Chemical (tertiary) recycling of fibreglass reinforced polyamide-6

It is well known that polyamide 6 (PA-6) can be depolymerised to regenerate caprolactam monomer by treatment with phosphoric acid, and can thus be sub jected to tertiary recycling (= according ASTM D 5033-90: the process techn ologies of producing chemicals from scrap or waste plastics). However, broa d general application of this process - widely used in industrial practice especially for PA-6 fibre waste - to fibreglass-reinforced or filled PA-6 i s precluded by the fact that phosphoric acid reacts with the fillers. This causes a high phosphoric acid consumption; moreover, the method gives an un satisfactory yield of caprolactam (around 56 %) and also requires costly di sposal of phosphorus-containing waste. Therefore, processes have been devel oped for tertiary recycling of fibreglass-reinforced or filled polyamide 6, which plays an important role as an engineering plastic. Two different pro cesses have been investigated, viz. hydrolytic depolymerisation and catalys ed depolymerisation in vacuum.