Polyester-based polyurethane, tensile properties

This paper presents results from aging polyester based polyurethanes In methanol and water environments and In other mixtures of these media. The Influence of aging on mechanical properties was assessed by measuring tensile strengths and elongations at... 

Hydrolysis studies compared a polycarbonate urethane with a poly(tetramethyl-ene adipate) urethane and a polyether urethane based on PTMEG. After 2 weeks in 80°C water, the polycarbonate urethane had the best retention of tensile properties [92], Polycarbonates can hydrolyze, although the mechanism of hydrolysis is not acid-catalyzed, as in the case of the polyesters. Polycarbonate polyurethanes have better hydrolysis resistance than do standard adipate polyurethanes, by virtue of the highest retention of tensile properties. It is interesting to note in the study that the PTMEG-based urethanes, renowned for excellent hydrolysis resistance, had lower retention of physical properties than did the polycarbonate urethanes. 

The tensile properties of polyester-based thermoplastic polyurethanes were studied as a function of the time of exposure of the plastics to water, methanol, methanol-water, methanol-Isooctane, and methanol-water-lsooctane. The resulting decrease In the tensile properties of the plastics was attributed to reaction of the plastics with water and methanol. As Indicated by the decrease In properties, reaction with methanol Is Initially faster, but the reaction rate with water Increases with time — presumably because of the autocatalytic nature of the reaction. Nuclear magnetic resonance spectroscopy Indicated that the reaction mechanisms with methanol and water were transesterification and hydrolysis, respectively. 

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

Generally, the polyol will have either a polyester or a polyether backbone. The polyurethane elastomers based on an ester backbone generally have better abrasion resistance, tensile strength, tear strength, and oil resistance. On the other hand, polyurethane elastomers based on a polyether backbone generally possess better low-temperature properties, resiliency, and resistance to hydrolysis. 

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