Compatibilization of Rubber/EVA Compounds for Sole Applications

Due to market competitiveness, outsole industry has to improve itself. This challenge, combined with the risk of a failure in the market, strongly promotes the research of innovative polymeric materials or blends. TPU (ThermoPlasticUrethane)/PU (PolyUrethane) and rubber/PU are the most known example of polymeric blends used in soles for technical applications.1 In last years, EVA (Ethyl Vinyl Acetate) has gathered great attention due to its great resistance to UV light and ozone and to its density: the acetoxy content has a strong influence because on one hand the acetoxy functional group reduces the polyethylene crystallinity degree, on the other, the polymer assumes a more amorphous and rubber-like character as the acetoxy content increases.2,3 “Rubber” indicates a wide range of materials used in outsole factories for fashion and/or technical articles. Natural and synthetic rubbers are important due to their versatile characteristics: SBR, IR and BR have good physical and process properties, compatibility and they are generally economic; NBR, EPDM, CR (Chloroprene rubber) are used in particular outsole products that have special requirements.4 However, rubber and EVA don't have a high compatibility degree each other; in fact, the aim of this study is to find an appropriate formulation that ensembles the advantages of rubber (good physical-mechanical properties) and EVA having 18% acetate content (optimal chemical resistance). Density, abrasion and tear resistance, breaking strength and elongation are evaluated according to the ISO regulations. IR spectra and SEM images have also been recorded. In more than fifty years of activity, Delta Spa is deeply involved in research of innovative materials for outsole products. Delta Spa has become one of the most important reality in this field: staring from PU and rubber to EVA and TR soles, the outstanding quality made it an international leader in outsole market.