Jitladda SakdapipanichYasuyuki TanakaJean Louis JacobJean D'AuzacMahidol UniversityTokyo University of Agriculture and TechnologyCIRAD Centre de Recherche de MontpellierUniversite de Montpellier2018-09-072018-09-071999-01-01Rubber Chemistry and Technology. Vol.72, No.2 (1999), 299-307003594752-s2.0-0004262747https://repository.li.mahidol.ac.th/handle/20.500.14594/25487The role of rubber in Hevea brasiliensis was analyzed based on the structural analysis of rubber in rubber trees as latex. The rubber obtained from a mature-tree which has never tapped before, so-called "virgin mature-tree" (Vir-NR), contained the gel fraction higher than 80%, while that from a regularly tapped mature-tree (Reg-NR) was less than 3%. The gel showed almost the same structure as a crosslinked rubber prepared from fresh latex in the presence of peroxide, with the molecular weight between crosslinks (MC) of 3 × 103. This value is extremely low comparing with that of 7 × 105observed for the soft-gel in rubber from high-ammonia latex and Pale crepe. The sol fraction from Vir-NR was an oxidative degraded product containing aldehyde and epoxide groups. Aging properties of Vir-NR are much worse than those of Reg-NR. This indicates that rubber accepts free-radicals to form C-C crosslinking and partly oxidative scission of main-chains during storage in laticiferous tubes of Hevea trees. This suggests that a possible role of rubber is a scavenger of free-radicals in latex, due to lack of the naturally occurring antioxidants. The consecutive tappings of latex from the first opening mature-tree resulted in the formation of rubber similar to that obtained from Reg-NR, after six days. This modification indicates that the new regulation mechanisms in latex biosynthesis, which is induced by exploitation, can avoid the rubber chain crosslinkings and increase their elongations.Mahidol UniversityMaterials ScienceArticleSCOPUS10.5254/1.3538802