Electron Beam Irradiation of Noncrosslinked LDPE–EVA Foam

The conventional cross-linking method using an electron beam for polyolefin foams is highly efficient, but the drawbacks are: costly equipment, nonuniform crosslinking, uneven dispersion of chemical foaming agents and additives, and relatively low gel content, which affect physical properties of the foam. In this paper, low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) were blended in an 80/20 ratio, and this noncrosslinked foam was exposed to various doses of electron beam irradiation in air. The foam was made using isobutane as the blowing agent. It has been found that foam with uniform cell structure was not achieved in the case of precrosslinked foam with more than 40% gel fraction. On the other hand, noncrosslinked foams are easily crosslinked to a gel content of about 57% with an electron beam irradiation under optimum conditions. The gel content of the postcrosslinked foams increases with increase in the irradiation dose, beam intensity, irradiation temperature and with the crosslinking coagent content. As derived from experimental studies, beam intensity seems to be the most essential parameter in regard to gel content homogeneity. Noticeable changes in mechanical properties, e.g. tensile strength, tear strength, compressive strength and hardness, were also observed. This paper also presents an experimental study on the manufacture of low-density open-cell foam.