AbstractThe oxidative degradation of cold drawn highly oriented high density polyethylene is studied by IR spectroscopy. Both gamma and ultraviolet radiation sources are used. It is found that under gamma radiation the oxidative degradation, as determined from carbonyl formation, is reduced very significantly but that the trans‐vinylene unsaturation in the polymer increases with draw ratio. Similar results are obtained for samples irradiated in vacuum or when the polymer is stabilized with a radical quencher. Annealing (with free‐ends) of the samples restores the rate of carbonyl formation over and above that of the undrawn polymer although restoration after annealing with fixed‐ends is not complete. There, is further increase in trans‐vinylene development after annealing. In stabilized samples, the effect of annealing on carbonyl and trans‐vinylene development appears to depend on draw ratio.Under ultra‐violet radiation, the oxidative degradation of drawn and unannealed samples is also reduced with increasing draw ratio. The same effect is observed in stabilized samples. Annealing, once again, restores the rate of oxidative degradation to that of the undrawn polymer. The main unsaturation product during ultraviolet irradiation is the vinyl end group and its development is suppressed with drawing. During ultraviolet irradiation of unannealed drawn samples, cracks, generally perpendicular to the draw direction (intrafibrillar cracks) appear on the sample and with further irradiation they penetrate into the sample. In the case of stabilized and unannealed drawn samples, cracks parallel to the draw direction (interfibrillar cracks) appear first and continued irradiation results in the appearance of intrafibrillar cracks. These observations may have significance in modelling the fibrous structures obtained by drawing semicrystalli