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High-density polyethylene (HDPE) composite films filled with carbon fibers (CF), carbon nanotubes (CNT) as well as hybrid filler of CF and CNT were prepared by melt mixing. The electrical and self-heating properties of the composite films were investigated. Results showed that: when the total content of filler was the same, (i) the electrical resistivity of composite films filled with hybrid fillers was lower than those with single filler; (ii) the composite films filled with hybrid fillers displayed more excellent self-heating performance such as a higher surface temperature ( T s ), a more rapid temperature response, and a better thermal stability. This indicates the synergetic effect of combination of CNT and CF on improvement of the electrical and self-heating properties of HDPE-based composite films. The synergy can be considered to be the result of the fibrous filler CF acting as long distance charge transporters and the CNT serving as an interconnection between the fibers by forming local conductive paths.

Temperature dependence of conductivity of polymer composites was analyzed using the DC component (frequency → 0 Hz) of AC conductivity in terms of thermal fluctuation-induced tunneling through thin barriers to evaluate the average gap distance ( D ) between adjacent vapor-grown carbon fibers (VGCFs) in a polyimide (PI) matrix. This approach was confirmed to be reasonable in comparison with direct calculation of the D value via the DC measurement. The direct DC measurement provides the average conductivity of the system, whereas the DC component (frequency → 0 Hz) of AC conductivity provides two or three types of phase lag mechanisms, the interface between the composites and electrode, the contact region between adjacent VGCFs and the impedance of VGCFs themselves. The best fit between experimental and theoretical frequency dependence of impedance was realized by the equivalent circuit models, which were classified into several phase lags. The D values calculated by the phase lag due to electron charge on adjacent VGCF surfaces were 1.20 and 1.00 nm for the composites with 3.11 and 6.28 VGCF vol% contents, respectively. The D values are independent of temperature from 25 up to 160 °C, which indicates high thermal resistivity of PI. Equivalent circuit with two units for the 3.11 vol% PI/VGCF composite and three units for the 6.28 vol% PI/VGCF composite was proposed to study the complicated relaxation behavior. The first unit was: interface between bulk and electrode; the second unit was: interface between adjacent VGCFs inserting PI; the third unit was: carrier movement within VGCFs.

This research dealt with a novel method of fabricating green composites with biodegradable poly (lactic acid) (PLA) and natural hemp fiber. The new preparation method was that hemp fibers were firstly blending-spun with a small amount of PLA fibers to form compound fiber pellets, and then the traditional twin-screw extruding and injection-molding method were applied for preparing the composites containing 10–40 wt% hemp fibers with PLA pellets and compound fiber pellets. This method was very effective to control the feeding and dispersing of fibers uniformly in the matrix thus much powerful for improving the mechanical properties. The tensile strength and modulus were improved by 39 and 92 %, respectively without a significant decrease in elongation at break, and the corresponding flexural strength and modulus of composites were also improved by 62 and 90 %, respectively, when the hemp fiber content was 40 wt%. The impact strength of composite with 20 wt% hemp fiber was improved nearly 68 % compared with the neat PLA. The application of the silane coupling agent promoted further the mechanical properties of composites attributed to the improvement of interaction between fiber and resin matrix.

The conductivity of composites with a carbon fiber (CF) content slightly higher than the percolation threshold was measured at increasing temperatures up to −10 °C. The tunneling effect was theoretically calculated using a rigorous nonparabolic potential barrier. The tunneling barrier width D and the surface area A were determined. For a polyethylene (PE) matrix, good agreement between theoretical and experimental results was obtained using D =1.00 nm and A =1.35 to 1.68 nm 2 at a 30-vol% CF content and using D =1.30 nm and A =1.25 to 1.28 nm 2 at a 25-vol% CF content. That is, almost perfect agreement between experiment and theory was obtained by adjusting the parameters except over the temperature ranges in which the β and γ relaxation peaks appeared. Dynamic loss modulus and positron annihilation measurements were also conducted. However, a theoretical analysis that was derived using a parabolic potential barrier produced inconsistent results. That is, the tunneling barrier width D was less than the c -axis length of a PE crystal unit, and the surface area A was considerably less than the a-b plane area of a PE crystal unit. This paper deals with temperature-dependent conductivity for polymer-filler composites by using nonparabolic function as potential barrier. The good agreement between theoretical and experimental results indicates that the evaluation by the fluctuation-induced tunneling effect is important to analyze temperature dependence of the conductivity of the polymer-filler composite systems except in the temperature ranges associated with the β and the γ relaxations.

The gelation mechanisms of ultra-high-molecular-weight polyethylene (UHMWPE) chains differed significantly in decalin and paraffin, although these are typical solvents used to gel spin UHMWPE fibers with high strengths and moduli. In both solvents, gelation was attributed to liquid–liquid phase separation driven by concentration fluctuations during the initial stage. The gelation speeds and temperatures differed significantly in the two solvents. In decalin, solvent flowed from the gels, syneresis occurred during crystallization and dry gel films were prepared. In contrast, in paraffin, many nucleating points appeared immediately, and no syneresis occurred even after quenching to room temperature. To prepare dry gel films, paraffin was blotted with filter paper, and paraffin residues were removed in hexane. However, the small-angle X-ray scattering spectra from both films were similar, indicating crystalline lamellae and ultradrawing. The gelation speeds and temperatures for decalin and paraffin differed significantly. In decalin, gel syneresis occurred by solvent flow from the gels accelerates crystallization, and dry gel films were prepared. In contrast, in paraffin, many nucleating points appeared immediately, and few syneresis occurred even after quenching to room temperature. To prepare dry gel films, paraffin was blotted with filter paper, and residual paraffin was removed in hexane. However, the small-angle X-ray scattering (SAXS) patterns from both films provided similar profiles indicating large crystalline lamellar stacking ensuring ultradrawing.

Simultaneous rotations of sample and X-ray detected counter are needed to evaluate orientation distribution of crystallites and amorphous chains oriented predominantly parallel to the film surface in addition to exact diffraction peak profiles obtained without the complicated intensity corrections. The rotation mode is known as “ –2 scanning” system ( : film, 2 : counter). The system has been mainly used in research and development institutes. However, such instruments are not produced at present. Recently, small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) intensities have been measured by using X-ray beam generated along one direction. The brand name of the instrument is “a simultaneous SAXS and WAXD measuring instrument”. The X-ray beam generated by the instrument has surely high luminance providing high degree resolution of peak profiles by diffraction and/or scattering. The sample stage and detector, however, are fixed, since the intensities for SAXS and WAXD are obtained by the digital display of the number of X-ray photons detected on the imaging plate. Such optical system contains controversial defect on evaluating orientation of crystal planes parallel to the surface of films prepared by T-die and inflation methods as well as the exact profile. The imaging plate cannot detect the diffraction intensity from the crystal planes existing in the angle range between incident beam and Bragg angle associated with the diffraction peak position of the individual crystal planes.

In an attempt to produce glittering gold fibers with high modulus and high strength, gold plating on the surface of poly(p-phenylene benzobisoxazole) (PBO) fibers was carried out by using an electroless plating method. Due to the difficulty in plating gold directly on organic and inorganic fibers, gold plating was carried out on the surface of copper-plated and nickel-plated fibers; for the latter the nickel was plated on the copper-plated fibers. Namely, composite fibers, termed PBO/Cu/Au and PBO/Cu/Ni/Au, were prepared. The morphology of plated fibers was studied by X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy and electrochemical polarization measurements. It was found that gold was uniformly plated on the PBO fiber, and the gold-plated fibers have good corrosion resistance. The electrical conductivities of the two kinds of gold-plated fibers were higher than 4 × 10⁴ S/cm, and their tensile strengths and Young’s moduli were greater than 1.9 GPa and 130 GPa, respectively, when estimated in terms of a single composite fiber.

With the purpose of improving the crystallization rate and toughness of polylactic acid (PLA) comprehensively, chemical modified microfibrillated cellulose (MMFC) and ethylene–glycidyl methacrylate copolymer (EGMA) were used in the preparation of the PLA/MMFC/EGMA composite. After controlled acetylation using acetic anhydride, MMFC exhibited an improved hydrophobicity, resulting in a much better dispersion in PLA matrix. To clarify the impact of MMFC on the crystallization behaviors and mechanical properties of PLA, PLA/MMFC composites with 1–20 wt% of MMFC were characterized using differential scanning calorimetry (DSC) analysis and stress–strain curves. It was revealed that in the presence of only a small amount of MMFC (3 wt%), the crystallization rate of PLA was enlarged for seven times when the crystallization occurred at 120 °C, and the tensile modulus and tensile strength were both increased by 25% compared with pure PLA. The effect of EGMA component on the crystallization and mechanical properties of PLA was considered based on the characterization of the PLA/MMFC/EGMA composite. It was confirmed from DSC thermograms that a small amount of EGMA (5 wt%) did not exhibit any negative impact on the crystallization of PLA in the case of PLA/MMFC-3 wt%/EGMA-5 wt% composite. Meanwhile, in the presence of the EGMA, PLA/MMFC-3 wt%/EGMA-5 wt% composite showed an obvious increase of elongation-at-break from 9.1 to 20.8 compared with pure PLA. A remarkable improvement of crystallization behavior and toughness of PLA was achieved due to cooperative effect of the small amount of MMFC and EGMA in the PLA composite.

In an attempt to improve the mechanical property of polyethylene composite at high temperature, crosslinking of ultrahigh-molecular-weight polyethylene (UHMWPE) and carbon fiber (CF) blends was carried out by using dicumyl peroxide (DCP). The specimens were prepared by gelation/crystallization from solutions. The effect of chemical crosslinking on mechanical and electrical properties of UHMWPE/CF blends with composition of 1/0, 1/0.25, and 1/1 (w/w) were investigated in detail. Electrical conductivity and thermal mechanical properties of the blends with the 1/1 composition were greatly improved by incorporation of enough content of CF and adequate crosslinking network formation. Surprisingly, the Young's modulus of the 1/1 blend reached 20 GPa at room temperature (20 °C). On the other hand, heat treatment at 135 °C played an important role for obtaining a high PTC effect for the UHMWPE-CF blend in which the PTC intensity reached 10⁷.

Developing high-performance anti-corrosion coating is an effective way of preventing metal surface from environmental corrosion. Polymethylhydrosiloxane (PMHS) precursor was utilized in combination with nano-zirconia (ZrO 2 ) particles to prepare SiC x O-ZrO 2 ceramic coating by means of high-temperature pyrolysis at 800 °C. A series of characterizations, including chemical structure, thermal stability, crystalline structure, microscopic morphology, and mechanical and electrochemical properties, were conducted to reveal the relation between the structure and the performance of the ceramic coatings. It was observed that the SiC x O-ZrO 2 coating containing 20 wt% ZrO 2 exhibited a hardness greater than 9H, impact resistance of 50 cm, water contact angle as high as 132°, and excellent corrosion resistance, which was attributed from the reparative effect of ZrO 2 on ceramic coatings. This coating shows significant potential for use in storage tank anti-corrosion applications. Graphical Abstract