THE MODE OF ACTION OF CORN STARCH AND A PROOXIDANT SYSTEM IN LDPE - INFLUENCE OF THERMOOXIDATION AND UV-IRRADIATION ON THE MOLECULAR-WEIGHTCHANGES

The mode of action of corn starch and a pro-oxidant system consisting of LDPE, styrene-butadiene copolymer (SBS) and manganese stearate (den oted as MB hereafter) as a system creating a (bio)degradable LDPE was analysed in line with ongoing research about degradable LDPE. Pure LDP E, LDPE with corn starch and LDPE with MB were subject to thermo-oxida tion (65 and 95 degrees C) and UV-irradiation. The degradation rates i n the different environments are discussed based on the molecular weig ht changes measured by SEC. In thermo-oxidation at both temperatures, LDPE with corn starch demonstrated the lowest degradation rate, even l ower than that of pure LDPE, in contrast to the situation in UV-irradi ated samples where pure LDPE was the most stable material. Addition of corn starch to LDPE thus has a stabilizing effect on the thermo-oxida tion mode while the same additive destabilizes the LDPE in, e.g. UV-ir radiation. This property would diminish the risk of degradation during the processing of such materials. Decreasing values of molecular weig ht were observed in thermo-oxidized LDPE-MB while the UV-irradiation r esulted instead in increasing molecular weight in the LDPE-MB. Large a mounts of radicals are formed during UV-irradiation which increases th e possibilities for chain elongation reactions. (C) 1997 Elsevier Scie nce Limited.