Study On Thermal Effects Of Polyurethane Elastomer During Extension-Retraction Process

Polyurethane elastomer, which can be made into all kinds of industrial products by injecting, blowing film, extruding, spinning etc., is of combination properties of both rubber and plastics. The products of polyurethane elastomer with good abrasion resistance, high mechanical strength, resisting avulsion intensity and good chemical resistance can be applied in various areas. Polyurethane elastomer shows the phenomenon of stress softening and hysteresis in the deformation process which is related to molecular motion. Besides, polyurethane elastomers prepared with different methods are of different properties, for example, dry-spinning polyurethane fiber presents better mechanical properties compared with melt-spinning polyurethane fiber, which is determined by the different microstructurial changes in the deformation process. Therefore, study on the microstructural changes and molecular motion of polyurethane elastomer in the deformation process is of important theoretical and practical value. Infrared thermography technology (IRT) is a useful method to measure the material surface temperature, which can reflect the thermal effect clearly. In this paper, the temperature and load changes of polyurethane elastomer during the extension-retraction process were simultaneously measured by an infrared thermography and a tensile testing machine (TTM). The microstructural changes under deformation were analyzed. The main works and results were presented as follows:1. The temperature change of dry-spinning polyurethane fiber in the loading-unloading cycles was measured and the stress softening phenomenon of the fiber was analyzed. A hyperelastic-viscoplastic model was applied to describe the features of mechanical behavior and thermal effect. The results indicated that all of these phenomena were related to the polyurethane structurial rearrangement and the generation of irreversible frictional heat in the first loading process.The first law of thermodynamics was used to discuss the internal energy change.2. The difference of the mechanical properties and thermal effect in the loading-unloading process was compared between dry-spinning and melt-spinning polyurethane fiber. The results showed that the stress softening of dry-spinning polyurethane fiber was more obvious than that of melt-spinning polyurethane fiber and the value of temperature difference between the first two loading process was larger as well. The phenomenon was derived from dry-spinning polyurethane fiber with larger hydrogen bond density, and therefore, the larger number of physical crosslinking pionts, which blocked the molecular motion to a certain extent.3. The thermoplastic polyurethane/attapulgite (TPU/AT) composites were prepared via solution-blending method. The SEM、FTIR and IRT combined with TTM were used to study the influence of AT on TPU matrix. The results demonstrated that the hydrogen bond interaction was affected and mechanical properties were improved with the addition of AT nanorods. The temperature and load changes of TPU/AT nanocomposites in the first loading process were more obvious than that of pure TPU. At the same time, the value of temperature difference between the first two loading process was larger in TPU/AT nanocomposites as well. The results indicated that with the addition of AT nanorods, small physical crosslinks were formed between AT and TPU matrix which hindered the molecular motion in the deformation process and finally affected the mechanical behavior and thermal effect.