IRRADIATED POLYETHYLENE .4. FREE RADICAL DECAY

Free radical decay was measured in linear polyethylene over the temperature range of 50° to 125°C. The radicals were formed by β- and γ-ray irradiation and their concentrations determined by e.s.r. techniques. Decay rates were measured in nitrogen, air, oxygen, and vacuum environments. The decay reaction which takes place by radical recombination can be resolved into two parts, one more rapid than the other. The rapid reaction takes place in an amorphous region or in a metastable crystalline one which is formed during irradiation; the latter region can become amorphous following a melting-solidification excursion and is, therefore, latently amorphous. The kinetics for the rapid reaction is second order, but tends toward first order as the dose and temperature are increased. The decay-rate constant values are dependent on the total radical concentration and the amount of metastable material. The slow decay reaction takes place in the crystalline region. Its rate-constant values can be related to vinyl-group decay and to the metastable material content. The effects of dose and temperature on the activation energies indicate that these energies can also be correlated with the metastable material. Variations in reaction order for the rapid decay reaction are accounted for with the aid of relationships in which the second-order decay constant is dependent on the decay time and the diffusion coefficient. © 1969.