Characterization of changes in structural, physicochemical and mechanical properties of rigid polyurethane building insulation after thermal aging in air and seawater

The purpose of this study was the identification of qualitative and quantitative changes in the visual appearance, chemical structure, morphology and selected physicochemical and mechanical properties of the closed cell rigid PU foam while heated in air and seawater for predicting its performance and durability. Specimens were aged at constant temperatures of 40 and 80 degrees C for a period of 10 weeks. Aging caused a yellowing of the samples. Scanning electron microscopy (SEM) revealed that foam pores lost their regularity. Differential scanning calorimetry (DSC) showed that the glass transition temperature (T-g) increased on average by 15 and 80%, respectively for samples heated at 40 and 80 degrees C. Water absorption (WS) also increased over time, respectively, by a maximum of 15 and 25%. The flexural strength (sigma(flex)) and compressive (sigma(comp)) strength showed a decreasing tendency, whereas for tensile strength (sigma(tens)), an increase was observed. The starting material was characterized by the sigma(flex), sigma(tens) and sigma(comp) of: 436, 413 and 284 kPa, respectively. The lowest determined sigma(flex) value was of 345 kPa, and sigma(comp) value was of 158 kPa. The highest determined sigma(tens) equaled to 608 kPa, respectively. The changes in flexural modulus were statistically insignificant and its average value was of 4.0 MPa.