Aging and degradation of polyolefins. III. Polyethylene and ethylene–propylene copolymers

Abstract

synopsisRates of oxygen absorption and formation of oxidation products were determined in ?-initiated oxidations of thin films of high-and lowdensity polyethylene, atactic and isotactic polypropylene, and of three ethylene-propylene copolymers. Radiation yields G for 0 2 absorbed and formation of hydroperoxides depend on dose rates and decrease sharply with increasing ethylene content of the copolymers and moderately with increasing crystallinity of any base polymer. G values for dialkyl peroxide and carbonyl formation, and therefore for chain initiation and termination, do not change much with polymer composition and crystallinity and not at all with dose rates. A few experiments with atactic polypropylene and an amorphous ethylene-propylene copolymer, initiated by di-tert-butylperoxy oxdate, indicate that 37 mole-% of ethylene in the polymer increases the efficiency of initiation and the tendency toward crosslinking. 15,000 102,7008Crystallinity by heat of fusion; a,,, = 427,200; all measured on our film by Dr. J. R.Knox.

A critical comparison of methods for hydroperoxide measurement in oxidized polyolefins

“…8 Dialkyl peroxides usually do not react with NaI/ isopropanol in the absence of a very strong acid. Decker et al 15 '16 have found that the iodometric methods can accurately measure hydroperoxides in solid, 7-irradiated polyolefins because total oxygen uptake agreed well (within 5-10%) with total analyzed oxidation products (predominantly hydroperoxides).…”

Co-oxidation kinetic model for the thermal oxidation of polyethylene-unsaturated substrate systems

“…In such a case of co-oxidation, Decker et al [9] showed that the oxidizability of ethylene propylene copolymer varies with the ethylene molar fraction e according to a pseudo-hyperbolic curve which can be approximated by the following function: k 3 ffiffiffiffiffi k 6 p ¼ 10 À4 Â 2 À 1:63 Â e 1 þ 3:13 Â e here k 3 and k 6 can be defined as the rate constants characteristic of a virtual homopolymer which would exhibit the same kinetic behavior as the copolymer under study. In fact, an approach in which the kinetic behavior of the copolymer could be predicted from the characteristics of the corresponding homopolymers would be far more satisfactory.…”

Natural Ageing of Stabilized and Unustabilized Ldpe Films Used as Greenhouses Covering Materrials: Atr-Ftir and Sem Analysis

“…This increase results from the self-reactivity of peroxyl radicals (react 9) produced from the split of hydroperoxides in the presence of oxygen [41,28] (react 6). Therefore, hydroperoxides are precursors of carbonyl species (ketone) and alcohols.…”