The effects of cauliflower-like short carbon fibers on the mechanical properties of rigid polyurethane matrix composites

Stress concentration and weak interfacial strength affect the mechanical properties of short carbon fibers (CFs) reinforced polymer composites. In this work, the cauliflower-like short carbon fibers (CCFs) were prepared and the point was to illuminate the effects of fiber morphology on the mechanical properties of the CCFs/rigid polyurethane (RPU) composites. The results indicated that the surface structure of CCFs could increase the surface roughness of the fibers and the contact area between fibers and matrix, thereby promoting the formation of irregular interface. Compared with pure RPU and initial CFs/RPU composites, the strength and toughness of CCFs/RPU composites were simultaneously improved. The satisfactory performance was attributed to the special fibers structure, which played an anchoring role and consumed more energy during crack propagation.     

Catalytic graphitization of PAN-based carbon fibers by spontaneously deposited manganese oxides

A simple method for the spontaneous deposition of manganese oxides on the surface of polyacrylonitrile (PAN)-based carbon fibers by a direct redox reaction between carbon fibers and permanganate ions is described. Catalytic graphitization of the PAN-based carbon fibers coated with manganese oxides was investigated by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results indicate that the graphitization of the PAN-based carbon fibers was accelerated in the presence of the manganese oxides even at the relatively low temperature of 1,600 °C.     

Polyelectrolyte multilayers on wood fibers: influence of molecular weight on layer properties and mechanical properties of papers from treated fibers

This paper compares the influence of the molecular weight of polylelectrolytes forming polyelectrolyte multilayers (PEM) on wood fibers on adhesion and paper strength. Sheets were made from fibers treated with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) of molecular mass 70,000 and 240,000, respectively, and of poly(dimethyldiallylammonium chloride) (PDADMAC)/poly(styrene sulfonate) (PSS) of molecular mass 30,000 and 80,000, respectively. The results were compared to what has recently been reported for PEM formation on fibers using a low-molecular-mass combination of PAH and PAA and a high-molecular-mass combination of PDADMAC/PSS. There was a less significant improvement in the case of the low-molecular-mass PDADMAC/PSS and the high-molecular-mass PAH/PAA. The adsorbed amounts of PAH and PDADMAC were also determined, showing a lower adsorbed amount of the low-molecular-mass PAH than of the high-molecular-mass PDADMAC. The amount of low-molecular-mass PDADMAC was similar to that found for high-molecular-mass PDADMAC/PSS. Individual fibers were partly treated and studied, showing a less significant decrease in wettability with low-molecular-mass PDADMAC/PSS than with the high-molecular-mass combination. The effect of the molecular weight on the adhesion was discussed in terms of the structure and wettability of the PEMs.     

进口中间相沥青碳纤维超高温石墨化处理后的特性分析

对P25、P55及XN-90三种进口中间相沥青碳纤维3000℃石墨化处理前后的微观形貌、晶体尺寸、力学性能、导电导热性能及其抗氧化性能进行了表征.结果 表明,三种碳纤维微观结构差异较大,均呈现出较为明显的"指纹"特征.三种碳纤维中XN-90热处理温度最高,晶体尺寸最大,石墨化程度最高,抗氧化性能最好.经过3000℃石墨...     

The influence of polarization of the sorbent on sorption of albumin by carbon fibers

The sorption of bovine serum albumin (BSA) on non-charged and polarized surfaces of carbon fibers (ACF) and carbon fibers modified with titanium hydroxide (ACF-Ti) was studied. It was shown that cathodic polarization considerably influences the reversibility of the BSA sorption and decreases the BSA sorption by ACF and ACF-Ti to a larger extent than anodic polarization. A change in the surface charge mainly influences sorption of albumin by ACF-Ti, which is due to different surface properties of the initial and titaniumcontaining adsorbents. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1496–1498, August, 1998.     

Modification effects of short carbon fibers on mechanical properties and fretting wear behavior of UHMWPE composites

The present work comparatively studied the modification effects of short carbon fiber (CF) on the mechanical properties and fretting wear behavior of ultra‐high molecular weight polyethylene (UHMWPE)/CF composites. The interactions between CFs and UHMWPE interface were also investigated in detail. The results showed that, with the increase in fiber content, the compressive modulus and hardness of the composites increased, while its impact strength decreased. It was found that filling of CF can reduce the friction and wear of UHMWPE. In addition, the UHMWPE‐based composites reinforced with nitric acid‐treated CF exhibited better mechanical properties, lower friction coefficient, and higher wear resistance than those of untreated UHMWPE/CF composites. This was attributed to the improvement of interfacial adhesion and compatibility between CF and UHMWPE matrix caused by surface chemical modification of CF. Copyright © 2015 John Wiley & Sons, Ltd.     

The influence of the length and concentration of chopped carbon fiber on physical and mechanical properties of siloxane matrix

In this paper, the influence of the concentration and length of chopped carbon fiber on the physical and mechanical characteristics of siloxane matrix was investigated. It is shown that the highest values can be achieved at 2–5 wt % loading of chopped carbon fiber with a length of 3 mm. In this case, the elastic modulus increases by five to eight times in comparison with unmodified composite. Destruction of such materials takes place in accordance with an adhesive–cohesive mechanism, which testifies to the existence of relative adhesion of siloxane binder to carbon fiber.     

非晶碳纳米球的低温石墨化(英文)

The investigation by SEM/TEM, porosity, and X-ray diffraction measurements of the graphitization process starting from amorphous carbon nanospheres, prepared by glucose carbonization, is reported. Aspects studied are the annealing temperature in the 750–1000 °C range, the type of inert carrier gas, and time of treatment in the 2–6 h range. It is investigated how these parameters influence the structural and morphological characteristics of the carbon materials obtained as well as their nanostructure. It is shown that it is possible to maintain after graphitization the round-shaped macro morphology, a high surface area and porosity, and especially a large structural disorder in the graphitic layers stacking, with the presence of rather small ordered domains. These are characteristics interesting for various catalytic applications. The key in obtaining these characteristics is the thermal treatment in a flow of N2. It was demonstrated that the use of He rather than N2 does not allow obtaining the same results. The effect is attributed to the presence of traces of oxygen, enough to create the presence of oxygen functional groups on the surface temperatures higher than 750 °C, when graphitization occurs. These oxygen functional groups favor the graphitization process.     

The influence of chemical treatment on the mechanical properties of windmill palm fiber

Bleached palm fiber without lignin, alkalized palm fiber without hemicelluloses and raw windmill palm fiber were prepared. Then, the chemical composition and the mechanical properties of the windmill palm fiber were investigated. Scanning electron microscopy, Fourier transform infrared spectroscopy and Raman microscopy were employed to characterize the structure and chemical composition. A universal material tester, nanoindentation and dynamic mechanical analysis were used to study the mechanical property of these samples. According to the results, bleach treatment removed most of the silica bodies as well as the lignin, smoothed the fiber surfaces and increased the hollowness to 50%. Alkali treatment removed most of the hemicelluloses, increased the surface roughness, and reduced the hollowness to 28%. Alkalized fibers have the highest tensile strength, elongation at break and elastic modulus, with values of 119.37 ± 27.21 MPa, 30.58 ± 5.87% and 10.75 ± 4.30 GPa, respectively. The raw material without treatment has the highest stiffness, while the alkalized samples are the most flexible fibers and sensitive to temperature.     

The influence of network structure on the macroscopic mechanical properties of crosslinked polymers

Neat and rubber-toughened epoxy resin systems EPN/BA and EPN/DDS with significantly different crosslink densities and glass transition temperatures were tested under widely different experimental conditions ranging from impact to long-term loading. The resulting deformation mechanisms were examined in order to ascertain the effects of network structure and toughening modifiers. Different toughening mechanisms were observed in low- and high-crosslink-density epoxy systems, modified with the same core-shell rubber particles.     

Structure and properties of fluorinated carbon fibers

The fluorination of carbon fibers results in a partial or total conversion of the carbon layers into CF layers. In constrast to the formation of intercalation compounds of carbon fibers, the fluorination causes considerable changes in the fiber texture which results in a marked decrease of tensile modulus and mechanical strength. The relationship between the structural changes and the resulting mechanical properties is studied by small-angle and wide-angle X-ray scattering.     

In situ fabrication and graphitization of amorphous carbon nanowires and their electrical properties

Individual amorphous carbon nanowires (a-CNWs) were fabricated inside a transmission electron microscope (TEM) by the electron beam induced deposition (EBID) method, and the a-CNWs were graphitized in situ by introducing Fe particles into these a-CNWs and controlled movement of the Fe particles in these CNWs. Detailed structural characterizations and electrical measurements were carried out, and it was found that the current-induced movement of Fe particles has significant effects in purifying the as-fabricated a-CNW, transforming the a-CNW into a graphitized-CNW (g-CNW). Two-terminal current voltage characteristics measurements showed that the g-CNW has a very good electrical conductivity with a resistivity of about 5.3 x 10(-4) Omega cm, a current carrying capacity of at least 4.35 mA, and a current density of 4.6 x 10(8) A/cm(2), and these values are comparable to those of multiwalled carbon nanotubes. Field emission characteristics of both a-CNWs and g-CNWs were also measured, and their respective Fowler-Nordheim plots were found to have basically a linear form.     

Spinneret geometry modulates the mechanical properties of man-made cellulose fibers

Cellulose - The production of cellulose-based textile fibers with high toughness is vital for extending the longevity and thus developing a sustainable textile industry by reducing the global...     

The effect of electron irradiation on the structure and mechanical properties of highly drawn polyethylene fibers

Two very different high-modulus polyethylene fiber samples, a low molecular weight melt-spun and drawn fiber, and a high molecular weight gel-spun and drawn fiber, have been subjected to electron beam irradiation to various doses in vacuum and in the presence of acetylene. The gel content after irradiation in acetylene was found to be much greater than for an equivalent dose in vacuum. The gel content–dose relationship could not be described by either Charlesby–Pinner analysis or the Inokuti equation. This is attributed to the polydispersity and the complications introduced by the unique morphologies of highly drawn fibers. Following previous studies, the tensile creep behavior was interpreted in terms of a model comprising two thermally activated processes in parallel, a low stress process relating to the amorphous network, and a high stress process relating to the continuous crystal fraction. Analysis of the creep behavior of the melt-spun, low molecular weight fiber irradiated in vacuum revealed crosslinking in the amorphous regions and chain scission in the crystal. Chain scission was found to be much reduced when irradiating in acetylene, for which a mechanism has been proposed. The creep rates and activation volumes of the high molecular weight, gel-spun fiber were found to be significantly lower, probably due to the unique morphology. In this case the dominant effect of irradiation on the mechanical properties can be attributed to chain scission rather than crosslinking.     

The influence of carbon non-stoichiometry on the electronic properties of thorium monocarbide ThC

The first-principle band structure calculations are employed to examine the influence of carbon non-stoichiometry on the structural and electronic properties of the cubic thorium monocarbide ThC. As a result, the equilibrium geometries, electronic bands, densities of states (DOS), Sommerfeld constants and Pauli paramagnetic susceptibility for ThC_1?x (where x = 0, 0.25 and 0.50) are obtained and analyzed in comparison with available experimental data. Additionally, the formation energies of carbon vacancies are theoretically estimated for ThC_1?x.The results obtained indicate that the introduction of carbon vacancies in ThC is accompanied by pronounced DOS changes due to the appearance of novel “vacancy states” in the near-Fermi region formed by comparable contributions of Th 6d and 5f states. The carbon deficiency strongly affects the structure and stability of thorium carbide. For example, for the hypothetical “over-deficient" composition ThC_0.50 the initial cubic structure undergoes significant tetragonal distortions. On the contrary, for ThC_0.75 the value of E_vf is positive and the cubic structure of this phase is preserved.     

The influence of nanostructured UV‐blockers on mechanical properties of carbon fiber epoxy composites during accelerated weathering condition

In a 3‐stage experimental approach, it was attempted to enhance the weathering performance of carbon fiber reinforced epoxy composites (CFRC). For this purpose, 2 types of UV‐blocking nanoparticles titanium dioxide (TiO₂) and zinc oxide (ZnO) were employed to separately be introduced into the composite matrix. In the first stage, the optimum content of nanoparticles was found to be 0.5 wt.% for both nanoparticles. The second stage of experiments revealed that addition of nanoparticles into CFRC could increase the strength of the composite around 6% to 12% depending on the nanoparticles used. In the third stage (weathering), it was demonstrated that nanoparticles significantly enhanced the weathering stability of CFRC. Finally, it was concluded that while TiO₂ could reinforce the composite more efficiently, ZnO nanoparticles provided a higher level of protection (62% improvement in weathering stability compared with neat composite). The higher protection efficiency of ZnO compared with TiO₂ was explained by its lower photocatalytic activity during weathering.     

The preparation, properties and application of carbon fibers for SPME

The conditions of preparation of new types of carbon fibers for solid phase micro extraction (SPME) prepared by methylene chloride pyrolysis (at 600 °C) on the quartz fiber (100 μm) as well as by supporting synthetic active carbon (prepared especially for this purposes) supported in a special epoxide-acrylic polymer is described. The properties of such carbon fibers for SPME were defined by determination of the partition coefficient of the tested substances (i.e., benzene, toluene, xylenes, trichloromethane and tetrachloromethane) and by the microscopic investigations with the application of the optical and scanning electron microscope.

The obtained carbon SPME fibers were applied to the analysis of some volatile organic compounds from its aqueous matrix. During chromatographic GC test, at the investigated SPME carbon fibers, we obtained different but mostly high partition coefficients for the determined compounds (Kfs from 120 for trichloromethane up to 11,500 for tetrachloromethane).

Owing to the high partition coefficients of the studied substances obtained on carbon fibers, it was possible to do the analysis of organic substances occurring in trace amounts in different matrices. In this paper, we present the analysis of BTX contents in the petrol analyzed with the application carbonized with CH₂Cl₂ SPME fiber (C1NM) and a headspace over the petrol sample (concentration of each BTX g/dm³).