Chemical modification of Sepiolite for Rubber Composites With Improved Mechanical Properties

Rubber composites cover a huge number of applications, of great importance for the human life, and the most important is for tyre compounds. They cannot be replaced by any other type of materials and they achieve the physical mechanical properties required by their applications only thanks to reinforcing fillers. High aspect ratio nanofillers have a huge potentiality for improve the mechanical reinforcement of rubber composites. Their use is nowadays hampered by their labile interaction with the rubber matrix: better static mechanical reinforcement are obtained but with larger hysteresis. In this work, sepiolite was selected as high aspect ratio filler thanks to the high thermal and mechanical stability. Sepiolite is a clay mineral, naturally occurring, easily available, commercially available at low price. The disadvantage of sepiolite is the low surface reactivity with the polymer chain. To make up for such drawback, different kinds of chemical modifications of sepiolite are proposed in this work, aimed at improving the chemical reactivity between the filler and the rubber matrix. Sepiolite was treated with HCl or was reacted with silanes, tetraethyl orthosilicate and bis(3- triethoxysylilpropyl)disulfide, prior to feeding into the rubber composite. Silanes were condensed on sepiolite surface or in the frame of specific synthesis to prepare nanoparticles. In all the chemical treatment, the fibrillary structure of sepiolite was maintained. Chemically treated sepiolite was used in partial replacement of silica in composites based on diene rubbers. Chemically treated sepiolite gave rise to a noticeable improvement of mechanical properties and hysteresis was maintained at the same level or was even reduced, with respect to composites with only silica as the filler.