SPECTROSCOPIC AND MECHANICAL CHANGES IN IRRADIATED STARCH-FILLED LDPE

LDPE containing corn starch (3.9%, 5.8% and 7.9% by weight) without further additives and corn starch in a pro-oxidant formulation (=masterbatch (MB): 10%, 15% and 20% by weight), were analysed by FTIR and drawtesting after irradiation for periods of up to 500 h. The carbonyl index for LDPE-20% MB after 500 h irradiation was 2.5 times the value obtained in pure LDPE and in LDPE-starch. The hydroperoxide index for the same material was three times the value obtained in pure LDPE and in LDPE-starch. During irradiation the tensile strength decreased to almost the same extent for all three materials-a mean value of 70% of the initial value was obtained after irradiation. The elongation at break for pure LDPE decreased during irradiation from 650 to 500%. The addition of starch and MB decreased the initial value from 650 to 500%. After irradiation the decrease was considerable-a mean value of 60% being recorded for the elongation at break of LDPE-MB. A material susceptible to photolysis is thus obtained by the addition of corn starch and a master batch containing LLDPE, styrene-butadiene copolymer (SBS) and manganese stearate. Incorporating only starch into LDPE did not significantly change the susceptibility of the material to photolysis. LDPE-MB is thought to degrade by an initial photo-oxidation (autoxidation) and a subsequent attack by microorganisms (i.e. biodegradation). Further ongoing studies on the biodegradation of pretreated LDPE-MB will be reported elsewhere. The induction time is accelerated by pretreatment. Irradiation or thermal treatment generate free radicals causing autoxidation which should facilitate a later biodegradation.