New frontiers for rubber: nanocomposites and renewable sources

The effect of non rubber components on the properties of rubber composites based on poly(1,4-cis-isoprene) and on the interaction of polymer chains with reinforcing fillers was investigated. Fatty acids, terpenes and ammonium cations were examined as the non rubber components. Carbon black and nanofillers such as clay minerals, carbon nanotubes and nano-graphite were considered as the reinforcing fillers. Fatty acids and terpenes are the by-products of poly(1,4-cis-isoprene) from natural sources, such as hevea brasiliensis, partenium argentatum, known as guayule and taraxacum kok-saghyz, the russian dandelion. The ammonium cations are the compatibilizers of clay minerals with polymer matrices. It is shown that fatty acids and terpenes act as plasticizers of poly(isoprene) chains, that remain amorphous at rest and form oriented crystallites under strain, developing the largest mechanical reinforcement, as in the case of TKS sample. Moreover, fatty acids are involved in the crystalline structure of organically modified clay minerals, as guest in the interlayer space. Such organoclays promote the immobilization of polymer chains, thanks to the higher volume fraction with respect to delaminated clays, without having intercalated polymer chains. In the case of composites based on carbon fillers, the polymer filler interfacial area was found able to account for the correlation between composite initial modulus and filler content: common master curve was defined for CNT and CB. However, low molecular mass chemicals, such as the ammonium cation and terpenes have preferential interaction with the carbon filler with respect to the polymer chains, remarkably enhancing the modulus at low strains. It is thus shown that by products in poly(1,4-cis-isoprene) from natural sources and modifiers of nanofillers provide great opportunities for developing new compounds properties and performances.