Evaluation of different expansion processes for poly(ethylene-co-vinyl acetate) foam-reinforced with micronized graphite

Poly(ethylene-co-vinyl acetate) is used in numerous industries due to its versatility and increasing development of reinforced foams with a variety of fillers as well as the method of expansion, impacting the properties of foams. By varying the type and content of the incorporated filler as well as the expansion method, it is possible to obtain different cell morphologies even with low filler content in the polymer matrix. On this basis, this study reports the development of EVA foams reinforced with small amounts of micronized graphite and expanded by two expansion methods, namely thermocompression with chemical blowing agents (CBA) and expansion in an autoclave with CO₂ in supercritical state as physical blowing agent (PBA). The main results show that the presence of a small amount of graphite reduces the density of foam, significantly increases the size of cells, and consequently, reduces the number of cells per unit area. The CBA foams had a lower density than PBA foams; however, the PBA foams exhibited a more homogeneous morphological structure. (author)