Weibull analysis of microbond shear strength at sisal fibre–polyester resin interfaces

An analysis has been made of the tensile strength of sisal fibres and the interfacial adhesion between fibres and polyester resin droplets. Density and microscopy methods were used to determine the cross-sectional area of the sisal fibres. The average tensile strength of treated sisal fibres decreased by a modest amount following treatment with 0.06 M NaOH. However, this treatment resulted in a substantial increase in the interfacial shear strength at the sisal fibre to polyester resin interface. Weibull analysis has been used successfully to analyse variability in tensile strengths and interfacial shear strength using probability of failure plots. Scanning electron microscopy has revealed the shape of resin droplets on the surface of treated and untreated sisal fibres and contact angles are much lower for droplets on treated fibres. Damage to the surface of fibres has been examined following shear testing. Weibull analysis is an effective tool for characterising highly variable fibre properties and evaluating the level of adhesion between polymer resin and the fibre surface.     

Unsaturated polyester resin (UPR) reinforced with flax fibers,untreated and cold He plasma-treated: thermal,mechanical and DMA studies

Hemp, jute, flax, bagasse, coconut and bamboo fibers are some of the natural fibers that have attracted attention for the preparation of composite materials because of their low cost compared with synthetics fibers (glass, carbon). The performance of a natural fiber as reinforcement in composite materials is linked to its ability in term of adhesion with the synthetic matrix. This depends mainly on the quality of the fiber surface. In order to improve this adhesion, a thin reactive coating is generally used. In this study, cold He plasma treatments have been carried out on reinforcing flax fiber. Composites with unsaturated polyester resin (UPR) have been used with untreated flax fibers and plasma-treated fibers. The data characterizing the thermal, mechanical (dynamic and static) will be presented in order to analyze the efficiency of the He plasma treatment on the composite performances.     

铜电极在弱碱性介质中腐蚀行为的研究

应用循环伏安法和现场椭圆偏光法研究了弱碱性介质中铜的腐蚀、钝化过程,并用二组分有效介质模型对光学实验结果进行了拟合。结果表明金属铜在腐蚀达到稳态时其表面氧化膜具有一定的组成和厚度;反应生成的CuO比Cu2O更为致密,因而对基体具有更好的保护作用;CuO的阴极还原过程可能会涉及到还原中间产物Cu^+的岐化反应,该岐化反应的进行有助于铜耐蚀性的提高;CuO的还原可以在小于-0.45V(vs.SCE)的电位范围内与Cu2O的还原同时进行,椭圆偏光实验不仅与电化学和光电化学实验的结果一致,还能定量地确定膜的厚度、折射率等性质;并根据有效介质模型,可以计算得到不同时刻电极表面膜组成的改变;从而为研究电极反应机理提供新的证据。     

Influence of Ethylene-Butyl Acrylate-Glycidyl Methacrylate Terpolymer on Compatibility of Ethylene Vinyl Acetate Copolymer/Olive Husk Flour Composites

The paper reports some results of an experimental study on ethylene vinyl acetate (EVA) copolymer/olive husk flour (OHF) composites incorporated at various filler ratios (15, 30 and 45 wt%) in the absence and the presence of ethylene-butyl acrylate-glycidyl methacrylate (EBAGMA) terpolymer used as a compatibilizer. The composite samples have been prepared by melt blending and their chemical structure, as well as morphological, mechanical and water absorption properties investigated. It is shown that the compatibility of EVA/OHF composites is improved by the addition of EBAGMA terpolymer. Indeed, FT-IR analysis shows that chemical interactions have occurred between the compatibilizer and the base blend components. Morphological results from SEM shows better dispersion of the wood particles in the EVA matrix and the resulting composite samples exhibit better tensile properties at break and lower water absorption than the uncompatibilized ones. Moreover, the results indicate that the loading concentrations of both OHF and EBAGMA have an effect on the composite properties.     

Influence of fibre extraction method,alkali and silane treatment on the interface of Agave americana waste HDPE composites as possible roof ceilings in Lesotho

Surface treatment is often necessary for strong composites. But the challenge for developing countries is to find chemicals and treatment procedures that are cheap and simple but maintain good composite properties. Mercerization followed by silane treatment of natural fibres is among the simplest and cheapest methods used to improve composite interfaces. This study investigates the effectiveness of this method to improve the bond between Agave americana fibres and post consumer HDPE. The influence of fibre extraction method, mercerization and mercerization followed by silane treatment on interfacial shear strength (ISS) and fibre properties is determined. The results indicate that ISS values are generally low but mercerization doubles the ISS values between Agave americana fibres extracted by traditional boiling of leaves and post consumer HDPE. Mercerization also improves fibre tensile and thermal properties. While triethoxyvinylsilane treatment of fibres after mercerization does not improve the ISS, it does not reduce it either, nor does it reduce tensile and thermal strengths of mercerized fibres. Fibres from non-boiled leaves resulted in poor fibre tensile strengths but improved ISS. There is a potential to use mercerization as cheap, simple technique to make Agave americana HDPE composites to provide cheap roof ceilings in Lesotho.     

Studies on short isora fibre-reinforced polyester composites

This paper reports the use of a natural fibre, isora, as reinforcement in unsaturated polyester resin. Isora is a bast fibre separated from the bark of Helicteres isora plant by retting process. Properties like tensile strength, flexural strength etc. have been studied as a function of fibre length and fibre loading using treated and untreated fibre. The mechanical properties were found to be optimum at a fibre length of 30 mm and a fibre loading of 30% by volume. The effects of alkali treatment on the fibre properties were investigated by SEM, IR and TGA. The mechanical performance of the treated isora fibre-reinforced polyester composites has also been investigated. SEM studies were carried out to investigate the fibre surface morphology, fibre pull-out and fibre–polyester interface bonding. SEM gave evidence for the changes that had occurred on the fibre surface during chemical treatment. The properties were found to be superior for the composite reinforced with treated fibre compared to the untreated fibre.     

Amino Functionalization of MWNTs and Their Effect on ILSS of Hybrid Nanocomposites

Multi-walled carbon nanotubes (MWNT) were oxidized by treatment with a mixture of sulfuric and nitric acids to introduce carboxyl groups on their surfaces. Triethylene tetraamine (TETA) was then grafted onto the oxidized MWNTs via a thionyl chloride route to obtain the amino-functionalized MWNTs (f-MWNT). The presence of amino functional groups on the MWNTs was confirmed using FT-IR, and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to compare the morphology of pristine MWNT (p-MWNT) and f-MWNT. Both the p-MWNT and f-MWNT were dispersed in epoxy resin using ultrasonic agitation and the suspensions were injected into E-glass fiber woven fabric using a specialized vacuum assisted resin transfer molding (VARTM) process in which a flow flooding chamber (FFC) was used to re-direct the suspension flow. Control samples were fabricated using the same E-glass fiber mat and unmodified epoxy resin following the same procedure. Compression shear testing (CST) was performed on all the manufactured samples to determine their Inter laminar shear strength (ILSS). Results show 41% increase in ILSS for hybrid composites containing p-MWNTs and a 61% increase for samples containing f-MWNTs relative to the control samples without MWCNT.     

Modification of BPDA-ODA Polyimide Films by Diimides

Diimides 4,4′-oxydiphenylene diphthalylimide (PT-ODA-PT) and diphenylbiphenyltetracarboxyimide (A-BPDA-A) of an evident affinity to polyimides have been dispersed in a matrix of poly(4,4′-oxydiphenylene biphenyltetracarboxyimide) (BPDA-ODA). Changes in thermal and mechanical properties of BPDA-ODA films modified by diimides have been found to depend on the amount of diimide added and the conditions of film preparation (stretching). It has been established that diimides can play two different roles. When dissolved in polyimide, they act as plasticizers improving the segment mobility of BPDA-ODA chains, which may be critically needed to achieve the better molecular packing. The films plasticized by diimides show lower T _g and the order–disorder transition temperature; the unstretched films exhibit better tensile properties, compared to unmodified films. However, dispersed beyond the limit of solubility in polyimides, diimides have detrimental effects on mechanical properties of the films. Though changes of the thermal properties of compositions derived from BPDA-ODA polyimide and microparticular diimides are less expressed than those of polyimide films plasticized by diimides, the compositions have poorer ultimate strength and shorter elongation at break. The conclusion may be drawn that the mechanical properties of the films modified by microparticular diimide are mainly controlled not by the interfacial interaction matrix–microparticles, but more likely by the much stronger macromolecular chain–chain interaction.     

Filler treatment effects on the weathering of talc-, CaCO3- and kaolin-filled polypropylene hybrid composites

Talc, calcium carbonate (CaCO₃), and kaolin hold considerable promise in the development of polymer composites for good mechanical properties and stability. Comparative studies on the usage of these minerals as single fillers in polypropylene (PP) have shown varying degrees of reinforcement due to their differences in terms of particle geometry, surface energy and affinity towards the matrix polymer. In this study, comparisons were made in terms of mechanical, thermal and weatherability properties between hybrid-filler PP composites (i.e. PP filled with either talc–CaCO₃ or talc–kaolin hybrid filler combinations), with particular attention directed towards the effect of surface modification of the fillers. The talc/CaCO₃ hybrid composites have shown exceptional performance in terms of flexural and impact properties. The contribution of talc in the talc–kaolin hybrid composite system has been significant in terms of enhancing the overall tensile and flexural properties. The ability of silane and titanate coupling agents in boosting the resistance of the composites to severe damage and degradation due to natural weathering has been shown.     

Numerical study of the single fibre push-out test: Part III. Singularity of interface stresses

The singular behaviour at the free edges of the fibre-matrix interface is analysed for the fibre push-out test geometry based on the boundary element method. The fibre push-out test has been extensively used to measure the fibre-matrix interfacial properties in polymer, ceramic and metal matrix composites. There are two free edges in the fibre push-out specimen: one is at the loaded fibre end and the other at the supported fibre end. The singular stresses can be expressed as a function of singular exponent and singular stress intensity. It is shown that the singular exponents obtained at both fibre ends are characteristic of composite constituent properties, such as Young's moduli of fibre and matrix, and does not vary with specimen dimensions. The singular exponents are real and identical for the shear and radial stress components at fibre ends where the wedge angles are the same. The singular stress intensities are also implicit in material properties, and vary with specimen dimensions, such as fibre to matrix radius ratio, fibre aspect ratio and support hole size. An interfacial failure criterion is proposed here based on the average stress concept to determine the critical singular stress intensities in mode I and mode II loads.