Influence on the cross-linking and plasticization degree of poly(ethylene-co-vinyl acetate) and evaluation of expansion capacity to the production of foams with supercritical CO 2

Abstract

The modification of a thermoplastic elastomer by cross-linking or plasticizing allows the manipulation of material properties for different applications. Cross-linking additives promote the increase of mechanical, thermal, and rheological properties, while the use of plasticizers has the opposite effect, giving the material soft properties. Such characteristics affect the development of polymeric foams directly, where the polymer matrix properties have large influence on the foaming capacity and morphology of the cells. This study investigated the use of cross-linking and plasticizer additives in ethylene-co-vinyl acetate copolymer, as well as its influence on the foaming capacity. The increasing content of cross-linking additive impacts on formation of preferentially closed cells, with high cell density and smaller size, while using plasticizers a higher occurrence of cell deformation and open cells was verified. The low formation of cells due to the decreasing of the polymer matrix thermal stability allows gases to escape during the processing and favors the cell coalescence effect. The foaming temperature is directly related to the polymer melt temperature, so, for the plasticizer-added samples, lower temperatures were required during the foaming than the samples with the cross-linking agent.