The effect of high-energy radiation on n-alkanes and polyethylene (PE) are reviewed. The article includes a description of (a) primary radiation events, formation, spatial distribution and decay of free radicals and radical migration mechanisms, (b) formation of cross-links and other stable products, (c) the effects of crystallinity, crystalline modifications and morphology on radiation cross-linking, and (d) radiation-induced changes in the crystal lattice and the destruction of crystallinity at high irradiation doses. An attempt is made to bring together conflicting views on various unsolved problems of the radiation physics and chemistry of these important and much studied substances. Long-chain paraffins are given considerable attention since their radiation behaviour often provides a link between that of PE and its short-chain analogues.

Radiation effects in polyethylene and n-alkanes

Polycaprolactone (PCL) crosslinked below the gel point either with peroxide or by exposure to ionizing radiation was compared by Theological studies. As a result of peroxide crosslinking, PCL increases in viscosity and shear rate dependence and exhibits increased dynamic moduli that converge at higher frequencies. The analysis of gases evolved from γ-irradiated PCL shows that the yield of hydrogen (G = 0.39) approximates the sum of the yields of carbon monoxide (G = 0.19) and carbon dioxide (G = 0.21). It is inferred that equal amounts of crosslinking and scission result from ionizing irradiation. As a result, PCL is converted by irradiation to a densely branched system. Steady shear viscosities do not depend strongly on dose and overlap at higher shear rates. Similarly, dynamic moduli, especially G″, become less sensitive to dose.

Katsuhiko Hamanaka

Papers

ESR studies of n-alkane diols irradiated by γ-rays; Identification of radicals and mechanism of radical migration