The Foaming Characteristics and Physical Properties of Natural Rubber Foams: Effects of Carbon Black Content and Foaming Pressure

Abstract

Natural rubber (NR) was foamed at different feeding ratios of carbon black and different foaming pressures. The cure characteristics were studied with respect to the carbon black content, and the effects of the foaming pressure and filler loading on the mechanical properties and morphologies of the foams were also investigated. With an increase of the filler loading, ML increased together with MH as a consequence of the initial rising viscosity and reinforcement resulting from carbon black. The values of ts2 and t90, however, increased with increasing carbon black content. The thickness of each of the struts formed inside the rubber matrix and the hardness both increased with increasing foaming pressure and carbon black content. The expansion ratio and micrographs of the foamed NRs supported the density characteristics. The tensile properties of the foamed NRs, such as their tensile strength, tear strength, and hardness, gradually increased with increased foaming pressure and carbon black content, while the elongation at break decreased.