CAN POLYETHYLENE BE A PHOTO(BIO)DEGRADABLE SYNTHETIC-POLYMER

A polymeric system based on LDPE would be qualified as a ''photo(bio)d egradable synthetic polymer'' for use as films or thin systems in plas ticulture and later in packaging where severe specific criteria should be respected. The evolution of such a system in environmental conditi ons should present three phases. In Phase I, corresponding to storage and use, in the presence of physicochemical and biological aggression, chemical evolution should be very limited and resistance to any micro organism should be observed. In Phase II a rapid abiotic degradation s hould occur until the complete destruction of physical (mechanical) pr operties and spontaneous fragmentation of the thin systems into more a nd more divided parts. Phase III corresponds to bioassimilation of hea vily transformed (oxidized) solid particles. Phase I should be predict ed and controlled on the basis of artificial photoaging or thermoaging experiments. Depending on the desired lifetime of the system, nonacce lerated, accelerated, or ultra-accelerated photoaging techniques could be used. The earliest fragmentation, which should be observed in Phas e II, should be predicted within the same experiment. The prediction o f the long-term fate of the polymeric materials should be based not on ly on the variations of physical properties but on a full analysis of the chemical evolution, i.e., determination of the major final transfo rmed groups of the macromolecular chains (and especially the acidic en d groups) and the molar mass distribution. In a recent BRITE-EURAM Eur opean contract, we developed an experimental protocol for the control of Phase III based on the use of pure cultures of strains from collect ions or selected adapted wild strains (from industrial polyethylene si te dumpings) which had been examined. Abiotically oxidized LDPE was th e only carbon source in a starving mineral medium. Bioerodibility caus ed by the carboxylic acid formed throughout abiotic degradation has be en observed.