sampling site SBR styrene butadiene rubber SEBS Styrene Ethylene Butylene Styrene SLK Silkeborg sam pling site UK United Kingdom WtE waste to energy Corresponding author E mail address gfar env dtu dk G Faraca Waste Management 95 2019 388 398 Contents lists available at ScienceDirect Waste Management journal homepage Plastics represents a very large group of individual polymers with different chemical and technical characteristics Hansen et al 2013 thus making plastic waste one of the most complex material mixtures from a recycling perspective Ragaert et al 2017 The most widespread polymers in use are PET HDPE LDPE PVC PP and PS Villanueva and Eder 2014 Other polymers with enhanced properties are also manufactured so called engi neered polymers e g ABS PC and PUR Indeed pure plastics has often high degradability as well as poor thermal mechanical and or aesthetic properties and may need specifi c chemical adjust ments e g plasticisers antioxidants and or stabilisers to reach the desired functionality Murphy 2001 Pitchard 1998 Knowl edge on the composition of plastic waste is therefore paramount for detailed modelling of plastic recycling processes as different product applications and polymers may have different recycling potential Today the main recycling solution for post consumer plastic waste is mechanical recycling where the waste is grinded washed and re melted e g via extrusion to form new secondary plastic materials that maintain the original chemical structure BiPRO CRI 2015 However one of the main barriers to recycling of mixed plastic waste is that nearly all polymers are immiscible polymer contamination leads to materials with poor mechanical properties and potential phase separation Pracella 2017 Also polymeric materials are affected by degradation processes which may occur during manufacturing usage and mechanical recycling Vilaplana and Karlsson 2008 The polymeric purity of post consumer plastic waste streams may be further lowered by the inclusion of multi polymer products two or more plastic polymers assembled together and by particle and or molecular contamination While particle contamination originates from presence of non plastic objects misplacements e g metal cans and non plastic parts attached to the plastic waste items interfering materials such as metallic wheels in a plastic toy molecular contamination can originate from contact materials product residues and substances intentionally added for the previous use of the plastic waste e g plasticisers stabilisers pigments and fl ame retardants Dahlbo et al 2018 Vilaplana and Karlsson 2008 The presence of these impurities affects the recovery yields that can be achieved by recy cling processes As such detailed information about the impurities in plastic waste streams is critical for further development of recy cling processes In order to recycle individual polymers the collected plastic waste needs to be sorted This is typically carried out in material recovery facilities MRF Hopewell et al 2009 Endless confi gura tions and combinations of unit processes exist for these MRF s but in EU near infrared NIR spectroscopy is often employed to iden tify individual polymers Ragaert et al 2017 Although very wide spread NIR separation techniques may be characterised by relatively low effi ciencies 57 89 according to Conte 2016 mainly due to the presence of black coloured plastics black prod ucts absorb the light scattered by the sensor leading to non identifi cation of the polymer Moreover despite the recent tech nological innovation recycled plastics are often considered of infe rior properties compared to virgin materials EC 2018a partly because of thermal mechanical degradation caused by the shear and the increase in temperature occurring during mechanical recy cling and partly due to contamination of the targeted polymer becauseoftheincomplete effi ciencyofsortingmachinery Eriksen et al 2018 Ragaert et al 2017 Moreover the chemical composition of plastics is subject to different legislations according to the application the product is used into e g food packaging vs automotive limiting the use of recycled plastics with unknown composition in high purity applications Detailed information of the source of plastics its characteristics and the presence of impu rities is needed to support effective recovery processes to improve the collection and source segregation of plastic waste and to pro mote recycling driven choices in the manufacture of plastic products Evaluations of plastic waste recycling are abundant in scientifi c literature e g throughcalculationofrecyclingindicators Huysveld et al 2019 material fl ow analysis Kuczenski and Geyer 2010 life cycle assessment Michaud et al 2010 and fi nancial analysis Sim es et al 2014 however the majority of studies have focused on plastic packaging materials e g Cimpan etal 2015 HageandS derholm 2008 Luijsterburgand Goossens 2014 Still with a focus on plastic packaging relatively few studies have addressed the material characteristics of plastic waste Bonifazi et al 2016 Camacho and Karlsson 2001 Dvorak et al 2011 Although it has been demonstrated that the waste material composition signifi cantly affects the results of environ mental assessment studies Bisinella et al 2017 few studies have combined investigations of plastic waste characteristics with eval uation of the recyclability of the plastic waste e g Eriksen et al 2018 While plastic packaging accounts for 40 of the plastic pro duction market Plastics Europe 2018 waste products from the remaining 60 of the plastic market are represented in literature mainly through assessments that include plastic waste as a portion of municipal solid waste e g Rigamonti et al 2010 Giugliano et al 2011 Very limited information about product types and applications polymers and impurities in plastic waste is available in literature despite this can play a critical role for the recycling effi ciencies the compliance with legislative requirements and design of recycling processes Only the study by Jacobsen et al 2018 documents information of plastic waste from recycling cen tres in Belgium The overall aim of the study was to provide an improved basis for evaluating the recyclability of plastic waste collected at Danish recycling centres With focus on three recycling centres in Den mark this was achieved through i sampling and detailed charac terization of plastic waste according to product applications material quality i e legislative requirements polymer types expected product life time and presence of potential impurities such as coloured plastic non plastic products and multi polymer products and ii assessment of the potential for recycling of the sampled plastic waste based on its specifi c characteristics by mate rial fl ow analysis modelling 2 Materials and methods 2 1 Sampling campaign and processing of samples The sampling campaign involved three recycling centres in the Danish municipalities of Copenhagen CPH Roskilde RKE and Silkeborg SLK CPH is the capital 600 000 inhabitants in the Sealand region while RKE and SLK are smaller cities 50 000 inhabitants in the Sealand and Northern Jutland countryside respectively At most Danish recycling centres plastic waste can be sorted in one of three containers i hard i e dense plastics ii plastics fi lms and iii PVC In addition to private citizens small companies are allowed to deliver their waste at recycling centres upon payment of a fee however this contribution is estimated to be low Milj styrelsen 2018 Some differences exist between the three analysed municipalities in SLK an additional container for plastic furniture exists not sampled within this study while in CPH collection of hard plastic and PVC waste is commingled a pilot program demonstrated that commingled collection followed by separation of the two waste fractions in a sorting facility could lead to higher purities The sampling methodology followed the principles defi ned in Edjabou et al 2015 For each plastic waste fraction hard plastics G Faraca T Astrup Waste Management 95 2019 388 398389 plastics fi lms and PVC and at each municipality one container was unloaded on the ground representing primary samples and divided into subsamples see Table B 1 in Appendix B The approaches for subsampling refl ected the inherent properties of each of the three fractions as described in the following and in Appendix B Hard plastic waste occurred as loose items the con tainer 1 Mg was thoroughly mixed and split into two halves by a robotic arm one half represented the subsample for charac terization Plastic fi lm waste occurred mainly as manually pressed in 60L plastic bags the container 200 kg was spread in an elongated pile and mass reduced by 1D splitting see Appen dix B 1 Saved increments represented the subsample PVC waste occurred as relatively large and loose items as no representative subsample could be obtained due to the bulkiness of the items the entirety of the PVC container 500 kg was characterised The presence of odd size products i e one dimension larger than 1 m in hard plastic waste was recorded at this stage odd size hard plastic products were not analysed further as it was not possible to obtain a representative sample see Appendix B 2 On the other hand odd size plastic fi lms could be further characterised as these items were represented by big fl exible bags that could be pressed into smaller items Hard plastic and plastic fi lm waste subsamples were fi lled into 120L paper bags that were alternatively saved or discarded until reaching lab samples of 40 80 kg that were transported to the lab for further characterisation see Section 2 2 no lab sample was created for PVC as mentioned earlier 2 2 Characterisation of plastic waste Hard plastic plastic fi lm and PVC waste were classifi ed accord ing to i product application ii legislative requirements quality iii polymer iv type of product v colour vi presence of impu rities and vii expected life time Table 1 The product applica tion categories refl ected the legal requirements of individual plastic market segments Brems et al 2012 Eriksen et al 2018 Plastics Europe 2018 and were assigned on site to plastic waste subsamples by visual inspection their weight was registered to determine the overall composition per application type odd size items not included Presence of misplacements i e non plastic products was also assessed at this stage The product application categories were merged into three quality categories i High Quality Food packaging ii Medium Quality Electrical and elec tronics Pharmaceuticals and Toys and iii Low Quality Non food packaging Automotive Construction and Other The distinc tion refl ects the expected quality of the waste products and is based on the existence of different levels of regulatory require ments within the EU legislation addressing the presence of chem icals in plastic product groups High Quality a large number of chemicals is restricted by legislation Medium Quality the restric tion includes fewer chemicals Low Quality few or no chemicals are restricted Eriksen et al 2018 Other physical or mechanical properties of plastics are not considered in this case The classifi ca tion into High Medium Low Quality thereby refers to the possibil ities of a plastic waste item belonging to a certain application group to be recycled into another group plastic waste can be recy cled into application groups represented by lower quality e g Food Packaging plastic High Quality can be recycled into products used in the Automotive sector Low Quality but Automotive plastic wastecannotberecycledintoFoodPackagingproducts legislation wise Technical aspects may also play a role but were not addressed in this study The polymer composition of hard plastic and plastic fi lm waste was assessed on the lab samples by use of Attenuated Total Refl ec tance Fourier infra red transformed spectroscopy 4300 Hand held ATR FTIR supplied by Agilent Technology see Appendix B 3 PVC container waste was not analysed by ATR FTIR analysis as the polymer was assumed to be known i e PVC also given that the types of products within the waste matched the typical appli cations of PVC products e g Hansen et al 2013 Lab samples were further characterized according to colour presence of interfering materials presence of multi polymer objects and expected lifetime Plastic waste products were subdi vided by visual assessment into clear black or other colours colour of PVC container waste was also assessed on site Presence of interfering materials and multi polymer parts was assessed by manually disassembling the products in the plastic waste lab sam ples Finally the expected lifetime of the waste products lab sam ples of hard plastic and plastic fi lm and the entirety of the PVC container was estimated based on data from Geyer et al 2017 and Kawecki et al 2018 and classifi ed in one out of three cate gories less than one year between one and ten years and more than ten years 2 3 Material fl ow analysis MFA of plastic waste The results from Sections 2 1 and 2 2 were used to establish a MFA of the mechanical recycling chain of the plastic waste with focus on evaluating recycling potentials as a consequence of the specifi c characteristics of the plastic waste in input Typical current sorting and recycling technologies were assumed separately for hard plastic plastic fi lm and PVC wast