Addition of unmodified nanoclay to improve the performance of unsaturated polyester resin coating on natural stone

In this study, an unsaturated polyester resin (UPR) thin coating containing styrene monomer has been used to consolidate Brown Emperor natural stone pieces. Different amounts (0.5-2 wt%) of nanoclay was added to reduce shrinkage during cure and to impart both stiffness and toughness. The uncured UPR-nanoclay hybrids were characterized by rotational rheology, the gelation was monitored by means of a texture analyzer and the viscoelastic and thermal properties were determined in the cured UPR-nanoclay films. Transmission electron microscopy (TEM) was used to establish the degree of dispersion of the nanoclay in the UPR-nanoclay composites. The mechanical performance of the UPR-nanoclay thin coated natural stone pieces was measured by means of 3-points bending and impact strength tests.Addition of nanoclay (0.5 and 1 wt%) increased noticeably the viscosity to the UPR resin. The gel time of the UPR resin was significantly decreased by adding small amounts of nanoclay due to the interactions between the filler and the styrene in the UPR resin. Moreover, addition of nanoclay decreased the shrinkage degree during curing of UPR resin. In the cured composites, improved thermal properties in UPR were reached by adding nanoclay due to the creation of a network between the filler and the polymer matrix. Bundle nanometric size nanoclay agglomerates were observed which did not affect the glass transition temperature but increased the viscoelasticity of the UPR-nanoclay composites. Furthermore, the improved properties of UPR by adding nanoclay produced enhanced impact strength to coated natural stone pieces, as both stiffness and toughness were improved by nanoclay addition. Finally, good adhesion of nanoclay filled UPR to the surface of natural stone was reached.