Use of calorimetric technique for studying radiation-chemical reactions in polyethylene

The kinetics of radiation-induced chemical processes in LDPE was studied by means of an adiabatic calorimeter, which allows the heat capacity of polymers to be measured in the course of gamma-irradiation. It was found that irradiation of virgin LDPE samples with a dose of 16 kGy was accompanied by an exothermic effect exceeding 1600 J/kg but led to an endothermic effect in the case of samples preirradiated with doses above 30 kGy. As is shown, the most likely explanations for the observed heat evolution is the reaction of disappearance of vinyl and vinylidene double bonds in the polymer. The rate of this reaction as found by calorimetric measurements is compared with data obtained by other methods.