Improvement in mechanical and structural integrity of natural stone by applying unsaturated polyester resin-nanosilica hybrid thin coating

In this study, an unsaturated polyester resin (UPR) thin coating containing styrene monomer has been used to consolidate Marrón emperador marble pieces. Different amounts (0.5–3 wt.%) of nanosilica was added to improve several properties, particularly the mechanical properties. The uncured UPR-nanosilica hybrids were characterized by rotational rheology, the gelation was monitored by means of a texture analyser and the viscoelastic and thermal properties were determined in the cured UPR-nanosilica films. Transmission electron microscopy (TEM) was used to establish the degree of dispersion of the nanosilica in the UPR-nanosilica composites. The mechanical performance of the UPR-nanosilica thin coated marble pieces was measured by means of 3-points bending and impact strength tests. Addition of nanosilica imparted pseudoplasticity and thixotropy to the UPR resin and an increase in viscosity was also produced. The rheology of the UPR-nanosilica solutions was fitted to the Casson’s model and an increase in yield stress was obtained. The gel time of the UPR resin was significantly decreased by adding small amounts of nanosilica due to the interactions between the filler and the styrene in the UPR resin. In the cured composites, improved thermal properties in UPR were reached by adding nanosilica due to the creation of a network between the filler and the polymer matrix. Bundle nanometric size nanosilica agglomerates were observed which affected the glass transition temperature and the viscoelasticity of the UPR-nanosilica composites. Finally, the improved properties in UPR obtained by adding nanosilica produced enhanced impact resistance to coated marble pieces, as both stiffness and toughness were improved by nanosilica addition.