A methodological approach for monitoring the curing process of fairing compounds based on epoxy resins

Epoxy resins, heavily loaded with fillers, are used as fairing compounds in coating systems to fill superficial imperfections and protect the hull of yachts and ships; they are complex composite materials whose final performance can be heavily affected by the conditions of application. In this paper the curing process of an innovative formulation was studied in function of the temperature and humidity, in order to evaluate how these environmental parameters influence the reaction evolution and gain further insight into the reaction mechanism. The study of the curing process was carried out by thermogravimetric analysis, differential calorimetric analysis and FT-IR spectroscopy. From the thermal analysis the obtained crosslink degree ranged between 92 and 99%, at 10°C and 25°C respectively. The samples cured at 25°C reached the maximum curing degree in one week independently from the humidity. The samples cured at lower temperature (10°C), even after two weeks, did not reach the complete crosslinking. On the other side, it was evident that the humidity did not influence the curing at 25°C, while it had a slight effect at lower temperature (10°C). Results from FTIR spectroscopy at 25°C evidenced changes in the bands characterizing the two components of the resin during the curing reaction, in particular the disappearance of the oxirane ring band. 1. Introduction Within the production of the naval sector a very important role is played by coating systems for vessel external surfaces, which are most exposed to aggressive environments, such as seawater or marine atmosphere, and thermal variations. According to the SOLAS regulation (Safety of Life and Sea), the coating systems protecting the hull must guarantee a minimum duration of 15 years with minimal maintenance. Therefore it is evident the necessity of accurately formulating these materials in order to obtain long lasting performances. The coating system are typically composed of: primer (~100μm), fairing compound (~2cm), finishing fairing compound (~300μm), tie coat (~100μm), undercoat (~100μm) and topcoat (~50μm). Fairing compounds and putties are composite materials whose application is crucial for smoothing the surface, filling possible defects or voids and contributing to isolate the hulls. In particular the high thickness of fairing compounds is a critical aspect from the mechanical point of view. As a consequence, more and more often these composites