Recycling a mixture of plastics: A challenge in today's environment

Thermoplastic materials can be remelted and reused. However, in many instances, they are not recycled after use. The Plastics Institute of America has long felt that the value of such materials has not been fully realized and that scrap plastics should be recycled as a material resource. We are presently establishing a body of knowledge with government and industry funding to facilitate the practical application of such recycling endeavors. The objective is to set up programs to learn ways in which plastics scrap might be fabricated into marketable items. If the scrap is segregated, i.e. a single material, the recycling is simpler than when the scrap is a mixture of plastics. Among projects and/or applications areas to be explored for commercial possibilities are the following: (1) Reclaiming the plastics residue from shredded autos. This source could yield more than one million tons of plastics by 1990 with the development of proper technology. (2) Bonding of plastics scrap to form composites which are expected to have application wood and virgin plastics substitutes in many wide-specification applications. (3) The use of auto shredder residue (ASR) a rock-wool like mixture in the manufacture of polymer concrete, replacing sand and gravel as the aggregate and incorporating in situ thermosetting type binders such as acrylics, melamines, phenolics, and polyesters. (4) Recovery and purification of polyethylene terephthalate (PET) from discarded soft drink plastic bottles and similar commercial usages. (5) Recycling of such single resin sources as polypropylene battery cases in making solid and foamed wide-spec items. The Plastics Institute was able to demonstrate major energy saving possibilities through recycling rather than through the heat generation programs for which much plastic scrap is targeted. For example, 1000 lb of high density polyethylene has a fuel value of 20 million BTUs, but recycling 1000 lb of HDPE waste into fabricated products would save as much as 39 million BTUs since 1000 lb of HDPE will not have to be made from ethylene. The Institute during 1983/84 sponsored postgraduate level applied research projects to develop technology for the recycling of a heterogeneous mixture of polymer waste. Auto shredder residue (ASR) because of its large volume and availability, was the major focus of the research. The ultimate objective is to convert the mixture as is into useable, saleable molding compounds. Quantity lots of selected formulae incorporating compatibilizers, bonding agents and flow modifiers into the ASR are currently being made into pellets. They will be processed into noncritical specification items to demonstrate the feasibility of using recycled residue for commercial applications. Presently, it is disposed of in landfills at high costs to the shredder companies as well as a negative impact on the environment. Once the objective of the program has been met by the molding and extrusion of the demonstrated parts, a final summary report will be made available for distribution. Graduate students at various universities have been working on each of four general tasks areas.