Abstract
High-density polyethylene (HDPE)/carbon black (CB) is widely used in positive temperature coefficient (PTC) composites. In order to expand its applications to fields that need good flexibility, polyolefin elastomer (POE) was incorporated into HDPE/CB composites as a secondary thermoplastic elastomer phase to provide flexibility. The effects of POE and CB content on the PTC performance and flexibility were investigated. Micro morphology and crystallization behavior are closely related to PTC properties. SEM was conducted to reveal phase morphology and filler dispersion, and DSC was conducted to research crystallization behavior. The results show that the incorporation of 18 wt.% POE can decrease the percolation threshold of conductive carbon black from 22.5 wt.% to 16 wt.%. When the CB content is 30 wt.%, the room temperature resistivity gradually increases with the increasing content of POE because of the barrier effect of POE phase, and the PTC intensity is gradually enhanced. Meanwhile, the PTC switching temperature shifts down to a lower temperature. The incorporation of 18 wt.% POE significantly increases the elongation at break, reaching an ultrahigh value of 980 wt.%, which means great flexibility has been achieved in HDPE/POE/CB composites. This work provides a new method of fabricating PTC composites with balanced electrical and mechanical properties.
Highlights
Conductive polymer composites (CPCs) exhibit a sharp electrical resistivity increase when the temperature is close to the melting point of the polymer, which is called the positive temperature coefficient (PTC) effect [1]
As early as the 1950s, the PTC effect was found in carbon black-filled polyolefin composites, which was first suggested by Frydman to be used in electrical circuit protection, selfregulating heaters, and temperature sensors [1]
The room temperature resistivity of High-density polyethylene (HDPE)/CB decreases dramatically by about 5.3 orders of magnitude in the range of CB content from 20 wt.% to 25 wt.%, while the room temperature resistivity of HDPE/polyolefin elastomer (POE)/CB decreases dramatically by about 3.0 orders of magnitude in the range of CB content from 15 wt.% to 20 wt.%, indicating that good conductive networks are formed in the concentration ranges
Summary
Conductive polymer composites (CPCs) exhibit a sharp electrical resistivity increase when the temperature is close to the melting point of the polymer, which is called the positive temperature coefficient (PTC) effect [1]. As early as the 1950s, the PTC effect was found in carbon black-filled polyolefin composites, which was first suggested by Frydman to be used in electrical circuit protection, selfregulating heaters, and temperature sensors [1]. Up to now, they are still widely used in these fields [2,3,4,5,6,7,8,9]. Batteries suffer from poor performance such as low charging and discharging rate and low charge and discharge capacity [13]. PTC composites are expected to be the heating material with great development potential
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