Excellent flexural properties of aminimide-cured epoxy resin as a matrix for mica-dispersed polymer composites

The flexural behaviour of mica-dispersed epoxy resin composites has been examined. The flexural strength and flexural modulus have been determined as a function of the volume fraction of mica flakes (V _f) for both aminimide-cured epoxy resin matrix and a conventional epoxy resin reference matrix. On the basis of microscopic observation of fractured surfaces, the effect of improving the particle-matrix interface has been analysed using the modulus reduction factor (MRF) in a modified form. It is found that there is a steady increase in the flexural modulus with the volume fraction of mica flake for the aminimide-cured epoxy resin matrix. In contrast, the increase in flexural modulus levels off at a high content of filler for the reference samples. It is noteworthy that the intact mica flakes without surface treatment exhibit a substantial reinforcing effect on the flexural strength in the case of aminimide-cured epoxy resin composites. A further surprise is the difference among the curing agents used. The reference epoxy resins behave just like conventional matrix resins, exhibiting 30 to 40% reduction in the flexural strength when a small fraction of mica is added. These superior properties of the matrix resin for the composites are ascribed to the characteristics of aminimide-cured epoxy resins such as hardness, toughness, and excellent adhesivity.     

Development of preforming pitch for carbon-carbon composites from coal-based precursors

Preforming pitch, a special type of pitch, used for the matrix formation of carbon-carbon composites, has been developed from suitable coal-based precursors, using the techniques of distillation, condensation and polymerization. The effects of various processing parameters, namely the temperature and period of heat treatment, and the atmosphere (inert or partial vacuum) during the heat treatment, on the characteristics of the resulting pitch have been studied. Some of the pitches were subjected to field trials from which the characteristics of a good preforming pitch leading to a carbon-carbon composite of density around 1.8 g cm^–3 have been identified.     

热塑性酚醛树脂对碳纤维环氧树脂基复合材料性能的影响

利用热重分析(TGA)、扫描电镜(SEM)和三点短梁法对添加不同含量的热塑性酚醛树脂(PF)的复合材料体系改性效果进行了研究,考察了不同含量的酚醛树脂对固化体系力学性能及热性能的影响.结果表明,随着酚醛树脂含量的增加,碳纤维环氧树脂基复合材料(CFRP)的弯曲强度和弯曲弹性模量呈递减趋势;层间剪切强度(ILSS)呈现先增加后减小的趋势,当酚醛树脂的含量为20%时,层间剪切强度达到111.31MPa,提高约7%;热稳定性较其它含量时高,复合材料体系的综合性能最好.     

Dynamic mechanical properties of carbon-carbon composites

The dynamic mechanical analysis (DMA) method was utilized to investigate the dynamic mechanical properties of the carbon-phenolic composite, and of carbon-carbon (C/C) composites carbonized at 1000°C, and graphitized at 2200°C. The measurements were performed in the temperature range 50–450°C. Results show that the carbon-phenolic composite has the highest storage modulus, while the carbonized C/C composites possess higher storage modulus than the graphitized C/C composite. The storage moduli of carbonized and graphitized C/C composite do not change significantly in the test temperature range. The tan , loss factor, of carbonized C/C composites increases 59.5% during the tests from 50 to 450°C, and that of the graphitized C/C decreases 9.74% in the same temperature range; graphitized C/C shows the highest tan at 50 °C. The carbon-phenolic composite shows a damping peak at 250 °C, which is probably due to the transition from glassy state to rubbery state of the phenolic matrix. The higher tan of the graphitized C/C composite may be due to matrix graphitization, fibre-matrix debonding and crack formation, which were observed on the micrographs.     

The mechanical properties of vinylester resin matrix composites reinforced with alkali-treated jute fibres

Jute fibres were subjected to alkali treatment with 5% NaOH solution for 0, 2, 4, 6 and 8 h at 30°C. The modulus of the jute fibres improved by 12, 68 and 79% after 4, 6 and 8 h of treatment, respectively. The tenacity of the fibres improved by 46% after 6 and 8 h treatment and the % breaking strain was reduced by 23% after 8 h treatment. For 35% composites with 4 h-treated fibres, the flexural strength improved from 199.1 to 238.9 MPa by 20%, modulus improved from 11.89 to 14.69 GPa by 23% and laminar shear strength increased from 0.238 to 0.283 MPa by 19%. On plotting different values of slopes obtained from the rates of improvement of flexural strength and modulus, against NaOH treatment time, two different failure modes were apparent before and after 4 h of NaOH treatment. In the first region between 0 and 4 h, fibre pull out was predominant whereas in the second region between 6 and 8 h, transverse fracture occurred with minimum fibre pull out. This observation was well supported by the SEM investigations of the fracture surfaces.     

Transmission electron microscopic study of three-dimensional polyacrylonitrile fibre-mesophase pitch matrix carbon-carbon composite

Conventional and high resolution transmission electron microscopy performed in this study provides some detailed microstructural information of a polyacrylonitrile (PAN) fibremesophase pitch matrix carbon-carbon composite which has not been published in open literature. The PAN fibre in this composite possesses a turbostratic structure throughout the fibre. The structure of the mesophase pitch matrix is graphitic and anisotropic. Near-fibre matrix crystallites are aligned roughly parallel to the fibre surface, exhibiting a flow-type morphology. The fibre-matrix interface in this composite is microfissured. Numerous microcracks exist both within the matrix and along partially bonded interfaces. The irregularly shaped interfacial microcracks readily expose the fibre surface topography. Microcracks within the matrix are formed between, and parallel to, the basal planes of the graphitic platelets. Such submicron-sized matrix cracks appear smaller and denser near the fibre-matrix interface.     

酚醛树脂对碳布性能的影响

以磷酸氢二铵改性人造棉为基体材料,酚醛树脂为改性剂,经喷涂、炭化制备燃料电池扩散层材料用碳布。研究了酚醛树脂含量对碳布强度、电阻率、厚度和密度的影响,并通过XRD谱图和SEM图片对碳布进行微观结构分析,探讨了酚醛树脂对碳布强度和电阻率的影响机理。结果表明,酚醛树脂在提高碳布强度的同时降低其电阻率。当酚醛树脂添加量为54%时,碳布强度提高40%,体电阻率降低至0.06Ω·cm。     

烷基硫醇自组装铜镀层及其树脂基复合材料界面性能研究

为改善金属转移法制备的铜镀层与碳纤维增强氰酸酯树脂基复合材料的界面粘附性能,选用4种烷基硫醇偶联剂自组装膜(SAMs)改性铜镀层.通过表征改性前后镀层表面形貌、表面极性变化、烷基硫醇与铜镀层之间的化学键合情况,研究不同烷基硫醇对铜镀层与复合材料界面结合强度的影响.结果表明：4种烷基硫醇不同程度地提高了铜镀层与复合材料的界面结合强度,具有反应活性基团和长链结构的11巯基-十一烷酸(MUA)和11巯基-十一烷醇(MUOL)因与复合材料产生化学键连接和分子链缠结作用,形成铜镀层-SAM-复合材料的界面结构,使界面结合强度提高超过70%.     

一种耐高温加成固化型酚醛树脂作为复合材料基体的评价

制备了烯丙基化程度可达 173%的烯丙基酚醛树脂(AN173),并与双马来酰亚胺(BMI)以 1 ∶1 的质量比进行共聚,制备了双马改性的烯丙基酚醛树脂(BMAN173) 。研究了该树脂工艺性,确定了其固化制度,考察了该树脂石英布复合材料层合板的耐热性和力学性能。实验结果表明,BMAN173 树脂具有良好的工艺性,适合于RTM、模压成型等多种成型工艺。BMAN173树脂固化物表现出良好的耐热性,其储能模量起始下降温度约为390℃, 起始热分解温度超过430℃。与传统酚醛树脂相比,该树脂的复合材料的高温力学性能优异,350℃弯曲强度和层间剪切强度保留率分别约为57%和62%;复合材料具有优异的热性能,其储能模量起始下降温度约为410℃,玻璃化转变温度超过了450℃。BMAN173树脂是耐高温复合材料的理想候选基体树脂。     

沥青树脂和炭纤维的复合性能

流化床催化裂化(Fluid catalytic ciracking,FCC)油浆富芳馏份(Fluid catalytic ciracking rich aromatic,FCCRF)与交联剂对苯二甲醇(1,4-benzenedimethanol,PXG)在催化剂对甲基苯磺酸(Para-toluene sulphonic acid,PTS)的作用下,加热至120℃以上,制得的沥青树脂是一种新型的热固性树脂。沥青树脂在一定条件下与炭纤维或炭纤维纸热压成型。成型料在空气中250℃-10h和300℃-2h热处理后,其热力学性能无明显变化;在强酸、强碱中处理1h~70h,质量几乎无变化;说明沥青树脂与炭纤维或炭纤维纸的复合材料热稳定性和化学稳定性尚好。沥青树脂与炭纤维或炭纤维纸的复合材料在高纯氮保护下,经950℃~1000℃热处理后制得炭/炭复合材料,由SEM观察可见炭/炭复合材料无空洞、劈裂,力学性能尚可,断口炭纤维拉出小于10μm,说明沥青树脂与炭有较强的亲和力,与炭纤维黏合很好。FCC油浆富芳馏份制备的沥青树脂,作为炭/炭复合材料的基质是可行的。     

呋喃树脂对煤沥青流变性能的影响

采用旋转黏度计测定了含有不同比例呋喃树脂的煤沥青的表观黏度。考察了呋喃树脂对煤沥青表观黏度、残炭率及软化点的影响。同时，采用扫描电镜(SEM)研究了添加呋喃树脂后煤沥青的表面形貌。结果表明，添加质量分数为3．6％～9．0％的呋喃树脂使煤沥青在达到相同黏度值时温度下降5℃～15℃，而残炭率不下降；由于呋喃树脂使煤沥青分子隔开从而改善了煤沥青的流动性能；另外加入适量的呋喃树脂可降低煤沥青的黏流活化能，有利于煤沥青在较宽温度范围内进行工艺操作。     

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.     

Structure and properties of unidirectionally reinforced PAN-resin based carbon-carbon composites

A study has been made of the structure and properties of in-house fabricated, unidirectionally reinforced polyacrylonitrile (PAN) fibre-phenolic plus furfuryl alcohol matrix carbon/carbon (C/C) composites comprising surface-treated (ST) as well as non-surface-treated (NST) carbon fibres. The composites are subjected to a final heat treatment of 1000 or 2000°C. Mechanical properties of the composites were found to be sensitive to the process parameters (particularly the final heat-treatment temperature) as well as fibre surface condition (ST or NST). For the composites comprising ST fibres, flexural strength and modulus of those heat treated at 2000°C were higher than those treated at 1000°C. For the composites comprising NST fibres, the results were the opposite. At the carbon fibre-reinforced plastic (CFRP) stage, strength and modulus of ST fibre composites were higher than those of NST composites by 400% and 100%, respectively, due to the stronger fibre-resin bonding in the ST composite. After the first carbonization treatment, the ST composites always possessed higher strength and modulus values than NST composites, whether the final heat treatment temperature was 1000 or 2000°C. In the ST series of composites, the improvement in strength and modulus became significant from the third densification cycle, while in the NST series, both second and third cycles were effective. Microstructure, particularly fibre-matrix interface morphology, has been studied using polarized light microscopy, scanning electron microscopy, and transmission electron microscopy, to help interpret the process-structure-property relationships.     

Viscoelastic behavior of thermo-rheologically complex resin matrix composites

A micromechanical analysis is given for the prediction of the viscoelastic response of resin matrix composites. The matrix is condidered as a viscoelastic material with temperature-dependent properties, and is modeled as a thermo-rheologically complex solid. The method is implemented for the determination of the response of a unidirectional carbon/epoxy composite subjected to various types of mechanical and/or thermal loadings. The reliability of the prediction is checked by comparison with a numerical solution, and good agreement is shown to exist in most cases.     

The properties of epoxy resin coated silica fillers composites

Epoxy resin coated silica fillers composites with high percentage of filler loading, such as 80 to 95 vol.% are able to be produced by a mechanical mixing technique. The advantages of high filler loading of theses materials are noted from the thermal and flexural modulus. Apparently, the materials exhibit low coefficient of thermal expansion (CTE) at as low as or below 10 ppm/°C and high flexural modulus of above 20 GPa. In general, these promising characteristics fulfill the requirement to be used as substrate materials in electronic packaging applications.     

The beneficial influence of matrix anisotropy in fiber composites

Summary It has been recently shown [1] that the stress concentrations in anisotropic materials with distinct complex or imaginary roots of the respective characteristic function are much higher than in materials with equal roots. It was further shown [2] that anisotropic materials with equal roots behave like quasi-isotropic materials. Modern carbon-carbon and metal-ceramic composites are intuitively using these facts to create much stronger materials by reinforcing the matrix properties.A theory is presented in this paper where the coupling of strongly anisotropic fibers along their axis with strongly anisotropic matrices along either the fiber direction or the transverse plane to the direction of the fibers, either deteriorates, or improves perceptibly the mechanical behavior of the composites. It was shown that anisotropy of the matrix, increasing its mechanical properties on the transverse isotropic plane of the composite, increased the transverse Poisson's ratio, whereas decreased the longitudinal shear modulusG _LC . This resulted in values of the eigenangle _c receding from the corresponding value _ic for the respective isotropic, case. This resulted in a deterioration of the mechanical performance of the composite since the material now has the tendency to develop higher stress concentrations for equivalent loadings.On the contrary, a strong anisotropic matrix along the direction of the fibers yielded the inverse results for the various moduli of the anisotropic composite. The most important result is the increase of the longitudinal shear modulusG _L , so that the ratioE _L /2G _L is consistently decreasing, thus yielding values of the eigenangle _c tending to approach the critical value _c for the isotropic material. This decrease of _c indicates the improvement of the quality of the composite, which develops relatively lower stress concentration factors approaching their respective isotropic values.This fact makes the anisotropic composite material to approach an equivalent state of quasi-isotropy and thus to improve the strength of the material by reducing considerably the eventual, anisotropic stress concentration factors of the respective structural elements.Examples with T300/N5208 Graphite-Epoxy composites and Borsic-1100 Aluminum metal-metal composites indicate clearly the beneficial effect of the anisotropy of their matrices.