Robert B. Turner

High Resiliency Polyurea Foam-An Improved Flexible Foam Matrix

It is likely that the development of urea technology for flexible seating foam applications has been hindered simply by a perceived incompatibility between the rapid isocyanate-amine reaction and the traditional «long» gel time foam processing requirements. We will show that the amine-isocyanate reaction rate can be controlled, thereby making urea technology useful in flexible foam applications. Conventional processability evaluations on low pressure metering equipment have shown that amine terminated polyether resins can be used in place of conventional polyols in typical foam formulations without jeopardizing desirable processing parameters. In addition, nonpolymer polyol reinforced polyurea foam matrixes have hardness properties comparable to or better than conventional polymer polyol filled urethane foams

Volume Rise During Flexible Urethane Foaming

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...

An Integrated View of Reactive Urethane Foaming

R. D. Priester, Jr., and R. B. Turner Dow Chemical Co., Texas Division Reactive urethane foaming results from a complex combination of kinetic events: bubble growth, microphase separation and urethane polymerization. An understanding of the fundamental role that urea segregation plays on reaction kinetics and cell opening is the purpose of this work. Temperature and height rise profiles were measured for a series of slabstock formulations differing in the amount of water isocyanate and/or catalyst package. Our crosslinking model predicted that 83-90% of the available isocyanate groups must react before a network of covalent bonds could develop. Instead, as the amount of water and/or TDI was increased in the formulation, the experimental gel points decreased from 75-45% conversion of isocyanate. Still, foams were strong enough to withstand cell opening. The source of that strength appeared to be provided by urea phase separation. Independent infrared and rheological measurements confirmed that urea segregation takes place at about 60% conversion of isocyanate, significantly raising the modulus of the reacting mixture and triggering cell opening during foaming. Furthermore, a consistent trend was observed in our experiments: at 40-60% conversion of isocyanate, a sudden acceleration in the rate of reaction appeared just prior to foams reaching is proposed : as a phase separated morphology develops, isocyanate groups become trapped within rich urea-water domains. This results in a more efficient use of the available water and a sharp rise in the rate of reaction and cell opening during foaming. Addition of triethanolamine to 3.5 and 5.5 pphp water foams disrupted the cell opening mechanism by changing the balance between microphase separation and network polymerization during foaming.