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

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 long-term 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 a devolatilizing 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.