Controlled interactions between silanol groups at the surface of sepiolite and an acrylate matrix: Consequences on the thermal and mechanical properties

Elastomer filled with fibrous clay (sepiolite) was manufactured using a hydrophilic elastomer matrix, poly 2-hydroxyethylacrylate (PHEA). The surface silanol groups located onto the channel sides of the sepiolite were functionalized with both octyltrimethoxysilane (OTMS) and 3-methacryloxypropyltrimethoxysilane (MPTMS), which form covalent bonds with the mineral surface and modify their properties. After the grafting of OTMS, PHEA is in contact with a non-polar chain, which prevents matrix–filler interactions. After the grafting of MPTMS, covalent bonds are formed between the acrylate groups of PHEA and MPTMS, which increase the matrix–filler interactions. After functionalization, there is no change in the structural and zeolitic water of the sepiolite which conserves its hydrophilic character. So, an equivalent distribution of the pristine and modified sepiolite is detected in the elastomeric matrices on transmission electron microscopy views of ultramicrotome cuts. The elastomeric macroscopic behavior is therefore related to the PHEA–sepiolite interactions. We show that the stronger the host–matrix interactions, the more important is the reinforcement effect. A direct relation between the interaction strength and the improvement of the mechanical properties was established. The control of the nature, quantity, and localization of the molecules grafted on the sepiolite surface allows us to manage the mechanical properties.