Thixotropic compositions: unsaturated polyester resins/modified bentonites

Nearly 40 quaternary ammonium chlorides were tested as modifiers of a bentonite (smectic clay). The modified bentonite was used as thixotropic agent for a general purpose unsaturated polyester resin. The modification changed the thermal characteristic of bentonites (DSC) and led to increased distance between layers in bentonite grains (X-ray diffraction). The structure of ammonium salt, namely the kind and size of substituents, had a significant effect on thixotropic properties of unsaturated resin compositions. The thixotropic properties were measured by recording viscosity hysteresis by rotary rheometer and evaluating the absolute and standard thixotropic indices. From the point of view of thixotropic properties of unsaturated polyester compositions, the best quaternary ammonium salt modifier had one benzyl and one slightly branched aliphatic hydrocarbon substituent.