Reaction urethane foam

Nonreactive additive flame retardants dominate the flexible urethane foam field. However, auto seating appHcations exist, particularly in Europe, for a reactive polyol for flexible foams, Hoechst-Celanese ExoHt 413, a polyol mixture containing 13% P and 19.5% Cl. The patent beHeved to describe it (114) shows a reaction of ethylene oxide and a prereacted product of tris(2-chloroethyl) phosphate and polyphosphoric acid. An advantage of the reactive flame retardant is avoidance of windshield fogging, which can be caused by vapors from the more volatile additive flame retardants. 

Urethane Polymers. An important use for glycerol is as the fundamental building block ia polyethers for urethane polymers (qv). In this use it is the initiator to which propylene oxide, alone or with ethylene oxide, is added to produce ttifunctional polymers which, on reaction with diisocyanates, produce flexible urethane foams. Glycerol-based polyethers (qv) have found some use, too, ia rigid urethane foams. 

This reaction is catalyzed by hydrogen chloride and yields can be essentially quantitative when using either free phosphonic acid or its diesters. The flame retardant, Eyrol 6, produced by Akzo Chemicals, Inc. and used for rigid urethane foams, is synthesized as follows (24). 

This reaction is of importance in the manufaeture of urethane foams. 

Unsaturated polyester resins (UPRs) Uralkyd resins, 202 Urea-methylol reaction, 410 Urethane alkyds, 241 Urethane coatings, 202 Urethane elastomers, implanted, 207 Urethane foams, tests for, 244 Urethane gels, 205 Urethane-grade ATPEs, 223 Urethane-grade polyol types, 212 Urethane-grade raw materials, 246 Urethane hydrogel, preparation of, 250-251... 

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

The physical properties for Reaction-Injection-Molded urethane foam cannot readily be determined because they are, as all sandwich structures, highly dependent on the particular shape of the article and the ratio of skin to foam or, in other words, the density distribution through the part. Typical densities for these new structural foams are 30 — 45 lbs./ft.3 with average moduli of elasticity of 120,000 — 250,000 p.s.i. The compression strengths are higher than those shown in Table VI for rigid foams without skins. 

Toluene diisocyanale is widely used in the manufacture of urethane plastics, particularly the urethane foamed plastics. Another isocyanate, diphenylmethane 4,4 -diisocyanaie, is produced by reaction of aniline and formaldehyde, followed by reaction with phosgene hcho coo.. 

Propylene Oxide. Propylene oxide is another basic chemical used in manufacturing intermediates for urethane foams (cushioning and insulation), coatings, brake fluids, hydraulic fluids, quenchants, and many other end uses.23 The classic industrial synthesis of this chemical has been the reaction of chlorine with propylene to produce the chloro-hydrin followed by dehydrochlorination with caustic to produce the alkylene oxide, propylene oxide, plus salt. 

Polyurethane is a condensation polymer generally formed by the reaction between a di-isocyanate and a hydroxylated-terminated resin known as polyol in the presence of a catalyst and a foaming agent The urethane foam formed as a result of this reaction is a cellular polymer that derives its mechanical properties in part from the cell matrix formed during its manufacture and in part from the intrinsic polymer properties. Choice of the di-isocyanate and polyol dictates the inherent polymer properties in addition filler materials may be added to the polymer to improve its mechanical properties. 

This reaction is often employed in the production of flexible urethane foams, which are frequently block copolymers of polyether or polyester segments joined to polyurea segments. (The polyester or polyether segments terminate in urethane segments resulting from reaction of polyether or polyester hydroxyl end groups with the isocyanate.)... 

They found the heat of reaction for 80 20 TDI and water to be 38.3 1.74 kcal mole", and that for 80 20 TDI and a poly(oxy-propylene)triol to be 42.5 0.76 kcalmole" (with two equivalents of NCO per mole in each case). Both separate reactions gave data which fit second-order kinetics up to 50% reaction. Preliminary attempts at calculating kinetic coefficients for both reactions during polyurea—urethane foam formation were given. It is believed that further efforts along this line will be needed to clarify the kinetics satisfactorily, however. 

Foams may be prepared by either one of two fundamental methods. In one method, a gas such as air or nitrogen is dispersed in a continuous liquid phase (e.g. an aqueous latex) to yield a colloidal system with the gas as the dispersed phase. In the second method, the gas is generated within the liquid phase and appears as separate bubbles dispersed in the liquid phase. The gas can be the result of a specific gasgenerating reaction such as the formation of carbon dioxide when isocyanate reacts with water in the formation of water-blown flexible or rigid urethane foams. Gas can also be generated by volatilization of a low-boiling solvent (e.g. trichlorofluoromethane, F-11, or methylene chloride) in the dispersed phase when an exothermic reaction takes places, (e.g. the formation of F-11 or methylene chloride-blown foams). 

Chemical Blowing Agents. The conventional gas-generation reaction for flexible urethane foams is the water-isocyanate reaction which was first described in a German patent (122). Its chemical reaction is shown as follows ... 

In the case of urethane-foam formation, tin catalysts (Table 8) mainly promote the reaction between isocyanate and hydroxyl groups, i.e., the formation of the urethane linkage. 

Preparation. Polyurethane foams (often referred to as urethane foams) are prepared by the reaction of a polyisocyanate with a polyol in the presence of a blowing agent, a surfactant, and a catalyst without external heating of the foaming system. The principle of preparation of urethane foams is based on the simultaneous occurrence of two reactions, i.e., polyurethane formation and gas generation in the presence of catalyst and surfactant, as shown below ... 

Flexible urethane foams include slabstock foam, molded foam, and pour-in-place foam. In some cases, the latter two foams can be called flexible RIM foams (RIM is an abbreviation for reaction injection molding). 

The blowing agent for microcellular elastomers is water. The amount of water should be accurate, and its accuracy can be obtained by a water-containing solution, such as liquid sodium sulfonate of vegetable oils containing a small amount of water. The catalysts to be used are those used in urethane foams, e.g., tertiary amines, and tin catalysts. The above ingredients are mixed and poured into a hot mold and cured in a defined period of time. After demolding, a post cure is applied to complete the polymer-formation reactions. 

The spraying process is carried out at ambient temperatures. The spraying of urethane-modified isocyanurate foam is not as easy as urethane-foam spraying because the cyclotrimerization reaction of isocyanate groups requires relatively higher temperatures than for urethane foams. An example of the spraying of urethane-modified isocyanurate foams was reported (198). The spraying was conducted with formulations at a low-NCO/OH equivalent ratio. 

The frothing process is widely used in rigid urethane foam pour-in-place applications. The frothing process of urethane-modified isocyanurate foams has been used for the insulation of petrochemical plants, e.g., spherical tanks, reaction towers, etc. (79). An example of the frothing system is shown below (71). 

The reaction of NCO groups and carboxylic acid groups resulted in the formation of amide linkages and carbon dioxide as blowing agent. This reaction has led to the invention of urethane foam preparation, and the polyurethane industry has become one of the biggest plastic industries. A model reaction of a polyamide foam formation is shown below ... 

Polyurethane Foams. Rigid polyurethane foam can be prepared by the reaction of a polyisocyanate, a polyol, a blowing agent, a catalyst and a surfactant. Detailed explanation of these foams are described in the sections on Rigid Urethane Foams and Miscellaneous Urethane Foams earlier in this chapter. 

Flexible polyurethane foams are blown with water, methylene chloride, and chlorofluorocarbons (CFCs). Carbon dioxide from the water/isocyanate reaction functions as the blowing agent. The methylene chloride and CFCs assist in the blowing and contribute properties such as added softness and resilience. The CFCs also contribute to the insulation properties of rigid urethane foams. 

Carbon Dioxide (COj) Until 1958 when halocarbons were first used as blowing agents for urethane foams carbon dioxide (COj) was the blowing agent used. The COj was liberated by the isocyanate-water reaction shown below (13). 

In 1991 Vandichel and Appleyard (15) described a new promising approach for the production of "soft" flexible slabstock urethane foam blown exclusively by COj generated by the water-isocyanate reaction. These workers found that by the addition to the formulation of certain hydrophilic materials a substantial hardness reduction is obtainable, thereby permitting a considerable reduction, or even total elimination, of CFC-11 from some "conventional" foam formulations. The hydrophilic additive is called CARAPOR 2001. An example is a foam produced with an ILD value of 80N at a density of 21.5 kg/m" (1.34 Ib/ft ) (15). 

Flexible Foams CO2 obtained in situ by the reaction of water with isocyanate has been the chief blowing agent for all commercially produced flexible urethane foams. The amount of water and tolylene diisocyanate (TDI) used determines foam density, providing most of the gas formed is used to expand the urethane polymer. Because water participates in the polymerization reactions leading to the expanded cellular urethane polymer, it has a very pronounced influence on the properties of foams. For better control of the foaming process most foam manufacturers employ distilled or deionized water (16). 

Reaction-injection-molded (RIM) urethane foams are using various tin/amine catalysts, with some special variations developed expressly for this processing technique. Amine/amine and tin/tin combinations are also under development (22). 

In rigid urethane foaming systems using the CO2 formed by the water-isocyanate reaction a balance of the relative rates between the urea... 

Tertiary amines alone can be used as catalysts, but for some applications, such as spraying, more speed is desirable. Metal salts, particularly tin salts, accelerate the foaming reactions, and can be used alone or in combination with the tertiary amine-type catalysts. Tin catalysts of importance for rigid urethane foams are stannous octoate and dibutyltin dilaurate. Stannous octoate will hydrolyze rapidly in the presence of a basic catalyst with loss of activity. Masterbatches containing stannous octoate and moisture are stable for only a few hours at room temperature. Resin masterbatches containing dibutyltin dilaurate may stay stable for months. For this reason this catalyst is preferred for foaming systems packaged for use at other locations or plants where the resin masterbatch is not used immediately (20). 

Temperature can also be used to control the urethane foaming reactions. Some delayed-action rigid urethane foaming systems have been made by premixing all of the foaming ingredients at temperatures down to -300°F(-184°C). When these systems are heated, foaming of the mass takes place (20). 

Polyester- and polyether-based rigid urethane foams generally require a surfactant, whether expanded with COj from the water-isocyanate reaction, or with an inert blowing agent such as fluorocarbon. Without surfactant the foam may collapse or have a coarse cell structure. Castor-oil-based systems generally do not require surfactants, but better results will be obtained if they are used (20). 

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