Durability of acrylic films from commercial aqueous dispersion: Glass transition temperature and tensile behavior as indexes of photooxidative degradation

The accelerated photo-ageing of dried films from two commercial acrylic dispersions, a BA/MMA and a EA/MMA formulation, potentially utilizable as protectives for stone surfaces, was followed by infrared spectroscopy and size exclusion chromatography, and the structural changes were correlated with the alteration of tensile mechanical properties and glass transition temperature. The copolymers underwent comparable molecular and structural changes that were related to the presence of acrylate units, more reactive towards oxidation and prone to chain-scissions, and of long side ester groups, which promote cross-linking reactions. Although such two main degradation-induced molecular changes did not globally affect glass transition in a significant extent, the progressive reduction of ultimate tensile strengths was directly related to the development of cross-linking. Thus suggesting that a rapid and efficient assessment of the degradative behavior of waterborne protectives, in terms of evaluation of their long-term properties, may be obtained from the monitoring of mechanical properties like stress-strain measurements, hereby considered as a suitable index of photooxidative deterioration. (C) 2010 Elsevier B.V. All rights reserved.