Effect of blowing agent type and blowing agent loading levels on mechanical and cell morphological properties of dry natural rubber cellular compounds

Cellular rubber is important in various industrial applications, due to its unique structural properties, such as its low density, cushioning performance, thermal and acoustic insulator properties and moderate energy absorption. In this study, the influence of blowing agent type and blowing agent loading levels on mechanical and morphological properties of cellular natural rubber were investigated. Three types of blowing agents namely NaHCO3, DNPT and isopropanol were used. The cellular rubber compounds were prepared using a conventional compression molding technique via a heat transfer foaming process. The mechanical properties were evaluated according to ASTM standards and the results yielded were observed to systematically correlate with the morphology of cellular compounds. Uneven morphology was observed in the compounds with 10 phr for all three blowing agents owing to high gas content in the rubber matrix. Overall, most of the properties of the cellular rubber compounds gradually decreased upon increasing the blowing agent loading levels in terms of mechanical properties, relative density, water absorption and crosslink density. In addition, isopropanol incorporated compound had the lowest compression set properties.