Polyisocyanate foam

BS 4840, Part 1, specifies that both types of polyurethane slab foam (Type 1. LD and HD) should have a maximum water vapor permeability normal to the major plane of the slab of 5.5 ng/(Pa s - m). BS 5241. Part 2 [26], specifies that the five types of spraycd-up rigid polyurethane and polyisocyanate foam (for thermal insulation or buoyancy applications) should have maximum values of 3.5, 5.5. or 8.5 ng (Pa s m). 

Polyurethanes. About 3% of the U.S. polyurethanes market in 1988 was derived from the condensation product of polyisocyanates with low molecular weight polyadipates having hydroxyl end groups (195). In 1986 this amounted to 29,000 t, or 4% of total adipic acid consumption. The percentage was similar in Western Europe. About 90% of these adipic acid containing polyurethanes are used in flexible or semirigid foams and elastomers, with the remainder used in adhesives, coatings, and spandex fibers. 

Foam may be made from such polycaprolactones by reaction with polyisocyanates in the presence of tin catalysts. 

Shoe adhesives. CR adhesives are used for the permanent attachment of shoe soles. For difficult-to-bond sole materials (plasticized PVC, EVA foaming soles, thermoplastic rubber, SBR) graft polymer solutions of Neoprene AD-G combined with a polyisocyanate provide a good adhesion. Another major area for CR contact adhesives is the manufacture of leather goods, particularly leather shoe sole bonding and belt lamination. 

PUR are a broad class of highly cross-linked plastics prepared by multiple additions of poly-functional hydroxyl or amino compounds. Typical reactants are polyisocyanates [toluene diisocyanate (TDI)] and polyhydroxyl molecules such as polyols, glycols, polyesters, and polyethers. The cyanate group can also combine with water this reaction is the basis for hardening of the one-part foam formulations. 

Processing of rigid foams from two part formulations involves combining measured quantities of the polyisocyanate with a polyhydroxyl such that there are no or limited reactive isocyanate functional groups. Moisture is not required to complete the cure. Once the reactants are combined the mixture is poured into a form where expansion and polymerization take place simultaneously. Cure times are usually very fast, on the order of minutes. 

Polyurethane foam Natural oil polyol, water, and surfactants were weighed into a 1 quart metal cup and premixed for 15 seconds at 1800 rpm using a pin type mixer. The catalyst was added and the mixture stirred an additional 15 seconds at 1800 rpm. The polyisocyanate was then added and the mixture stirred at 2400 rpm for 3 seconds and immediately transferred to a 15 x 15 x 10 wooden box lined with a polyethylene bag. The buns were allowed to cure overnight before testing. 

Polycarbodiimide foams from polyisocyanates and 0.001-1% by weight of phospholine or phospholidine [82],... 

Aromatic polyisocyanates Aromatic polyisocyanates are primarily used for a wide variety of PU foamed plastics, elastomers, and adhesives. More than 90% of PUs are produced from aromatic polyisocyanates. The isocyanate group bonded to an aromatic ring is more reactive toward water or hydroxyl groups than that bonded to an aliphatic compound. The most important aromatic diisocyanates are also given in Figure 4.7. 

The afterglow of open-cell foams (punking) can be suppressed by the addition of flame-retardants such as boron trioxide or aluminum hydroxide. Hybrid foams with good mechanical properties and low combustibility can be produced from PF resins and polyisocyanates.104... 

Rigid Foam. This is made by mixing short polyfunctional polyol with di- or higher polyisocyanate, and foaming either with volatile liquid or with isocyanate and water. The largest use is in building insulation, with... 

The polyisocyanates which can be used for preparing isocyanate-based foams are mainly aromatic compounds and some aliphatic or aralkyl polyisocyanates. TDI (toluene diisocyanate) is widely used for flexible foams. Pure MDI (diphenylmethane diisocyanate) is used for elastomers and coatings. Modified TDI and modified MDI are used for high-resilience flexible foams. Polymeric isocyanates (polymeric MDI or oligomeric MDI) are mostly used for preparing rigid urethane and isocyanurate foams, and in part, for preparing flexible and semi-flexible foams. 

The three component streams are in a recycle mode at the desired flow rates before foaming. During foaming, surfactant and precursor are premixed before they come in contact with the polyisocyanate in the power mixer. The foaming mixture is then discharged through multiple nozzles in the spreader (Figure 5). 

Molded materials such as foams or pressed shapes can also be obtained from chemically modified wood solutions [4]. Foams, for example, can be prepared by adding an adequate amount of water as a foaming agent and a polyisocyanate compound as a hardener to a 1,6-hexanediol solution of ally-lated wood, all of which are then mixed well and heated. When heated at 100°C, foaming and resinification are initiated within 2 min and completed within several minutes. If a promoter such as triethylamine is added, rapid reactions occur even at room temperature and foams can be obtained within several minutes. The foam has a low apparent density of 0.04 g/cm, a... 

Chem. Anlagen Bischo (Reut) Foams Prepared from Phenoplast and Di- and/or polyisocyanates. BDR Pht. 2,542,900 (1977)... 

H.F. Bluhrn, USP 3256214(1966) CA 65, 9132(1966) [Ptepn of explosive polyurethane resins, which are suitable for use as sensitive coatings for AN blasting compns and for prepn of foamed resin expls is described. The resins, which can be cured at RT, ate prepd by reaction of an org polyisocyanate with a nitric acid partial ester of a polyhydroxy compd including a component contg > OH groups reactive with the isocyanate. For example, equal parts by wt of an-hydroenneaheptitol nitrate (13.77 wt %N as... 

Polyisocyanates are very reactive compounds and produce various polymers such as fibers, resins, elastomers, foams, coatings and adhesives by the reaction of polyaddition, polycondensation or stepwise polymerization. 

The polyisocyanate-based polymer-forming reactions can be classified into three types of reactions addition reactions, condensation reactions, and cyclotrimerization reactions. Among the isocyanate reactions shown in Table 2, the addition reaction is the major isocyanate reaction in polyurethane foam preparation. A model addition reaction is shown below ... 

The major raw materials for making isocyanate-based foams include the following compounds polyisocyanates, polyols, catalysts, blowing agents, surfactants, epoxides, and flame retardants. 

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 ... 

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. 

These foams can be prepared by the proper choice of equivalent weight and functionality of the polyols employed. Polyisocyanates can be considered as the joining agents of the polyols. A rough classification of the three kinds of foams based on the type of polyols used is shown in Table 14. 

Different foams can be prepared by the proper choice of polyols, which will be described later. Polyisocyanates are used as joining agents... 

Specialty Isocyanate Technology. The polyisocyanates employed for HR foams are TDI, liquid MDI, mixtures of TDI and liquid MDI or crude MDI. In addition to these polyisocyanates, specialty isocyanates can be used alone or in combination with the above polyisocyanates. 

Preparation of Microcellular Foams. The major polyols for microcellular elastomers include aliphatic polyester diols having a molecular weight of about 1,000 to 3,000, and poly-epsilon-caprolactones. Poly(oxytetramethylene) glycols (PTMEG) can also be used. The polyisocyanates to be used for microcellular elastomers are TDI-prepolymers and liquid MDI, i.e., carbodiimide-modified MDI or urethane-modified MDI. Low-molecular-weight, active-hydrogen compounds such as chain extenders (difunctional compounds) and... 

Preparation of Integral-Skin Flexible Foams. The major polyisocyanates for use in making integral-skin flexible urethane foams are liquid MDl and TDl prepolymers. In order to make light-stable integral-skin foams, aliphatic diisocyanates, e.g., HDl (hexamethylene diisocyanate) and IPDl (isophorone diisocyanate) in modified forms are used. 

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