Polyurethane . foam thermal degradation

Rychly J, Lattuati-Derieux A, Lavedrine B, Matisova-Rychla L, Malikova M, Csomor-ova K, et al. Assessing the progress of degradation in polyurethanes by chemiluminescence and thermal analysis, n. flexible polyether- and polyester-type polyurethane foams. Polym Degrad Stab 2011 96(4) 462-9. 

Polyurethane materials are extremely versatile in that it is possible to produce a large variety of structures which range in properties from linear and flexible to crosslinked and rigid. The crosslinked PURs are thermosets, which are insoluble and infusible and therefore cannot be reprocessed by extrusion without suffering extensive thermal degradation. At present, the main sources of recyclable waste are flexible PUR foams and automobile waste. Waste and scraps of these materials may consist of 15-25% by weight of total PUR foam production. 

Thermal degradation of foams is not different from that of the solid polymer, except in that the foam structure imparts superior thermal insulation properties, so that the decomposition of the foam will be slower than that of the solid polymer. Almost every plastic can be produced with a foam structure, but only a few are commercially significant. Of these flexible and rigid polyurethane (PU) foams, those which have urethane links in the polymer chain are the most important. The thermal decomposition products of PU will depend on its composition that can be chemically complex due to the wide range of starting materials and combinations, which can be used to produce them and their required properties. Basically, these involve the reaction between isocyanates, such as toluene 2,4- and 2,6-diisocyanate (TDI) or diphenylmethane 4,3-diisocyanate (MDI), and polyols. If the requirement is for greater heat stability and reduced brittleness, then MDI is favored over TDI. 

Modesti, M. Lorenzetti, A. Besco, S. Hrelja, D. Semenzato, S. Bertani, R. Michelin, R.A.. Synergism between flame retardant and modified layered silicate on thermal stability and fire behaviour of polyurethane nanocomposite foams. Polym. Degrad. Stab. 2008, 93, 2166-2171. 

Determination of 4,4/-methylenedianiline (5a) in hydrolyzed human urine may serve as a biomarker for exposure to methylenebis(4-phenyl isocyanate) produced on thermal degradation of polyurethane foam. The urine is hydrolyzed with H2SO4 and 4,4 -methylenedianiline (5a) is derivatized to the corresponding pentafluoropropionamide. 

Three methods that were used to measure the chemical changes associated with oxidative degradation of polymeric materials are presented. The first method is based on the nuclear activation of lsO in an elastomer that was thermally aged in an, 802 atmosphere. Second, the alcohol groups in a thermally aged elastomer were derivatized with trifluoroacetic anhydride and their concentration measured via 19F NMR spectroscopy. Finally, a respirometer was used to directly measure the oxidative rates of a polyurethane foam as a function of aging temperature. The measurement of the oxidation rates enabled acceleration factors for oxidative degradation of these materials to be calculated. 

Tang, Z., Maroto-Valer, M., Andresena, J. M., Miller, J. M., Listemann, M. L., McDaniel, P. L., Morita, D. K., and Furlan, W. R. Thermal degradation behavior of rigid polyurethane foams prepared with different fire retardant concentrations and blowing agents. Polymer, 43, 6471-6479 (2002). 

Polyurethane. Two polyurethane foams (Stepan Bx 250A, and General Electric Polyurethane) exhibited the best overall performance. The thermal performance of these insulations was initially excellent and degraded very slowly (see Fig. 13a). Both of these insulations survived the entire test series (over 4200 thermal cycles or the equivalent of approximately 15 years of airline service), with no evidence of structural failure. 

Kinetic studies have been made on the thermal decomposition of a poly(oxypropylene)triol-toluene di-isocyanate copolymer foam. Following a diffusion rate-controlled step, the cellular structure collapses to a viscous liquid and degradation then occurs on a random scission basis. Products of degradation of A-monosubstituted and A A-disubstituted polyurethanes have been analysed by direct pyrolysis in the ion source of a mass spectrometer. The mono-substituted polymers depolymerize quantitatively to di-isocyanates and diols, whereas the disubstituted materials decompose selectively to secondary amines, olefins, and carbon dioxide. The behaviour of the monosubstituted polymers has been confirmed in an i.r. study of the degradation of model compounds. A study of the thermal degradation in vacuum of polyurethanes prepared from butanediol, methylene bis(4-phenylisocyanate), and hexanedioic acid-ethylene glycol-propylene glycol polyesters has been reported and reaction mechanisms proposed. ... 

Zhu et al. studied polyurethane foams from soy reinforced with cellulose microfibers. They found an increase on the onset degradation temperature of the thermal degradation of polyurethane with the addition of 2 wt % cellulose fibers. They attributed this fact to the insulator effect of cellulose fibers [52]. Navarro-Baena et al. studied shape memory PU based on PLA-PCL-PLA block copolymer and reinforced with both CNCs and PLA grafted CNCs [72]. Aside the increment on the shape memory behavior of the polyurethane-based nanocomposites, they reported an increase on the thermal stability of the PU matrix in particular, they reported that, although CNCs improved the thermal stability of both PCL and PLEA blocks, in particular the thermal stability of the PCL block was improved in the nanocomposites increasing the maximum degradation temperature of about 40 with respect to the PCL block of the neat PU-matrix [72]. 

Zhang and co-workers [48, 49] used Py-GC-MS to study the effect of fire retardant concentrations on the thermal degradation of rigid polyurethane foams prepared with different blowing agents. Kim and co-workers [50] in their characterisation of polyurethanes identified polyol and diisocyanate in residues. 

Maslowski H, Kozlowski K and Czuprynski B (1977) Method of thermal degradation of waste rigid polyurethane foams to obtain raw materials for foam synthesis, Polish Patent 94 455. 

Polyurethane materials exist in a variety of forms including flexible or rigid foams, chemical resistant coatings, specialty adhesives and sealants, and elastomers. Most polyurethanes are thermoset materials they cannot be melted and reshaped as thermoplastic materials. Once the reactions have ceased the thermoset polyurethanes are cured and cannot be heat shaped without degradation. The thermal stability results from the croslinking degree of polymer chains (the crosslink density) and from the nature and frequency of repeating units within the polymer chains. 

The third polyurethane specimen, Last-A-Foam, exhibited good thermal performance for approximately 800 cycles (approximately 3 years of airline service) before experiencing a large degradation in thermal performance. The failure of the Last-A-Foam was first detected by a significant increase in the hydrogen boil-off rate. Visual examination of the warm insulation at that time revealed only a few very fine tributary type cracks. When the insulation was examined immediately after the next test period. 

Polyurethanes are manufactured by addition of polyols (polyether or polyester) with polyvalent isocyanates. Polyether-polyols are sensitive to oxygen. Thermal-oxidative degradation typically occurs during the manufacture of flexible foams when water is used to form carbon dioxide as blowing agent. Large PUR slab stock... 

Polyether-polyols used for manufacturing flexible foams are always equipped with antioxidants to prevent uncontrolled thermal autoxidation. Polyurethanes with polyester polyol segments are less sensitive to thermal-oxidative degradation than those with polyether polyol structures however, they can be subject to degradation reactions as a result of hydrolysis [38]. 

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