Peroxidised polyolefins

Figure 4. Schematic representation of material tests (a) and (b) and eco-toxicity tests (c) for peroxidised polyolefins.

Table 4. Time-scale for biodegradation of peroxidised polyolefins...

PP is used in impact modified forms in films, bottles and crates and in unmodified form in ropes and twines. It is frequently present in domestic and industrial waste plastics in association with the polyethylenes. Owing to its pendant methyl groups PP is more readily peroxidised than the other polyolefins and it is not normally separated from them in domestic packaging waste. 

As with the poly (dienes), the polyolefins peroxidise to biodegradable products through the intermediate unstable hydroperoxides. Scheme 3 illustrates this process for poly(ethene), (PE). Poly(propene) (PP) peroxidises much more rapidly than PE due to the tertiary carbon atom (Scheme 2) and the higher proportion of vicinal hydroperoxides formed [6,9]. In-chain hydroperoxide formation continues steadily in all the polyolefins provided oxygen is available and the rate of biodegradation correlates with the rate of abiotic peroxidation. 

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