Abstract
ABSTRACTDuring the formation of flexible urethane foams, isocyanate and water react to form urea dimers and oligomers which eventually segregate as a microdisperse solid phase. The role that urea segregation plays on reaction kinetics and flowability during foaming is examined in this work. Temperature and volume rise profiles were measured for a series of foam systems by varying the amount of water (2-6 pphp), isocyanate (90, 110, 130 index), and amine or tin catalysts in the formulation. Model calculations showed that 84-90% conversion of isocyanate (NCO) groups was required to form a crosslinked polymer network. However, volume rise was found to stop at 40-70% NCO conversion. This indicates that gelation is due to phase separation rather than covalent crosslinking. A sudden acceleration in the rate of reaction (dT/dt), detected before foams reached a constant volume, is thought to indicate microphase separation during foaming. A mechanism is presented to correlate temperature and volume rise profiles w...
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