Alternative sources of Natural Rubber: from latex to tyre. Influence of non rubber components on polyisoprene properties and final vulcanizates

In this PhD Thesis, research was performed on poly(1,4-cis-isoprene), from natural sources such as Hevea Brasiliensis (HNR), Parthenium Argentatum (GR), Taraxacum Kok-Saghyz (TKS) and from Ziegler-Natta catalysis. Study on isolation from latexes and purification of raw rubber samples led to the collection of non rubber components and to the preparation of purified rubber samples, GR-P from GR-R. Detailed characterization was performed. Poly(1,4-cis-isoprene)s from natural sources had high molecular mass, similar molecular mass distribution, very similar glass transition and high steric purity. In particular, stereoerrors were not detected in TKS. Proteins and fatty acids were in all the samples, with larger relative amount of the unsaturated ones in GR and TKS. Large amount of terpenes was identified in GR-R. All poly(isoprene)s underwent to thermo-oxidative degradation and antioxidants, aromatic amines phenols and amino oxide, have to be added. Delayed strain induced crystallization of TKS and GR samples led to the orientation of polymer chains and to the formation of oriented crystalline phase. Large mechanical reinforcement was obtained with TKS, that had only a low amount of by products. Poly(1,4-cis-isoprene)s from natural sources showed different behaviours in sulphur based vulcanization. Very fast vulcanization was obtained with GR-R and the reaction of terpenes with sulphur and sulphur based chemicals was demonstrated. Such reactivity led to minor sulphur addition to the polymer chains, with consequent lower density of the crosslinking network. Composites were prepared with carbon allotropes, both nano and nano-structured. For CB and CNT as the carbon allotropes in poly(isoprene) matrix, in the absence of non rubber components, common correlation was found, between the initial modulus of the composites and the specific interfacial area, with the construction of a sort of “master curve”. Layers stacked in nanosized graphite crystals prevented the interaction with the polymer chains and experimental points due to nanosized graphite did not lie on the “master curves”. Terpenes present in GR-R were able to substantially enhance the filler networking phenomenon, thanks to their preferential interaction, with respect to poly(isoprene) chains, with the carbon allotropes. CNT caused the enhancement of modulus at all the frequencies and the expansion of the rubbery plateau, for all poly(isoprene)s. Hysteresis of composites was correlated with values of friction coefficient. CNT gave extraordinary mechanical reinforcement, allowing to hypothesize its reaction with sulphur based vulcanization system. Key parameters of the vulcanization reactions such as the induction time and the activation energy were correlated with specific interfacial areas, for composites based on CB and CNT. Most results revealed the effect of non rubber components, that propose great opportunities for the development of innovative materials.