The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series o...The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with various gamma-irradiation doses in HDPE/CB composite containing 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value in HDPE/CB composite is about 16.7 wt% and the suitable gamma-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad. The result observed for the second set of samples suggests that gamma-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure. Therefore, a suitable irradiation dose, about 20 Mrad, can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure, so that the positive temperature coefficient (PTC) effect remains while the negative temperature coefficient (NTC) effect is suppressed. A new interpretation of the conductive mechanism, which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.展开更多
The study on the correlation between electrical percolation and viscoelastic percolation for carbon black（CB） filled high-density polyethylene（HDPE） conductive composites was carried out through examining the fill...The study on the correlation between electrical percolation and viscoelastic percolation for carbon black（CB） filled high-density polyethylene（HDPE） conductive composites was carried out through examining the filler volume fraction dependence of the volume resistivity（ρ） and normalized dynamic storage modulus,G c/G p,in which G c,G p are dynamic storage modulus of the composites and the matrix respectively. The results revealed that the critical filler volume fraction of viscoelastic percolation approached the lower threshold（φ1） of the electrical percolation,indicating an insulator-semiconductor change corresponding to the beginning of network structure formation. Substituting K for A,a modified Kerner-Nielson equation was obtained and used to analyze the formation of network structure. It is suggested that parameter K is associated with CB volume fraction. [WT5HZ]展开更多
The study on the correlation between time dependence of electrical resistivity and dynamic storage modulus for carbon black(CB) filled polymer composites was carried out. With the increase of the dynamic storage modul...The study on the correlation between time dependence of electrical resistivity and dynamic storage modulus for carbon black(CB) filled polymer composites was carried out. With the increase of the dynamic storage modulus(G′) as well as the normalized dynamic storage modulus(G′_ c /G′_ p), the volume resistivity(ρ) deceases with the increase of annealing time beyond the T_ m of the composites. It is believed that this phenomenon can be used for examining the development of agglomerate structure of filled composites and illustrating the micro-mechanism of the NTC behavior. It is assumed that melting treatment to CB filled composites results in a higher modulus and lower resistivity due to more even local dispersion of the particles and formation of perfect CB network structure within the matrix.展开更多
Thermal conductivity (TC) of high density polyethylene/multiwall carbon nanotube (HDPE/MWCNT) composite films was measured by laser pulse method. It is found that the TC increased quickly with the increase of MWCNT fr...Thermal conductivity (TC) of high density polyethylene/multiwall carbon nanotube (HDPE/MWCNT) composite films was measured by laser pulse method. It is found that the TC increased quickly with the increase of MWCNT fraction when the volume fraction of MWCNT was below 3.35%. However,as the volume fraction of MWCNT was over 3.35%,the increasing rate became slow. A new percolation model was proposed based on the effect of MWCNT network to simulate the TC of HDPE/MWCNT composite films. The simulation result was in good agreement the experimental data well. In addition,the relationship of TC with the increase of temperature was also discussed.展开更多
The blends prepared by incorporation of carbon black (CB) or graphite powder (GP) inHto high-density polyethylene (HDPE) matrix have been novel and extensively applied polymeric positive temperature coefficient (PTC) ...The blends prepared by incorporation of carbon black (CB) or graphite powder (GP) inHto high-density polyethylene (HDPE) matrix have been novel and extensively applied polymeric positive temperature coefficient (PTC) composites. A phenomenological model was proposed on the basis of the GEM equation and the dilution effect of filler volume fraction due to the thermal volume expansion of the polymer matrix. Accordingly, the contribution of the thermal expansion of the matrix to the jump-like PTC transition of the composites was quantitatively estimated and a mechanical explanation was given. It was proved that the contribution of the volume expansion to PTC effect decreased for HDPE/CB composites crosslinked through electron-beam irradiation. Furthermore, the influences of the filler content, temperature and crosslinking on the self-heating behavior as well as the nonlinear conduction characteristics at electrical-thermal equilibrium state were examined. Based on the electric-field and initial resistivity dependence of the self-heating temperature and resistance dependence of the critical field, the mechanisms of the self-heating of the polymeric PTC materials were evaluated. The intrinsic relations between macroscopic electrical properties and microscopic percolation network at electrical-thermal equilibrium state were discussed according to the scaling relationship between the self-heating critical parameter and the conductivity of materials.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant No: 19875050, 10075041, 10075044).
文摘The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with various gamma-irradiation doses in HDPE/CB composite containing 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value in HDPE/CB composite is about 16.7 wt% and the suitable gamma-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad. The result observed for the second set of samples suggests that gamma-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure. Therefore, a suitable irradiation dose, about 20 Mrad, can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure, so that the positive temperature coefficient (PTC) effect remains while the negative temperature coefficient (NTC) effect is suppressed. A new interpretation of the conductive mechanism, which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.
文摘The study on the correlation between electrical percolation and viscoelastic percolation for carbon black（CB） filled high-density polyethylene（HDPE） conductive composites was carried out through examining the filler volume fraction dependence of the volume resistivity（ρ） and normalized dynamic storage modulus,G c/G p,in which G c,G p are dynamic storage modulus of the composites and the matrix respectively. The results revealed that the critical filler volume fraction of viscoelastic percolation approached the lower threshold（φ1） of the electrical percolation,indicating an insulator-semiconductor change corresponding to the beginning of network structure formation. Substituting K for A,a modified Kerner-Nielson equation was obtained and used to analyze the formation of network structure. It is suggested that parameter K is associated with CB volume fraction. [WT5HZ]
文摘The study on the correlation between time dependence of electrical resistivity and dynamic storage modulus for carbon black(CB) filled polymer composites was carried out. With the increase of the dynamic storage modulus(G′) as well as the normalized dynamic storage modulus(G′_ c /G′_ p), the volume resistivity(ρ) deceases with the increase of annealing time beyond the T_ m of the composites. It is believed that this phenomenon can be used for examining the development of agglomerate structure of filled composites and illustrating the micro-mechanism of the NTC behavior. It is assumed that melting treatment to CB filled composites results in a higher modulus and lower resistivity due to more even local dispersion of the particles and formation of perfect CB network structure within the matrix.
基金Supported by the National Natural Science Foundation of China (Grant No. 90606008 and 50706057)
文摘Thermal conductivity (TC) of high density polyethylene/multiwall carbon nanotube (HDPE/MWCNT) composite films was measured by laser pulse method. It is found that the TC increased quickly with the increase of MWCNT fraction when the volume fraction of MWCNT was below 3.35%. However,as the volume fraction of MWCNT was over 3.35%,the increasing rate became slow. A new percolation model was proposed based on the effect of MWCNT network to simulate the TC of HDPE/MWCNT composite films. The simulation result was in good agreement the experimental data well. In addition,the relationship of TC with the increase of temperature was also discussed.
基金supported by the National Natural Science Foundation for Distinguished Young Scholars(Grant No.50125312)the National Natural Science Foundation of China(Grant Nos.50133020,50003007).
文摘The blends prepared by incorporation of carbon black (CB) or graphite powder (GP) inHto high-density polyethylene (HDPE) matrix have been novel and extensively applied polymeric positive temperature coefficient (PTC) composites. A phenomenological model was proposed on the basis of the GEM equation and the dilution effect of filler volume fraction due to the thermal volume expansion of the polymer matrix. Accordingly, the contribution of the thermal expansion of the matrix to the jump-like PTC transition of the composites was quantitatively estimated and a mechanical explanation was given. It was proved that the contribution of the volume expansion to PTC effect decreased for HDPE/CB composites crosslinked through electron-beam irradiation. Furthermore, the influences of the filler content, temperature and crosslinking on the self-heating behavior as well as the nonlinear conduction characteristics at electrical-thermal equilibrium state were examined. Based on the electric-field and initial resistivity dependence of the self-heating temperature and resistance dependence of the critical field, the mechanisms of the self-heating of the polymeric PTC materials were evaluated. The intrinsic relations between macroscopic electrical properties and microscopic percolation network at electrical-thermal equilibrium state were discussed according to the scaling relationship between the self-heating critical parameter and the conductivity of materials.
