The variation of degradation, as measured by change in percentage elongation with time, was evaluated at different temperatures for low density polyethylene-starch composite films containing varying amounts of manganese and iron as pro-oxidant. An equation for change of peroxy radicals with time was derived to reflect change of percentage elongation with time. This equation was then used in curve fitting results of percentage elongation of films and estimating oxidative degradation rates in the form of half lives of starch polymer composite films. This adaptation of the model by Guryanova appears to describe remarkably well the variation in elongation of polyethylene film with degradation, and may also be instrumental in linking variation of mechanical properties to chemical kinetics. The model was applied to experimental data and the curve parameters and half-lives derived appeared to vary in an Arrhenius fashion with temperature. The variation of the curve parameters with temperature in conjunction with the model equation describing percentage elongation with time were then used to derive an equation describing degradation with temperature and time for low density and linear low density polyethylene-starch composite films containing metal pro-oxidants.