Polymerization compounding of polyurethane-fumed silica composites

Polymerization Compounding (PC) offers the possibility to design composite materials by controlling the architecture of a grafted polymer on the surface of solid substrates to be incorporated in a polymer matrix. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or else as a special surface treatment to enhance solid/polymer interface properties in the composite. The PC process is illustrated here with fumed silica as a solid substrate and polyurethane as a matrix. The hydroxyl sites on silica particles were reacted consecutively with a toluene diisocyanate (TDI) compound and then with either bis-phenol-A (BA) or hydroxy-terminated polybutadiene (HTPB) in order to obtain the desired coating. Soxhlet extractions were conducted to confirm grafting of the polymer on the solid surface. The amount of grafted polymer was evaluated by thermogravimetric analysis. Modified particles were incorporated into HTPB/TDI compounds at concentrations as high as 25% w/w. Water absorption, thermorheological as well as mechanical properties all show clear contribution of the improved bonding between the solid phase and the binder.