Rheological and mechanical properties of composites made from wood flour and recycled LDPE/HDPE blend

The effect of compounding method is studied with respect to the rheological behavior and mechanical properties of composites made of wood flour and a blend of two main components of plastics waste in municipal solid waste, low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The effects of recycling process on the rheological behavior of LDPE and HDPE blends were investigated. Initially, samples of virgin LDPE and HDPE were thermo-mechanically degraded twice under controlled conditions in an extruder. The recycled materials and wood flour were then compounded by two different mixing methods: simultaneous mixing of all components and pre-mixing, including the blending of polymers in molten state, grinding and subsequent compounding with wood flour. The rheological and mechanical properties of the LDPE/HDPE blend and resultant composites were determined. The results showed that recycling increased the complex viscosity of the LDPE/HDPE blend and it exhibited miscible behavior in a molten state. Rheological testing indicated that the complex viscosity and storage modulus of the composites made by pre-mixing method were higher than that made by the simultaneous method. The results also showed that melt pre-mixing of the polymeric matrix (recycled LDPE and HDPE) improved the mechanical properties of the wood–plastic composites.     

Thermoplastic composites from maleic anhydride modified post-consumer plastics

In attempts to identify potential applications for refined commingled postconsumer plastics, a feedstock containing about 80% polyethylene (PE) and lesser amounts of poly(ethylene terephthalate) (PET), polystyrene (PS), polypropylene (PP), and poly(vinyl chloride) (PVC) was modified through functionalization with maleic anhydride in a co-rotating intermeshing twin-screw extruder. The modified and unmodified blends were compounded with various fillers and reinforcements such as glass fibers, mica flakes, talc, and calcium carbonate. Injection molded composites based on the modified matrix had, in general, superior mechanical and thermal properties. These findings are discussed in view of the improved adhesion resulting from reactions and/or enhanced polar interactions at phase boundaries. Several compounds prepared in this work had overall property data comparable to, or approaching those, of equivalent commercial HDPE molding compounds that are commonly used in “durable” applications.     

Peroxide modification of a multicomponent polymer blend with potential applications in recycling

A mixture of seven immiscible “virgin” plastics, namely low and high density polyethylene (LDPE and HDPE), polypropylene (PP), polyvinyl chloride (PVC), crystal and high impact polystyrene (PS and HIPS), and polyethylene terephthalate (PET), in proportions representative of those currently found in post-consumer plastics containers, was compounded in a corotating twin-screw extruder. The mechanical properties of the blend were improved through the addition of relatively high concentrations of a dialkyl peroxide which was also found to drastically affect the blend morphology. The results are interpreted in terms of improved dispersive mixing favored by the similarity in the rheological behavior of the modified blend components, improved physical properties of certain blend components upon peroxide modification, and, possibly, enhanced intefacial adhesion. © 1994 John Wiley & Sons, Inc.     

Product design with glass fiber reinforced polymer blends,with potential applications in recycling

This paper addresses the issue of compositional variation in multiphase, multi-component polymer mixtures equivalent to those found in commingled waste streams, such as those obtained from reclamation/recycling operations of post-consumer containers. By using virgin resins, the effects of variations in the composition of matrices containing high density polyethylene (HDPE) as the major phase on the properties of composites containing varying amounts of glass fiber and different adhesion promoters are studied. The results obtained on injection molded thin-section parts indicate that it is possible, through the addition of glass fibers and in the presence of suitable adhesion promoters, to obtain enhanced and reproducible properties with relatively little dependence on matrix composition. Preliminary structural and flow analyses were performed with commercial software on different types of plastic parts that could be eventually molded from actual mixed waste plastics suitably modified through glass reinforcement. Experimentally generated rheological and mechanical property data on HDPE based blends containing 20 wt% glass fibers and different adhesion promoters were used for the simulation. Issues concerned with injection molding and product performance of glass-fiber reinforced blends are discussed.     

Effects of gamma-irradiation on mechanical characteristics of recycled polyethylene blends

The recycling of polymeric materials has gained increasing attention in the world because of economic and environmental considerations. Therefore, blends of low cost plastics such as polyolefins, Polystyrene, and poly(vinyl chloride) present in polymeric waste are of particular interest. Among the different methods for recovering plastic residues, a two-step process, developed by two of the authors, permits the production of materials with controllable composition and homogeneous characteristics. The paper discusses the behavior of recycled 75/25 blends of low density polyethylene (LDPE) and high density polyethylene (HDPE) after exposure to various does of gamma-irradiation (10–2000 kGy) in the presence of oxygen. Mechanical testing, differential scanning calorimetry, gel permeation chromatography, and infrared spectroscopy have been used to investigate the effects of gamma-irradiation on the polymer material. Mechanical strength was found to increase with irradiation doses up to 100 kGy, followed by a small decrease and a tendency to stabilization at higher doses. The degradation process is discussed.     

废旧塑料的回收与利用

综述了利用区块链技术进行废旧塑料的回收.使用区块链技术建立的塑料银行可以激励人们自发地回收废旧塑料.废旧塑料的回收流程大多是线下的,监管困难,使用区块链技术可以使用户在区块链上查询全流程的回收数据,便于监管.在废旧塑料的分选和利用方面,介绍了聚乙烯和聚丙烯的分选,聚对苯二甲酸乙二酯与聚氯乙烯混合固体塑料的分选.废旧塑料...     

Methods for polyurethane and polyurethane composites,recycling and recovery: A review

Recent progress in the recycling and recovery of polyurethane and polyurethane composites is reviewed. The various types of polyurethane waste products, consisting of either old recycled parts or production waste, are generally reduced to a more usable form, such as flakes, powder or pellets, depending on the particular type of polyurethane that is being recycled. The various recycling technologies for material and chemical recycling of PU materials have greatly contributed to improve the overall image regarding the recyclability of polyurethanes in recent years, by far the most important being regrinding and glycolysis. These technologies open an emerging, effective and economic route for recycling polyurethane rigid foams and composite. Polyurethane foam in automotive seating has been successfully recycled using regrind technology. Glycolysis of polyurethanes can be economically acceptable, but still requires more development in order to tolerate more contamination in the post-consumer material. Current technologies can recover the inherent energy value of polyurethanes and reduce fossil fuel consumption. Energy recovery is considered the only suitable disposal method for recovered material for which no markets exist or can be created. Increasing waste-to-energy and other thermal processing activities involving gasification, pyrolysis and two-stage combustion has contributed for the disposal of significant amounts of scrap PU without many difficulties. It is concluded that many of the plastic feedstock recycling processes appear to be technically feasible and robust enough to warrant further development in the future.     

废弃交联聚乙烯回收利用研究进展

综述了目前国内外用于废弃交联聚乙烯(XLPE)回收利用的几种主要方法的研究进展,包括粉末化填料回收法、热剪切塑化回收技术、超临界流体处理回收法、超声辅助挤出回收技术、固相剪切碾磨回收法等,并指出相应的技术原理和优缺点。     

Self-compatibilization of polymer blends via novel solid-state shear extrusion pulverization

The mechanochemistry of a novel economical solid-state shear extrusion (SSSE) pulverization is investigated. SSSE compatibilizes incompatible blends in situ; the process has great potential in recycling of post-consumer plastic waste (PCPW). It is proposed that SSSE causes this self-compatibilization of blends by rupturing polymer chains and allowing them to recombine with their neighboring chains. When this recombination involves dissimilar chains at an interface between powder particles, block copolymers are formed, and if the chain transfer reactions are possible, graft copolymers are formed. These copolymers at the interfaces in the phase-separated, incompatible blend lower the interfacial tension and increase the adhesion at the interfaces, thus compatibilizing the blend. Our nuclear magnetic resonance (NMR) and rheology studies reveal the formation of long chain branches (LCBs) in an linear low-density polyethylene (LLDPE), which is equivalent to the formation of graft copolymers in blends. With NMR, an increase from ∼ 0.2 to ∼ 2.0 of the number of LCBs per 1000 carbon atoms is observed due to pulverization of the LLDPE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1179–1187, 1997     

Qualitative and quantitative contaminants assessment in recycled pellets from post-consumer plastic waste by means of spectroscopic and thermal characterization

The complexity of any plastic recycling initiative lies in the heterogeneous nature of the post-consumer commingled plastic waste stream: recycling treatments are challenging without prior reliable sorting. A suitable identification system should be able to recognize different plastics and blends. Nowadays, the main technique used as quality control in plastic waste sorting centers is differential scanning calorimetry, whose result can be purely qualitative or semi-quantitative, since only the crystalline fraction is evaluated. Moreover, the time required for data acquisition is relatively long. Infrared spectroscopy is an alternative, faster technique extensively used in applied research, but not widely utilized in industry. In this work, the cross-use of infrared spectroscopy and calorimetry is tested in a real, practical case: the quality control of recycled pellets (namely composed of polyolefins only), which represent the output of a commingled plastic recycling plant and are used as secondary raw materials for different applications. Appropriate infrared spectroscopy calibration curves were built to allow the quantitative analysis with respect to the most common polymers found in the commingled plastic waste stream; the composition and contaminants in the recycled pellets were thereby determined and tracked through different production batches through the cross-use of the two techniques outlined above.     

The effect of plastic addition on coal caking properties during carbonization

The recycling process of waste plastics using coke ovens is now being studied. The effect of plastic addition on coal caking property was investigated. It was revealed that thermal decomposition products of plastics interacted with bituminous coal during carbonization in coke ovens. The effect of plastic addition on coal caking property varied with types of plastics. The addition of aliphatic polymers such as polyethylene (PE), polypropylene (PP) and poly(vinyl chloride) (PVC) had only a small effect on coal caking property and coke strength and in some cases PE addition increased coke strength. On the other hand, the addition of polystyrene (PS), poly(ethylene terephthalate) (PET) and terephtalic acid (TFA) inhibited coal expansion and fusion, decreased maximum fluidity and total dilatation, and deteriorated the coke strength. These differences were discussed from the viewpoint of the interaction between thermal decomposition products of plastics and hydrogen in coal. It was suggested that the radical formed as a result of PS or PET thermal decomposition abstracted hydrogen from coal, which resulted in the decrease in coal caking property.     

Recycling of commingled plastics waste containing polypropylene,polyethylene, and paper

Polymer waste recycling is a major technical problem, because large amounts of synthetic polymers are produced every day and polymeric wastes are gathered from municipal solid wastes. There are a few polyolefins, such as polyethylene (PE) and polypropylene (PP) with huge amounts of paper in the waste materials. In order to recycle the commingled plastics waste that contains paper, hydrolytic treatment is needed prior to conventional processing. In this project, the optimum conditions of hydrolytic treatment of paper and the mechanical properties and morphological state of different compositions of PP high‐density PE (HDPE) blends with paper were studied. Ethylene‐propylene‐diene copolymer (EPDM) was added to improve the mechanical properties of blends. The results show that the hydrolytic treatment of paper improves the mechanical properties, such as the tensile strength and modulus of the PP/HDPE/paper composites relative to the untreated samples, and up to 30% paper can be added to commingled PP and HDPE blends. The EPDM was used as an impact modifier. The plastics waste containing paper can be used in applications such as artificial wood. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2573–2577, 2001     

Pyrolysis of mixed plastics for the recovery of useful products

Thermal and catalytic pyrolysis of polystyrene (PS) with low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), poly-ethylene terephthalate (PET) plastics were carried out in a 25 cm³ stainless steel micro reactor at around 430–440 °C under 5.5–6.0 MPa of N₂ gas pressure for 1 h. Three reactions of each plastic with PS were conducted in the ratio of 1:1, 1:2 and 1:3. The amount of PS was varied to explore its role and reactivity. In all coprocessing reactions, ratio 1:1 afforded the best yields in the form pyrolytic oils. SIM distillation of hexane soluble portion showed that the low boiling fractions were not found and fractions were obtained only after 96 °C + boiling point. It could be due to the vaporization of high volatile components. In most of the binary pyrolysis, light cycle oil (LCO) fractions have low recovery than heavy cycle oil (HCO). GC identified some very important chemical compounds present in the liquid products obtained from the pyrolysis of mixed plastics. The results obtained from this study have shown usefulness and feasibility of the pyrolysis process of the mixed plastics as an alternative approach to feedstock recycling.     

Techno-Economic Comparison of Bio-Cycling Processes for Mixed Plastic Waste Valorization

Mixed plastic waste is challenging for any recycling process. Here, an enzymatic recycling process is compared with a biotechnological upcycling process for valorizing mixed plastic waste constituted by PLA, PET, and PP. Both process routes are modeled in Aspen Plus, analyzed for bottlenecks, cost drivers, and sensitivity regarding enzymatic and microbial performance. While enzymatic recycling is only viable for uniform plastic feedstock, biotechnological upcycling operating at optimized process conditions reveals the potential to produce carbon-neutral succinic acid from mixed plastic waste.     

Hydrocarbon fuels produced by catalytic pyrolysis of hospital plastic wastes in a fluidizing cracking process

A mixture of post-consumer polyethylene/polypropylene/polystyrene (PE/PP/PS) with polyvinyl chloride (PVC) waste was pyrolyzed over cracking catalysts using a fluidizing reaction system operating isothermally at ambient pressure. The influences of catalyst types and reaction conditions including reaction temperatures, ratios of catalyst to plastic feed, flow rates of fluidizing gas and catalyst particle sizes were examined. Experiments carried out with various catalysts gave good yields of valuable hydrocarbons with differing selectivity in the final products dependent on reaction conditions. A model based on kinetic and mechanistic considerations associated with chemical reactions and catalyst deactivation in the acid-catalyzed degradation of plastics has been developed. The model gives a good representation of experimental results from the degradation of commingled plastic waste. The results of this study are useful for determining the effects of catalyst types and reaction conditions on both the product distribution and selectivity from hospital plastic waste, and especially for the utilization of post-use commercial FCC catalysts for producing valuable hydrocarbons in a fluidizing cracking process.     

Which plastic package has the lowest contribution to taste and odor?

Although plastics have made significant inroads in the packaging area, little work has been done in the U.S. to evaluate their effect on the taste and odor of the package contents. This is especially relevant for food, beverage, liquor, and bottled water. Rohm and Haas contracted with an independent consulting firm, which uses a professional panel familiar with the effects of packaging, to assess the sensory impact of different plastics on the taste of water. Four types of plastics were tested: polyvinyl chloride (PVC), high-density polyethylene (HDPE), polycarbonate (PC), and polyethylene terephthalate (PET). Two forms of each polymer were evaluated, bottles and plaques, which were aged in water for four weeks at room and elevated temperature (120°F). The professional panel evaluated the taste and odor of the water on a numerical intensity scale and characterized any observed effect with words. The numerical rating permitted the effects of the plastic materials to be compared directly. PVC had the lowest contribution to taste and odor of all of the plastics. PVC was followed by PET and then PC and HDPE. Therefore the two current packaging materials, HDPE and PC, were not the best! This implies that water and other taste-sensitive products could be more appealing if packaged in appropriately formulated PVC.     

含孔片状废旧PET增韧水泥基复合材料的制备及性能评价

废旧塑料高值化利用对促进塑料循环利用具有重要意义。从提高填充材料和基体的啮合强度出发,开发以含孔废旧塑料为增韧材料的增韧水泥基复合材料是废旧塑料高值化利用的有效途径之一。以含孔片状废旧聚对苯二甲酸乙二醇酯(PET)和水泥复合,制备了增韧水泥基复合材料,并考察其抗折强度、冲击性能和拉伸拔脱载荷,分析了其增韧机理。相比未用PET增韧水泥基体,增韧水泥基复合材料的冲击强度由14.6 J/m^2增加到36.7 J/m^2,增加了1.5倍,抗折位移也由0.66 mm陡增至7.4 mm,但抗折强度由7.67 MPa降低到2.85 MPa。上述结果表明,含孔废旧PET塑料片和水泥基体形成的互穿结构起到了传递、分散载荷的作用,使增韧水泥基复合材料由瞬态脆性破坏转变为渐进式韧性破坏,虽然水泥基体的抗折强度降低,但显著延长了水泥基体的弯曲断裂过程,使增韧后的水泥基复合材料具有更强的抵抗碎裂的能力。此外,在研究范围内,水泥基复合材料中废旧PET塑料片材越多,单位塑料片对复合材料的增韧贡献度越大,具有增韧“筷子效应”。     

Study of masterbatch effect on miscibility and morphology in PET/HDPE blends

The present work studies the morphology in poly(ethylene-terephthalate)/polyethylene (PET/HDPE) polymer blends and its impact on blend properties. Mixing process in blend preparation is the important parameter for the type of obtained blend morphology and final blend properties, so two different mixing processes were used. In the first one, all components are mixed together while another one includes two step mixing procedure using two different types of masterbatch as compatibilizers for PET/HDPE system. Such blends can be considered in terms of PET polymer recycling in the presence of HDPE impurities in order to find suitable compatibilizers, which will enhance the interactions between these two polymers and represents the possible solution in recycling of heterogeneous polymer waste. The morphology of the studied PET/HDPE blends was inspected by scanning electron microscopy to examine the influence of the mixing process and various compositions on blends morphology, and interactions between PET and HDPE. The surface properties were characterized by contact angle measurements. The effect of the extrusion on the samples thermal behaviour was followed by DSC measurements. FTIR spectroscopy was used for the determination of interactions between blend constituents. It can be concluded that the type of mixing process and the carefully chosen compatibilizer are the important factors for obtaining the improved compatibility in PET/HDPE blends.     

Vinyl recycling: An update

Despite industry protests to the contrary, in September, 1989, few people believed that PVC bottles were recyclable in the same sense that PET soft drink bottles and HDPE milk bottles were. At that time, however, OxyChem announced its post-consumer recycling initiative, offering to buy bottles back from anywhere in the United States. By paying prices comparable to that of PET ($0.06–$0.10/1b) and paying the freight from the recycler's dock, recycled PVC has begun to appear. Collection is handled by existing waste haulers and recyclers as an addon to their overall program. Promotional materials were generated to aid in visual separation of PVC from other plastics; in addition, automated sortation is being engineered by two laboratories with financial assistance from the Vinyl Institute. In general, PVC is reprocessed in the same fashion as other plastics: it must be ground, washed, and pulverized or repelletized. Care must be taken to minimize heat history and in some cases to boost stability and lubricity before pelletization. Material is resold into permanent, semi-permanent and packaging applications.     

Chemical Recycling of Mixed Plastic Wastes by Pyrolysis – Pilot Scale Investigations

Chemical recycling of plastic wastes can be a useful complement to mechanical recycling to achieve the required plastics recycling rates and to establish a circular economy that is climate neutral and resource-efficient. Different mixed plastic wastes that are subject to future recycling efforts are studied under uniform conditions of intermediate pyrolysis characterized by a medium heating rate and pyrolysis temperature. Product distributions and selected product properties are determined, and process mass and energy balances are derived. Product yields and compositions are highly dependent on the waste pyrolyzed. The results show that pyrolysis is a suitable process to recover chemical feedstock from various complex mixed plastic wastes.