Waste Plastics (waste + plastic)

Distribution by Scientific Domains

Selected Abstracts

Catalytic conversion of waste plastics: focus on waste PVC

Mark A Keane
Abstract Effective waste management must address waste reduction, reuse, recovery/recycling and, as the least progressive option, waste treatment. The increase in plastic waste production is a serious environmental issue. Plastics consumption continues to grow and while plastic recycling has seen a significant increase since the early 1990s, consumption still far exceeds recycling. Waste plastic can, however, serve as a potential resource and, with the correct treatment, can be reused or serve as hydrocarbon raw material or as a fuel. PVC, highly versatile with many applications, is non-biodegradable and has a high Cl content (56% of the total weight). Waste PVC incineration is highly energy demanding and can result in the formation of toxic chloro-emissions with adverse ecological, environmental and public health impacts. The Cl component must be removed from any waste PVC derived gas or oil before it can be used. An overview of the existing waste plastic treatment technologies is provided with an analysis of the available literature on thermal and catalytic PVC degradation. Thermal degradation results in random scissioning of the polymer chains generating products with varying molecular weights and uncontrolled Cl content. There is a dearth of literature dealing with the catalytic dechlorination of PVC. A case study is presented to illustrate the role heterogeneous catalysis can play in PVC waste treatment. The efficacy of Pd/Al2O3 to promote PVC dechlorination is demonstrated, where a significant decrease (by up to a factor of 560) in the liquid fraction Cl content is recorded in addition to differences (relative to thermal degradation) in the gas phase product, i.e. higher C1C4 content with preferential alkane formation. Copyright 2007 Society of Chemical Industry [source]

Prototypes for building applications based on thermoplastic composites containing mixed waste plastics

M. Xanthos
Automotive shredder residue (ASR) and a complex residue obtained as a by-product in the tertiary recycling of nylon-6 fibers from used carpets were evaluated as potential additives in thermoplastic composites to be used for building applications. Prototype blocks were prepared by the "intrusion" process using various ratios of the waste streams and low-density polyethylene (LDPE) in the absence of compatibilizers. Hence, product morphologies and corresponding properties were largely controlled through processing. They were evaluated for their short-term and longterm mechanical properties, flammability, thermal conductivity, and heavy-metal and total organic carbon leaching characteristics. Encapsulation of the waste feedstock by LDPE during molding in a single-screw extruder significantly reduced the leachable content. In an effort to further reduce the leachable content, the mixtures were processed in two stages by precompounding in adevolatilizing twin-screw extruder prior to molding. In comparison to the as-received wastes, improved homogenization decreased the leachable heavy-metal content by at least 98%. The carpet residue feedstock consisting of polypropylene, styrene-butadiene rubber and calcium carbonate appears to be an attractive low-cost, high-volume material with consistent properties and could be used as filler in thermoplastic composites. Comparison of their performance characteristics suggested that the carpet residue composites would be favored versus ASR composites as replacement of the wood thermal barrier components in a novel steel-based stud assembly. [source]

Dissolution of waste plastics in biodiesel

Ying Zhang
The dissolution behavior of polystyrene (PS) and low-density polyethylene (LDPE) in biodiesel was investigated with an eye towards developing methods to dispose waste plastics by burning them with fuel. To complement and guide the experimental investigations, molecular dynamics simulations were performed to calculate solubility parameters, cohesive energy densities, Flory-Huggins , parameters and phase diagrams of the target systems. Dissolution kinetics of PS and LDPE in methyl esters was monitored by gravimetry, from which parameters such as dissolution rates, activation energies, and scaling indices were estimated. The shear viscosity of the polymer solutions was measured to ascertain their suitability as fuel mixtures. The dissolution of PS in biodiesel appears to be controlled by the diffusion of polymer chains through a boundary layer adjacent to the polymer/solvent interface. Taken together, the experimental and modeling studies provide a predictive toolbox to design biodiesels of different compositions that will dissolve commodity polymers such as PS and LDPE to be used as fuels in engines. POLYM. ENG. SCI., 2010. 2009 Society of Plastics Engineers [source]