STIMULI-RESPONSE FILM FORMATION IN WATERBORNE TWO-COMPONENT POLYURETHANE SYSTEMS (WB 2K-PUR); MECHANISMS LEADING TO SURFACE MORPHOLOGY EVOLUTION

摘要

Although it is well established that the presence of water may significantly alter polyurethane film formation leading to polyurethane/polyurea (PUR/PUA) compositional gradients, the effect of water on molecular surface partitioning, defined as the preferential shifting of individual components between phases, leading to specific morphological features has not been addressed in waterborne two component polyurethanes (WB 2K-PUR). This study focuses on qualitative and quantitative aspects of partitioning phenomena driven by physical and chemical processes during film formation. Internal reflection infrared imaging (IRIRI) measurements show the presence of crosslinker-rich, evenly distributed hydrophobic microdomains at the film-air (FA) interface for films crosslinked at high humidities. Increased crosslinking temperature over the range of 20 to 40°Cresults in larger microphase separated domains and greater extents of dewetting behavior due to enhanced mobility of individual components. A film formation model is proposed which incorporates the rate losses of water and neutralizing agents on microphase separation and evolution of surface topographical features in WB 2K-PUR. These studies also show that polyols containing neutralized acid groups exist in a metastable thermodynamic state at the intermediate stages of film formation, and that enhanced polyol mobility due to hydroplasticization and elevated temperatures facilitate dynamics for microphase separation.