Water-blown foam

Semiflexible molded polyurethane foams are used in other automotive appHcations, such as instmment panels, dashboards, arm rests, head rests, door liners, and vibrational control devices. An important property of semiflexible foam is low resiHency and low elasticity, which results in a slow rate of recovery after deflection. The isocyanate used in the manufacture of semiflexible foams is PMDI, sometimes used in combination with TDI or TDI prepolymers. Both polyester as well as polyether polyols are used in the production of these water-blown foams. Sometimes integral skin molded foams are produced. 

Whether the one-shot process or prepolymer technique is used, the development of a foam involves the juxtaposition of gas generation and the development of tensile strength within the developing foam. The evolution of gas can be via the use of blowing agents or the in situ generation of CO2 from the reaction of water with an isocyanate to produce a water-blown foam. In any case, the gas evolution creates an internal pressure that must be resisted by the development of a gel structure via polymerization reactions as shown in Figure 3.13. 

For flexible foams in which CFC s have typically been employed as auxiliary blowing agents, entirely water-blown foams can be achieved with the performance additives. 

In recent years, the ban on the use of CFCs resulted in major changes in foam formulations. A number of studies were carried out on the use of 100% water-blown foams for both rigid and flexible foams. These studies required modifications or improvements in raw materials, e.g., polyisocyanates, polyols, catalysts and surfactants. 

C02 blown foam - A polyurethane foam in which all of the gas from expanding or blowing is carbon dioxide (CO2) generated by the chemical reaction between water and isocyanates also called water-blown foam (3). cold-cure foam - See Cold molding. 

The continuous evolution of carbon dioxide from water-blown foam from the earliest times of reaction is a mechanism for significant heat loss from free-rise foam, the magnitude of which will depend on the scale of foaming. This observation offers an explanation for the departure from adiabaticity, lower than expected maximum reaction temperature, in smaller scale foaming. 

With the use of ABA, both the available densities and the available foam hardnesses were lowered in comparison to the purely water blown foams, as in these cases gas volume was produced without generation of urea. Softening of foam was also achieved chemically, either with the use of an additive to change the urea morphology [13] or with the use of crosslinkers in combination with a low isocyanate index [14]. 

One of the early consequences of not using CFCs has been some scorching and discoloration in fire-retarded water-blown foams, because of the exothermic isocyanate hydrolysis reaction (CFC blowing agents tended to act as heat removers). It has been suggested that the scorch process is accentuated by certain flame retardants. 

It is useful for the preparation of flame-retardant flexible or rigid polyurethane foams. In the foam applications, where it is often used as a blend with a triaryl phosphate such as in SAYTEX RB 7980 (higher hydroxyl number) or RX 8500 (lower hydroxyl number). Its advantage is that it allows flexible polyurethane foam to reach high temperatures in the water-blown foaming step without scorch (thermal damage). 

Flame retardancy in various polymers has been discussed both in general terms [77] and for particular types of polymers including polyvinyl chloride (PVC) [78], polystyrene foam [79], unsaturated polyester resins [80, 81], polyisocyanurate-polyurethane (PU) water-blown foams [82], ethylene-vinyl acetate copolymers [83], and plastic and rubber cables [84]. 

In a simple foam formulation for a water-blown foam of polyol, diisocyanate, water, silicone surfactant, and tertiary-amine and stannous octoate catalyst, the first reaction to occur is water with isocyanate to liberate carbon dioxide, which nucleates to form gas cells and begins foam expansion. This reaction of water with isocyanate is the most energetic reaction that will occur, and it has about twice the heat of rection of either amine with isocyanate or hydroxyl with isocyanate. 

Types of extruders manufactured by Berstorff for the processing of thermoplastic elastomers are reviewed. These include extmsion compounding lines and machineiy for the extmsion and coextrusion of water blown foam profiles. 

Uses Surfactant for MDI-based molded polyurethane foam systems, providing efficient cell opening and bulk stabilization in all-water-blown foams nonhydrolyzable Properties Cl. to straw low-vise, liq. insol. in water sp.gr. 0.9658 (21 C) vise. 28.9 cps vapor pressure 7.6 mm Hg (21 C) f p. -65 C b.p. > 149 C hyd. no. 226 flash pt. (CC) 113 C... 

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