Cast polyurethane elastomers with improved dynamic fatigue resistance

Abstract

Cast polyurethane (PU) elastomers have been widely used in dynamic applications, such as rollers and wheels, where a low heat buildup, high‐loading resistance, and good cut‐growth resistance are desired. Because of their different molecular structure, cast PU elastomers do not perform in the same way in highly demanding dynamic applications. Small variations in the viscoelastic properties can result in significant differences in the longevity of the wheels and rollers that are subjected to a large number of cyclic compressive deformations. Therefore, it is of great interest to understand dynamic performance of urethane elastomers based on various backbones. Dynamic mechanical analysis (DMA) is commonly used to differentiate the dynamic performance of elastomers, but it only provides characterization of the dynamic behavior of a given elastomer at small deformation in the linear viscoelastic regime, where information such as the heat buildup and load‐bearing capability of elastomers cannot be obtained. As such, we developed a stress‐controlled flexometer on the basis of the ISO4666/4 method that enabled measurement of the heat buildup and load‐bearing capabilities of urethane elastomers in a large dynamic deformation environment. Moreover, a dynamometer was constructed to evaluate wheels based on different urethane elastomers under load at various speeds; this allowed close simulation of the urethane elastomers in a real application environment. In this article, the viscoelastic properties of cast urethane elastomers based on different backbones were studied by DMA. The heat buildup and load‐bearing capabilities of the elastomers were investigated via the stress‐controlled flexometer, and the performance of the wheels based on various prepolymer systems were evaluated with the dynamometer. Correlations between the material viscoelastic behavior and the heat buildup were established. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Improved dynamic properties of thermoplastic polyurethanes made fromco‐monomericpolyester polyol soft segments based on azelaic acid

“…In dynamic applications such as rollers and wheels, a low heat build-up is one of the desired properties of TPUs. 39 This study also shows that a co-monomeric polyester polyol could be used to modify the hysteresis value and tensile set of TPU to make it suitable for dynamic applications.…”

“…For reference, 0% hysteresis indicates no energy absorption and therefore illustrates perfectly elastic materials, whereas 100% hysteresis indicates complete energy absorption, resulting in no recovery after deformation. The area within the closed loop is the amount of mechanical energy converted into heat during the cycle 39 …”

“…The area within the closed loop is the amount of mechanical energy converted into heat during the cycle. 39 For clarity of presentation, tensile hystereses of the TPUs after one cycle are depicted in Figures 7 and 8. Figure 7 represents the hysteresis curves for all TPUs and Figure 8 represents the hysteresis of TPUs without BDSA-based TPU.…”

Thermal and mechanical properties of thermoplastic urethanes made from crystalline and amorphous azelate polyols

“…TPU prepared with 1,3‐PDO azelate polyol had the lowest percent hysteresis, demonstrating low heat build‐up compared with other TPUs. In dynamic applications such as rollers and wheels, a low heat build‐up is one of the desired properties of TPUs . Tensile set seems to be influenced by the diol chain length rather than its structure.…”

Polyurethane elastomers based on 1,3 and 1,4‐bis(isocyanatomethyl)cyclohexane

“…As discussed earlier, loss compliance is directly related to heat buildup in polyurethane elastomers. The lower the loss compliance value and the more constant the value remains over a wide temperature range, the better an elastomer is in its ability to resist the hysteretic heat build up under dynamic load application 21, 22. Figure 4 shows loss compliance of the three elastomers chain extended with Ethacure 100.…”