Study On The Properties Of Carbon Nanotube/Polymer Composite Thermistors

Polymer materials with positive temperature coefficient(PTC) is sensitive to temperature, and was widely used in many industries, like over-current protectors or self-regulating heaters, which have been drawing more and more attention due to its sensitiveness to temperature characteristics.At present, commercial thermistors are the carbon black (CB) filled high density polyethylene (HDPE) composites. At an elevated temperature, the crystalline regions of HDPE begin to melt, and the resulting volumetric expansion of matrix leads to a disconnection of the previously connective pathways of CB, consequently resulting in a sharp increase in electrical resistance (the PTC effect). Although the CB/HDPE thermistors have been widely applied over several decades, there still exist some challenges for the CB/HDPE thermistors. The high filler contents over 20wt-30wt% and low thermal stability are two crucial disadvantages due to the intrinsic low electrical conductivity of CB and poor thermal stability, greatly hindering practical applications of the CB/HDPE thermistors in some fileds, especially in some rigorous conditions of high applied voltage and large current in electric transferring and communication industries.Carbon nanotubes (CNTs) exhibit much higher electrical and thermal conductivity and larger aspect ratio than CB, which is beneficial to fabricate optimal conductive networks and can obtain high-performance thermistors. The PTC effects of the CNT filled polymer composites have been widely investigated.In our work, we prepared the CNT/HDPE and CNT/POM composite thermistors, investigated the related technical properties, such as PTC effects, voltage-current cures, electrical resistance at room temperature, and responding rates, and compared them with commercial CB/HDPE composites, in order to reduce the amount of conductive filler and explore the potentials of the CNT-based thermistors in high-current and high-voltage applications. We found for the first time that the CNT/HDPE thermistors exhibit much higher resistance to high applied voltage than the CB/HDPE thermistors, The maximum holding voltage and the holding current of the CNT/HDPE thermistors are 3.9 V and 182.9 mA, increasing by 178.5 % and 128.6% in comparison with the holding voltage of 1.4 V and holding current of 80 mA for the commercial CB/HDPE thermistors,that is, the CNT-based thermistors can still retain a low resistance even under a high applied voltage. The high voltage-resistance characteristics of the CNT-based thermistors are mainly attributed to the high thermal conductivity of CNT networks, indicating that the CNT-based composites can be applied as high-performance thermistors in electric power transfer, communication industries.