Molecular Modification and Compatibilization of Collected Polyethylene

The increasing use of plastics in packaging materials leads to growing amounts of plastic waste. Recycling material is generally regarded as advantageous. But in fact very few products are made from plastic waste, partly this can be explained by that little is known about the recycling process and the properties of collected materials. There is a need for injection moulding grades of recycled polyethylene, while large amounts of extrusion grades are available from packaging waste. A controlled way of de-branching or partly degrading PE would be desirable. Peroxides are commonly used to crosslink polyolefins, but under certain conditions a chain scission reaction occur. Another problem encountered with recycling of polyethylene are the poor miscibility of low amounts contaminations, i. e. polypropylene. A compatibilizer can improve properties of such polymer blends, in this work EPDM is used as compatibilzer. Studies of mechanical properties and viscosity measurements show that it is possible to partly degrade PE with peroxide exposing it to high temperature and oxygen. The properties of PE/PP blends were improved with EPDM as compatibilizer.     

Recovery of polypropylene and polyethylene from packaging plastic wastes without contamination of chlorinated plastic films by the combination process of wet gravity separation and ozonation

Wet gravity separation technique has been regularly practiced to separate the polypropylene (PP) and polyethylene (PE) (light plastic films) from chlorinated plastic films (CP films) (heavy plastic films). The CP films including poly vinyl chloride (PVC) and poly vinylidene chloride (PVDC) would float in water even though its density is more than 1.0 g/cm³. This is because films are twisted in which air is sometimes entrapped inside the twisted CP films in real existing recycling plant. The present research improves the current process in separating the PP and PE from plastic packaging waste (PPW), by reducing entrapped air and by increasing the hydrophilicity of the CP films surface with ozonation. The present research also measures the hydrophilicity of the CP films.In ozonation process mixing of artificial films up to 10 min reduces the contact angle from 78° to 62°, and also increases the hydrophilicity of CP films. The previous studies also performed show that the artificial PVDC films easily settle down by the same. The effect of ozonation after the wet gravity separation on light PPW films obtained from an actual PPW recycling plant was also evaluated. Although actual light PPW films contained 1.3% of CP films however in present case all the CP films were removed from the PPW films as a settled fraction in the combination process of ozonation and wet gravity separation. The combination process of ozonation and wet gravity separation is the more beneficial process in recovering of high purity PP and PE films from the PPW films.     

Two-stage thermal gasification of polyolefins

Plastic pellets of polyethylene (PE), polypropylene (PP), and polystyrene (PS) were gasified in a two-stage thermal degradation process. The first stage is the conversion of polyolefins to distilled oils using a melting vessel. In the second stage, the oils from the first stage are gasified using a tubular reactor. The distilled oil yields of PE, PP, and PS in the first stage were 84, 89, 92 wt%, respectively, each at 470°C. The total gas yields of PE, PP, and PS in the second stage were 80, 74, and 6.2 wt%, respectively, each at 800°C. The main components of the product gas for PE and PP were methane and olefins such as ethene and propene. Some aromatic oils, including benzene, toluene, and xylene, were also produced as by-products. The amount of carbonaceous residue, or coke, was very low (less than 1 wt%). By dividing the process into two stages, the coking rate was considerably reduced compared with direct gasification of the polyolefins. Received: July 19, 2000 / Accepted: September 17, 2000     

Sink–float density separation of post-consumer plastics for feedstock recycling

The paper focuses on current mechanical waste processing technologies and out-of-the-box processes linked to the processing of coal and mineral resources, to ensure high-quality feedstock recycling of polyolefin-rich post-consumer plastic fractions. Moreover, the study aims to provide the basis for the technical and economic feasibility of the chemical recycling route of this plastic fraction. When evaluating common mechanical processes, either dry or wet ones, sink–float separation in a cylindrical centrifugal force separator achieves the best results. It combines the advantages of a simple, robust apparatus of low complexity and high capacity with selective separation through the accelerated settling of particles in the centrifugal field. Furthermore, the disconnection of the separation medium feed from the solid input increases residence times. Based on the above findings, a pilot-scale plant was constructed which consists of a centrifugal force separator and a hydro jig for the pre-separation of heavy waste components. Several test campaigns were conducted to separate polyolefins from various waste fractions. Two-stage processing in the centrifugal force separator rendered almost 90 wt% of polyolefin content in the produced lightweight fraction and of polyolefin recovery. One-stage processing, on the other hand, resulted in reduced polyolefin content in the lightweight fraction.

     

New characterisation method of electrical and electronic equipment wastes (WEEE)

Innovative separation and beneficiation techniques of various materials encountered in electrical and electronic equipment wastes (WEEE) is a major improvement for its recycling. Mechanical separation-oriented characterisation of WEEE was conducted in an attempt to evaluate the amenability of mechanical separation processes. Properties such as liberation degree of fractions (plastics, metals ferrous and non-ferrous), which are essential for mechanical separation, are analysed by means of a grain counting approach. Two different samples from different recycling industries were characterised in this work. The first sample is a heterogeneous material containing different types of plastics, metals (ferrous and non-ferrous), printed circuit board (PCB), rubber and wood. The second sample contains a mixture of mainly plastics. It is found for the first sample that all aluminium particles are free (100%) in all investigated size fractions. Between 92% and 95% of plastics are present as free particles; however, 67% in average of ferromagnetic particles are liberated. It can be observed that only 42% of ferromagnetic particles are free in the size fraction larger than 20 mm. Particle shapes were also quantified manually particle by particle. The results show that the particle shapes as a result of shredding, turn out to be heterogeneous, thereby complicating mechanical separation processes. In addition, the separability of various materials was ascertained by a sink–float analysis and eddy current separation. The second sample was separated by automatic sensor sorting in four different products: ABS, PC–ABS, PS and rest product. The fractions were characterised by using the methodology described in this paper. The results show that the grade and liberation degree of the plastic products ABS, PC–ABS and PS are close to 100%. Sink–float separation and infrared plastic identification equipment confirms the high plastic quality. On the basis of these findings, a global separation flow sheet is proposed to improve the plastic separation of WEEE.     

Characterization of post-consumer polyolefin wastes by hyperspectral imaging for quality control in recycling processes

In this paper new analytical inspection strategies, based on hyperspectral imaging (HSI) in the VIS–NIR and NIR wavelength ranges (400–1000 and 1000–1700 nm, respectively), have been investigated and set up in order to define quality control logics that could be applied at industrial plant level for polyolefins recycling. The research was developed inside the European FP7 Project W2Plastics “Magnetic Sorting and Ultrasound Sensor Technologies for Production of High Purity Secondary Polyolefins from Waste”. The main aim of the project is the separation of pure polyethylene and polypropylene adopting an innovative process, the magnetic density separation (MDS). Spectra of plastic particles and contaminants resulting from post-consumer complex wastes and of virgin polyolefins have been acquired by HSI and by Raman spectroscopy. The classification results obtained applying principal component analysis (PCA) on HSI data have been compared with those obtained by Raman spectroscopy, in order to validate the proposed innovative methodology. Results showed that HSI sensing techniques allow to identify both polyolefins and contaminants. Results also demonstrated that HSI has a great potentiality as a tool for quality control of feed (identification of contaminants in the plastic waste) and of the two different pure polypropylene and polyethylene flow streams resulting from the MDS-based recycling process.     

Rapid discrimination of plastic packaging materials using MIR spectroscopy coupled with independent components analysis (ICA)

Plastic packaging wastes increased considerably in recent decades, raising a major and serious public concern on political, economical and environmental levels. Dealing with this kind of problems is generally done by landfilling and energy recovery. However, these two methods are becoming more and more expensive, hazardous to the public health and the environment. Therefore, recycling is gaining worldwide consideration as a solution to decrease the growing volume of plastic packaging wastes and simultaneously reduce the consumption of oil required to produce virgin resin. Nevertheless, a major shortage is encountered in recycling which is related to the sorting of plastic wastes. In this paper, a feasibility study was performed in order to test the potential of an innovative approach combining mid infrared (MIR) spectroscopy with independent components analysis (ICA), as a simple and fast approach which could achieve high separation rates. This approach (MIR-ICA) gave 100% discrimination rates in the separation of all studied plastics: polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS) and polylactide (PLA). In addition, some more specific discriminations were obtained separating plastic materials belonging to the same polymer family e.g. high density polyethylene (HDPE) from low density polyethylene (LDPE). High discrimination rates were obtained despite the heterogeneity among samples especially differences in colors, thicknesses and surface textures. The reproducibility of the proposed approach was also tested using two spectrometers with considerable differences in their sensitivities. Discrimination rates were not affected proving that the developed approach could be extrapolated to different spectrometers. MIR combined with ICA is a promising tool for plastic waste separation that can help improve performance in this field; however further technological improvements and developments are required before it can be applied at an industrial level given that all tests presented here were performed under laboratory conditions.     

Processing scheme based on selective dissolution to recycle food packaging and other polymeric wastes and its economic analysis

This investigation proposes the development of the selective dissolution process for recycling food packaging and other polymeric wastes. This process takes into account that the specific solvent of a particular polymer which is to be separated, must be a non-solvent for the remaining polymers. Likewise, taking into account the solubility of each polymer into various solvents as well as its production costs, the order of the polymers produced can be polyvinylchloride (PVC), polypropylene (PP), polyethylene (PE), polystyrene (PS), polybutadiene (PB), polyacrylnitrile (PAN), polyesters (PES), nylon and polyurethanes (PU). However, cost analysis of the process revealed that the recycling of food packaging polymers in the order of PE, PVC, PP, and PS is more cost-effective.     

Investigation of hydrocyclones for the separation of shredded fridge plastics

The recycling of fridges produces a mixed plastic product of limited value. In order to maximise its value, the separation of the individual polymers that include high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC) and polyethylene (PE) must take place. The effectiveness of a hydrocyclone system for the separation of these plastics, using both water and calcium chloride solutions, has been investigated. In addition a qualitative procedure for the determination of the HIPS content of a mixed ABS/HIPS product, by selective dissolution in R-limonene, has been developed. It was found that the effective density of separation depended on the particle size and aspect ratio. As the particle size and aspect ratio decreased, the separation became more efficient and the offset between separation density and hydrocyclone medium density decreased. This suggests that, for efficient density separation, closely sized, fine plastic fractions are required. Using these criteria, it was found that the removal of high density plastic such as PVC was readily achieved using a hydrocyclone. A partial separation of HIPS from ABS was found to be possible, taking advantage of a small density difference, using a hydrocyclone medium density of 1035kgm(-3).     

Pyrolysis of polyolefins for increasing the yield of monomers' recovery

Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objective of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCl(4)/MgCl(2) for cracking a mixture of polyolefins consisted of 46%wt. of low density polyethylene (LDPE), 30%wt. of high density polyethylene (HDPE) and 24%wt. of polypropylene (PP). Two sets of experiments have been carried out at 500 and 650°C via catalytic pyrolysis (1% of Z-N catalyst) and at 650 and 730°C via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7%wt. and 42.4/44.7/13.9%wt. at 650 and 730°C while via catalytic pyrolysis were: 6.5/89.0/4.5%wt. and 54.3/41.9/3.8%wt. at 500 and 650°C, respectively. At 650°C the monomer generation increased by 55% up to 23.6%wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management.     

Recycling plastics from automotive shredder residues: a review

Automotive shredder residue (ASR) is an inevitable by-product of car recycling, i.e. removal of all liquids and hazardous or valuable components from the car and shredding of the hulk, followed by the recovery of steel, iron, and non-ferrous scrap. The European Union (EU) ELV Directive requires attaining higher recovery and recycling rates, resulting in a reduction of the amount of ASR going to landfill. The most plausible methods to achieve a considerable reduction of ASR are as follows: either recycling of separated materials and dismantled bulky parts, such as bumpers, dashboards, cushions, and front and rear windows, or else systematic sorting of the commingled and size-reduced materials, resulting from shredding. After a brief comparison of the actual situation in the EU, the USA, and Japan, the characteristics of actual ASR are reviewed, as well as some of the most prominent efforts made to separate and recycle specific fractions, such as polyolefins, ABS, or polyurethane. Attention is paid to some major players in the EU and to some of the pitfalls that besiege these ventures.     

Alternative polymer separation technology by centrifugal force in a melted state

In order to upgrade polymer waste during recycling, separation should take place at high purity. The present research was aimed to develop a novel, alternative separation opportunity, where the polymer fractions were separated by centrifugal force in melted state. The efficiency of the constructed separation equipment was verified by two immiscible plastics (polyethylene terephthalate, PET; low density polyethylene, LDPE), which have a high difference of density, and of which large quantities can also be found in the municipal solid waste. The results show that the developed equipment is suitable not only for separating dry blended mixtures of PET/LDPE into pure components again, but also for separating prefabricated polymer blends. By this process it becomes possible to recover pure polymer substances from multi-component products during the recycling process. The adequacy of results was verified by differential scanning calorimetry (DSC) measurement as well as optical microscopy and Raman spectroscopy.     

Advances in the recycling of plastic wastes for metallurgical coke production

This paper aims to provide useful knowledge on the use of plastic wastes as additives to coking blends for the production of metallurgical coke. It focuses on the influence that the composition of plastic wastes has upon the development of coal fluidity, the generation of pressure during the coking process and the quality of the cokes produced in a semipilot oven. Several plastic mixtures of two types of thermoplastics, polyolefins (HDPE, LDPE and PP) and aromatic polymers such as PET, were used. The overall addition rate of plastics to a medium-fluid coal blend was 2 wt%. It is shown that polyolefins, weaker modifiers of coal fluidity, may be employed to maintain coke quality but that they have a negative effect on the generation of coking pressure, while plastics of the aromatic type such as PET, a strong modifier of coal fluidity, can be used to counteract the generation of coking pressure. From the results, it is deduced that the protocol developed is useful for determining the optimum amount of each type of polymer (polyolefins and aromatic polymers) that is needed in order to counteract the generation of pressure during the coking process and to maintain the quality of the cokes.     

Enhancement of the recycling of waste Ni-Cd and Ni-MH batteries by mechanical treatment

A serious environmental problem was presented by waste batteries resulting from lack of relevant regulations and effective recycling technologies in China. The present work considered the enhancement of waste Ni-Cd and Ni-MH batteries recycling by mechanical treatment. In the process of characterization, two types of waste batteries (Ni-Cd and Ni-MH batteries) were selected and their components were characterized in relation to their elemental chemical compositions. In the process of mechanical separation and recycling, waste Ni-Cd and Ni-MH batteries were processed by a recycling technology without a negative impact on the environment. The technology contained mechanical crushing, size classification, gravity separation, and magnetic separation. The results obtained demonstrated that: (1) Mechanical crushing was an effective process to strip the metallic parts from separators and pastes. High liberation efficiency of the metallic parts from separators and pastes was attained in the crushing process until the fractions reached particle sizes smaller than 2 mm. (2) The classified materials mainly consisted of the fractions with the size of particles between 0.5 and 2 mm after size classification. (3) The metallic concentrates of the samples were improved from around 75% to 90% by gravity separation. More than 90% of the metallic materials were separated into heavy fractions when the particle sizes were larger than 0.5 mm. (4) The size of particles between 0.5 and 2 mm and the rotational speed of the separator between 30 and 60 rpm were suitable for magnetic separation during industrial application, with the recycling efficiency exceeding 95%.     

Development of composite materials by mechanochemical treatment of post-consumer plastic waste

Improvement of mechanical properties of recycled mixed plastic waste is one of the fundamental goals in any recycling process. However, polymer immiscibility makes the development of any effective reprocessing method difficult. In this work, a polymer milling process with liquid CO2 was applied to polymeric mixed waste, obtaining a powder material which was successfully utilized as a matrix for a new composite material. Developed materials have interesting mechanical properties and material performance can easily be improved. Investigations on selected mixtures of PP and PE clearly showed evidence of chemical compatibilization.     

Assessing recycling versus incineration of key materials in municipal waste: The importance of efficient energy recovery and transport distances

Recycling of materials from municipal solid waste is commonly considered to be superior to any other waste treatment alternative. For the material fractions with a significant energy content this might not be the case if the treatment alternative is a waste-to-energy plant with high energy recovery rates. The environmental impacts from recycling and from incineration of six material fractions in household waste have been compared through life cycle assessment assuming high-performance technologies for material recycling as well as for waste incineration. The results showed that there are environmental benefits when recycling paper, glass, steel and aluminium instead of incinerating it. For cardboard and plastic the results were more unclear, depending on the level of energy recovery at the incineration plant, the system boundaries chosen and which impact category was in focus. Further, the environmental impact potentials from collection, pre-treatment and transport was compared to the environmental benefit from recycling and this showed that with the right means of transport, recyclables can in most cases be transported long distances. However, the results also showed that recycling of some of the material fractions can only contribute marginally in improving the overall waste management system taking into consideration their limited content in average Danish household waste.     

New Multi-Scale Hybrid System Based on Maple Wood Flour and Nano Crystalline Cellulose: Morphological,Mechanical and Physical Study

In the first part of this work, composites based on polypropylene (PP) and maple wood flour (MF) were prepared by melt compounding using twin-screw extrusion followed by compression molding. The morphological and mechanical properties of the composites were analyzed for three samples: PP, MF/PP and MF/PP containing maleic anhydride grafted polypropylene (MAPP) as coupling agent. The results showed that MF/PP composites have improved mechanical properties, especially tensile modulus (+33 %), with only 8 % increase in density. The addition of MAPP further improved the mechanical properties, in particular tensile modulus (up to 51 %), which could be related to better fiber/matrix adhesion. In the second step, nano crystalline cellulose (NCC) was added to all samples to produce NCC-MF/PP hybrid composites. From the mechanical analysis performed, the hybrid composites with MAPP have improved properties, especially tensile (+53 %) and flexural (+40 %) moduli. These results confirmed that multi-scale hybrid NCC-MF composites can substantially improve the mechanical properties of polyolefins with limited increase in density (14 %) leading to high specific properties.     

Enrichment of the metallic components from waste printed circuit boards by a mechanical separation process using a stamp mill

Printed circuit boards incorporated in most electrical and electronic equipment contain valuable metals such as Cu, Ni, Au, Ag, Pd, Fe, Sn, and Pb. In order to employ a hydrometallurgical route for the recycling of valuable metals from printed circuit boards, a mechanical pre-treatment step is needed. In this study, the metallic components from waste printed circuit boards have been enriched using a mechanical separation process. Waste printed circuit boards shredded to <10mm were milled using a stamp mill to liberate the various metallic components, and then the milled printed circuit boards were classified into fractions of <0.6, 0.6-1.2, 1.2-2.5, 2.5-5.0, and >5.0mm. The fractions of milled printed circuit boards of size <5.0mm were separated into a light fraction of mostly non-metallic components and a heavy fraction of the metallic components by gravity separation using a zig-zag classifier. The >5.0mm fraction and the heavy fraction were subjected to two-step magnetic separation. Through the first magnetic separation at 700 Gauss, 83% of the nickel and iron, based on the whole printed circuit boards, was recovered in the magnetic fraction, and 92% of the copper was recovered in the non-magnetic fraction. The cumulative recovery of nickel-iron concentrate was increased by a second magnetic separation at 3000 Gauss, but the grade of the concentrate decreased remarkably from 76% to 56%. The cumulative recovery of copper concentrate decreased, but the grade increased slightly from 71.6% to 75.4%. This study has demonstrated the feasibility of the mechanical separation process consisting of milling/size classification/gravity separation/two-step magnetic separation for enriching metallic components such as Cu, Ni, Al, and Fe from waste printed circuit boards.     

Preparation and Characterization of Clay Nanocomposites of Plasticized Starch and Polypropylene Polymer Blends

Plasticized starch (PLS) is a renewable, degradable, and inexpensive polymer, but it suffers from poor mechanical properties. The mechanical properties can be improved by blending PLS with polyolefins, nonetheless, at high PLS content, the mechanical properties remain poor. Here we show that addition of clay can greatly improve the mechanical properties of PLS/polypropylene blends at high starch content. Unmodified and organically modified montmorillonite clays, MMT and Cloisite 30B respectively, were added to blends of glycerol-plasticized starch and polypropylene, compatibilized using maleated polypropylene. TEM indicates that MMT is well dispersed in the PLS phase of the blends, while Cloisite 30B is located both within the PLS phase as well as at the interface between PLS and PP. At high PLS content, the addition of clay increased the tensile strength and tensile modulus by an order of magnitude, while reducing the ultimate elongation only slightly. Such improvements are attributable to both the addition of clay as a reinforcing component, as well as to the change in the two phase morphology due to addition of clay.     

Recycling and recovery routes of plastic solid waste (PSW): A review

Plastic solid waste (PSW) presents challenges and opportunities to societies regardless of their sustainability awareness and technological advances. In this paper, recent progress in the recycling and recovery 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 treatment 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 thermal 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 recycling 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 general 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 integration 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.