Polyurethanes degradation

Woodhouse described a degradable polyurethane prepared with a novel amine chain extending agent. As with the insertion of lactic acid into the backbone, bio-degradability was achieved, but the fragments appeared problematic. Thus, while biodegrading polyurethanes are fairly simple to prepare, one must be aware of the product to which a polyurethane degrades. The use of TDI as the isocyanate would clearly raise concerns from the FDA. 

Akutsu, Y., Nakajima-Kambe, T., Nomura, N. Nakahara, T. (1998). Purification and properties of a polyester polyurethane-degrading enzyme from Comamonas acidovorans TB-35. Applied and Environmental Microbiology, 64, 62-7. 

Allen, A. B., Hilliard, N. P. Howard, G. T. (1999). Purification and characterization of a soluble polyurethane degrading enzyme from Comamonas acidovorans. International Biodeterioration and Biodegradation, 43, 37-41. 

Boubendir, A. (1993). Purification and biochemical evaluation of polyurethane degrading enzymes of fungal origin. Dissertation Abstracts International, 53, 4632. 

Nakajima-Kambe, T., Onuma, F., Akutsu, Y. Nakahara, T. (1995). Determination of the polyester polyurethane breakdown products and distribution of the polyurethane degrading enzyme of Comamonas acidovorans strain TB-35. Journal of Fermentation and Bioengineering, 83, 456-60. 

Polyester polyurethanes degrade In humid environments. The expected lifetime of five years for the best polyester polyurethanes at 25° C [1] Is frequently not achieved [2,3]. The ordinary degradation Is due to hydrolysis of the polyester component [4]. Acid produced catalyzes additional hydrolysis, thus Increasing the rate autocatalytlcally [5]. Larger acid numbers In the polyester dlol from which the polyurethane Is made Increase the degradation rate of the polyurethane [5]. Polyester polyurethanes can also be attacked by fungi [2]. 

Esterases and polyurethanases can hydrolyze polyurethanes resulting in changes on the surface of PU film. In vivo, cholesterol esterase can initiate polyurethane degradation while a number of PU-degrading enzymes have been described from micro-organisms, such as Candida rugosa lipase or esterases from Pseudomonas chlororaphis, for example, polyurethanase [105]. 

A variety of processes for polyurethane degradation by reaction with different glycols has been described in the literature during the last 30 years.76-83 Polyurethane glycolysis is usually carried out with an excess of glycols at temperatures around 200 °C and in many cases working at atmospheric pressure. After several hours of reaction, the polyurethane is completely liquefied and depolymerized, and catalysts are not necessary. 

Hydrolysis is the second most important method of chemical recycling of polyurethanes. Various studies have been published dealing with polyurethane degradation by reaction with liquid water (150-200 °C) or steam (200-320 °C).85 90 The hydrolytic reaction proceeds as shown in Scheme 2.4. 

Polyurethane chemolysis by reaction with ammonia or various amines has been described in the literature. Sheratte92 has proposed a process based on polyurethane decomposition by various agents. Several examples were provided for polyurethane degradation with ethanolamine (120 °C), ammonia and ammonium hydroxide (180 °C), diethylene triamine (200 °C) and other basic reagents. In all cases the process involves, simultaneously or subsequently, reaction with propylene oxide, which allows the different amines obtained to be quantitatively converted into polyols according to the reaction shown in Scheme 2.6. The polyols derived from this process were used in the reformulation of new polyurethanes by polymerization with the corresponding isocyanate, and were suitable for application in rigid foams. 

M. Murugesan, V. Murali Madhav, D. Jeyakumar. Rapid biochemical characterisation of polyurethane degrading fungi using amperometric biosensor technique. Bulletin of Electrochemistry, No. 15, pp. 452-470, 1999. 

It is believed that most of PUR biodegradation occurs by the action of esterases, however polyester-polyurethane degrading enzymes have been purified and their characteristics have been reported. These enzymes have a hydrophobic binding domain at the surface of the PUR, and a catalytic domain [22]. But there is no evidence that the urethane linkage has been broken. 

McBane JE, Santerre JP and Labow RS. The interaction between hydrolytic and oxidative pathways in macrophage-mediated polyurethane degradation. J... 

The response of polyurethanes to thermally activated autoxidation depends upon polymer structure. In general, polyurethane degradation by this mechanism is suppressed by the addition of antioxidant to the polymer. Ultraviolet initiated autoxidation is suppressed by a suitable screen (e.g. carbon black, titanium dioxide) or a combination of antioxidant and ultraviolet absorber. Irganox 1010 and Tinuvin P (Ciba-Geigy) are particularly suitable antioxidant and ultraviolet absorbers, respectively, for polyurethanes. Polyurethane structures with enhanced resistance to ultraviolet initiated autoxidation may be possible. 

Several studies have been conducted on biostable polyurethanes to elucidate the effects of hard segment chemistry on polyurethane degradation rate. Tang et al. [104,105] observed the effects of hard segment chemistry and hard segment content... 

Polyurethane degradation is a common issue for polyurethane-based medical implants. The degradation mechanisms vary depending on the type of polyurethane used and their environment. For example, polyester polyurethane undergoes hydrolytic... 

Figure 22.17 Histological progression of polyurethane degradation in vivo 6 and 9months.

A two-stage method of waste polyurethane degradation is described in [79]. In the first stage, scission of the polyurethane chain takes place at a temperature of 120°C in the presence of dialkanolamine and metal hydroxide e.g., KOH). Under these conditions, the reaction products include polyols, aromatic amines, short-chain ureas, and urea derivatives. The second stage is based on the alcox-ylation of the hydroxyl groups and the primary and secondary amine groups, e.g., by the use of propylene oxide. In this way, polyols with a hydroxyl number of 156-271 mg KOH/g and viscosity within the range of 1950-57 000 mPa s can be obtained. The flexible foams prepared from recycled polyols revealed favorable mechanical properties. 

A. Troev K, Atanasov V I, Tsevi R, Grancharov G and Tsekova A (2000) Chemical degradation of polyurethanes. Degradation of microporous pol5Tirethane elastomer by dimethyl phosphonate, Polym Degrad Stabil 67 159-165. 

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