Linear low density polyethylene (LLDPE)/high density polyethylene (HDPE) blends doped conductive graphite powders were constructed by the traditional melt‐blending method to acquire the conductive compatible polymer composites, and corresponding positive temperature coefficient (PTC) effect of electrical resistivity was investigated. The results indicated that the room‐temperature resistivity gradually decreased and PTC effects were remarkably enhanced by regulating the graphite contents or LLDPE/HDPE ratios. Especially, with increasing graphite contents, the polymer‐fixed composites showed the notable double PTC effects, originating from the volume expansion of the co‐crystallization or their fraction. Whereas, with increasing the LLDPE/HDPE ratio, the PTC effects of the graphite‐fixed composites occurred at the lower temperature, even far below the melting points of the co‐crystallization. Therefore, the regulation of co‐crystallization morphology of compatible polymer matrices was a new idea in the improvement of PTC materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46453.

The economical graphite‐filled thermoplastic urethane/ultra‐high molecular weight polyethylene (TPU/UHMWPE) composites with the segregated structure were constructed by the combination of mechanical crushing and melt blending method. The low percolation threshold of 1.89 wt% graphite in the adjustable segregated composites was obtained and high electrical conductivity was about 10−1 S m−1 at 10 wt% graphite loadings owing to the formation of three‐dimensional conductive networks. Moreover, when the graphite loadings were over the percolation threshold, the remarkable positive temperature coefficient (PTC) effect of electrical resistivity for TPU/UHMWPE‐Graphite composites were achieved, originating from the combined thermal motion of TPU and UHMWPE. Meanwhile, the outstanding repeatability of PTC effects was obtained after 5‐time cycles. Therefore, economical conductive polymer composites were still the promising field in the practical application of PTC materials.

In this work, amorphous polystyrene/chlorosulfonated polyethylene composites doped with multiwalled carbon nanotubes (PS/CSPE‐MWCNT) were constructed by in situ polymerization to form semi‐interpenetrating networks. The MWCNTs showed excellent dispersion and selective location in the PS regions. High electrical conductivity and low percolation threshold (0.89 wt %) for the composites were achieved. An enhanced positive temperature coefficient (PTC) behavior for amorphous PS/CSPE‐MWCNT composites was first reported, nearly without a negative temperature coefficient (NTC) effect when the conductive fillers were beyond the percolation threshold, similar to those of crystalline polymer composites. Moreover, a PTC intensity of more than five orders of magnitude and excellent repeatability of the PTC effect were achieved. This study offers new insight into the development of novel PTC materials with low percolation threshold. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47053.

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In this work, electrically conductive polyethylene/polypropylene-flake graphite composites with different ratios (HDPE/PP-FG) were prepared by simple mechanical blending (Mec) and melt blending (Mel) technologies, combining with the grinding technique. According to the effect of preparation technique, dual continuous microstructures for Mec-HDPE/PP-FG composites were self constructed by controlling specific molding temperature. As a result, the percolation threshold of 1.33 wt% of Mec-HDPE 1 /PP 4 -FG was achieved, much lower than that of Mel-HDPE 1 /PP 4 -FG (7.02 wt%) and the maximum in conductivity was over 10 À3 S/m at about FG content of 6 wt%. However, Mel-HDPE 1 /PP 4 -FG only showed the electrical conductivity of about 8.0 Â 10 À11 S/m when FG content was 6 wt%. Meanwhile, Mec-HDPE/PP-FG composites presented obvious positive temperature coefficient (PTC) effect of electrical resistivity, without negative temperature coefficient (NTC) effect and PTC intensity was up to 6.57 orders of magnitude, far higher than those of Mel-HDPE/PP-FG composites. In addition, the excellent repeatability in PTC behaviors for Mec-HDPE/ PP-FG was achieved after several run cycles. Therefore, the study on economical and facile polymer materials with high performance PTC characteristics had the great significance in practical application.