Formulation and Characterization of Silane Modified Acrylic Based Transparent Organic-Inorganic Hybrid Coatings for Improved Instrumented Indentation Hardness of PMMA

Acrylic substrates made from polymethylmethacrylate (PMMA) are anticipated to develop craze and scratches owing to their continual wear. In this study, novel silane modified acrylic resin based organic-inorganic hybrid coating materials have been formulated to provide protection to PMMA substrates against wear. Varied amounts (5, 10 and 15 % wt./wt.) of tetraethoxysilane (TEOS) were added to the acrylic resin solution (containing xylene and 10% ammonia) and the resultant hybrid coating materials were then coated on PMMA substrates through the dip coating method. The hybrid coating materials were transformed into hard coats upon hydrolysis, condensation and cross-linking. The coated samples were characterized to assess the effect of TEOS addition on optical and mechanical properties as well as abrasion resistance of the hybrid coatings. Hardness, stiffness and reduced elastic modulus of the dry coatings obtained through the instrumented indentation technique were observed to increase (up to ca. 56%, 28% and 65% respectively) whereas their viscous nature and plasticity decreased with the addition of TEOS. The hybrid coatings also demonstrated improved wet abrasion resistance which augurs well with their physico-mechanical properties. These observations can be ascribed to the combined contributions of organic-inorganic phase interactions in the coating materials via hydrogen bonding and the formation of cross-linked silica structures as observed through infrared spectroscopy and microscopy.