Modification of precursor pitch for general performance carbon fibre by blending naphthalene-derived isotropic and mesophase pitches

Modification of an isotropic precursor pitch (IMP) for general performance carbon fibre (GPCF) was carried out by blending isotropic and mesophase pitches (IP and MP, respectively), both of which were synthesized from naphthalene using HF/BF₃ as catalysts because they carried a large amount of naphthenic hydrogens. Both IP and MP were miscible with IMP at temperatures higher than their softening points. The softening point of the blended pitch dropped remarkably, being lower than 200° C with 40% IP. Such lower softening points made spinning much smoother. Modification also enhanced the stabilization reactivities of pitch fibre, the time required for the sufficient stabilization at 270° C decreasing by 20 and 30 min by blending with 20% IP and 20% MP, respectively. The mechanical properties of the resultant carbon fibres were also improved.     

Control of molecular orientations in mesophase pitch-based carbon fibre by blending PVC pitch

Coal tar-derived mesophase pitch and its blends with PVC pitch in 5 or 10 wt% were spun at temperatures from 340 to 390° C by applying pressurized nitrogen. The parent mesophase pitch and the blended pitch showed an excellent spinnability at temperatures from 360 to 380° C and from 350 to 380° C, respectively, to give a thin pitch fibre of 10m diameter. The transverse texture of the fibres from the parent mesophase pitch showed the radial orientation regardless of a higher spinning temperature of 390° C. In contrast, those from the blended pitches showed random orientation even at the lower spinning temperature of 350° C. The amounts of the blend extruded by spinning at each temperature under 0.2 kg cm^–2 G^–1 were always larger than those of the mesophase pitch. It is clarified in the present study that blending PVC pitch can realize stable spinning at lower temperatures, where the molecular orientation in the transverse section of the resultant carbon fibre was controlled through decreasing the viscosity of the whole mesophase pitch.     

Blending mesophase pitch to improve its properties as a precursor for carbon fibre Part 1 Blending of PVC pitch into coal tar and petroleum-derived mesophase pitches

The blending of mesophase pitch with isotropic PVC pitch was studied to improve their properties as a precursor for carbon fibre. PVC pitch prepared at 420° C which remained almost isotropic was found to be miscible with coal tar-derived mesophase pitch without reducing the anisotropic content and spinnability. The tensile strength of pitch fibres remained unchanged by the blending; however, the reactivity for stabilization was enhanced. The resultant carbon fibres from the blend exhibited slightly higher tensile strength. In contrast, petroleum-derived mesophase pitch failed to dissolve the PVC pitch, leaving a number of isotropic droplets. The structural factors of mesophase pitches with regard to their compatibility with PVC pitches are briefly discussed.     

A structural study on the stabilization and enhancement of mesophase pitch fibre

The components of coal tar-derived mesophase pitch fibre and its blend with polyvinyl chloride (PVC) pitch were studied for chemical changes after the stabilization. Microanalyses, solubility and solid ¹³C NMR measurements were performed. The temperature was found to be very influential on the progress of the stabilization. At a temperature of 230° C, PVC pitch enchanced the oxygen uptake of both fusible pyridine soluble (PS) and non-fusible pyridine insoluble (PI) fractions in the pure mesophase pitch, so shortening the time required for complete stabilization and raising more rapidly the softening point of the PS fraction. More oxygen-containing functional groups, such as phenolic, ether, carboxylic and carbonyl groups, were formed in both fractions. It is noted that any increase in the aromatic ring size of the PI fraction is rather limited at this temperature. In contrast, stabilization of PVC pitch at a higher temperature of 300° C, accelerated the increase in PI without accelerating oxygen uptake of both fractions. Hence, the softening point of the remaining PS was unchanged or even lowered. An increase of aromatic ring size of the PI component by stabilization was marked at the higher temperature. Suggested stabilization schemes and the role of added PVC pitch in accelerating stabilization are discussed for each of these temperatures taking account of the above results.     

Some factors for the high performances of mesophase pitch based carbon fibre

The tensile strength and Young's modulus of the carbon fibres prepared from naphthalene derived mesophase pitch were studied by varying the spinning temperature, heating rate and final temperature of the stabilization and graphitization temperatures to find the best properties obtainable from the particular pitch. The heating rate was very influential on the tensile strength of the fibre; a slow heating of 0.5° C min^–1, provided the highest strength, as high as 5 GPa at the optimum final temperature of stabilization. A higher or lower final temperature reduced the strength. Insufficient oxygen uptake or decomposition of oxygen groups at the surface of the fibre could induce defects, reducing the strength. In contrast, Young's modulus of the fibres was rather insensitive to preparation conditions. The carbonization and graphitization temperature influenced the mechanical properties as follows: the strength increased stepwise with the carbonization temperature, whereas the modulus increased sharply with the graphitization temperature. The structural factors most influential differed with these properties.     

Structure and properties of mesophase pitch carbon fibre with a skin-core structure carbonized under strain

Coal tar mesophase pitch fibres stabilized at 270° C to different extents were carbonized under strain by the constant load or constant length, using different heating rates, and further graphitized at 2500° C. Shallow and moderate stabilization provided a skin-core structure in the resultant fibres which exhibited higher orientation, tensile modulus, and better graphitizability after calcination at 1300° C and graphitization at 2500° C than deep stabilization. The tensile strength and modulus of the graphitized fibre was significantly improved through the strained carbonization when the stabilization was performed to a moderate extent. The strain tended to give an onion-like alignment in the fibre to improve the preferred orientation of carbon planes. Larger load and more rapid heating during carbonization modified the structure and properties of resultant fibres through a significant longitudinal elongation. The stabilization extent of pitch fibres governs the mobility or fusibility of mesogen molecules at the carbonization which allows their better alignment by the strain.     

Morphological structure study of pitch fibre surfaces by scanning tunnelling microscopy: influence of the mesophase content

The surface morphology of pitch fibres with different mesophase contents was studied by scanning tunnelling microscopy (STM) and the results were related to their mechanical properties. The tensile strength and modulus increase with the mesophase content and correspondingly the surface structure becomes more anisotropic. Inversely, the STM method can also be used to evaluate the precursor mesophase content of a pitch-based carbon fibre.     

同步氢化/热缩聚法制备中间相沥青

通过同步氢化/热缩聚反应,制得中间相沥青（MP）;重点研究了四氢萘（THN）用量对MP性质的影响。研究表明THN增加,MP的软化点（SP）随之降低,H/C随之提高,不溶分随之减少;偏振光显微镜研究表明THN用量少于8%时,MP的形貌为分布不均的各向异性与各向同性两种沥青的混合物;而随着THN的增加,各向异性沥青逐渐趋于以中间相小球形态,并且较为均匀地分布到各向同性沥青基质之中。MP经保温处理后,纺丝性能得到改善,最终制得横截面呈无规结构的沥青基碳纤维。     

Preparation of anisotropic mesophase pitch by carbonization under vacuum

Anisotropic mesophase pitch of high solubility and low melting temperature was prepared from petroleum pitch by carbonizing under vacuum conditions at 430° C for 5 h. The solubility and melting temperature were 55 wt% in quinoline and 270° C respectively, at complete development of anisotropic mesophase pitch. This solubility is much higher than that of mesophase pitch from the same feedstock using refluxing and gas blowing conditions. Yields of the mesophase pitch of complete anisotropic development were 60 wt% under vacuum. The structure of these mesophase pitches were analysed in terms of preparative procedures which create high solubility of a completly anisotropic material.     

Enhanced mesophase formation of petroleum pitch by polyaromatic hydrocarbon addition

Enhanced mesophase yield was achieved for A-240 pitch by addition of aromatic hydrocarbon compounds (anthracene and acenaphthylene) as nucleating agents. A-240 pitch was acid/solvent extracted prior to adding the aromatic hydrocarbons. The mesophase yields increased by significant amounts at 1 wt% addition of the nucleating agents, but decreased at 3 wt% addition. A source of Brönsted acids was required to initiate the catalytic reaction enhancing the mesophase formation.     

Diels-Alder reaction of mesophase pitch insoluble fractions with maleic anhydride

Pyridine insoluble fractions in the mesophase pitches derived from a decant oil (PMP-PI) and naphthalene (NMP-PI) were found to be rendered almost completely soluble in pyridine by the Diels-Alder reaction with maleic anhydride, maintaining their optical anisotropy and molecular association. Their solubility in pyridine reached up to 95 wt % by the reaction at 175–200 °C. Solubilized fractions were analysed to obtain their average structures, suggesting that PMP-PI consists of aromatic nuclei of peri-condensed rings connected through a small number of methylene and aryl-aryl linkages, having a molecular weight (MW) of 1800, and that NMP-PI consists of oligomeric naphthalene with a large number of naphthenic groups (MW 1000). Such structures are basically much the same as those of their soluble fractions, although the molecules in Pls were much larger. The reaction sites in such structures for the Diels-Alder reaction are discussed.     

Oxidation properties of mesophase pitch prepared by a heterogeneous nucleation method

Mesophase pitches prepared by a heterogeneous nucleation method from various mixtures of coal tar-derived isotropic pitch and petroleum-derived mesophase pitch (MP-P) were oxidatively stabilized, and the dependence of chemical reactivity and stabilization rate on their chemical structure was investigated. The rate and amount of oxygen uptake of the mesophase pitch fibres, revealed by thermogravimetry, increased under given conditions of oxidation with the amount of added MP-P, but the rate of stabilization showed a reverse trend. The lower chemical reactivity of coal tar-derived mesophase pitch (MP-C) appears to induce a slower rate of oxygen uptake, while the higher content of pyridine-insoluble fraction and higher aromaticity of MP-C may result in a lesser content of oxygen being required for stabilization, as compared with MP-P.     

同步氢化/热缩聚法制备中间相沥青的工艺研究

系统地研究了在氢化剂量固定情况下,反应温度与时间对同步氢化/热缩聚法所制得的中间相沥青(MP)性质的影响,并制得了可纺MP。研究表明反应时间同为4h时,MP的软化点和不溶分含量随反应温度的提高而升高;偏光结果显示,低温产物为中间相小球和各向同性基质的混合物,高温产物为连续中间相。反应温度同为410℃时,MP软化点和不溶分含量均随反应时间的延长而显著提高,经历了从中间相小球到小球发生融并,最后形成了马赛克织构的中间相。纺丝性能测试表明,反应温度为410或420℃,反应4h制得的中间相沥青,可以熔融纺丝,经氧化和碳化后制得两组碳纤维。     

Improved the electrochemical property of multiwall carbon nanotubes by mesophase pitch fluoride coating

The surfaces of two types of multiple wall carbon nanotubes (MWCNTs), namely, straight and distorted tubes, were modified by mesophase pitch fluoride coating (PFC). Brunauer–Emmett–Teller analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to compare the specific surface area (SSA), functional groups, and micrograph of the MWCNTs with and without modified coating. Results show that PFC can improve the SSA of the straight tube (55 %) more significantly than that of the distorted tube (7.27 %). However, surface coating is more easily implemented on the latter (F/C = 0.48) than on the former (F/C = 0.44) because of self-structure features. Electrochemical measurements indicate that PFC may enhance the specific surface capacitance and energy density of the two MWCNTs because of the effect of functional groups on the modified surface.     

两亲性超支化聚合物对PVDF膜的共混改性

采用对苯二甲酰氯(TPC)为偶联剂,将不同分子量的端羟基聚乙二醇(MPEG,Mn分别为350,750,2 000)接枝到超支化聚酯(HPE)分子周围,合成了两亲性超支化聚合物(HPE-g-MPEG),并将其与聚偏氟乙烯(PVDF)共混,通过相转化法制备了PVDF多孔膜.用SEM,XPS,水接触角,BSA吸附等对共混膜的结构和性能进行了表征.XPS结果表明,超支化聚合物在膜表面呈现富集现象,该富集现象随聚乙二醇(MPEG)分子量的增大而加强.同时,随着聚乙二醇(MPEG)分子量的增大,膜表面的水接触角下降,BSA吸附量减少,表明共混膜的亲水性和抗污染能力提高.     

A microscopic study on the oxidative stabilization of a coal-tar-based mesophase pitch and its blends with PVC pitch

Coal-tar-based mesophase pitch and its blends with PVC pitch at 5 or 10 wt% were oxidatively stabilized at 230, 270 and 300°C for variable periods to clarify the progress of stabilization and the effects of the blending with PVC pitch on the stabilization reactivity. PVC pitch which was prepared from PVC by heat-treatment at 420°C for 2h enhanced the stabilization reactivity of whole pitch fibres to shorten the stabilization time to a half of that for mesophase pitch alone. PVC pitch carrying considerable amounts of aliphatic components and large molecular weight may initiate, as a trigger, the stabilization reactions of mesophase constituent molecules. Carbonized fibres of 30μm diameter after stabilization at 270 and 300°C exhibited a skin-core structure, while fibres of 10μm diameter showed no skin-core structure, indicating a homogeneous progress of stabilization in the radial direction of the latter fibres. Lower stabilization temperatures provoked no skin-core structure even in the thick fibres. The rate of core diminishing became relatively slower in the later stage of the stabilization, even when the reactivity of the pitch fibres was enhanced by blending with PVC pitch and using a higher stabilization temperature. The diffusion of the oxidant and stabilization reactivity of the pitch fibres are discussed comparatively.     

聚己二酸丙三醇酯增韧改性聚乳酸的研究

以丙三醇(G)、己二酸(A)为原料,制备了一种新型聚乳酸(PLA)增韧改性剂--聚己二酸丙三醇酯(PGA).通过熔融共混的方法制备了PGA/PLA共混物,并*利用偏光显微镜(PoM)、动态力学分析(DMA)等对其动态热机械性能、冲击强度及相态结构进行了表征.研究结果表明,PGA的加入改善了PLA材料的柔性,PGA含量为15%的PGA/PLA共混物的冲击强度达到48.0J/m,比纯PLA提高了300.0%.