Tunable Pyroresistive Behavior in Conductive Polymer Composites with a Secondary Elastomer Phase

Positive-temperature-coefficient (PTC) polymer composites have emerged as a class of smart materials with notable interest and success, particularly in the field of overcurrent protection, self-regulating heating, and temperature sensing. However, a key problem with these composites is the negative temperate coefficient (NTC) effect, where past the peak PTC temperature, the electrical resistivity decreases due to the reagglomeration of the conductive filler. This opposing and unintended behavior compromises performancewhich can be greatly hazardous in situ. Currently, physical (e.g., via irradiation) or chemical cross-linking of the composite polymer matrix remains the main method for negating NTC behavior, which substantially increases cost, reduces flexibility, and negates the possibility to recycle the material at the end of its life. Herein, we investigate a dispersed secondary-phase composite made of high-density polyethylene (HDPE), a high-temperature copolyester thermoplastic elastomer (TPE), and graphitic nanoplatelets (GNPs). It is demonstrated that the conductive polymer composite blend presents a unique and tunable pyroresistive response and a marked suppression of the NTC characteristic, even at very low content of the secondary polymer phase (2.5 wt % of TPE). Moreover, the formulation exhibits the ability to switch self-regulation temperature at specific ratios. The results are formulated through simple melt compounding without postprocessing, providing a cost-effective and safe solution to undesirable NTC properties and preserving the end-of-life option of thermo-mechanical recycling.