Sustainable materials for tyres. 2. High aspect ratio natural fillers for rubber compounds with low dissipation of energy

High compatibility of high aspect ratio nanometric filler with an elastomeric composite was achieved in this research using the chemical modification of the nanometric filler. Rubbers cannot be used for any relevant application, even after crosslinking. Reinforcing fillers are required to achieve the required mechanical properties. Carbon black and silica are the traditional reinforcing fillers, largely used for rubber compounds for tyre applications. Increasing research efforts are for reinforcing fillers with nanosize, high aspect ratio and thus high surface area. The research here reported was focused on a nanometric high aspect ratio filler, naturally occurring. Low cost clay mineral, easily available and with fibrillar structure, such as sepiolite Pangel S9, was selected as nanofiller. The research was aimed at improving the compatibility of sepiolite with the rubber matrix. To achieve this goal, sepiolite Pangel S9 was treated with tetraethyl orthosilicate in the presence of basic catalyst obtaining amorphous nanosilica onto the surface of the filler. Sepiolite was also treated with HCl, removing different amounts of magnesium and obtaining a larger reactivity with the silane (triethoxy(n-octyl)silane) preserving the original fibrillar structure of sepiolite, used for promoting the chemical bond with the unsaturated rubber chains, through vulcanization. Both modified sepiolites were used in NR based composites replacing a partial part of silica. With such chemically modified sepiolite, better dynamic-mechanical and static reinforcement were obtained for rubber composites based on diene rubbers such as natural rubber and poly(1,4-cis-butadiene) and silica as the main filler. Chemical modification and characterization of sepiolite, preparation and properties of rubber compounds are presented.