A phase-transition model of reprocessible thermadapt shape memory polymer

A new type of thermadapt shape memory polymer (SMP) has not only the processability of thermoplastic SMP, but also the excellent shape fixation of thermosetting SMP. To enhance the application of this thermadapt SMP within industrial sectors, a comprehensive constitutive model based on phase transition is being proposed as an indicative descriptor of the semi-crystalline thermadapt SMP's salient features, predominantly related to its two-way shape memory effect (SME) and thermal reprocessability. The concept of cooling elongation is also introduced in this model for modeling the two-way SME during the crystallization process. The molecular mechanism of chain-packing has been studied and used to establish phenomenological formulas. In addition, to systematically assess the temperature-time dependence of the crystallization process, the Avrami equation is improved by incorporating the distribution of polymer chain segments. This strategy provides a detailed investigation into the evolving pattern of the crystallization process in response to various temperature and time conditions. Compared with the experimental results, it is found that our model can well capture mechanical behavior in multiple shape memory cycles, including the two-way SME and reshaping process caused by bond exchange reaction. Furthermore, the potential application of SMP in smart mandrels is explored because the cooling elongation feature is able to endow it with self-adaptive expansion ability.