Current challenges in thermodynamic aspects of rubber foam

Natural rubber (NR) foam can be prepared by the Dunlop method using concentrated natural latex with chemical agents. Most previous studies have focused on the thermodynamic parameters of solid rubber in extension. The main objective of this study is to investigate the effect of the NR matrix concentration on the static and dynamic properties of NR foams, especially the new approach of considering the thermodynamic aspects of NR foam in compression. We found that the density and compression strength of NR foams increased with increasing NR matrix concentration. The mechanical properties of NR foam were in agreement with computational modelling. Moreover, thermodynamic aspects showed that the ratio of internal energy force to the compression force, F_u/F, and the entropy, S, increased with increasing matrix concentration. The activation enthalpy, ∆H_a, also increased with increasing matrix concentration in the NR foam, indicating the greater relaxation time of the backbone of the rubber molecules. New scientific concepts of thermodynamic parameters of the crosslinked NR foam in compression mode are proposed and discussed. Our results will improve both the knowledge and the development of rubber foams based on the structure-properties relationship, especially the new scientific concept of the thermodynamical parameters under compression.