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The mechanism for the change in the size of the geometry of graphite crystallites in polyacrylonitrile-based carbon fibers heat treated at 1500–2500 °C is proposed. The study indicated that the growth transition temperature of graphite crystallites in carbon fibers is 2000 °C. Above 2000 °C, the interlayer space (d002) decreases slowly and an ordered graphitic structure forms. Below 2000 °C, the variation in the size of the crystallites along the directions of the axis (La‖) and the radius (La⊥) of the carbon fibers that were heat treated at various temperatures was almost the same and the crystallite form factor, La‖/La⊥, which is nearly 1. Above 2000 °C, La‖/La⊥ increases rapidly because the anisotropy of the arrangements of the crystallites in the carbon fibers and the geometry of the crystallites change from being square to becoming rectangular. The crystallite thickness (Lc) also increases with an increasing temperature and below 2000 °C the crystallite form factor (La‖/Lc) increases rapidly. Above 2000 °C, the La‖/Lc stabilized at 3.1. The different growth models in the different directions are the intrinsic root for the variations in the crystallite geometries that underwent high-temperature heat treatments.

Pyrolysis mechanism of nitrogen in carbon fibers, heat-treated at various temperatures, was investigated, in relation to the nitrogen chemical bonding states. Nitrogen content shows exponential decreasing with increased temperature and extended time. The pyrolysis of nitrogen exhibited time-temperature equivalence. Nitrogen atoms containing hydrogen in the amorphous region and at the edge of microcrystalline, and the double-bonded nitrogen in pyridine rings are easily pyrolyzed, while nitrogen atoms in the six-member ring of the graphite sheets are difficult to be pyrolyzed.

A kind of rapid heating method which takes advantage of carbon fiber conductivity to shorten the cycle time of VARIM was designed in present paper. The processing cycle time, curing degree, glass transition temperature and mechanical properties of the laminates fabricated by carbon fiber internal resistive heating aided VARIM (R-VARIM) were studied. The results revealed that the cyle time of R-VARIM with con-water cooling process is only 450s, it is about 52% lower than that of previous study. Lower cooling rate before glass transition temperature is useful to complete cure of resin and improve the properties of the composites.

This article focuses on experimental studies on the wetting behavior between different carbon fibers (CFs) and epoxy as function of temperature, hardener addition, and progressive curing of the resin. The results indicate that surface sizing plays a key role in wettability of the CF with epoxy. There is a critical temperature for good-wetting of DGEBA-DDS mixture/CF. Complete wet- ting can be obtained for resin/CF after a period of curing time. Moreover, chemical reactions can not only improve the wettability but also strengthen interactions between the curing resin and CF. These results could provide an essential implication for understand- ing the formation process of interphase region of CF/epoxy composites. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000-000, 2012

Three-dimensional (3-D) spacer fabric composite is a novel lightweight sandwich structure, the reinforcement of which is integrally woven with two facesheets connected by continuous fibers (named piles) in the core. Usually the 3-D spacer fabric composite without extra reinforcement is called mono-spacer fabric composite, which provides outstanding facesheet / core debonding resistance. However, its mechanical properties cannot meet the demand of structure application because of the thin facesheet and low load-bearing capacity of high piles. Hence, two reinforcement methods were developed by laminating additional weaves at the facesheet and filling foam materials in the core to strengthen the facesheet and piles, respectively. This paper aims to investigate the influences of reinforcement methods on the mechanical behaviors and damage modes of 3-D spacer fabric composites under flatwise compressive, shear, edgewise compressive and three-point bending loads, by comparing with mono-spacer fabric composites. The results indicate that additional weaves reinforcement can enhance edgewise compressive and flexural properties effectively. Foam filling is one of the best options to improve the flatwise compressive and shear properties, and especially, there are synergistic effects between piles and foam under flatwise compressive load. Besides, the failure modes of reinforced and mono-spacer fabric composites are different.

In this paper, the distribution and variation of resin pressure were tested by a specially designed measuring system, reflecting the resin flow during the process. Based on this system, the effects of the applied pressure, the lay-up of laminate and the variety of bleeder on resin pressure were investigated. It indicated that the transfer of resin pressure along the laminate thickness direction was not instantaneous. The resin pressure of the laminate boundaries and the resin flow behavior both were influenced by the studied factors. These results are valuable for the modification of the resin flow model and the precise determination of the boundary conditions.

The bulk tiles of ceramic fibers reinforced aerogel were prepared from two reinforcements, evenly dispersed ceramic fibers and sintered tiles. It has been found that ceramic fiber-reinforced aerogels showed higher thermal conductivity than aerogel itself. Shrinkage of aerogels in chopped fiber reinforced aerogel composites showed similar tendency as pure aerogel during gelation, but the shrinkage was prohibited during supercritical drying. By contrary, in the case of sintered tile reinforced aerogel, shrinkage of aerogel was completely limited in both gelation and drying processes. Average of about 50% increase of compressive strengths of the sintered tile reinforced aerogel to sintered tiles were obtained with an average density increase of about 36%, their thermal conductivity depressed slightly.

Good wetting plays an important role in improving the degree of adhesion at interfaces between fibres and matrices in composites. The contact angle of an epoxy resin, as a widely used polymeric matrix, was studied by impregnation in single glass capillaries at the manufacturing temperature of the composites. In order to obtain the net wicking mass for capillary experiments, the meniscus force at the bottom of the glass tube was investigated, with the help of the Wilhelmy technique, conducted by using glass sticks with various diameters. Results show that the contact angles resulting from equilibrium using both capillary impregnation and the Wilhelmy experiment are consistent, which indicates the reliability of the practical evaluation of the effect of the meniscus on the penetration mass. The contact angle of this epoxy resin was approximately 60° resulting from the equilibrium of the capillary impregnation and the Wilhelmy experiments at 80°C.

A novel PMR-type polyimide based on 3,3′4,4′-oxydiphthalic dianhydride (ODPA), 4,4′-methylenedianiline (MDA) with nadic ester (NE) endcaps was studied. Its random copolymers, which incorporated pyromellitic dianhydride (PMDA) and p-phenylenediamine (PPD) into the backbone, were synthesised. They are characterised in abbreviation as OPM (ODPA/PMDA-MDA) and OMP (ODPA-MDA/PPD) respectively. Oligomers with various molecular weights and components were synthesised, in order to compare the influence of the chemical structure and the crosslink density of polyimides on the final properties. MOPM, which contained an identical backbone to OPM but was terminated with a mono-nadic endcap, was also synthesised to see whether the different endcaps of oligomers could impact enhanced thermal properties. The thermo-oxidative stability, processing and mechanical properties of these polyimides were tested. The results showed that incorporation of PMDA or PPD into the ODPA-MDA homopolyimide (abbreviated as OM) could greatly enhance the Tg, while retaining comparable thermo-oxidative stability and reasonable processing properties.

The densification mechanism of polyacrylonitrile carbon fibers during carbonization from 900 to 1 400 °C was investigated. The density, elemental composition, microstructure and weight loss of the fibers, as well as the gases released during the process were analyzed to reveal the mechanism. Results indicated that the density of the fibers was strongly dependent on the carbonization temperature and reactions involved indifferent temperature regimes. Condensation, pyrolysis and graphitization reactions were dominant at low ( 1 250 °C) temperatures, respectively. The amount of small molecule gas released and the fiber density both increased rapidly with temperature when condensation reactions dominated. The fiber density decreased as a result of nitrogen release when pyrolysis reactions dominated above 1050 °C while the fiber density increased due to the growth and increase in order of the graphene layers during graphitization. The two fiber density maxima found with increasing carbonization temperature were attributed to the different reactions.

The study is aiming to investigate the anti-depression effect and possible mechanism of Pingyu Formula (Pingyu), which is an herbal supplement derived from Chinese Traditional Medicine. Tail suspension test (TST) and forced swimming test (FST) were used to investigate the anti-depression effect. The cyclic AMP (cAMP) levels, CREB and BDNF mRNA expression in rats' hippocampi were investigated via ELISA or RT-PCR method respectively. The results showed that Pingyu (75.0, 150 mg/kg, p.o.) reduced the duration of immobility in the FST and TST significantly, while the locomotor activity was not affected. Furthermore, the cAMP level was significantly increased after the treatment of Pingyu (50.0 mg/kg, p.o.) compared with the control group. Levels of the CREB-1, CREB-2 and BDNF mRNA expression were also increased after treatment of Pingyu. In summary, a possible pharmacological mechanism on anti-depression effect of Pingyu was related to the regulation of cAMP signaling pathway.

PingYu capsule was a novel compound botanical drug, being composed of the extracts from Radix et Rhizoma Ginseng, Fructus Jujubae and Radix et Rhizoma Glycyrrhizae, which were the classical herbal medicines in China. Depression is one of psychological and/or physiological disorders. In the recent decades, depression affected the people's health seriously. This study was designed to demonstrate the possible mechanism on antidepressant-like effect of PingYu capsule. Rats were used as an animal model and the hippocampus were removed from the rat brain after the administration of PingYu capsule 8 hours later. The weighed hippocampus were homogenized quickly and the total protein content, cyclic adenosine monophosphate (cAMP) level, cAMP dependent protein kinase (PKA) activity, and phosphorylated cAMP response element binding protein (CREB) level were examined via ELISA as well as the determination of phosphodiesterase type IV (PDE4) activity. As a result, the PDE4 activity was inhibited significantly by PingYu capsule at the dose of 0.5 mg/ml in vitro . The cAMP level, PKA activity, and Phospho- CREB level were all markedly increased after the treatment of PingYu capsule (50 mg/kg, p.o.) compared to the blank control. In conclusion, the possible mechanism on antidepressant-like effect of PingYu capsule was involved with the activation of cAMP / PKA / CREB Signaling Pathway.

The optical properties of rare-earth organic complexes-doped poly(methyl methacrylate) (PMMA) have been studied because of their great prospect of application in optical devices, such as optical fibers, fiber lasers, amplifiers and waveguides. Eu 3+ , Pr 3+ and Tb 3+ ions were encapsulated in tri(dibenzoylmethane) (DBM) and tri(thenoyltrifluoroacetone) (TTA) chelates, then Eu 3+ complexes were doped in MMA before the polymerization, and stirred thoroughly during the polymerization. These complexes were characterized by elementary analysis, FT-IR, XPS and ICP, and fluorescent properties of rare earth complexes-doped PMMA were measured by fluorescence spectrometer. Analysis reveals that Eu(TTA) 3 is a promising dopant for use in rare-earth-doped PMMA in the research, the complex can be doped to high concentrations in PMMA systems without quenching, providing means for polymer amplification devices. For the rare-earth-doped PMMA samples, an effective energy transfer between the ligands and rare-earth ions is observed and discussed. To our knowledge, the effect of molecular weight of PMMA on the fluorescent properties of rare-earth-doped PMMA has not been reported, and the result indicates that the larger the molecular weight of PMMA is, the better the fluorescent property of the system.