Role of gel content on the structural changes of masticated natural rubber

In this study, natural rubber (NR) containing various amounts of gel was prepared by accelerated storage hardening to investigate the role of gel content on the structural changes of masticated NR. The NR samples containing various amounts of gel were subjected to mastication at various times, and subsequently characterized for the change of gel content, molecular weight, and Mooney viscosity to evaluate the role of gel content on these parameters. Furthermore, an oscillatory shear experiment using a strain sweep test was applied in this study to elucidate the structural changes of rubber samples after mastication. The results revealed that the Mooney viscosity was related to the percentage of gel fraction that has been proven to be the result of the interactions of proteins and phospholipids at the chain ends. The gel fraction of NR can be decomposed into a sol fraction by shear force during mastication and the mastication time for decomposition of gel relates to the initial gel content of the rubber. After mastication for 15 min, although the gel fraction of NR can be decomposed to 0% w/w, the interactions of proteins and phospholipids at the chain ends still existed, and their quantities is corresponded to the gel content of raw rubber.