Degradable polyurethanes performance

Abrasion-resistant duties may involve abrasion in an aqueous phase or abrasion by dry particulate materials. The selection of the polyurethane type is most important to obtain the best results. Polyester-based polyurethanes perform best in dry abrasion due to their low hysteresis properties and excellent resistance to cut initiation and propagation. However, polyester polyurethanes are susceptible to hydrolytic degradation, and therefore polyether polyurethanes are normally used for aqueous abrasion duties. 

Autoclave sterilization is one of the most difficult common sterilization environments for a medical adhesive, and it is commonly used in hospitals and health care facilities for reusable devices. Autoclaves sterilize with high-pressure steam. Temperatures inside the sterilization chamber typically can reach 130°C with pressures above ambient. Certain adhesive systems, such as polyurethanes, may show hydrolytic degradation in such environments especially after multiple cycles. Epoxies perform the best under multiple autoclave exposures. However, on certain substrates, light-cured acrylics and cyanoacrylates will also perform fairly well. 

It is well known that conventional polyester-based urethane elastomers extended with butanediol can withstand continuous use temperatures of about 80 °C. At higher temperatures, a reduction in the physical and mechanical properties is seen due to degradation of the material. The thermal stability of the polyurethanes is related to the nature of the starting materials such as the aromatic diisocyanate and diol chain extender. The hard segment of the urethane elastomer is primarily responsible for temperature resistance, and the soft segment determines the material s performance at low temperature. 

Spirckel, M., Rengier, N., Mortaigne, B., Youssef, B., and Bunel, C. Thermal degradation and fire performance of new phosphonate polyurethanes. Polymer Degradation and Stability, 78, 211-218 (2002). 

Allophanate and biuret bonds in polyurethane foam can be determined by degrading the foam with amines and subsequently performing quantitative titrations. This methodology is not of interest for routine analysis but is sometimes useful for fundamental understanding of the polymerization reaction. 

Yashitake and Furukawa investigated the thermal degradation mechanism of a.y-diphenyl alkyl allophanates and carbanilates as model compounds for crosslinking sites in polyurethane networks by pyrolysis-high-resolution GC/ FTIR (Py-HR GC/FTIR). Pyrolysis was performed at 250°C, 350°C, 450°C, and 500°C. 

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. 

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. 

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