Preparation of multiscale graphene oxide‐carbon fabric and its effect on mechanical properties of hierarchical epoxy resin composite

Graphene oxide (GO) was used to modify the surface of carbon fiber layers through electrophoretic deposition, forming a multiscale reinforcement fabric. By adjusting the experimental parameters, the resulting GO‐carbon fabric showed productive and homogenous distribution of thin and less‐agglomerate GO platelets on carbon fiber surface, remarkably enlarging the surface area and roughness of carbon fabric. To investigate the effect of GO sheets on composites, GO‐carbon fabric and carbon fabric‐reinforced hierarchical epoxy resin composites were respectively manufactured. Mechanical tests demonstrated that after introducing GO flakes on carbon fabric, both the flexural strength and interlaminar shear strength of composite had achieved an increase, especially the interlaminar shear strength rising by 34%. Through fractography analysis, it was found that in pure carbon fabric‐reinforced epoxy composite, the fiber/matrix debonding fracture mechanism predominated, while after the GO decoration on carbon fiber surface, the composite featured a stronger interfacial bonding, leading to the enhancement in mechanical properties of hierarchical epoxy resin composite. POLYM. COMPOS., 37:1515–1522, 2016. © 2014 Society of Plastics Engineers     

Glass fibre reinforced composites of triglycidyl-p-aminophenol

Glass fibre reinforced epoxy composites were fabricated from the matrix resins diglycidyl ether of bisphenol A (DGEBA) and triglycidyl-p-aminophenol (TGAP) using diethylene triamine as curing agent. The epoxy laminates were evaluated for their mechanical properties, dielectrical properties and chemical resistance. Significant improvement in fiexural strength but a slight deterioration in dielectrical properties were observed on incorporation of an epoxy fortifier into the resin system before fabricating the composites.     

Reinforcement of epoxy resins with multi-walled carbon nanotubes for enhancing cryogenic mechanical properties

Epoxy resins are widely applied in cryogenic engineering and their cryogenic mechanical properties as important parameters have to be improved to meet the high requirements by cryogenic engineering applications. Carbon nanotubes (CNTs) are regarded as exceptional reinforcements for polymers. However, poor carbon nanotube (CNT)–polymer interfacial bonding leads to the unexpected low reinforcing efficiency. This paper presents a study on the cryogenic mechanical properties of multi-walled carbon nanotube reinforced epoxy nanocomposites, which are prepared by adding multi-walled carbon nanotubes (MWCNTs) to diglycidyl ether of bisphenol-F epoxy via the ultrasonic technique. When the temperature decreases from room temperature to liquid nitrogen temperature (77 K), a strong CNT–epoxy interfacial bonding is observed due to the thermal contraction of epoxy matrix because of the big differences in thermal expansion coefficients of epoxy and MWCNTs, resulting in a higher reinforcing efficiency. Moreover, synthetic sequence leads to selective dispersion of MWCNTs in the brittle primary phase but not in the soft second phase in the two phase epoxy matrix. Consequently, the cryogenic tensile strength, Young's modulus, failure strain and impact strength at 77 K are all enhanced by the addition of MWCNTs at appropriate contents. The results suggest that CNTs are promising reinforcements for enhancing the cryogenic mechanical properties of epoxy resins that have potential applications in cryogenic engineering areas.     

Utilizing Vacuum Bagging Process to Prepare Carbon Fiber/CNT-Modified-epoxy Composites with Improved Mechanical Properties

In this work, the effects of carbon nanotube-modified epoxy and carbon nanotube-enriched sizing agent on the tensile properties and failure mode of unidirectional carbon fiber/epoxy composites were investigated. Laminates of carbon fiber/epoxy composites at different concentrations of carbon nanotube and sizing agent were fabricated by hand layup vacuum bagging process. Scanning electron microscopy analysis was conducted to unveil the relation between the macroproperties and the composites’ microstructure. Experimental results showed that the carbon nanotube-modified epoxy/carbon fiber composite showed 20% enhancements in the Young’s modulus compared to the pristine epoxy/carbon fiber composite. The scanning electron microscopy analysis of the fracture surfaces revealed that incorporating carbon nanotube into the epoxy matrix with utilizing the vacuum improves the interfacial bonding and minimizes the voids that act as crack initiators. This microstructure enhances the interfacial shear strength and load transfer between the matrix and the fabrics and consequently the tensile characteristics of the formulated composite.     

一种高温环氧树脂的工艺及力学性能

对比研究了国产MERICAN 3768和国外CYCOM 890 RTM两种高温环氧树脂的工艺性和力学性能。同时选取典型航空结构,采用双轴向碳纤维织物和真空灌注工艺制备了对比零件。结果表明,国产MERICAN 3768树脂的浸润性、流变固化特性和力学性能均与国外CYCOM 890 RTM树脂相当,均具有优异的工艺性和力学性能,与纤维匹配性好,满足航空应用对树脂的要求。     

RTM用双马来酰亚胺树脂及其复合材料的制备与性能研究

采用一种含醚键双马单体对双马来酰亚胺树脂进行改性,制备了一种适用于复合材料树脂转移模塑成型工艺(RTM)的高韧性双马来酰亚胺树脂基体,并研究了其流变特性、耐热性能、力学性能及其复合材料的力学性能。树脂体系的流变性能数据表明树脂在注射温度(100℃)下具有较长的适用期(~3 h),能够满足RTM成型的要求。树脂浇注体的拉伸强度为115 MPa,断裂延伸率为3.1%,弯曲强度为159 MPa,玻璃化转变温度为270℃,表明树脂具有较高的韧性和耐温等级。以本树脂体系作为基体制备得到的碳纤维增强复合材料具有较高的力学性能,同时在230℃下具有较高的力学性能保持率。     

Effect of rubber/matrix interfacial modifications on the properties of a rubber-toughened epoxy resin

The interface of a rubber-toughened epoxy resin was modified by using epoxide end-capped carboxyl-terminated butadiene and acrylonitrile random copolymer (CTBN). The end-capping epoxides were formulated with different ratios of flexible diglycidyl ether of propylene glycol (DER732) and rigid diglycidyl ether of bisphenol-A (Epon 828). The microstructure and the fracture behavior of these rubber-modified epoxy resins were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The thermal and mechanical properties were also investigated. With an increase in the amount of end-capping DER732, the interfacial zone of an undeformed rubber particle and the degree of cavitation of the rubber cavity on the fracture surface were greatly increased. At the maximal addition of DER732, fracture energy (GIc) for this toughened epoxy resin containing 10phr CTBN rubber increases up to 2.4 fold compared to that of a conventional CTBN-toughened epoxy resin, but the thermal and the mechanical properties remained quite unaffected. The modification on the interfacial property provides a new technique in the improvement of fracture toughness of a rubber-toughened epoxy resin.     

环氧树脂/短切碳纤维复合材料性能研究

制备出了短切碳纤维增强TDE-85环氧树脂复合材料,研究了碳纤维的含量对复合材料力学性能和耐热性能的影响。结果表明,碳纤维的加入有利于复合材料力学性能和耐热性能的提高,并在碳纤维含量为0.25%时,复合材料的拉伸强度、冲击韧性、弯曲强度和弯曲模量达到最大,分别提高了29.33%、25.31%、30.28%和68.93%。此外,对复合材料的弯曲断裂面进行了微观形貌分析,结果表明一定量的碳纤维可以较好地分散在树脂基体中,同时,碳纤维原丝和树脂基体的界面结合比较弱,主要依赖于两相之间的物理嵌合。     

Enhancing hygrothermal resistance of aeronautical carbon fabric/epoxy composites via air plasma processing

Air plasma processing is introduced as a surface modification technique for carbon fibers to enhance the hygrothermal resistance of carbon fabric/epoxy composites. On carbon fiber surface subjected to 4-min plasma processing, there are 37.6% of carbon species present as –C–O–C groups and 9.3% of carbon species as –COOH groups. The moisture adsorption behavior of composites can be described by Fick’s law. Increase in temperature accelerates the initial moisture adsorption rate and results in a higher diffusion coefficient. The decreasing interlaminar shear strength (ILSS) of composites is mainly ascribed to the loss of adhesion at the fiber/matrix interface. A lower equilibrium moisture content of composites is caused by air plasma processing, which leads to the improved interfacial bonding strength and the higher retention rate of ILSS of carbon fabric/epoxy composites. The interface sensitivity and temperature dependence of moisture adsorption for carbon fabric/epoxy composites are discussed. The results presented herein demonstrate an effective strategy for enhancing hygrothermal resistance of carbon fiber-reinforced composites.     

Effects of surface modification on rheological and mechanical properties of CNT/epoxy composites

Despite superior properties of carbon nanotubes (CNTs), physical properties of the CNT/epoxy composites are not improved significantly because interfacial bonding between the CNTs and the polymer matrix is weak. CNTs were treated by an acidic solution to remove impurities and modified subsequently by amine treatment or plasma oxidation to improve interfacial bonding and dispersion of nanotubes in the epoxy matrix. The functional groups on the surface of treated CNTs were investigated by X-ray photoelectron spectroscopy. The surface modified CNTs were embedded in the epoxy resin by ultra-sonication and the cured nanotube containing composites were characterized by field emission scanning electron microscopy. Rheological properties of nanotube containing epoxy resin and mechanical properties of the modified CNT/epoxy composites were improved because the modification of CNTs improved dispersion and interaction between the CNT and the epoxy resin.     

Processing and properties of resol and epoxy blends for resin transfer molding

Blends of epoxy and resol matrices for resin transfer molding (RTM) have been prepared and characterized with the double aim of improving the processability of resols and the fire resistance of epoxies. The reaction rate of the overall system is enhanced by the exothermic reaction between the epoxy and an aliphatic amine, which also promotes the resol reaction. In addition, the mechanical behavior of the resol is improved as the shear stress increases with the addition of epoxy resins. However, blending also produces a reduction of the intrinsic fire resistance of phenolic resins. The study demonstrated the feasibility of producing blends for matrices of composites processed by resin transfer molding. The recommended range for the epoxy content was determined through a balance of processability, fire resistance, and mechanical properties of the composites obtained. Moreover, the effects of fiber surface modifications were studied as a way to promote higher shear stresses in the epoxy-resol matrix composite without jeopardizing the fire resistance properties.     

Low-temperature fast curable behavior and properties of bio-based carbon fiber composites based on resveratrol

Environmentally friendly materials are an integral part of sustainable chemistry, and bio-based polymer composites are an important class of materials. The manufacture of composites is expected to reduce or even eliminate the use of adjuvants, considering the importance of reducing energy consumption and avoiding health and environmental risks. In this study, a phenyl-containing, polyfunctional, bio-based epoxy resin (TGER) was synthesized, and carbon fiber-reinforced, bio-based epoxy resin composites were fabricated by vacuum-assisted resin infusion using two aromatic amine curing agents, 4,4′-diaminodiphenylmethane (DDM) and 3,3′-diethyl-4,4′-diaminodiphenylmethane (DEDDM). Curing reactions and rheological behavior studies showed that TGER had higher curing reactivity toward DDM and DEDDM than to diglycidyl ether of bisphenol A (DGEBA) and possessed good processability. The results indicated that the resveratrol-based epoxy resin displayed low-temperature fast curing properties. The evaluation of the mechanical properties of the carbon fiber composites showed that the flexural strengths of CF/TGER/DDM and CF/TGER/DEDDM were 520 and 628 MPa, respectively. The initial decomposition temperature of CF/TGER composites is above 200°C. Furthermore, the carbon fiber–reinforced biopolymers possess excellent heat resistance. Therefore, carbon fiber-reinforced, resveratrol-based epoxy resin composites are promising candidates as alternatives to petroleum-based high-performance carbon fiber composites.     

Comparison of mechanical properties of epoxy composites reinforced with stitched glass and carbon fabrics: Characterization of mechanical anisotropy in composites and investigation on the interaction between fiber and epoxy matrix

The primary purpose of the study is to evaluate and compare the mechanical properties of epoxy‐based composites having different fiber reinforcements. Glass and carbon fiber composite laminates were manufactured by vacuum infusion of epoxy resin into two commonly used noncrimp stitched fabric (NCF) types: unidirectional and biaxial fabrics. The effects of geometric variables on composite structural integrity and strength were illustrated. Hence, tensile and three‐point bending flexural tests were conducted up to failure on specimens strengthened with different layouts of fibrous plies in NCF. In this article, an important practical problem in fibrous composites, interlaminar shear strength as measured in short beam shear test, is discussed. The fabric composites were tested in three directions: at 0°, 45°, and 90°. In addition to the extensive efforts in elucidating the variation in the mechanical properties of noncrimp glass and carbon fabric reinforced laminates, the work presented here focuses, also, on the type of interactions that are established between fiber and epoxy matrix. The experiments, in conjunction with scanning electron photomicrographs of fractured surfaces of composites, were interpreted in an attempt to explain the failure mechanisms in the composite laminates broken in tension. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Study on the mechanical properties and microstructure of high-performance carbon fiber/epoxy composites

A high-toughness epoxy has been prepared using carboxyl-terminated butadiene acrylonitrile (CTBN) as a toughening agent to modify the AG-80 epoxy resin. High-performance carbon fiber/epoxy (CF/EP) composites are fabricated using the CTBN-toughened epoxy resin as the matrix and two types of CF, namely, T800SC and T800HB, as reinforcement. The mechanical properties of the matrix, surface properties of the CFs, tensile properties, and fracture morphologies of the composites are systematically investigated to elucidate the key factors influencing interfacial bonding in high-performance CF/EP composites. The results reveal that the most significant improvement in toughness is achieved when the CTBN content is 6.90 wt.% in the epoxy resin. Owing to the high content of polar functional groups and excellent surface wettability of T800SC, the T800SC/EP composite exhibits superior mechanical properties compared with the T800HB/EP composite.     

Studies on the properties of glass fiber reinforced epoxy composites of DGEBA / epoxidized polyhydric alcohols with or without fortifier

Differential scanning calorimetry (DSC) technique was used to study the curing reaction of diglycidyl ether of bisphenol A (DGEBA) resin and different di- and trifunctional polyhydric alcohols with phthalic anhydride as curing agent and triethylamine as catalyst with or without fortifier. The thermal stability of the cured products was also studied by thermogravimetric analysis (TGA). Using these data, different glass fiber reinforced epoxy composites were fabricated and their mechanical and electrical properties and their resistance to chemicals were studied as well. Activation energies of curing reactions range within 75.1 to 88.3 kJ mol^?1. The cured products have good thermal stability; the composites have good mechanical strength, electrical insulation properties and chemical resistance. 36 to 53% improvement in flexural strength has been observed when fortifier was added to the DGEBA-diluent systems.     

Effects of moisture absorption on mechanical and viscoelastic properties in liquid thermoplastic resin/carbon fiber composites

This article investigated the effect of moisture on the tensile strength and in‐plane shear of laminated composites. For this, the results of a composite system based on a new thermoplastic Elium® 150 resin were compared to a traditional epoxy resin result. Both composites were fabricated via VARTM using a 0/90° plain weave carbon fiber fabric. For the non‐conditioned specimens, the thermoplastic composites presented 30% more tensile resistance in comparison to epoxy composites. For conditioned specimens, this difference was 14%. These results were related to plasticization, which tends to favor the polymer softening providing a greater matrix plastic deformation, promoting a ductile fracture of the composite. On the other hand, the in‐plane shear properties were 30% higher for the thermosetting laminates for both conditions. In this case, moisture may have favored the formation of surface cracks and weakened the fiber/matrix interfacial adhesion. Additional analysis based on design of experiments has shown that the Elium® 150 resin significantly affects all responses and presented in fact a better behavior in comparison to Epoxy resin. While the conditioning effects have featured a statistically noticeable contribution to the tensile strength, the presence of the moisture did not provide a significant enhancement to the in‐plane shear strength. Besides that, the unknown fractographic aspects of the fracture surfaces of both composites were used as a complementary tool for the mechanical characterization. POLYM. ENG. SCI., 59:2185–2194, 2019. © 2019 Society of Plastics Engineers     

碳纤维/聚苯并(噁)嗪复合材料的界面与力学性能的关系研究

本文采用含不同上胶剂的碳纤维与苯并(噁)嗪树脂复合,制备碳纤维/聚苯并(噁)嗪单向复合材料,研究了碳纤维表面上胶剂对于复合材料的层间剪切强度(ILSS)、弯曲性能、断口形貌及动态机械性能的影响.结果表明,含有环氧树脂上胶剂的碳纤维/苯并(噁)嗪树脂基复合材料(EPCF/PBZ)的ILSS和弯曲性能优于含非环氧类树脂上胶剂的碳纤维/苯并(噁)嗪树脂基复合材料(VECF/PBZ)和不含上胶剂的碳纤维/苯并(噁)嗪树脂基复合材料(USCF/PBZ).环氧树脂上胶剂改善了纤维与苯并(噁)嗪树脂的粘结性能,使复合材料的内耗峰峰高降低,能量损耗减小.电镜照片同样验证了这一结果.     

机织/针织混合铺层对复合材料力学性能的影响

为使纺织复合材料同时具有机织结构复合材料和针织结构复合材料的综合力学性能,通过混合铺层方式制备机织/针织混合结构复合材料。以芳纶机织平纹织物和针织罗纹织物为增强体,以环氧树脂为基体,调整复合材料中增强体的铺层顺序,利用真空辅助成型技术制备四层层压机织/针织混合结构复合材料。通过对复合材料拉伸性能、弯曲性能和冲击性能的测试,分析混合铺层和铺层顺序对芳纶环氧树脂复合材料力学性能的影响。结果表明,混合铺层和铺层顺序对芳纶环氧树脂复合材料的弯曲强度和冲击强度有较大影响,特别是对罗纹结构复合材料纬向弯曲强度和冲击强度的改善。当采用相同铺层方式,罗纹织物为受力面时,机织/针织混合结构复合材料具有较大弯曲强度和冲击强度。     

Mechanical,thermal, and burning properties of viscose fabric composites: Influence of epoxy resin modification

The influence of epoxy resin modification by 3‐aminopropyltriethoxysilane (APTES) on various properties of warp knitted viscose fabric is reported in this study. Dynamic mechanical, impact resistance, flexural, thermal properties, and burning behavior of the epoxy/viscose fabric composites are studied with respect to varying content of silane coupling agent. The results obtained for APTES‐modified epoxy resin based composites reinforced with unmodified viscose fabric composites are compared to unmodified epoxy resin based composites reinforced with APTES‐modified viscose fabric. The dynamic mechanical behavior of the APTES‐modified resin based composites indicates improved interfacial adhesion. The composites prepared from modified epoxy resin exhibited a twofold increase in impact resistance. The improved adhesion between the fiber and modified resin was also visible from the scanning electron microscope analysis of the impact fracture surface. There was less influence of resin modification on the flexural properties of the composites. The 5% APTES modification induced early degradation of composites compared to all other composites. The burning rate of all the composites under study is rated to be satisfactory for use in automotive interior applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46673.     

Non-destructive evaluation of bonded structures with lock-in thermography

Lock-in thermography is employed for non-destructive evaluation of several types of bonded structures, which are commonly encountered in industrial applications. Specimens were fabricated to simulate: adhesively bonded aluminium joints, which are commonly used in aeronautical and automotive fields; bonds between pipes of poly(vinyl chloride) (PVC) employed in the transport of liquids (sewage systems); and bonds between plates of Plexiglas which are widely used in the manufacturing of aquaria. Amongst bonded structures, the composite materials are very important, which are generally made of carbon, glass, or Kevlar^? aramid fibers and epoxy resin, and which find application in many industrial fields, especially the aeronautical industry, because of their higher strength and lower weight as compared to metallic materials. It is known that surface plasma treatment of a material improves its adhesion, but it is also known that this treatment will degrade over time if the material is not bonded immediately. Thus, to assure quality, any bonded system should be monitored by the most effective non-destructive technique. To obtain information about the ability of lock-in thermography to assess the performance of such plasma treatment, several specimens were fabricated from either composites (carbon, or Kevlar^? fabric layers plus epoxy resin), or glass plates with and without surface plasma treatment before bonding. In addition, a sample was obtained from a piece of a typical insulated wall of refrigerator vehicles, which actually is a sandwich of polyurethane foam between two plates of fiberglass. The results obtained show that lock-in thermography is a useful tool for non-destructive evaluation of bonded structures.