Experimental assessment of the effectiveness of hydrophobic UV-cured coatings in protecting glass surfaces against stress corrosion

The stress corrosion is the phenomenon of decrease of the tensile strength over time, when annealed glass is subjected to a long-term tensile load. As the strength of glass is controlled by the size of superficial flaws, the stress corrosion is related to the sub-critical growth of cracks during aging in the given environment, under load. The classical theory to account for this phenomenology involves the chemical reaction of water molecules with silica, taking place at the tip of the cracks. Such a reaction replaces strong chemical bonds with weaker ones, thus leading to sub-critical crack growth. The stress corrosion put a strong limit to the exploitable tensile strength of annealed glass and it does not allow the application of high long-term loads. In the present work, a number of hydrophobic polymeric coatings, produced with the UV-curing technology, is applied to the surface of glass specimens, to constitute a barrier between humidity and glass surface, thus preventing the chemical reaction at the base of the stress corrosion. Innovative formulations are used to produce polymers with graded properties, in order to maximize adhesion on the side in contact with the glass surface and the hydrophobicity on the side exposed to the environment. Their effectiveness in protecting glass surfaces is assessed experimentally, in term of load-carrying capacity of glass coated plates tested under biaxial bending with a coaxial double ring setup