Environmental effects on epoxy adhesives employed for restoration of historical buildings

Fiber reinforced composites based on epoxy resins are used in the restoration of historical buildings, for example in the restoration of the Basilica di S. Francesco (Assisi, Italy). In the study presented, the epoxy resin that served as matrix in the composite, was analyzed, focusing the attention on the factors that could affect its durability in service. The characteristics of the epoxy resin during cure were first evaluated. Thermal, chemical and mechanical properties were, then, measured on samples exposed, after curing, to levels of humidity, temperature and water above the ordinary values. The comparison between the properties of the cured resin calculated before and after the treatment, provided information on the effects of different environmental conditions. It was found that the thermal treatments yield a post-curing process, leading to an increase in glass transition temperature and a strengthening of the system; the exposition to moisture or water gives rise to a reduction in Tg, while it does not affect considerably the mechanical properties of the resin; finally, the effects of thermohygrometric treatments are more complex