Preparation of Controllable and Repeatable Crystalline States through Step-by-Step Self-Nucleation Programming and Its Application for Improving the PTC Reproducibility of trans-1,4-Polyisoprene/Carbon Black Composites

Polymers with a positive temperature coefficient (PTC) effect have exhibited poor reproducibility due to the rearrangement of the conductive network. In order to improve the reproducibility of PTC solely by regulating the crystalline states for semicrystalline polymers, the self-nucleation (SN) effect is used to achieve the repeatability of the skeleton crystal (SC) and driving crystal (DC). The melting of the DC contributes to the PTC performance, while the presence of the SC limits the migration of conductive fillers during the melting of the DC. In this work, a comparative study was conducted first on the SN process of trans-1,4-polyisoprene (TPI) and TPI/carbon black (TPI/CB) composites. It was found that the addition of CB narrowed the melt memory range from 42 to 9 °C, and the overall SN efficiency was reduced by 40%. Repeatable and appropriate content ratios of the SC and DC were prepared through step-by-step SN programming, which improved the reproducibility of PTC effectively.