Dynamic self-stiffening in polyacrylonitrile/thermoplastic polyurethane composites

Abstract In this study, the self-stiffening under cyclic dynamic strain has been observed in polymeric blends containing polyacrylonitrile (PAN) and various contents of thermoplastic polyurethanes (TPU). The increase of the stiffness depends on the phase diagram of the blend, and it was found that the efficiency of self-stiffening decreases when phase separation occurs. Also, TPU containing alternative hard and soft blocks. When the hard block content in TPU increases, the self-stiffening becomes more effective. The interactions between PAN and TPU were investigated by different characterization methods. The soft and hard blocks of TPU plays different roles on the self-stiffening of the PAN/TPU blends, and the interface in between hard blocks and PAN matrix is crucial for the mechanical enhancement. These results indicate that the interface in between polymer chains with significant property difference could possibly lead to unique behaviors. Here, we observe that the fatigue life of PAN films under cyclic strains increases to more than 28 times, as well as the cyclization peak shifts to lower temperature and becomes broader with the addition of 0.5 wt % TPU. These interfaces induced unique behaviors, such as self-stiffening and longer fatigue life, would be valuable for the future developments of adaptable structural materials.