The chemistry in thermal reprocessing

The chemistry of the reprocessing of thermoplastics is not simply a question of heating the polymers to a temperature above their melting point and then re-extruding to produce new products. The thermal reprocessing of many of the thermoplastics is accompanied by unwanted degradation processes that change the chemical and physical properties of the materials. Polymers may be considered to be affected in five ways  

Random initiation Terminal initiation Depropagation Transfer Scission 

The observed products from the thermal degradation of a wide range of thermoplastics can be accounted for by the differences in the rate constants ki, fed, fef, fes, and fet. For example, if fed fef, the polymer tends to depolymerise to the monomer in almost quantitative yield, whereas if fed fef the products will include large fragments arising from the chain scission reaction. 

Each polymer will be affected to different extends by the chemical and physical changes during reprocessing. 

Some of the original PVC materials in post-consumer waste may have been coloured already and the reprocessed materials will therefore reflect 

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