Stabilisation of LDPE cross-linked in the presence of peroxides I. Kineticstudy of the oxidation

The oxidation resistance of LDPE, cross-linked in the presence of dicumyl p eroxide and stabilised with a commercial antioxidant, bis[(3-t-butyl-2-hydr oxy-5-metyl)phenyl] sulphide (Irganox 1081) was investigated. Oxidation ind uction time, ti, as found by isothermal DTA, was used as the criterion of e valuation of LDPE resistance to oxidation. Without the peroxide, Irganox 10 81, at concentrations in the range 0.1-0.5% w/w, was found to inhibit LDPE oxidation. Its depletion rate at temperatures in the range 195-225 degreesC , as measured by oxidation induction time, t(i), may be described as a zero -order reaction with activation energy E = 141.4 kJ/mol. Simultaneous addit ion of 2.0% w/w dicumyl peroxide and 0.1-0.4% w/w Irganox 1081 to LDPE by r olling at 130 degreesC was observed to reduce oxidation induction time to t (i) = 0. After cross-linking at 180 degreesC and 5.0 MPa for 20 min, the sa me compositions recovered their resistance to oxidation over the whole conc entration range of Irganox 1081. (C) 2000 Elsevier Science Ltd. All rights reserved.