High‐density polyethylene/carbon black conductive composites. II. Effect of electron beam irradiation on relationship between resistivity–temperature behavior and volume expansion

A study on the contribution of thermal volume expansion to electrical properties is carried out for high‐density polyethylene (HDPE)/carbon black (CB) composites irradiated by an electron beam. The results show that the volume expansion obviously generates the positive temperature coefficient (PTC) characteristic of resistivity for unirradiated HDPE/CB composites, but the contribution of volume expansion is decreased for crosslinked HDPE in the composites by electron beam irradiation. A higher degree of crosslinking produced by irradiation in the molten state limits the movability of HDPE chains and CB particles so effectively that it decreases the PTC intensity, which is compared with that irradiated at room temperature. It is suggested that the differences in the resistivity–temperature behavior are not explained satisfactorily on only the basis of the thermal volume expansion, and the decreased movability of HDPE chains and CB particles are believed to be the most fatal factors in lowering the PTC effect. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3117–3122, 2002; DOI 10.1002/app.10050     

Resistivity–volume expansion characteristics of carbon black‐loaded polyethylene

The resistivity and volume expansion of carbon black (CB)/high‐density polyethylene (HDPE) composite with different CB volume fractions at different temperatures were measured simultaneously. A model based on Meyer's theory is proposed to explain the positive temperature coefficient resistance (PTCR) effect. The relationship between resistivity and volume expansion was determined. It was found that the phase change is the main cause of the PTC effect in the crystalline polymer PTC materials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 53–58, 2000     

Factors influencing the resistivity–temperature behavior of carbon black filled isotactic polypropylene/high density polyethylene composites

The relationship between morphology and resistivity–temperature behavior of carbon black (CB) filled isotactic polypropylene/high density polyethylene (iPP/HDPE) composites was investigated. The positive temperature coefficient intensity for all composites studied in this paper was lower than one and the negative temperature coefficient (NTC) effect was obvious. The factors influencing resistivity–temperature behavior include the CB contents, types of the polymer matrices and their composition, which determine the phase morphology and thus the conductive network. The types of iPP and HDPE influenced the NTC effect, while the morphology of the composites mainly influenced the initial volume resistivity of the composites.     

Morphology and electrical properties of carbon black-filled poly(ε-caprolactone)/poly(vinyl butyral) blends

Electrical properties of poly(ε-caprolactone) (PCL)/poly(vinyl butyral) (PVB) blends containing carbon black (CB) were studied as a function of a small amount of PVB content and a wide range of molecular weight of PVB. For samples with the same CB content, the intensity of positive temperature coefficient (I_PTC, defined as the ratio of peak resistivity to resistivity at room temperature) of the blends was increased, with PVB content greatly and molecular weight of PVB weakly. As the band spacings of PCL spherulites in PCL/PVB blends decrease with PVB content and molecular weight of PVB, the changes of the positive temperature coefficient property are ascribed to the morphological difference (i.e., period of twisted lamellae) in the blends. We confirmed our previous conclusion that the origin of the positive temperature coefficient phenomenon is the changes of the distribution of the CB on the melting of the crystalline phase. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 193–199, 1998     

Positive temperature coefficient effect and mechanism of compatible LLDPE/HDPE composites doping conductive graphite powders

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.     

Conductive-filler-filled poly(≥-caprolactone)/poly(vinyl butyral) blends. II. Electric properties (positive temperature coefficient phenomenon)

The electric properties of poly(ε-caprolactone) (PCL)/poly(vinyl butyral) (PVB) blends containing carbon black (CB) were studied as a functions of the PVB content and crystallization time. Comparison of the electric properties between the two cases (PCL/PVB blends and pure PCL) provided us useful information on the origin of the positive temperature coefficient (PTC) phenomenon of the resistivity. In this article, we report the influence of the morphology and the spherulitic structure on the distribution of CB, which results in the resistivity changes. Blending a small amount (up to 5%) of PVB caused significant changes in the electric property at a constant CB content. Both the resistivity and the intensity of PTC increased with the PVB content. These changes are ascribed to the change of CB distribution. A model is proposed to explain these results using Ohe's theory. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:409–416, 1997     

Effect of coefficient of thermal expansion on positive temperature coefficient of resistivity behavior of HDPE–Cu composites

Positive temperature coefficient of resistivity (PTCR) characteristics of (high density polyethylene) HDPE–Cu composites has been investigated with reference to the conventional HDPE–CB (carbon black) composites. Plot of resistivity against temperature of HDPE–CB composites showed a sudden rise in resistivity (PTC trip) at 127°C, close to the melting temperature of HDPE. However, the PTC trip temperature (98°C) for HDPE–Cu composites was appeared well below the melting temperature of HDPE. Addition of 1 phr nanoclay in the composites resulted in an increase in PTC trip temperature of HDPE–Cu composites, whereas no significant effect of nanoclay on PTC trip temperature was evident in case of HDPE–CB–clay composites. We proposed that the PTC trip temperature in HDPE–Cu composites was governed by the difference in coefficient of thermal expansion (CTE) of HDPE and Cu. The room temperature resistivity and PTC trip temperature of HDPE–Cu composites were very much stable upon thermal cycling. DMA results showed higher storage modulus of HDPE–Cu composites than the HDPE–CB composites. Thermal stability of HDPE–Cu composites was also improved compared to that of HDPE–CB composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High‐density polyethylene/carbon black conductive composites. I. Effect of CB surface modification on its resistivity–temperature behavior

The effect of the interaction between a polymeric matrix and conductive particles of carbon black (CB), especially the interaction enhanced by oxidizing CB (o‐CB), on the resistivity–temperature behavior of its composites was studied. The results reveal that the interaction between ethylene‐vinyl‐acetate and CB is stronger than that between high‐density polyethylene and CB. The room temperature resistivity of the o‐CB filled system subsequent to thermal cycles increases to a lower extent in comparison with those filled with virgin CB. Moreover, the resistivity decrease of composites filled with o‐CB needs a longer time than that of the virgin CB filled system during isothermal annealing, meaning that the resistivity–temperature behavior of the former is much more stable than that of the latter. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3112–3116, 2002; DOI 10.1002/app.10049     

HDPE/CB复合体系PTC行为的工艺研究

采用高结构导电炭黑(CB)Vxc—72与半晶聚合物高密度聚乙烯(HDPE)进行熔融共混，制备复合型导电高分子材料。研究了该复合体系中偶联处理、混炼时间、辐射及退火处理等工艺因素对其PTC(电阻—温度效应)性能的影响。结果表明，当辐照剂量为140—160kGy、炭黑非均匀分散且进行退火处理时复合体系具有最佳的PTC性能，但混炼时间过长、偶联处理均会使复合体系PTC强度降低。     

Effect of the carbon black structure on the stability and efficiency of the conductive network in polyethylene composites

Composites of high‐density polyethylene (HDPE) with different kinds of carbon black (CB) were prepared through melt blending. The influence of the CB structure on the stability and efficiency of the conductive network in HDPE/CB composites were mainly investigated. Scanning electron microscopy was used to observe the morphology of the CB primary aggregates. The relationship between the temperature‐resistivity behaviors of the composites and the crystallization behaviors of the matrix were also investigated. High‐structure CB built an effective conductive network at a low filler content compared to the low‐structure one because of its branched morphology. Therefore, the composite containing high‐structure CB revealed a lower percolation threshold. The composite containing low‐structure CB obtained a stronger positive temperature coefficient (PTC) intensity because the cluster network was fragile and easily damaged during matrix melting. The reproducibility of the results of PTC effect of the composite containing high‐structure CB was better than that of the composite containing a low‐structure one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

LDPE/carbon black conductive composites: Influence of radiation crosslinking on PTC and NTC properties

The electrical resistivity of low‐density polyethylene/carbon black composites irradiated by ⁶⁰Co γ‐rays was investigated as a function of temperature. The experimental results obtained by scanning electron microscopy, solvent extraction techniques, and pressure‐specific volume‐temperature analysis techniques showed that the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects of the composites were influenced by the irradiation dose, network forming (gel), and soluble fractions (sol). The NTC effect was effectively eliminated when the radiation dose reached 400 kGy. The results showed that the elimination of the NTC effect was related to the difference in the thermal expansion of the gel and sol regions. The thermal expansion of the sol played an important role in both increasing the PTC intensity and decreasing the NTC intensity at 400 kGy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2742–2749, 2002     

The correlativity of positive temperature coefficient effects in conductive silicone rubber

A thorough study on the positive temperature coefficient (PTC) effects of conductive silicone rubber was made. Various conductive silicone rubbers with apparent differences in PTC anomalies (defined as the ratio of peak resistivity to room temperature resistivity) were chosen. The correlation between the size of the PTC anomaly and both the thermal expansion coefficient of conductive silicone rubber and the interaction between silicone rubber and carbon black (CB) were found. The effects of cross‐linking on the temperature effect of resistivity of conductive silicone rubber were also studied. The results testify the important role of the interaction between silicone rubber and CBs in the temperature effect of resistivity of conductive silicone rubber. Copyright © 2005 Society of Chemical Industry     

Improvement of polyimide/polysulfone composites filled with conductive carbon black as positive temperature coefficient materials

In this study, polyimide (PI)/polysulfone (PSF) blends filled with carbon black (CB) were developed for the use as positive temperature coefficient (PTC) materials in order to achieve the volume resistivity as lower than 10⁴ Ω.cm at room temperature. The weight ratios of PI/PSF were various from 100/0 to 10/90 with CB varied from 0 to 20 wt%. The use of conductive filler was reduced when PSF was blended with PI; the blends clearly possessed a percolation threshold decreased by 90%. The electrical conductivity of the CB-filled blends was higher than those of CB-filled pure PI. The transition temperature for PTC material was reported in the range of 180 to 210 °C. The preferential location of CB filler in PI domains could be observed using the optical microscope. In addition, the composites met the standards for the obtained mechanical and thermal properties, exhibiting the potential use as PTC materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48482.     

Effect of the high‐density polyethylene melt index on the microcellular foaming of high‐density polyethylene/polypropylene blends

The effect of high‐density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high‐melt‐index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004     

The Stabilization Effect of Tris(hydroxymethyl)aminomethane and Oxidation of Carbon Black on the Resistivity-Temperature Character of Carbon Black-Filled Polyethylene

Carbon black (CB)-filled high density polyethylene (HDPE) composites, incorporating with or without tris(hydroxymethyl)aminomethane (Tris), were prepared by melt blending. The effects of CB oxidation and Tris incorporation on the resistivity-temperature characters were studied. The negative temperature coefficient effect (NTC) effect and the isothermal variation of resistance with time were reduced by incorporating Tris, and oxidation of CB enhanced the effects of Tris addition. The reason lies in the increase of polarity resulting from CB oxidation and the interaction between Tris and CBs.     

Study on time‐dependent resistance of carbon black‐loaded high‐density polyethylene composites during the isothermal course

Carbon black (CB)‐loaded high‐density polyethylene composites were prepared using conventional blending. The resistance and temperature (R‐T) relations under constant heating rates and the resistance and time (R‐t) relations at different isothermal temperatures have been studied. The results of the R‐T and differential scanning calorimetry (DSC) curve demonstrated a correlation between the positive temperature coefficient/negative temperature coefficient transition and the melting course. At isothermal temperatures below T_PTC/NTC, the resistance displayed a sharp increase and thereafter a mild decrease with time. The time to reach the highest resistance became shorter with rise in the isothermal temperature. The ratio between highest resistance and initial resistance was maximum at T_peak of the DSC curve. When the isothermal temperature was higher than T_PTC/NTC, the resistance attenuated with time. The attenuation fits to a first order exponential decay function. The calculated time constant τ decreased with rise in isothermal temperature. The attenuation discrepancy under different isothermal temperatures reduced as the heating rate before the isothermal courses was higher. A model based on polymer chain diffusion and CB movements at high temperature is proposed. The model can explain the results obtained in R‐T and R‐t measurements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2258–2263, 2001     

高密度聚乙烯/多壁碳纳米管和高密度聚乙烯/炭黑导电复合材料阻温特性的研究

采用溶液法制备了高密度聚乙烯/多壁碳纳米管（PE-HD/MWCNTs）和PE-HD/炭黑(CB)导电复合材料,并研究了该复合材料的阻温特性。结果表明,与PE-HD/CB复合材料相比,PE-HD/MWCNTs复合材料的室温电阻率更低,并且可以具有较高的正温度系数（PTC）强度和较小的负温度系数（NTC）效应,因而具有更加广泛的应用前景。同时通过对PE-HD/MWCNTs复合材料阻温全过程进行分析,发现PTC效应由碳纳米管向晶区扩散及基体体积膨胀效应共同导致,而NTC效应则是由于碳纳米管的热运动形成的相互接触所致,而并非粒子附聚。     

Electrical properties and morphology of carbon black‐filled HDPE/EVA composites

The sensitive effect of weight ratio of the high‐density polyethylene (HDPE)/ethylene‐vinylacetate copolymer (EVA) on the electrical properties of HDPE/EVA/carbon black (CB) composites was investigated. With the EVA content increasing from 0 wt % to 100 wt %, an obvious change of positive temperature coefficient (PTC) curve was observed, and a U‐shaped insulator‐conductor‐insulator transition in HDPE/EVA/CB composites with a CB concentration nearby the percolation threshold was found. The selective location of CB particles in HDPE/EVA blend was analyzed by means of theoretical method and scanning electron micrograph (SEM) in order to explain the U‐shaped insulator‐conductor‐insulator transition, a phenomenon different from double percolation in this composite. The first significant change of the resistivity, an insulator‐conductor transition, occurred when the conductive networks diffused into the whole matrix due to the forming of the conductive networks and the continuous EVA phase. The second time significant change of the resistivity, a conductor‐insulator transition, appeared when the amorphous phase is too large for CB particles to form the conductive networks throughout the whole matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on the comprehensive performance of graphite and additives filled high density polyethylene composites

The comprehensive performance of graphite and additives filled high‐density polyethylene (HDPE) composites is studied in this article. Four graphites with different particle diameters are used as conductive fillers in HDPE/graphite. Plasticizer, nucleator, and certain particle diameter graphite are employed to prepare HDPE composite. The behavior of crystallization and the distribution of graphite are also studied by means of SEM. An orthogonal design experiment is taken to optimize the content of the filler. The experimental results indicate that the positive temperature coefficient (PTC) effect is related to the particle diameter of graphite. And the bending strength of HDPE/graphite composite with the plasticizer and nucleator is two times less than that of HDPE‐graphite blends. Meanwhile, the high PTC intensity (the ratio of peak resistivity to room temperature resistivity) is also preserved. An excellent comprehensive performance conductive composite is prepared. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008