光谱电化学方法研究: 茜素红S在玻碳电极上的电化学行为

本文首次用长光程光透薄层电解池, 以现场光谱电化学方法研究了茜素红S在酸性溶液中于玻碳电极上的电化学行为, 发现在1.00-0.60V电位范围内存在三个电化学反应过程和一个化学反应过程, 并根据电化学和光谱数据, 提出了电极过程的机理。     

茜素与β-胡萝卜素自由基抗氧化和一氧化氮释放 的研究

在均相体系中利用紫外吸收光谱法,研究了偶氮二异丁睛(AIBN)引发的亚油酸(LH)过氧化反应,发现茜素(Alz)和β-胡萝卜素(β-C)对LH过氧化均有抑制作用,并表现出协同效应。膨胀计法研究表明Alz和β-C对AIBN引发的苯乙烯自由基聚合有阻滞作用,发现Alz与β-C间存在明显的协同阻、缓聚作用。通过在培养的人脐静脉内皮细胞中的研究表明,Alz可促使内皮细胞释放一氧化氮(NO),其作用比乙酰胆碱(Ach)更为显著。     

A comparison of the mechanical strength and stiffness of MWNT-PMMA and MWNT-epoxy nanocomposites

The surface of multi-wall carbon nanotubes (MWNTs) was functionalized by covalent linking of long alkyl chains. Such functionalization led to a much better tube dispersion in organic solvents than pristine nanotubes, favored the formation of homogenous nanocomposite films, and yielded good interfacial bonding between the nanotubes and two polymer matrices: a thermo-set (Epon 828/T-403) and a thermoplastic (PMMA). Tensile tests indicated, however, that the reinforcement was greatly affected by the type of polymer matrix used. Relative to pure PMMA, a 32% improvement in tensile modulus and a 28% increase in tensile strength were observed in PMMA-based nanocomposites using 1.0 wt% nanotube filler. Contrasting with this, no improvement in mechanical properties was observed in epoxy-based nanocomposites. The poorer mechanical performance of the latter system can be explained by a decrease of the crosslinking density of the epoxy matrix in the nanocomposites, relative to pure epoxy. Indeed we demonstrate that the presence of nanotubes promotes an increase in the activation energy of the curing reaction in epoxy, and a decrease of the degree of curing.     

Melt mixing of polycarbonate/multi-wall carbon nanotube composites

—Composites of polycarbonate (PC) with multi-wall carbon nanotubes (MWNT) of different concentrations are prepared by diluting a PC based masterbatch containing 15 wt% MWNT using melt mixing in a DACA-Micro Compounder (4 g scale). Electrical resistivity measurements indicate that the percolation of MWNT is reached between 1 and 1.5 wt%. In addition, melt rheology was applied as another sensitive method to detect the percolation of the nanotubes. Atomic Force Microscopy and visual observations of the composite dispersions in a PC-solvent were used to characterise the state of MWNT dispersion. Differential Scanning Calorimetry and Dynamic Mechanical Analysis were applied to detect changes in the glass transition temperature of PC as a result of processing and of MWNT interactions with the PC matrix including the state of dispersion. In addition, DMA confirmed the reinforcement effect of the nanotubes. The results show that the nanotube incorporation also influences the processing behaviour. Due to the enhancement in melt viscosity by adding nanotubes and the enhanced shear forces, the molecular weight of the PC in the composites is reduced as compared to PC extruded under the same conditions. This effect leads to changes in the glass transition temperature and modulus which counteracts the effects originating from the nanotube-polymer interaction.     

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

Transverse tensile properties of spun-type carbon fabric/phenolic composites

The transverse tensile properties of phenolic composites reinforced with spun-type carbon fabrics (spun C/P composites) have been investigated in order to evaluate the adherent failure behavior of composites in the transverse (90°) direction due to tension. The transverse tensile strength of the spun C/P composite is about 3.4 times higher than that of the conventional composite reinforced with filament type carbon fabrics (filament C/P composites). It is found from stress–strain curve of composites that it exhibits above 4 times higher failure strain than the filament C/P composite. However, the transverse tensile modulus of the spun C/P composite is similar to that of the filament C/P composite. The results indicate that the protruded fibers of spun yarns between the interlaminar layers in the spun C/P composite play an important role in improving the transverse tensile properties by the effects of fiber bridging. Consequently, this result suggests that use of spun yarn type carbon fabrics as reinforcement in a phenolic composite may significantly contribute to improving the interfacial properties of carbon/phenolic composites.     

Modelling of the transverse strength of fibre reinforced epoxy composite at low and high temperature

Process-induced thermal residual stresses and matrix failure of unidirectional carbon fibre reinforced composites (CFRP) have been investigated by finite element analysis (FEA). We used a partial discrete FEA model based on a unidirectional composite consisting of a microscopic area of fibres and matrix surrounded by a homogenised composite area. The FEA provided information about the stress state in the matrix and the fibre–matrix interface. The transverse strength of the composite was calculated regarding matrix failure and fibre matrix debonding. The influence of the temperature on the Young's modulus, the non-linear stress–strain behaviour and the strength of the matrix were investigated in detail. Following this approach it was possible to incorporate the resulting microresidual stresses on the transverse strength of the composite. Tensile tests of the neat resin and of the composite were performed in the temperature range of ?40°C to 60°C. The results of the FEA modelling are in good agreement with the experimental results of the transverse tests.     

Improvement in damage tolerance of CFRP laminate using the hybridization method

Flexible epoxy resin was used as an interphase matrix to improve the transverse properties of carbon fiber reinforced plastic (CFRP) laminates. The use of flexible interphase is considered to act as the energy absorber and prevent the fiber/matrix interface cracking. The purposes of the present study are fabrication and characterization of CFRP laminates with flexible interphase. The effect of the flexible interphase on the damage tolerance of CFRP laminates was investigated. It was confirmed that transverse strength was improved and transverse crack progress was suppressed in the laminates with flexible interphase.