Waste Management 29 (2009) 2625–2643
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Waste Management
journal homepage: www.elsevier.com/locate/wasman
Recycling and recovery routes of plastic solid waste (PSW): A review
S.M. Al-Salem *, P. Lettieri, J. Baeyens
Centre for CO2 Technology, Department of Chemical Engineering, School of Process Engineering, University College London (UCL), Torrington Place, London WC1E 7JE, UK article info abstract
Article history: Plastic solid waste (PSW) presents challenges and opportunities to societies regardless of their sustain- Accepted 4 June 2009 ability awareness and technological advances. In this paper, recent progress in the recycling and recovery Available online 3 July 2009 of PSW is reviewed. A special emphasis is paid on waste generated from polyolefinic sources, which makes up a great percentage of our daily single-life cycle plastic products. The four routes of PSW treat- ment are detailed and discussed covering primary (re-extrusion), secondary (mechanical), tertiary (chemical) and quaternary (energy recovery) schemes and technologies. Primary recycling, which involves the re-introduction of clean scrap of single polymer to the extrusion cycle in order to produce products of the similar material, is commonly applied in the processing line itself but rarely applied among recyclers, as recycling materials rarely possess the required quality. The various waste products, consisting of either end-of-life or production (scrap) waste, are the feedstock of secondary techniques, thereby generally reduced in size to a more desirable shape and form, such as pellets, flakes or powders, depending on the source, shape and usability. Tertiary treatment schemes have contributed greatly to the recycling status of PSW in recent years. Advanced thermo-chemical treatment methods cover a wide range of technologies and produce either fuels or petrochemical feedstock. Nowadays, non-catalytic ther- mal cracking (thermolysis) is receiving renewed attention, due to the fact of added value on a crude oil barrel and its very valuable yielded products. But a fact remains that advanced thermo-chemical recy- cling of PSW (namely polyolefins) still lacks the proper design and kinetic background to target certain desired products and/or chemicals. Energy recovery was found to be an attainable solution to PSW in gen- eral and municipal solid waste (MSW) in particular. The amount of energy produced in kilns and reactors applied in this route is sufficiently investigated up to the point of operation, but not in terms of integra- tion with either petrochemical or converting plants. Although primary and secondary recycling schemes are well established and widely applied, it is concluded that many of the PSW tertiary and quaternary treatment schemes appear to be robust and worthy of additional investigation. Ó 2009 Elsevier Ltd. All rights reserved.
Contents
1. Introduction ...... 2626 2. Re-using, sorting and primary recycling ...... 2627 2.1. Benefits of re-using and major sorting techniques ...... 2627 2.2. Primary recycling of PSW ...... 2628 3. Mechanical recycling ...... 2628 3.1. Overview ...... 2628 3.2. Existing plants and technologies applied in mechanical recycling...... 2629
Abbreviations: ABS, acrylonitrile butadiene styrene; API, alliance for the polyurethane industry; ASR, automotive shredder residues; BFBs, bubbling fluidised beds; BHET, bis-(2-hydroxyethylene-terephthalate); BTX, benzene, toluene and xylene; CAPE, carboxylated polyethylene; CCGT, combined cycle gas turbine ; DEFRA, department of environment and rural affairs (UK); DMSO, dimethylsulfoxide; DMT, dimethyltryptamine; ELTs, end-of-life tyres; FRs, flame-retardants; GCC, gulf council countries; GHGs, greenhouse gases; HCV, high calorific value ; HDPE, high density polyethylene ; IWM, integrated waste management ; LCA, Life Cycle Assessment; LDPE, low density polyethylene; LHV, lower heating value; LLDPE, linear low density polyethylene; MAPE, maleated polyethylene; MDPE, medium density polyethylene; MSW, municipal solid waste; MSWI, municipal solid waste incinerator; MSWIPs, municipal solid waste incineration plants; PA 6, nylon 6 or polyamide 6; PAH, poly aromatic hydrocarbons; PBT, polybutylene theraphalate; PE, polyethylene; PEN, polyethylene (2,6-naphthalenedicarboxylate); PET, polyethylene theraphalate; PI, polyisoprene; PMMA, polymethyl methacrylate; PP, polypropylene; PS, polystyrene; PSW, plastic solid waste; PU, polyurethane; PVC, polyvinylchloride; PVDF, polyvinylidene fluoride; R&D, research and development; RHDPE, recycled high density polyethylene; TBE, tetrabromoethane; TDM, titanium-derived mixture; VCC, viable cascade controller; XRF, X-ray fluorescent. * Corresponding author. Tel.: +44 (0) 207 679 7868; fax: +44 (0) 207 383 2348. E-mail address: [email protected] (S.M. Al-Salem).
0956-053X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2009.06.004 2626 S.M. Al-Salem et al. / Waste Management 29 (2009) 2625–2643
4. Chemical recycling ...... 2631 4.1. What is chemical recycling?...... 2631 4.2. Thermolysis schemes and technologies ...... 2631 4.2.1. Pyrolysis (thermal cracking of polymers in inert atmospheres) ...... 2631 4.2.2. Overview of pyrolysis plants and advanced technologies ...... 2632 4.2.3. Gasification ...... 2634 4.2.4. Common gasification technologies ...... 2634 4.2.5. Concluding remarks on pyrolysis and gasification ...... 2636 4.2.6. Hydrogenation (hydrocracking) ...... 2637 4.3. Other chemical recycling schemes ...... 2637 5. Energy recovery ...... 2639 5.1. Grate technology (co-incineration by direct one stage combustion process of waste)...... 2640 5.2. Fluidised bed and two stage incineration ...... 2640 5.3. Rotary and cement kiln combustion ...... 2640 6. Conclusion ...... 2641 References ...... 2641
1. Introduction (EA, 2008). PSW from commercial grade resins have been success- fully recycled from a number of end-products, including: automo- Ever since the first industrial scale production of synthetic bile parts, appliances, textiles, mulches, greenhouses and films. polymers (plastics) took place in the 1940s, the production, PSW treatment and recycling processes could be allocated to four consumption and waste generation rate of plastic solid waste major categories (Mastellone, 1999), re-extrusion (primary), (PSW) has increased considerably. Thus, PSW recycling has been mechanical (secondary), chemical (tertiary) and energy recovery a focus of many researchers in the past few decades. Such re- (quaternary). Each method provides a unique set of advantages search is also driven by changes in regulatory and environmental that make it particularly beneficial for specific locations, applica- issues. tions or requirements. Mechanical recycling (i.e. secondary or Plastics are used in our daily lives in a number of applications. material recycling) involves physical treatment, whilst chemical From greenhouses, mulches, coating and wiring, to packaging, recycling and treatment (i.e. tertiary encompassing feedstock recy- films, covers, bags and containers. It is only reasonable to find a con- cling) produces feedstock chemicals for the chemical industry. En- siderable amount of PSW in the final stream of municipal solid ergy recovery involves complete or partial oxidation of the waste (MSW). In the European Union countries, over 250 106 ton- material (Troitsch, 1990), producing heat, power and/or gaseous nes of MSW are produced each year, with an annual growth of 3%. In fuels, oils and chars besides by-products that must be disposed 1990, each individual in the world produced an average of 250 kg of of, such as ash. MSW generating in total 1.3 109 tonnes of MSW (Beede and The continued development of recycling and recovery technolo- Bloom, 1995). Ten years later, this amount almost doubled levelling gies, investment in infrastructure, the establishment of viable mar- at 2.3 109 tonnes. In US, PSW found in MSW has increased from kets and participation by industry, government and consumers are 11% in 2002 (USEPA, 2002) to 12.1% in 2007 (USEPA, 2008). Fig. 1 all considered priorities of the highest order (Scheirs, 1998). A Life illustrates the different sectors of the UK and US MSW fractions. Cycle Assessment (LCA) approach to MSW technologies will assist Thermoplastics contribute to the total plastic consumption by in identifying environmental impacts associated with the alterna- roughly 80%, and are used for typical plastics applications such tives in a ‘cradle to grave’ fashion identifying the most sustainable as packaging but also in non-plastics applications such as textile fi- options. 90% of plastics used today are synthesized using non- bres and coatings (Dewil et al., 2006). While plastics are found in renewable fossil resources. It is essential to integrate waste man- all major MSW categories, containers and packaging plastics (bags, agement (IWM) schemes in the production cycle of plastics and sacks, and wraps, other packaging, other containers, and soft drink, treatment schemes of PSW. Whilst recycling is considered a sustain- milk, and water containers) represent the highest tonnage (USEPA, able practice, implying an integrated waste management (IWM) 2002; USEPA, 2008). In durable goods, plastics are found in appli- scheme provides a more sustainable developed use of energy and ances, furniture, casings of lead-acid batteries, and other products. supplies (Fig. 2). LCA schemes aid in the selection, application of In the UK, recent studies show that PSW make up 7% of the final suitable techniques, technologies and management programs to waste stream (Parfitt, 2002). Packaging accounts for 37.2% of all achieve specific waste management objectives and goals. IWM tar- plastics consumed in Europe and 35% worldwide (Clark and Hardy, get is to control the waste generation from processes to meet the 2004). needs of a society at minimal environmental impact and at an effi- Increasing cost and decreasing space of landfills are forcing con- cient resource usage by activating the potentials of waste preven- siderations of alternative options for PSW disposal (Zia et al., tion, re-use and recycling. The IWM cycle can be grouped into six 2007). Years of research, study and testing have resulted in a num- categories, namely: (i) waste generation, (ii) waste handling, sorting ber of treatment, recycling and recovery methods for PSW that can and processing at the source, (iii) collection, (iv) separation and pro- be economically and environmentally viable (Howard, 2002). The cessing, (v) transfer station handling and waste transport, (vi) dis- plastic industry has successfully identified workable technologies posal. The functional groups are paramount, since they enable us for recovering treating, and recycling of waste from discarded to develop and define a framework for evaluating impacts of pro- products. In 2002, 388,000 tonnes of polyethylene (PE) were used posed changes in solid waste functions (Al-Jayyousi, 2001). to produce various parts of textiles, of which 378,000 tonnes were Due to the high thermal resistance of plastics (resulting from made from PE discarded articles (Gobi, 2002). The plastic industry the addition of additives and other stabilizers whilst processing), is committed to meeting the current needs of today without com- the rapid market changes and introduction of the open loop recy- promising the needs of tomorrow. In the UK, 95% of PSW arising cling concept (manufacturing products from a number of products from process scrap ( 250,000 tonnes) has been recycled in 2007 of less quality), energy recovery is limited and might be considered S.M. Al-Salem et al. / Waste Management 29 (2009) 2625–2643 2627
accurate identification of the primary plastic contained in a partic- ular item, followed by some type of manual or automated sorting are essential. In the case of plastic bottle sorting, automated tech- niques do exist but are not always applicable due mainly to a dif- ference in shape and size, or the existence of paint and coating which delays the analysis technique, etc. Another way of sorting (common in Asian recycling lines) is density sorting. Density sort- ing methods are not particularly helpful, because most plastics are
very close in density (qHDPE = 0.941, qMDPE = 0.926–0.940, qLDPE = 0.915–0.925, qLLDPE = 0.91–0.94, qPP = 0.96 g/cc). In the case of rigid PSW resulting from electronic parts, a heavy medium separation is usually applied (Kang and Schoenung, 2005). This can be done by adding a modifier to water or by using tetrabromoethane (TBE). However, this is a costly process and can lead to contamination of the recovered plastic (Veit et al., 2002; Kang and Schoenung, 2005). To enhance the effectiveness of density separation, hydrocy- clones are commonly used. Hydrocyclones, which use centrifugal force, enhance material wettability. Some of the factors affecting li- quid separation of a given material are its wettability, its variation in density (from porosity, fillers, pigments, etc.), shape factors of size-reduced particles, and its level of liberation from other mate- rials. Even surface air bubbles, which can attach to plastics as the result of poor wetting or surface contamination, can cause an indi- vidual flake of material to float in a solution less dense than that of bulk material (APC, 1999). Fig. 1. Dense and film plastic fraction in MSW in the UK (top) and the US (bottom). A practical way of PSW sorting is by triboelectric separation, Source: Parfitt (2002) and USEPA (2008). which can distinguish between two resins by simply rubbing them against each other. A triboelectric separator sorts materials on the in the developmental stages, especially in the case of PSW (DeGas- basis of a surface charge transfer phenomenon. When materials are pari, 1999). In all recycling processes (plastic, metal, paper recy- rubbed against each other, one material becomes positively cling, etc.), technical and economic feasibility and overall charged, and the other becomes negatively charged or remains commercial viability of advanced recycling methods must be con- neutral. Particles are mixed and contact one another in a rotating sidered in each step of the recycling chain (Frisch, 1999). Collec- drum to allow charging. Materials with a particle size of approxi- tion, processing, and marketing are each critical to the success of mately 2–4 mm were the highest in both purity and recovery in chemical recycling and energy recovery. Today, with few excep- the triboelectric process (Xiao et al., 1999). tions, these technologies remain developmental and have not yet PSW can also be sorted by a speed accelerator technique, devel- proven to be sustainable in a competitive market. Nevertheless, oped by Result Technology AG (Switzerland). This technique uses a they remain of considerable interest for their longer term poten- high-speed accelerator to delaminate shredded waste, and the del- tial. The aim of this review is to focus on the various recycling aminated material is separated by air classification, sieves, and methods of PSW, i.e. mechanical, chemical and energy recovery, electrostatics (Kang and Schoenung, 2005). Using X-ray fluorescent in response to the current waste generation rates and production (XRF) spectroscopy, different types of flame-retardants (FRs) can technologies. be identified. On this basis, MBA Polymers, Inc. has developed a technology that can separate pure resin with FRs (Toloken, 1998; 2. Re-using, sorting and primary recycling APC, 2003). The same company has also announced a joint venture with European Metal Recycling Limited (EMR), to establish a plas- 2.1. Benefits of re-using and major sorting techniques tic recovering plant from shredded PSW. The plant will employ state of the art technologies that will result in a 60,000 tonnes/year Plastics are used in a number of applications on a daily basis. commissioning in the year 2009. Yet some plastic items end up in the waste stream after a single No matter how efficient the recycling scheme is, sorting is the use only (single-life or cycle) or a short time after purchase, e.g. most important step in the recycling loop. One of the main issues food packaging. Re-using plastic is preferable to recycling as it uses that recyclers face is the removal of the paint on plastics. Proper- less energy and fewer resources. In recent years, multi-trip plastics ties of recycled plastics can be compromised because of stress have become a more popular choice leading to PSW reduction in concentration created by these coating materials (Kang and Scho- the MSW final stream. In the UK, recyclable and returnable plastic enung, 2005). Grinding could be used to remove coatings, e.g. crates used in transport and other purposes, have quadrupled from chrome from plated plastics can be removed by simple grinding, 1992 (8.5 million tonnes) to 2002 (35.8 million tonnes) (JCR, 2006). sometimes assisted with cryogenic methods to enhance the liber- Re-using plastics has a number of advantages, characterised by (i) ation process and to prevent the plating materials from being conservation of fossil fuels since plastic production uses 4–8% of embedded in the plastic granules. These cryogenic methods pro- global oil production, i.e. 4% as feedstock and 4% during conversion vide good liberation, but the actual separation of plastic particles (Perdon, 2004; JCR, 2006); (ii) reduction of energy and MSW, and from the paint is problematic (Biddle, 1999). Another way of
(iii) reduction of carbon-dioxide (CO2), nitrogen-oxides (NOx) and paint and coating removal is abrasion, best applied on whole sulphur-dioxide (SO2) emissions. parts of significant size. Solvent stripping is also used by recy- A number of techniques have been developed in order to sepa- clers, which involves the dipping of the coated plastic into a sol- rate and sort PSW (MOEA, 2001; EPIC, 2003). In the recycling vent, liberating coatings from the plastic. This method is industry, sorting and identification must be attempted within a applicable for compact disc coating removal (Biddle, 1999; Kang short time to positively affect a recycler’s finances. Both fast and and Schoenung, 2005). 2628 S.M. Al-Salem et al. / Waste Management 29 (2009) 2625–2643
Environment Emissions to: Societal System Energy Air Industrial Landfill Water Society Raw Materials Soil Waste Creation
Environment Emissions to:
Energy Societal System Air
Raw Landfill Water Materials Waste prevention Soil
Role of waste prevention Emissions to: Environment Air Societal System Energy Water IWM Landfill Raw Soil Materials
Role of Integrated Waste Management
Fig. 2. Respective roles of waste prevention and integrated waste management. In Life Cycle Assessment (LCA) studies, a ‘system’ is defined (with boundaries indicated by broken lines). Energy and raw materials from the ‘environment’ are used in the system. Emissions, including solid waste, leave the system and enter the environment. Waste prevention includes the role of cleaner production, innovative services, sustainable consumption and prevention by design. Source: Kirkby et al. (2004).
The high temperature aqueous-based paint removal method re- of challenges, namely the need of selective and segregated collec- lies on the hydrolysis of many coatings in hot water, thus liberating tion. Kerbside systems are required to collect relatively small the coating from the plastic. Olefin based plastics can be handled quantities of mixed PSW from a large number of sources. This with this technique due to the fact that this type of plastics can poses a resource drain and involves significant operating costs in not be degraded under these conditions (Plastic Technology, many countries, especially considering the current market situa- 1994). Nevertheless, none of these techniques are completely sat- tion. Taking into account current market prices for virgin resins, isfactory and they require that processing conditions be carefully a 0.45$ is the return on average from every converted kg of poly- controlled. Furthermore, degradation (mainly photo-oxidative) olefin (EEC, 2009). during these processes decreases the resale value of these recycle products. 3. Mechanical recycling 2.2. Primary recycling of PSW 3.1. Overview Primary recycling, better known as re-extrusion, is the re-intro- duction of scrap, industrial or single-polymer plastic edges and Mechanical recycling, also known as secondary recycling, is the parts to the extrusion cycle in order to produce products of the process of recovering plastic solid waste (PSW) for the re-use in similar material. This process utilizes scrap plastics that have sim- manufacturing plastic products via mechanical means (Mastellone, ilar features to the original products (Al-Salem, 2009a). Primary 1999). It was promoted and commercialized all over the world recycling is only feasible with semi-clean scrap, therefore making back in the 1970s. Mechanical recycling of PSW can only be per- it an unpopular choice with recyclers. A valid example of primary formed on single-polymer plastic, e.g. PE, PP, PS, etc. The more recycling is the injection moulding of out of specification LDPE complex and contaminated the waste, the more difficult it is to re- crates (Barlow, 2008). Crates that do not meet the specifications cycle it mechanically. Separation, washing and preparation of PSW are palletised and reintroduced into the recycling loop or the final are all essential to produce high quality, clear, clean and homoge- stages of the manufacturing. nous end-products. One of the main issues that face mechanical Currently, most of the PSW being recycled is of process scrap recyclers is the degradation and heterogeneity of PSW. Since chem- from industry recycled via primary recycling techniques. In the ical reactions that constitute polymer formation (i.e. polymeraddi- UK, process scrap represents 250,000 tonnes of the plastic waste tion, polymerization and polycondensation) are all reversible in and approximately 95% of it is primary recycled (Parfitt, 2002). Pri- theory, energy or heat supply can cause photo-oxidation and/or mary recycling can also involve the re-extrusion of post-consumer mechanical stresses which occur as a consequence. Length or plastics. Generally, households are the main source of such waste branching of polymer chains can also occur from the formation stream. However, recycling household waste represents a number of oxidised compounds and/or harsh natural weathering condi- S.M. Al-Salem et al. / Waste Management 29 (2009) 2625–2643 2629 tions (Mastellone, 1999; Basfar and Idriss Ali, 2006; Al-Salem, Milling: Separate, single-polymer plastics are milled together. 2009b). Due to the previously stated reasons, it is very important This step is usually taken as a first step with many recyclers to have a customer ready to purchase the product to achieve a sen- around the world. sible economical and environmental practice. Nevertheless, Washing and drying: This step refers to the pre-washing stage mechanical recycling opens an economic and viable route for (beginning of the washing line). The actual plastic washing PSW recovery, especially for the case of foams and rigid plastics process occurs afterwards if further treatment is required. (Zia et al., 2007). Both washing stages are executed with water. Chemical A number of products found in our daily lives come from washing is also employed in certain cases (mainly for glue mechanical recycling processes, such as grocery bags, pipes, gut- removal from plastic), where caustic soda and surfactants ters, window and door profiles, shutters and blinds, etc. The quality are used. is the main issue when dealing with mechanically recycled prod- Agglutination: The product is gathered and collected either to ucts. The industrial PSW generated in manufacturing, processing, be stored and sold later on after the addition of pigments and and distribution of plastic products is well suited for the use as a additives, or sent for further processing. raw material for mechanical recycling due to the clear separation Extrusion: The plastic is extruded to strands and then pellet- of different types of resins, the low level of dirt and impurities ized to produce a single-polymer plastic. present, and their availability in large quantities. Quenching: Involves water-cooling the plastic by water to be Mechanical recycling of PSW has also become an important is- granulated and sold as a final product. sue in R&D, where numerous researchers have devoted their efforts to. Recent literature published shows a great interest in utilizing Other single-polymer PSW go through different schemes. Many polyolefins that end up in the PSW stream. Table 1 summarizes re- foams (namely polyurethane, PU) are powdered and grinded to a cent literature in direct relation to PSW mechanical recycling, uti- particle size less than 0.2 mm using two-roll milling, cryogenic lizing reclaimed and scrap in the studied schemes on bench and grinders or precision knife cutters. Another process used in pilot scales. mechanical recycling is re-bonding, in which recycled foam flakes originating from flexible slab stock foam production waste are usu- 3.2. Existing plants and technologies applied in mechanical recycling ally blown from storage silos into a mixer that consists of a fixed drum with rotating blades or agitators, where the foam flakes are Recycling PSW via mechanical means involves a number of sprayed with an adhesive mixture (Zia et al., 2007). Fig. 4 shows treatments and preparation steps to be considered. Being a costly a schematic illustration of the re-bonding process. One of the main and an energy intense process, mechanical recyclers try to reduce advantages of this process is the ability to obtain a clean product these steps and working hours as much as possible. Generally, the with new properties, i.e. higher density and lower hardness. first step in mechanical recycling involves size reduction of the In the case of PU, 10% binder is added to the 90% scrap. Waste is plastic to a more suitable form (pellets, powder or flakes). This is shredded and mixed with binder (dyes can also be added) and the usually achieved by milling, grinding or shredding (Zia et al., mixture is then compressed. PU recyclate granules are used as filler 2007). The most general scheme was described by Aznar et al. in polyester moulding compounds and give added toughness to the (2006) and is illustrated in Fig. 3. The steps involved are usually material. This process yields a variety of products such as carpet the following (Aznar et al., 2006; SubsTech, 2006): underlay and athletic mats from recovered pieces of flexible foams. The re-bond process incorporates both a surprising amount of flex- Cutting/shredding: Large plastic parts are cut by shear or saw ibility and a wide variability in the mechanical properties of the fi- for further processing into chopped small flakes. nal product. PVC represents an interesting case too, in terms of Contaminant separation: Paper, dust and other forms of impu- mechanical recycling. With the health issues related to it, Recovi- rities are separated from plastic usually in a cyclone. nylÓ Co. (UK) deals with post-consumer PVC to reproduce two Floating: Different types of plastic flakes are separated in a grades via mechanical recycling. Due to its structure and composi- floating tank according to their density. tion, PVC can easily be mechanically recycled in order to obtain
Table 1 Summary of mechanical recycling studies in direct relation to utilizing scrap and reclaimed materials (namely blended with single virgin polymers).
Reference Main single-polymer plastics used Comments
Kowalska et al. (2002) PP (Malen P F-401) Thermoplastics were mixed and extruded with fillers (waste rubber granulate, whiting, cel- Waste LDPE lulose fibres and wood flour) to obtain an optimum blend composition Waste PVC The blend contained <50 wt% of secondary LDPE, >50 wt% of comminute rubber scrap and Reclaimed LDPE films <0.1 wt% of blowing agent Suspension PVC 3–4 l/h of water permutation was achieved with the blend making it a satisfactory mixture Strapasson et al. (2005) PP/LDPE blends (0/100, 25/75, 50/50, 75/25 and Thermoplastics were mixed and extruded with fillers (waste rubber granulate, whiting, cel- 100/0 wt/wt%) via injection moulding louse fibres and wood flour) to obtain an optimum blend composition Lei et al. (2007) RHDPE Composites based on RHDPE and natural fibres, made through melt blending and compres- sion moulding were studied, so were the effects of fibres and coupling agent (type/concen- tration) on the composite properties The use of MAPE, CAPE and TDM improved the compatibility between the fibre and RHDPE, and mechanical properties of the resultant composites compared well with those of virgin HDPE composites Meran et al. (2008) LDPE, HDPE and PP The tensile strength relation was monitored in PP since the loss of mechanical and physical properties did not exceed 50% in the films studied Brachet et al. (2008) PP Modification of mechanical properties of recycled PP from post-consumer containers with
the addition of stabilizers, elastomer (EOR) and CaCO3 were studied