Polyurethane elastomers ageing

Crystallinity in Hydrolytically Aged Polyester Polyurethane Elastomers... 

The detrimental effect of organotin catalysts of tetravalent tin on compression set of polyurethane elastomers after heat-ageing exposures is attributed to free-radical generation and cleavage of the ether bonds of polyether-based urethane foams resulting in polymer breakdown. 

Fig. 13.9. Effect of dry heat ageing on the properties of a typical commercial polyurethane (diamine-cured). (Source P. Wright A. P. C. Gumming, Solid Polyurethane Elastomers, Maclaren Sons, London, 1969.)...

The effects occurring by cyclical fatigue of polyurethane elastomer are influenced by the unitary stress values and accentuated by the concomitant polymer ageing. Figure 3.307. As expected, the deformations. Table 3.108, and durability. Figure 3.308, are changed, too. 

Figure 3.308. Variation of durability of polyurethane elastomer samples under the conditions of concomitant static fatigue and accelerated ageing with the solicitation effort (M = 6000 g/mol) [207],...

Figure 3. 332. ATG curves of the polyurethane elastomer supposed to static fatigue and accelerated ageing [910] 1) control 2) 9.7 MPa 3) aged 200 hr at 9.7 MPa 4) static fatigue at 9.7 MPa and concomitant accelerated ageing.

Table 3.116. Variation of the number of cycles until fracture, N, of a crosslinked polyurethane elastomer, suppose concomitantly to dynamical fatigue and accelerated ageing (v = 4 Hz, T = 60 °C) [917]...

Bhargava S, Kubota M, Lewis RD, Advani SG, Prasad AK, Deitzel JM. Ultraviolet, water, and thermal aging studies of a waterborne polyurethane elastomer-based high reflectivity coating. Prog Org Coat 2015 79 75-82. 

Fig. 61 CL dependencies on testing time recorded on aged hydroxyl-terminated polybutadiene based polyurethane elastomer. Testing temperature 120 °C. The data were taken from [06C1]. (1) pristine sample, (2) weathered sample for 105 days, (3) weathered sample for 140 days.

Another problem is that some persons are allergic to the proteins often found in natural rubber. This can be avoided by the use of a polyurethane condom. Unfortunately, as now made, these are more likely to tear (7-9% of the time) than the rubber latex condoms (2% of the time).65 It has been suggested that they be made of guayule rubber latex, which is free of the allergens.66 Thermoplastic elastomers, such as polystyrene-6-(ethylene-co-butene)-Apolystyr ene have been used to make gloves that are more resistant to ozone than those made of natural rubber.67 These should resist aging better than those made of natural rubber. It should be possible to mold a condom without holes from a thermoplastic rubber. 

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. 

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