Flexible polyurethane foams prepolymer process

Basically, flexible polyurethane foams are formed from polyols and isocyanates. The polyols have hydroxyl functionalities of at least 2 if the foam is to be made by a prepolymer process and of 3 or more if the foam is to be made by a "oneshot" process. The prepolymer process proceeds in two distinct steps while in the one-shot process, all reactants are intensively mixed together at the begiiming of the foaming process. Early in the development of urethane foams, the polyols were polyester diols now, however, by far the largest volume of polyols for urethane foams are poly(propylene oxide) polyols or poly(propylene oxide) polyols containing up to 25... 

Polyurethane foams may be rigid, semi-rigid or flexible. They may be made from polyesters, polyethers or natural polyols such as castor oil (which contains approximately three hydroxyl groups in each molecule). Three general processes are available known as one-shot, prepolymer or quasi-prepolymer processes. These variations lead to 27 basic types of product or process, all of which have been used commercially. This section deals only with flexible foams (which are made only from polyesters and polyethers). Since prepolymers and... 

Special rules apply to the world of hydrophilic polyurethanes. These alternate rules are based on the fact that hydrophilic polyurethanes can and should be processed in water. Rather than emulsifying a prepolymer with a polyol, as would be done with a hydrophobic polyurethane, hydrophilics are mixed with water. While the properties of the foam are governed loosely by the guidelines described above, one has more flexibility and control of the formulation and process by which the polyurethane is made. For example, the water can serve as a heat sink to closely control the temperature of the foam the water controls the rate of reaction. 

Reaction-Injection Moiding System Liquid compositions, mostly polyurethane-based, of thermosetting resins, prepolymers, monomers, or their mixtures. Has good processibility, dimensional stability, and flexibility. Processed by foam molding with in-mold curing at high temperatures. Used in auto parts and office furniture. Also called RIM. 

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