Long-term stabilization of polyethylene — evaluating antioxidants and their testing methods - (in English)
Polyethylenes are widely used for the insulation of cables and for pipes. A lifetime of 40 to 50 years is generally desirable for this purpose and stabilization of the polyethylene is thus of prime importance. The paper ranks antioxidants according to their effectiveness. Four commercial grade antioxidants: 4,4-thio-bis-(3-methyl-6-tert-butyl-phenol) (I); 2,2'-thio-bis-(4-methyl-6-tert-butyl-phenol) (II), 2,2'-thio-diethylene-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)] propionate (III) and 4,4'-bis-(α,α-dimethyl benzyl)diphenylamine (IV) were tested in two polyethylenes, conventional low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). The conventional accelerated aging test was used. The ageing process was followed by testing the samples every fourth week until elongation at break showed a substantial decrease. The carbonyl index, crystallinity, oxygen induction time and molecular weight distribution were also determined during the course of ageing. The samples containing I and II were degraded between 20 and 36 weeks. With III and IV, stabilized polyethylene had an ageing time of approximately one year. The test methods used did not clearly indicate the beginning of the degradation process.
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