Polymer Science U.S.S.R. Vol. 31, No. 5, pp. 1007-1011, 1989 0032-3950/89 $10.00+.00 Prinled in Poland ~ 1990 Pergamon Press plc CHANGE IN THE PHYSICOMECHANICAL PROPERTIES OF POLYETHYLENE ON RADIATION AGEING* YE. V. BYSTRITSKAYA,YE. V. BYKOV, A. L. POMERANTSEV, O. N. KARPUrmIN and Y~. A. F~DOROVlCn Institute of Chemical Ph)sics, U.S.S.R. Academy of Sciences (Received 28 October 1987) The changes in the physicomechanical properties of LDPE are considered in the kinetic and diffusion regimes of radiation oxidation. In the kinetic regime fall in the instant modulus and strength at low doses is due to degradation of the macromolecules and at high doses to accumulation of oxygen-containing groups. In the diffusion regime strength is determined both by the size of the absorbed dose and depending on the dose rate by the ratio of the thicknesses of the internal crosslinked and external oxidized layers. In the heterogeneous sample the presence of a crosslinked layer does not lead to rise in the strength of the material as compared with that of the uniformly oxidized film. RADIATION ageing of PE in air is accompanied by change in its physicomechanical properties. Depending on the relation between the geometric dimensions of the sample and the dose rate p two fundamentally different situations appear [1, 2]. For the flat sample of thickness h on fulfilment of the condition h ,,/ 2Dco "~1[2 (~ is the thickness of the oxidized layer; D is the oxygen diffusion coefficient; co is the concentration of oxygen at the surface of the sample, a and b are coefficients deter- mined through the kinetic parameters of the radiation oxidation process [3, 4]) oxidation accompanied by degradation proceeds uniformly over the entire thickness of the sample. In thick samples h>2~ oxidative degradation occurs only in the surface layers to a depth ~ from each side and the internal layer to which oxygen does not penetrate be- cause of diffusion hindrances is subject to radiation crosslinking. The present work considers the patterns of change in the physicomechanical properties of PE in these two different cases. The experiment was conducted on LDPE of grade 107-01K (Mw ~ 2 x 105, degree of crystallinity ~ 50Yo) containing 0"lYo stabilizer di-fl-naphthyl-p-phenylene diamine. The samples in the form of films and plates 0.1 to 1-5 mm thick were pressed in air at 423 K and pressure 3.4 x 106 Pa and exposed to y-radiation from a 6°Co source in air and in vacuo. The dose rate was varied from 9 to 110 rad/sec. To measure the mechanical characteristics we cut out of the samples blades measuring 13 x 3"5 mm. * Vysokomol. soyed. A31: No. 5, 917-921, 1989. 1007 This article is protected by the copyright law. You may copy and distribute this article for your personal use only. Other uses are only allowed with written permission by the copyright holder.