Flexible and rigid foams are used in a variety of applications including seat cushions, rigid plastic furniture, void fillers in walls, and insulation on pipes, and generally in the furniture, bedding, and vehicle industries to name but a few examples. Flexible foam, in particular, is often used as an insulative material to prevent the rapid spread of fire. Traditionally, flexible foams have been made from polyurethanes which can be flammable and may readily smoke when exposed to high temperatures and fire. In response polyurethane foams have been formed that are at least partially fire retardant and heat resistant, with the polyurethane foams made fire retardant by including a fire retardant constituent during formation of the polyurethane foam. Polyurethane foams can generally be made fire resistant by adding one of the following types of fire retardant constituents, a non-reactive liquid, an isocyanate-reactive additive, or a filler. Flexible and rigid foams spiked with various additive or filler fire retardants are often used as insulative materials to prevent the spread of small flames for a short time duration. Unfortunately, most polyurethane foams that include fire retardant fillers are known to melt and shrink and will not provide a long term thermal and fire protective insulative char necessary for a long duration of protection in hostile environments of heat and fire.
A variety of fire retardant constituents can be used in polyurethane foams, however, the fire retardants typically used in foams, and especially polyurethane foams, are either an additive type filler or a reactive type fire retardant, such as the isocyanate-reactive additive. Additive loaded fire retardants are fillers and do not become a part of the backbone or molecular structure of the foam and are instead held by the structure of the foam as a filler composition, meaning the filler fire retardants are not bound in the polymer network of the foam. Neither the additive or reactive type fire retardants are ablative and therefore are not considered to be effective insulators for use in a hyperthermal environment. Furthermore, the additively loaded fire retardant foams suffer from friability and leaching of the additives because they are not part of the backbone of the molecules used to form the foam and are instead held by the structures of the foam as a filler composition. In order to increase the fire retardancy of the foam, typically more filler fire retardants are added to the foam; however, as the amount of filler increases the physical and mechanical properties of the foam suffer. What this means is that to increase fire retardancy physical and mechanical properties must often be sacrificed. Thus, it is desired to have a foam which includes a fire retardant that is not a filler, but which instead has the fire retardant incorporated into the molecular structure or backbone of the foam so that the fire retardant is part of the polymer network. It is also preferred if the fire retardant not only imparts fire retardancy capabilities, but that it does not negatively effect the physical and mechanical properties of the foam. Importantly, it is desired to have a foam that possesses good fire retardancy or resistance and is relatively lightweight.
Reactive fire retardants have been used in some polyurethane foams, however, foams made from the reactive fire retardants are generally not water activated and are not ablative because they lack highly stable oxidative materials. Also, the reactive additives tend to adversely effect the viscosity of the prepolymers so that chlorofluorocarbon compounds (CFC) are typically used to foam a prepolymer. In fact nearly all commercial foams are blown by CFCs. This means that the prepolymer is undesireable to use because CFCs can be illegal to use in certain concentrations and are environmentally hazardous compounds. The impact of CFC regulations will have an impact on reactive fire retardant technologies used in the future, as CFC regulations may limit the amount of CFC available to be used. Such regulations may cause quality problems for the fire retardant foams formed with CFC. Because of CFC regulations, in some foam water is used as a partial replacement for the CFCs. Unfortunately, the water causes higher exotherms during the flexible foam formation. Because of the higher exotherm the foams have a tendency to scorch, with the scorching of the foam caused by degradation of fire retardants found in the foam prepolymer. Therefore the foam is scorched because typically the water has reacted with the reactive fire retardants to degrade the fire retardants and scorch the foam.
Many fire retardant foams use a chlorofluorocarbon (CFC) to foam the constituents and to form the finished polyurethane foam. The use of a CFC, as mentioned, is undesirable because it is environmentally unfriendly, as it is well known that CFCs are damaging to the ozone layer. As such, it is generally undesirable to form polyurethane foams which use CFCs in the foaming process. Consequently, it is desired to have a process which excludes the use of CFCs in forming polyurethane foams.
Isocyanate-reactive additives can be particularly useful in polyurethane and polyurea foams because the isocyanate-reactive additives become bound in the polymer network. Typically, the isocyanate-reactive fire retardant will cause the foam to char thereby inhibiting the spread of fire and the transmission of heat. But, the char is insufficient as the isocynate-reactive fire retardants do not form a sufficient char suitable for long term fire protection. While isocyanate-reactive foams are fire retardant, the fire retardant capabilities of such foams could still be improved and in general it is desired to improve the fire retardant capabilities of polyurethane and polyurea foams, as the polyurethane foams are known to burn and smoke despite the inclusion of fire retardants.
Incorporation of a fire retardant into a polyurethane or polyurea foam imparts at least some fire retardancy to the foam. However, for certain uses a foam that is highly fire retardant is required. Most polyurethane foams when exposed to sustained flames and heat will, after a time, breakdown and allow the continued dissipation of the fire and transmission of heat. It is desired to have a foam that does not lose significant mass as a result of sustained exposure to heat and flames and that does not allow the transmission of significant amounts of heat. Specifically, it is desired if the foam sustains integrity at a heat flux of 75 kW/m.sup.2 for 20 minutes or longer and that allows heat equal to less than 250 kJ to evolve. It is also desired if the foam does not allow significant amounts of CO.sub.2 and CO to be released. Preferably, less than 0.025 kg/kg of CO and 0.60 kg/kg of CO.sub.2 will be released from the foam. As such, it is desired to have a flexible foam which when exposed to intense fire and heat retains most of its mass and does not allow for the transmission of significant amounts of heat.
Another problem associated with many polyurethanes or polyureas is that when the polyurethanes are formed hazardous fumes are often produced as a result of the reaction forming the polyurethane foam. Most prepolymers for forming a polyurethane foam have large amounts of unreacted N.dbd.C.dbd.O, typically close to 100% free N.dbd.C.dbd.O. Also, while the foam is being made some free N.dbd.C.dbd.O is released, so that when the foam is formed the free N.dbd.C.dbd.O is released into the atmosphere causing the production of hazardous fumes. Obviously, the production of toxins is environmentally unfriendly and is an undesired result associated with foam formation. It is desired to have a foam that when produced does not result in the formation of toxic fumes. More particularly, it is desired to have a prepolymer that has very little free N.dbd.C.dbd.O and it is desired to have a prepolymer that does not release significant amounts of N.dbd.C.dbd.O into the atmosphere during foam formation. It is also preferred that the foam is hydrophilic so that it can be catalyzed by an aqueous solution.
Ablative foams have been described, for example, in Liu U.S. Pat. No. 5,151,216, wherein the ablative foam is a low density foam. While an ablative foam capable of dissipating heat is described, it is not a water blown foam and the patent does not describe a carborane disilanol fire retardant incorporated into the molecular backbone or polymer network of the foam. Also, the patent does not teach forming a prepolymer and a synthesis does not occur. It is desired to have an ablative foam that is water blown and that can include a carborane disilanol fire retardant because water blown foams are environmentally friendly and a carborane disilanol in the molecular backbone imparts excellent fire resistance.
Polyurea foams which result from reacting a prepolymer with an amount of aqueous solution are known. These foams, however, typically have a filler fire retardant incorporated therein, with the filler added when the prepolymer is reacted with the aqueous solution. As such, the filler does not become part of the molecular backbone of the foam molecule. It is desired to have a polyurea foam which has a highly engineered molecular structure whereby the fire retardant is part of the molecular backbone of the finished polymeric foam.
An example of a polyurethane foam composition which does not have a fire retardant in the molecular backbone was disclosed in both Murch et al. U.S. Pat. No. 4,230,822 and Murch et al. U.S. Pat. No. 4,066,578. In both patents a prepolymer was made which included a hydrophilic polyoxyalkylene diol and a polyol having a hydroxyl functionality greater than 2, with the mixture capped by an isocyanate. The prepolymer was then reacted with an excess of water and a slurry containing a flame retardant such as alumina trihydrate or a phosphorous compound. An example of a phosphorous compound is ammonium polyphosphate. Importantly, because the fire retardant is incorporated into the foam during formation, the fire retardant is not included in the molecular backbone of the foam, instead the fire retardant is a filler. When a fire retardant is incorporated with the foam during foam formation the fire retardant will be a filler and not part of the molecular backbone. The Murch foams not only allow for the spread of fire eventually, but undesirably allow for the transmission of heat. Although the Murch systems temporally provide protection against the spread of flame, such systems allow the spread of heat from prolonged exposure to fire.