Polyurethanes hydrolysis

Schollenberger, C. S. and Stewart, F. D., "Thermoplastic Polyurethane Hydrolysis Stability," Urethanes In Elastomers and Coatings (articles from the Journal of Elastoplastlcs) pp. 46-74, Technomlc Publ. Co., Inc., Westport (1973). 

Polyols, diamines and carbon dioxide are the final products formed by polyurethane hydrolysis. The reaction between the diamine and phosgene allows the corresponding isocyanate to be formed, whereas the subsequent polymerization of this isocyanate and the polyols yields the starting polyurethane again. 

Polyurethane chemolysis can be performed by processes similar to those applied to PET. Thus, polyurethane glycolysis yields a mixture of polyols, which can be reused in the formulation of new polyurethanes. Likewise, polyurethane hydrolysis leads to the formation of polyols, diamines and carbon dioxide. The diamine can be subsequently transformed into the corresponding isocyanate by reaction with phosgene, whereas the polymer-... 

Immobilized lipase from Humicola lanuginosa Entrapment on polyurethane Hydrolysis of olive oil... 

Hydrolytic stability of polyurethanes depends on the composition and concentration of the weakest groups. Polyesterurethanes have considerably lower resistance to hydrolysis than polyether or polybutadiene based polyurethanes. Hydrolysis of ester groups is catalyzed by acid groups formed as the product of hydrolysis. Therefore, an efficient way of slowing down the process is to block the acid formed, which is usually carried out by adding carbodiimides. Such solutions are temporary since after the consumption of all carbodiimide the process accelerates again. 

C.S. SchoUenberger and ED. Stewart, Thermoplastic polyurethane hydrolysis stability. Journal of Elastomers and Plastics, 3(l) 28-56,1971. 

The polyurethane hydrolysis is interesting, although it is not used on a larger scale as a method of polyurethane recycling. As a rule, the process is carried out at temperatures varying from 200 to 350°C and elevated pressure. The products include polyols and various amine derivatives. The polyols obtained in this way can be used in the manufacturing of new polyurethane articles. 

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organonitnles arises both from the reactivity of the C=N bond, and from the abiHty of the cyano substituent to activate adjacent bonds, especially C—H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxyHc acids and esters, aldehydes, ketones, large-ring cycHc ketones, imines, heterocycles, orthoesters, and other compounds. Some of the more common transformations involve hydrolysis or alcoholysis to produce amides, acids and esters, and hydrogenation to produce amines, which are intermediates for the production of polyurethanes and polyamides. An extensive review on hydrogenation of nitriles has been recendy pubHshed (10). 

Almost all IDA derived chain extenders are made through ortho-alkylation. Diethyltoluenediamine (DE I DA) (C H gN2) (53), with a market of about 33,000 t, is the most common. Many uses for /-B I DA have been cited (1,12). Both DE I DA and /-B I DA are especially useful in RIM appHcations (49,53—55). Di(methylthio)-TDA, made by dithioalkylation of TDA, is used in cast urethanes and with other TDI prepolymers (56). Styrenic alkylation products of TDA are said to be useful, eg, as in the formation of novel polyurethane—polyurea polymers (57,58). Progress in understanding aromatic diamine stmcture—activity relationships for polyurethane chain extenders should allow progress in developing new materials (59). Chlorinated IDA is used in polyurethane—polyurea polymers of low hysteresis (48) and in reinforced polyurethane tires (60). The chloro-TDA is made by hydrolysis of chloro-TDI, derived from TDA (61). 

Thermoplastic polyurethane elastomers have now been available for many years (and were described in the first edition of this book). The adipate polyester-based materials have outstanding abrasion and tear resistance as well as very good resistance to oils and oxidative degradation. The polyether-based materials are more noted for their resistance to hydrolysis and fungal attack. Rather specialised polymers based on polycaprolactone (Section 25.11) may be considered as premium grade materials with good all round properties. 

Poly(tetramethylene oxide) polyols (PTMEG) are high performance polyethers that are crystalline waxes at molecular weights above 650 and liquids at lower molecular weights. They are only available as diols, but they produce adhesives with good hydrolysis resistance and moisture resistance, which is why these adhesives are even used in medical devices, blood bags, catheters, and heart-assist devices [25]. Certain thermoplastic polyurethane adhesives and solvent-borne adhesives are also based on PTMEG s. 

Effect of chain structure on the hydrolysis of polyester polyurethanes... 

Hydrolysis studies compared a polycarbonate urethane with a poly(tetramethyl-ene adipate) urethane and a polyether urethane based on PTMEG. After 2 weeks in 80°C water, the polycarbonate urethane had the best retention of tensile properties [92], Polycarbonates can hydrolyze, although the mechanism of hydrolysis is not acid-catalyzed, as in the case of the polyesters. Polycarbonate polyurethanes have better hydrolysis resistance than do standard adipate polyurethanes, by virtue of the highest retention of tensile properties. It is interesting to note in the study that the PTMEG-based urethanes, renowned for excellent hydrolysis resistance, had lower retention of physical properties than did the polycarbonate urethanes. 

It is speculated that the water does not diffuse as easily into the polycarbonate as into the PTMEG urethane, making the polycarbonate more resistant to plasticization by water and subsequent hydrolysis. The tensile properties of the PTMEG polyurethane eventually returned to nearly the original tensile properties, if the material was allowed to dry at room temperature for 2 weeks. This observation lends credence to the idea that the PTMEG urethane was plasticized by water. 

The Ford hydroglycolysis process is an example of a combined approach for die depolymerization of PURs. In a reactor, polyurethane foam is reacted with a mixture of water, diethylene glycol, and alkali metal hydroxides at high temperature to form polyols. When sodium hydroxide is added as a catalyst, a cleaner polyol is formed because all of the carbamates and ureas in the product are converted into amines and alcohols by hydrolysis.33... 

Meluch et al.10 reported that high-pressure steam hydrolyzes flexible polyurethane foams rapidly at temperatures of 232-316°C. The diamines are distilled and extracted from the steam and the polyols are isolated from the hydrolysis residue. Good results were obtained by using reclaimed polyol in flexible-foam recipes at file 5% level. Mahoney et al.53 reported the reaction of polyurethane foams with superheated water at 200°C for 15 min to form toluene diamines and polypropylene oxide. Gerlock et al.54 studied the mechanism and kinetics of the reaction... 

Example 1. Hydrolysis of Polyurethane in a Pyrex Hydrolysis Reactor.54 A... 

PURs. See Polyurethanes (PUs, PURs) Pyrex hydrolysis reactor, hydrolysis of polyurethane in, 573 Pyrolysis, 208... 

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