Role of physical polymer-filler interactions in network formation and compression set of silicone elastomers

Understanding the physical and chemical processes between filler and the polysiloxane network allows tuning the elastomer properties by the right choice of the silica character. In this work, compression set (CS) and cross-link density (CLD) of silicone elastomers were controlled by non-covalent interactions between silica filler and polymer. The physical interactions were tuned by the accessible surface area and silanol surface groups of the silica. For hydrophilic silica with silanol groups at the surface, a close relation between CS and physical CLD was found. The physical CLD was assigned to pronounced polymer-filler interactions which induced adsorption of the silicone chains on the silica surface. This inhibited chain mobility leading to a rise of the CS with increasing physical CLD. The addition of silicone oil or hydrophobization of the silica lowered the non-covalent polymer-filler interactions and decreased the compression set of the silicone elastomer. Especially low surface area hydrophobic fumed silica yielded an exceptionally reduced compression set within the studied series of silicone compounds. The results provide an understanding of the role of non-covalent interactions on network formation and compression set of silicone elastomers.