Conditions were sought for optimal modification of smectic (layered) aluminosilicates (LAS) with quaternary ammonium salts (QAS). The effect of structure of substituents at nitrogen atom in QAS on thixotropic properties of unsaturated polyester resin (UP) modified with LAS was studied. The results of these studies as well as the properties of thixotropic UP resins modified with bentonites treated with QAS are to be presented.

The properties of modified resins were measured at 25ºC with three types of rotary viscometers. Thixotropic properties of resins were evaluated by measuring the index of thixotropy as recommended by literature. A new alternative parameter measuring the thixotropic properties was also proposed and called the absolute thixotropy index. Compared with the previous methods of characterizing thixotropic properties, namely the thixotropy index, the new approach has the advantage of eliminating the arbitrary choice of shear rate and time of shear before moving to the next rate. The new index can also be related to the molecular interpretation of the phenomenon as a measure of energy of intermolecular interactions that are destroyed by shear force.

By taking into account the surface area of hysteresis loop, energy of intermolecular interactions, absolute thixotropy index (I_at) and classical thixotropy index (IT), the best set of composition and processing parameters were established for the structure of QAS modifying bentonites as thixotropic fillers. The best properties had the QAS with at least one benzyl substituent and an aliphatic group consisting of > 8 carbon atoms and having branched structure. The optimal content of filler in the UP compositions was ca. 2 wt.%

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