Polystyrene degradation mechanisms

Yu, J., Yi, B., Xing, D., Liu, R, Shao, Z. and Fu, Y. 2003. Degradation mechanism of polystyrene sulfonic acid membrane and application of its composite membranes in fuel cells. Physical Chemistry Chemical Physics 5 611-615. 

Oxygen plays a very important role in the degradation of polystyrene. The activation energy for the thermal degradation above 350 °C decreases to 90 kJ mol" in the presence of an excess of oxygen [47]. The degradation mechanism involves depropagation. Thermal-oxidative products include benzaldehyde, benzoic acid,... 

Kerr [67] very well (Figs. 24 and 25). Madorsky and co-workers have also made an extensive study of polystyrene degradation (see Ref. 59), and agree with Gordon s degradation mechanism. 

Selected examples of recycled resins are listed in Table 16.9. Polystyrene degradation during processing proceeds by the chain scission mechanism. 

Polystyrene (PS) is considered an excellent polymer suitable for various commercial and domestic applications. PVC and PS stand second and third in the world, respectively, as far as the consumption of polymers is concerned. The structure and composition of various products formed during the degradation process and their mutual interactions in the ultimate degradation mechanism depends on the compatibility of polymeric components in the blends. PS/PVC blends with different compositions have been prepared (Ahmad et al. 2007) in the forms of film and powder. Thermal degradation was studied at various heating rates in an inert atmosphere. Pure PS degrades in one step between 300 °C and 400 °C, producing monomer, dimer (2,4-diphenyl-1-butene), trimer(2,4,6-triphenyl-l-hexane). 

Polystyrene degradation does not noticeably begin at less than 200 °C. Depending on temperature, various dominant degradation mechanisms can be detected Below 300 °C, mainly chain cleavage occurs, and few or no volatile products form. Above 300 °C, increasing depolymerization occurs, and volatile products with monomers (45%) and oligomers are formed [20]. 

Despite the considerable volume of research on polystyrene degradation over 40 years, there remain aspects of the degradation mechanism which are controversial. A number of recent contributions have provided additional information, without fully resolving the conflicting... 

Whilst this prediction of in vivo stability is largely borne out in practice, there is some evidence that other factors are involved and that unexpected degradation mechanisms operate within the body. One of the first observations of degradation of these polymers was made by Oppenheimer" who was working on the carcinogenic properties of plastics. In attempting to elucidate the mechanisms by which plastic films induced tumours after subcutaneous implantation in rodents, certain radiolabelled polymers were employed. " C-labelled polystyrene, polyethylene and poly(methyl methacrylate) were implanted and urine, faeces and respiratory CO2 were monitored for periods over a year. With the polystyrene, nothing radioactive was excreted in the urine until 21 weeks, but some radioactivity was detected after this time. With polyethylene, radioactive species were excreted after 26 weeks and with poly(methyl methacrylate), this occurred after 54 weeks. 

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