Urethane processing

In the urethane process a small amount of water is added to convert some isocyanate functionalities into CO2 gas and amines. The degree of foaming can be controlled by the amount of water added. 

DuPont introduced this urethane process in 1961 that operates in a two-stage expansion system. The main idea is to introduce into the... 

Advances in urethane processing involve changes in starting chemicals as well as improvements in processes. The chemicals have led to the use of low-cost polyether polyols, high-resilience (HR) "cold cure" foams, safer to handle than prepolymers, catalysts, and chain extenders. A major process improvement was the use of flat-top bun technology for low-density urethane foams. This technology... 

The Showa Denka Company practices this reaction with a PX—MX mixture (24), whereas Mitsubishi Gas Chemical Company uses high purity MX first to form the dicyanide (25). In both processes, hydrogenation to the diamine follows. y -Xylenediamine is reacted with phosgene to give / -xylene diisocyanate, which is used in urethane resins (26—28). 

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Glycerol is used in nearly every industry. The largest single use is in dmgs and oral care products including toothpaste, mouthwash, and oral rinses (Table 3). Its use in tobacco processing and urethane foams remains at a fairly even consumption level. Use in foods and cosmetics is growing. 

This simple reaction is the bedrock of the polyurethane iadustry (see Urethane polymers). Detailed descriptions of the chemistry and process have been published (65—67). Certain carbamates are known to reversibly yield the isocyanate and polyol upon heating. This fact has been commercially used to synthesize a number of blocked isocyanates for elastomer and coating appHcations. 

In the second step, a papermaking method is also used for the fine fibers, less than 0.1 tex (1 den). This process is usually followed by a high pressure water jet process instead of the third step. In the fourth step, to obtain the required properties in specific appHcations, a polyurethane is selected out of the segmented polyurethanes, which comprises a polymer diol, a diisocyanate, and a chain extender (see Urethane polymers). A DMF—water bath for coagulation is also controlled to create the adequate pore stmcture in combination with fibers. 

Polymers. AH nitro alcohols are sources of formaldehyde for cross-linking in polymers of urea, melamine, phenols, resorcinol, etc (see Amino RESINS AND PLASTICS). Nitrodiols and 2-hydroxymethyl-2-nitro-l,3-propanediol can be used as polyols to form polyester or polyurethane products (see Polyesters Urethane polymers). 2-Methyl-2-nitro-l-propanol is used in tires to promote the adhesion of mbber to tire cord (qv). Nitro alcohols are used as hardening agents in photographic processes, and 2-hydroxymethyl-2-nitro-l,3-propanediol is a cross-linking agent for starch adhesives, polyamides, urea resins, or wool, and in tanning operations (17—25). Wrinkle-resistant fabric with reduced free formaldehyde content is obtained by treatment with... 

Polyuretha.ne, A type of spunbonded stmcture has been commercialized in Japan based on thermoplastic polyurethanes (15). This represents the first commercial production of such fabrics, although spunbonded urethane fabrics have been previously discussed (16). The elastomeric properties claimed are unique for spunbonded products and appear to be weU suited for use in apparel and other appHcations requiring stretch and recovery. Polyurethanes are also candidates for processing by the meltblown process. 

Urethanes are processed as mbber-like elastomers, cast systems, or thermoplastic elastomers. The elastomer form is mixed and processed on conventional mbber mills and internal mixers, and can be compression, transfer, or injection molded. The Hquid prepolymers are cast using automatic metered casting machines, and the thermoplastic peUets are processed like aU thermoplastic materials on traditional plastic equipment. The unique property of the urethanes is ultrahigh abrasion resistance in moderately high Shore A (75—95) durometers. In addition, tear, tensUe, and resistance to many oUs is very high. The main deficiencies of the urethanes are their resistance to heat over 100°C and that shear and sliding abrasion tend to make the polymers soft and gummy. 

There are many suppHers of urethane systems in the United States. The TSE Company suppHes the mbber form many companies supply the prepolymer forms. It is estimated that close to 68,000 t of these mbbers are used in the United States if aU forms are included. Uses include sport wheels (roUer blades, ski wheels) printing, paper, and steel processing roUs gears pump liners appHance components and soHd industrial tires. 

Glean-Up Solvent. Dimethyl sulfoxide is used to remove urethane polymers and other difficult-to-solvate materials from processing equipment. 

The addition polymerization of diisocyanates with macroglycols to produce urethane polymers was pioneered in 1937 (1). The rapid formation of high molecular weight urethane polymers from Hquid monomers, which occurs even at ambient temperature, is a unique feature of the polyaddition process, yielding products that range from cross-linked networks to linear fibers and elastomers. The enormous versatility of the polyaddition process allowed the manufacture of a myriad of products for a wide variety of appHcations. 

The late 1950s saw the emergence of cast elastomers, which led to the development of reaction injection mol ding (RIM) at Bayer AG in Leverkusen, Germany, in 1964 (see Plastics processing). Also, thermoplastic polyurethane elastomers (TPUs) and Spandex fibers (see Fibers, elastomeric) were introduced during this time. In addition, urethane-based synthetic leather (see Leather-LIKEmaterials) was introduced by Du Pont under the trade name Corfam in 1963. 

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