Development of the scratch resistance on acrylic sheet with basic colloidal silica (SiO2)—methyltrimethoxysilane (MTMS) nanocomposite films by sol–gel technique

The formation of scratch‐resistant coating film prepared from colloidal silica and a polysiloxane matrix was investigated. Methyltrimethoxysilane (MTMS) was hydrolysed and mixed with silica sol (SiO₂) at various compositions to form the hybrid hard‐coating nanocomposite film. The hydrolysed MTMS (polysiloxane) acts as the polymeric binder that is covalently linked to the colloidal silica surface and provides adhesion for the scratch resistant coating film to the substrate. The ratio between the polymeric matrix and the SiO₂ nanoparticles was found to play a major role in controlling the coating film appearance and its resistance to scratching. At a SiO₂ content < 30 wt.%, the agglomeration of the hydrolysed polysiloxane was observed and caused the opacity of the coating film. At a SiO₂ content >70 wt.%, there was not enough polysiloxane to act as a binder for the SiO₂, therefore a shrinkage upon solidification of the coating film caused cracking within the nanocomposite film. The optimum ratio was found to be at 40 wt.% ≤SiO₂ ≤60 wt.%, where the films had a transparent, crack free hard coating, with excellent scratch resistance, good adhesion and very good environmental resistance. The nanoindentation revealed that the nanocomposite film, at the optimum loading, possessed a higher strength with a higher SiO₂ loading. Film properties, including hardness, scratch resistance, adhesion and environmental resistance were also examined. The morphology of nanocomposite films was identified by atomic force microscopy (AFM) and scanning electron microscopy (SEM). © 2011 Canadian Society for Chemical Engineering