Change of polymeric gel structure of several foamed plastic insulations deteriorated by moisture

Abstract

Foamed plastic insulations require long-term performance under sustainable development goals. However, in recent years, it has been reported that foamed plastic insulations installed in high-humidity environments, such as under waterproof sheets on a rooftop, absorb moisture and subsequently increase thermal conductivity.The study aims to estimate both moisture absorption and changes in physical properties of foamed plastic insulations after exposure to high humidity and discuss the moisture-induced deterioration based on the results of several experiments.We observe what changes occur in three types of foamed plastic insulation, phenolic foam, polyurethane foam, and extruded polystyrene foam, in a deterioration condition with moisture. In the first step, we verify that the moisture exists in what form and whether moisture condenses inside or blends with the material after deterioration occurs. Precisely, comparing weight changes before and after high-temperature humidity deterioration with two test results. One is changing a polymeric gel structure of the deteriorated insulation with X-ray CT, and another is the amount of adsorbed water vapor on the surface of each insulation with the gas adsorption method. Results from these studies refer that the deteriorated phenolic foam and moisture are assumingly miscible to transform polymeric gel structure.The second step compares how moisture deterioration affects insulation’s thermal characteristics. We evaluated in our previous study when insulations are exposed to the seasonal humidity cycle to apply typical seasonal fluctuation in Northeast Asian countries, affecting more critical damage than a persistent condition to samples. Therefore, we examine the relationship between thermal characteristics and moisture deterioration effect in humidity fluctuations. Resultantly, the phenolic foam’s polymeric gel structure is changed, and its thermal property is affected by humidity swings.The results provide a part of the moisture deterioration mechanism, miscible behavior between moisture and foamed plastic insulations to change polymeric gel structure, which shifts thermal properties.