ABSTRACT
References ....................................................................................................................................308
Some of the properties common to both polyether and polyester urethane rigid foams are:
1. The ability to be foamed-in-place by pouring or spraying 2. Versatility in obtaining a broad range of physical properties 3. Combination of high strength and light weight 4. Good heat-resistance properties 5. Excellent adhesion to metal, wood, glass, and ceramics
The equivalent weight of the polyol or combination of polyols has a considerable in¥uence on foam properties. In general, as the average equivalent weight of the polyol decreases from ≈300 to ≈100 or less, the resulting foam has
1. Higher compressive strength 2. Higher closed-cell content 3. Lower rate of water vapor permeability 4. Lower water absorption 5. Higher heat resistance 6. Lower rate of gas loss in solvent-blown systems 7. Greater tendency toward brittleness 8. Greater tendency to scorch 9. Higher cost per pound of foam
In addition, higher exotherms are developed with lower equivalent weight polyols in both the semi-prepolymer and one-shot methods of preparation.
