Recycling of polyurethanes

Glycolysis is the most promising approach for the chemical recycling of polyurethanes.1 The chemistry of PUR depolymerization is complicated by the presence of other chemical groups in the polymer, such as ureas, allophanates, and biurets. 

Popular Plastics and Packaging 44, No.3, March 1999, p.76-86 PROGRESS IN RECYCLING OF POLYURETHANES... 

Recycling. The methods proposed for the recycling of polyurethanes include pyrolysis, hydrolysis, and glycolysis. Regrind from polyurethane RIM elastomers is used as filler in some RIM as well as compression molding applications. The RIM chips are also used in combination with rubber chips in the construction of athletic fields, tennis courts, and pavement of working roads of golf courses. 

Three methods of recycling of polyurethane foam have been proposed hydrolysis, pyrolysis and glycolysis. 

Today, several industrial plants based on glycolytic treatment are in operation for the chemical recycling of polyurethane wastes, mainly those generated from the insulation and automotive sectors.2... 

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. 

FIGURE 6.6 Recycling of polyurethane waste via partial decomposition in kneader. (After Muller, P. and Reiss, R., Die Makromol. Chem., Macromol. Symp., 57, 175, 1992. With permission.)... 

Chemical recycling of polyurethanes by ammono-lytic cleavage of urethane and urea bonds under supercritical conditions has been described [48]. It is well known that a number of low-boiling materials give enhance solubility and reactivity under supercritical conditions. Ammonia has a critical point at 132.45°C and 112.8 bar (11.28 MPa) with a density of 0.235 g/cm. Being able to act as hydrogen-bond donor and acceptor, it provides good solubility for polyurethanes and... 

K. C. Frisch, D. Klempner, and G. Prentice, Recycling of Polyurethanes, Advances in Plastics Recycling, Vol. 1, Technomic, Lancaster, PA, 1999. 

Highlights the recycling of polyurethanes, poly(vinyl chloride), mixed pla.stics, rubber tires, car batteries, and more... 

There has been little past nationwide activity in the recycle of polyurethanes (PUR) or phenolics even though these resins are among the largest produced. These two resins comprised 9.5% by weight of the resins produced in the U.S. in 1989 (refer to Table 1.2 in Part 1). An overview of some recent work is summariaed here. 

K. C. Frisch and co-workers, eds., Recycling of Polyurethanes—Advances in Plastics Recycling, Technomic Publishing Co., Inc., Lancaster, Pa., 1999. 

The regeneration of monomers from recovered components has been included for completeness, but in reality the concept of chemical dismantling is unlikely to be realized on any large scale. There are several possible options for the chemical recycling of polyurethanes. Polyesters and polyamides can be broken down into their chemical parts by hydrolysis, and pyrolysis can be used to reeover PMMA and polyolefines. There are problems of scale, however, and possible atmospherie pollution problems. This is not a solution for the present time, but the technology is potentially available, against a time when petroleum becomes much less available and much more expensive. 

Recycling of polyurethane is more difficult than recycling of thermoplastics, since the thermoset polyurethane cannot be melted and reformed. Some mechanical recycling of polyurethane, using ground-up material as a filler in new materials, has been attempted. Most efforts, however, are devoted at chemical treatment to break down the material into polyol, which can then be used in production of new plastics. 

Figure 44 Apparent density and compressive strength of poiyurethane foams measured in parallel and perpendicular rise directions. Reproduced from Bogdal, D. Prociak, A. Pielichowski, J. In Application of Microwave Irradiation for Chemical Recycling of Polyurethanes, Proceedings of Global Symposium on Recycling, Waste Treatment and Clean Technology, REWAS, Madrid, 2004." ° ...

Scheirs R (1998) Recycling of polyurethanes, in Polymer Recycling Science, Technology and Applications (Ed. Scheirs R) J. Wiley Sons, Chichester, pp. 340-377. 

Neuray M P, Sulzbach H M and Wirth J, Methods for the recycling of polyurethane and pol5Tirethane composites, www.henneckemachinery.com. 

Simioni F, Modesti M and Rienzi S A (1991) Recycling of polyurethane waste, Cellular Polymer P Int Conf, London. 

Lentz H and Mormann W (1992) Chemical recycling of polyurethanes and separation of the components by supercritical ammonia, Macromol Symp 57 305-310. 

Troev K, Grancharov G, Tsevi R and Tsekova A (2000) A novel approach to recycling of polyurethanes chemical degradation of flexible polyurethane foam by triethyl phosphate, Polymer 4 l 70l7-7022. 

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