Study of the formulations and process conditions in the crosslinking of polyethylene foams at atmospheric pressure

The aim of this work is the study of the foaming process of a commercial polyethylene in the presence of a crosslinking agent. Foams have been produced under nearly atmospheric pressure conditions, which commonly occur during polymer rotomolding. Different processingtemperatures and different combinations of blowing agent/kicker (azodicarbonamide/zinc oxide) and crosslinking agent (dicumyl peroxide) concentrations have been employed. Thus, the melt viscosity, crosslinking degree, and temperature of the gas evolution and its rate have been changed to a certain degree. The obtained results have revealed that all these factors are critical to obtaining uniform and low‐density foams. Under certain processing temperatures and with an appropriate formulation, foam densities have been reduced up to 70% with respect to nonfoamed polymer. The interactions among the different components of the formulation have also been observed, and the results have led to the conclusion that in this kind of process, when a low pressure is applied, the foam density can be controlled by an adequate synchronization of the melt‐crosslinking, foaming, and gas‐expansion processes.