Chemistry, polymer dynamics and mechanical properties of a two-part polyurethane elastomer during and after crosslinking. Part II: moist conditions

Abstract

This work addresses the impact of fabrication conditions (curing procedure, moisture) on the properties of a two-part polyurethane system. While Part I treats the chemical, dielectric and mechanical properties during cure and storage in dry conditions, this second part focuses on these properties, along with the caloric glass transition, in moist conditions, with moisture being introduced at different times during and right after cure. It is shown that the presence of water during fabrication severely affects final properties (increased polymer mobility, reduced mechanical stiffness) by reacting with isocyanate (forming primary amines and urea) and thereby lowering crosslink density, even for seemingly uncritical humidity conditions. Other chemical side reactions involving moisture are also identified. Water furthermore accelerates polymer dynamics substantially. Overall, moisture during cure and storage is clearly identified as a cause for property variations of PU.