Extrinsic conducting and superconducting polymer systems. IV. Superconducting properties of YBaCuO composites based on PVDF/PS/carbon black and PVDF/PS/copper polymer systems

In this work, the critical temperature (T_c) of a series of polymeric superconducting systems is determined which, sintered or not, are obtained through the incorporation of the superconducting ceramic YBaCuO into two extrinsic conducting polymer systems: PVDF/PS/carbon black and PVDF/PS/copper. In addition, the diamagnetic characteristics of these systems are studied on the basis of susceptibility measurements as a function of temperature. As regards the unsintered systems and according to the experimental results, copper-based composites can be termed as insulating materials and the samples with the highest carbon black content as reaching metalliclike conductivities. In no case, however, is an abrupt leap in conductivity observed as a function of temperature, indicating the superconducting nature of these systems from an electrical point of view. On the contrary, magnetic susceptibility measurements as a function of temperature detect in all cases a superconducting transition, i.e., a shift in the critical temperature range, bringing it close to that of pure YBaCuO (≈100 K). After sintering, the samples retained their original shape as well as reasonable mechanical properties. The electrical conductivity study confirmed the absence of superconductivity as a consequence of polymer combustion during sintering and thereby implying the disappearance of the orthorhombic phase of YBaCuO, which X-ray evidence proved to be accountable for superconductivity in this ceramic material. © 1996 John Wiley & Sons, Inc.     

Electrical conductivity of polystyrene/styrene-butadiene block copolymer blends containing carbon black

The electrical resistivity and mechanical properties of carbon black (CB)-filled polystyrene (PS)/styrene-butadiene block copolymer (SB) blends have been studied. Good electrical performance was achieved with pure SB and PS/SB blends indicating an inhomogeneity of these materials and the heterogeneous micro-dispersion of the CB particles. The percolation threshold of the filler inside SB or PS/SB blends is around 3.6 wt%, which is lower than that expected for incompatible PS/PBD blend. The addition of small amount CB decreases the elongation at break of PS/SB blends indicating some disturbance at the interface of these compatible material. Received: 28 July 1996/Revised version: 1 October 1996/Accepted: 3 October 1996     

Electrical and mechanical properties of conducting carbon black filled composites based on rubber and rubber blends

The electrical and mechanical properties of new conductive rubber composites based on ethylene–propylene–diene rubber, acrylonitrile butadiene rubber (NBR), and their 50/50 (weight ratio) blend filled with conductive black were investigated. The threshold concentrations for achieving high conductivity are explained on the basis of the viscosity of the rubber. The electrical conductivity increases with the increase in temperature whereas the activation energy of conduction decreases with an increase in filler loading and NBR concentration in the composites. The electrical hysteresis and electrical set are observed during the heating–cooling cycle, which is mainly due to some kind of irreversible change occurring in the conductive networks during heating. The mechanisms of conduction in these systems are discussed in the light of different theories. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 887–895, 1999     

Dispersion of fillers and the electrical conductivity of polymer blends filled with carbon black

Dispersion state of carbon black(CB) was studied in polymer blends which are incompatible with each other. It was found that CB distributes unevenly in each component of the polymer blend. There are two types of distribution. (1) One is almost predominantly distributed in one phase of the blend matrix, and in this phase fillers are relatively homogeneously distributed in the same manner as a single polymer composite. (2) In the second, the filler distribution concentrates at interface of two polymers. As long as the viscosities of two polymers are comparable, interfacial energy is the main factor determining uneven distribution of fillers in polymer blend matrices. This heterogeneous dispersion of conductive fillers has much effect on the electrical conductivity of CB filled polymer blends. The electrical conductivity of CB filled polymer blends is determined by two factors. One is concentration of CB in the filler rich phase and the other is phase continuity of this phase. These double percolations affect conductivity of conductive particle filled polymer blends.     

Electrical properties of structured HIPS/gamma‐irradiated UHMWPE/carbon black blends

HIPS/UHMWPE and HIPS/XL‐UHMWPE containing carbon black (CB) are unique systems in which CB is attracted to the PE, and thus structuring takes place affecting the morphology and the resultant electrical properties. UHMWPE, having a very high viscosity, was chosen as the dispersed phase within HIPS in place of a conventional polymer in order to explore possibilities of obtaining unique structures that would induce the CB to segregate and form a conductive network. XL‐UHMWPE particles also constitute an interesting dispersed phase, maintaming their highly porous and intricate structure even subsequent to melt processing. In both cases the CB is located at the interface; however, differences in resistivity values are observed. When low UHMWPE or XL‐UHMWPE contents are incorporated, the HIPS/XL‐UHMWPE/CB compositions have lower resistivities due to the heterogeneity of the interface, even at high shear rates. When high UHMWPE or XL‐UHMWPE contents are utilized, the trends reverse: HIPS/UHMWPE/CB depict enhanced conductivity, due to the dominance of UHMWPE particle coalescence and the resultant decrease in surface area. This is contrary to what happens with the XL‐UHMWPE particles, where the surface area increases with their higher contents, since they do not coalesce.     

Studies on polycarbonate/polystyrene/polycarbonate-g-polystyrene blends. III. Optical properties of PC/PS/PC-g-PS blends

Polycarbonate (PC)/polystyrene (PS) blend is a typical immiscible system. It is, however, still transparent. In this paper, this irregular phenomenon is clarified experimentally and theoretically. A new method of obtaining birefringence-free polymers without sacrificing orientation in materials is proposed. This involves combining suitable amounts of PC and PS in the form of a blend. The observed drastic reduction in birefringence is the result of the compensation of positive and negative contributions to the overall birefringence. ©1997 SCI     

Electrical properties of polyethylene and carbon black particle blends prepared by gelation/crystallization from solution

Composite materials based on low molecular weight polyethylene (LMWPE), ultra-high molecular weight polyethylene (UHMWPE) and carbon black (CB) particles were prepared by gelation/crystallization from solution. The positive temperature coefficient (PTC) intensity for the 90/10 (LMWPE/UHMWPE) composition exceeded five orders of magnitude for the specimens heat-treated at a suitable temperature, which was almost equal to that observed with LMWPE-CB blends prepared by a kneading method. In comparison with LMWPE-CB blends, much promoted reproducibility of PTC effect and inhibition of the negative temperature coefficient (NTC) effect were achieved.     

Physico-mechanical properties and automotive fuel resistance of EPDM/ENR blends containing hybrid fillers

This research aimed to investigate the effect of blend ratios on cure characteristics, mechanical and dynamic properties, morphology and automotive fuel resistance of ethylene-propylene diene rubber (EPDM) and epoxidized natural rubber (ENR) blends containing carbon black and calcium carbonate hybrid filler. The composition of EPDM/ENR blends varied were 100/0, 70/30, 50/50, 30/70 and 0/100 %wt/wt. All ingredients used for preparing each blended compound, except for the curatives, were mixed in a kneader. Thereafter, the compound was further mixed with curatives on a two-roll mill and then were vulcanized together with shaped by compression molding before determining cure characteristics, mechanical properties, morphology and weight swelling ratio in three automotive fuels; gasohol-91, diesel and engine oils. The results indicated that Mooney viscosity and cure time of EPDM/ENR blends tended to decrease with increasing ENR content, while cure rate index and crosslink density increased. Tensile strength of all EPDM/ENR blends is lower than that of the individual EPDM and ENR. This is attributed to the incompatibility between nonpolar and polar nature of EPDM and ENR, respectively, supporting by the glass transition temperature form dynamic mechanical thermal analysis (DMTA) and scanning electron micrographs (SEM). Owing to the differences in polarity of automotive fuels and rubbers, weight swelling of EPDM/ENR vulcanizates decreased in diesel and engine oils, but increased in gasohol-91 with increasing in ENR content.     

Compatibilization effect of graft copolymer on immiscible polymer blends. II. LLDPE/PS/LLDPE-g-PS systems

The compatibilizing effect of graft copolymer, linear low density polyethylene-g-polystyrene (LLDPE-g-PS), on immiscible LLDPE/PS blends has been studied by means of ¹³C CPMAS NMR and DSC techniques. The results indicate that LLDPE-g-PS is an effective compatibilizer for LLDPE/PS blends, and the compatibilizing effect of LLDPE-g-PS on LLDPE/PS blends depends on the PS grafting yield and molecular structure of the compatibilizers and also on the composition of the blends. It was found that LLDPE-g-PS chains connect two immiscible components, LLDPE and PS, through solubilization of chemically identical segments of LLDPE-g-PS into the noncrystalline region of the LLDPE and PS domain, respectively. Mean while, LLDPE-g-PS chains connect the crystalline region of LLDPE by isomorphism, resulting in an obvious change in the crystallization behavior of LLDPE. © 1996 John Wiley & Sons, Inc.     

Microstructure and compatibility of PVDF/PS blends in the presence of PVA

This research refers to a compatibility study of binary and ternary PVDF blends with PS and PVA by means of the determination of the polymer polymer interaction parameter χ₁₂ calculated from melting point depression analysis of the blends. In addition, a PVDF spherulite growth rate study was conducted in the binary and ternary blends with PS and/or PVA. The nucleation factor is determined by applying the Lauritzen–Hoffman theory. The results obtained show PVA to be capable of compatibilizing PVDF/PS systems when present in concentrations of 30 vol%.     

Electrical and thermal properties of composite of liquid crystalline polymer filled with carbon black

The electrical resistivity and thermal conductivity of a liquid crystalline polymer (LCP) filled with a commercial carbon black (CB) of various volume fractions (?) is investigated. The percolation threshold (?_c) is found at about 3%, and the resistivity (ρ) as a function of (? ? ?_c) satisfies the exponential function. Although the pure LCP is highly anisotropic in thermal and mechanical properties after processing, the composite samples exhibit no preferential direction for electrical conduction. Samples of ? below ?_c exhibit a negative temperature coefficient of resistivity while those above ?_c show almost no temperature dependence from room temperature to 200°C. In addition, the samples at lower ? have higher thermal conductivity in the LCP flow direction than those measured in the transverse and thickness directions, and they approach the same value at higher ?. This result indicates that preferential molecular alignment of the matrix LCP is responsible for the behavior of the thermal conductivity of the composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1549–1555, 2001     

炭黑对CR/TPI并用胶性能的影响

研究了炭黑种类及用量对CR/TPI并用胶的影响.结果表明:随着炭黑粒径的增大,混炼胶焦烧时间有增大的趋势,正硫化时间也随之延长;硫化胶交联程度降低;硫化胶的拉伸强度、断裂伸长率、压缩生热温升、屈挠性能和炭黑分散度随之降低;常温下回弹性能、磨耗性能提高;硫化胶的老化性能略有提高.添加炭黑N330硫化胶的综合性能最好.随着炭黑N330用量的增加,硫化胶拉伸强度先增大后减少,炭黑40份左右达到最大值,断裂伸长率减少,磨耗性能和屈挠性能降低,压缩生热温升、邵尔A硬度增大,常温下回弹性能提高.     

Studies on the blends of carbon dioxide copolymer. III. NBR/PPC systems

In this paper, the blends of the carbon dioxide copolymer, poly(propylene carbonate) (PPC), with nitrile rubber (NBR) were studied by DSC, DMA, TEM and TG. PPC can enhance the mechanical properties of NBR, while oil resistance and tensile set at break of NBR/PPC systems were as good as that of NBR. The coagent of triallylisocyanurate or maleic anhydride with carbon black can much improve the curing efficiency of dicumyl peroxide in NBR/PPC systems. © 1996 John Wiley & Sons, Inc.     

Modulation of electrical properties in single-walled carbon nanotube/conducting polymer composites

The preparation and electrical characterization of a new class of composite layers formed by dispersing single-walled carbon nanotubes (SWNT) in 1,8-diaminonaphthalene polymer, the poly(1,8-DAN), are described.The material was grown on the surface of Pt plates by electropolymerization of 1,8-diaminonaphthalene (1,8-DAN) monomer in the presence of nanotubes. This synthesis method allows the simultaneous deposition of both the host polymer matrix and the filler nanotubes. A series of composite films were prepared using untreated nanotubes as well as nanotubes treated with KOH, HNO₃ and HNO₃/H₂SO₄ solutions. The structural features of the nanotubes and of the films produced have been investigated using Raman spectroscopy. Insight into the nature of nanotube dispersion and nanotube-polymer association was gained by AFM and STM analysis and by FE-SEM inspection after removing the outermost portion of composite films.The charge transport in composite films is found to be strongly enhanced by the nanotube insertion. Depending on the SWNTs processing, currents up to 30 mA, higher by a factor of about 140 than those of the pure poly(1,8-DAN) films, were measured with an applied voltage of 250 mV.     

Electrical conductivity in carbon black-loaded polystyrene-polyisoprene blends. Selective localization of carbon black at the interface

Summary The electrical conductivity of carbon-black loaded polystyrene-polyisoprene blends has been studied. In this ternary system, the filler is at the interface of co-continuous polyblends as confirmed by the very low value of the filler percolation threshold (0.2 vol % for blends compression molded at 250°C) and by optical microscopy. As a result of the selective localization of carbon black at the interface, the percolation threshold is very sensitive to the compression molding temperature.     

Electrical and mechanical behaviors of carbon nanotube‐filled polymer blends

Four carbon nanotube (CNT)‐filled polymer blends, i.e., CNT‐filled polyethylene terephthalate (PET)/polyvinylidene fluoride, PET/nylon 6,6, PET/polypropylene, and PET/high‐density polyethylene blends, have been injection‐molded and characterized in terms of their microstructures, electrical conductivities, and mechanical properties. The distribution of CNTs in the polymer blends has been examined based on their wetting coefficients and minimization of the interfacial energy. The electrical conductivity and mechanical properties have been related to the cocontinuous polymer blends, the conductive path formed by CNTs, the CNT distribution, and the intrinsic properties of the constituent polymers. It is found that to obtain a CNT‐filled polymer composite with both high electrical conductivity and good mechanical properties, it is preferred that most CNTs distribute in one polymer phase, while the other polymer phase(s) remain neat. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 477–488, 2006     

Thermal decomposition of cellulose/synthetic polymer blends containing grafted products. II. Cellulose/polyacrylonitrile blends

The homogeneous grafting of acrylonitrile onto cellulose was carried out in a dimethyl sulfoxide/paraformaldehyde solvent system. The grafted products were added to cellulose/polyacrylonitrile (PAN) blends as compatibilizers. The thermal decomposition behavior of the blends was investigated by thermogravimetry. The thermal stability of the blends with higher grafted product content was lower by more than 100°C than that of the blends without grafted product. The accessibility values of the former blends were larger than those of the latter. The microphase-separated structures of the grafted product blends were finer than those without the product. Dynamic mechanical measurements and differential scanning calorimetry were performed to estimate the glass transition temperatures, T_g, of the blends. The variation in T_g was smaller than that in characteristic temperatures determined by thermogravimetry. The difference in thermal decomposition behavior was correlated to that in compatibility. Thermogravimetry was found to be effective for estimating the compatibility in cellulose/PAN blends containing grafted products. © 1996 John Wiley & Sons, Inc.     

Morphology development and exclusion of noncrystalline polymer during crystallization in PVDF/PMMA blends

Morphology development during the crystallization of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends was investigated at various crystallization temperatures (T_C) by means of time-resolved light scattering measurements and atomic force microscopy (AFM). A coarse spherulite obtained at a high T_C of 162 °C was found to be developed with a two-step crystallization process. The ordering in the spherulites (Pr) increased with time at the early stages and then decreased at the later stages. The rate of spherulite growth started to decrease when Pr started to decrease. In contrast, in the compact spherulite obtained at a low T_C of 148 °C, Pr decreased monotonously with time while the growth rate was constant. AFM observation revealed that such characteristic crystallization behavior is attributed to the exclusion of PMMA from the crystal growth during the crystallization; i.e., the amount of excluded PMMA becomes larger as the distance from the spherulite center increases and the crystallization temperature rises.