NATURAL RUBBER FROM ALTERNATIVE SOURCES. THE KEY ROLE OF LOW MOLECULAR MASS COMPONENTS

摘要

This work was focused on poly(l,4-cis-isoprene) from Ziegler-Natta catalysis and from different natural sources: Hevea Brasiliensis (HNR), Parthenium Argentatum (GR) and Taraxacum Kok-Saghyz (TKS). Chemical composition of poly(isoprene) samples and main polymer characteristics were determined. The following aspects were investigated: strain induced crystallization and reinforcement and behaviour in sulphur based crosslinking. The role of low molecular mass components of poly(isoprene) samples was investigated. It was found that NR samples amorphous at low strains generate highly oriented crystallites under stretching, because crystallization involves chains that are mostly oriented along the stretching direction. The presence of terpenes or unsaturated fatty acids seem to favour the amorphous nature at low strains of GR and TKS samples, respectively. The HNR sample, crystalline at rest, was not able to develop oriented crystallinity. Oriented crystalline phase led to the highest mechanical reinforcement, shown by TKS sample. GR showed the fastest vulcanization. Reaction of terpenes with sulphur based chemicals was demonstrated by performing the reaction between a thiol and a sesquiterpene such as Guayuline A. GR crosslinked samples revealed the lowest crosslinking density, with a large amount of short sulphur bridges, suggesting the effect of mobile hydrogen atoms on terpene molecules.