1 Introduction

This chapter describes post-consumer plastic recycling, where "recycling" refers to plastic material and may involve material recycling, chemical recycling or thermal recycling.

In material recycling, the material of the original application is restored but in another form. The recycling can involve a pure material or a mixture. Recycling of the pure material often occurs in the production of the merchandise, e.g. the production of insulating roofing materials. Various plastic manufacturers return rejected parts and the trim from fabrication processes back to the production process, thus contributing to the formation of new plastic products. This procedure, known in the plastics industry as regrinding, can be repeated numerous times, as long as the percentage of regrinds remains low. Material recycling in mixtures occurs when plastic materials from the households are collected. Because most polymers, even of the same species, do not mix well in the melt, a demixed polymer is normally not useful in recycling. One example of mixed material recycling is the production of park benches from household plastics, which were first produced in Germany in the 1990s.

Chemical recycling relates to a chemical change and usually involves a crude mixture of polymeric material, e.g. for thermosetting materials; it may be of interest to chemically treat the plastic in order to return to the initial monomers or similar materials. From the thermodynamics point of view, it should be noted that the production of polymers from monomers is an exothermic process and as a...