Nano-epoxy resins containing electrospun carbon nanofibers and the resulting hybrid multi-scale composites

For the first time, electrospun carbon nanofibers (ECNFs, with diameters and lengths of ∼200 nm and ∼15 μm, respectively) were explored for the preparation of nano-epoxy resins; and the prepared resins were further investigated for the fabrication of hybrid multi-scale composites with woven fabrics of conventional carbon fibers via the technique of vacuum assisted resin transfer molding (VARTM). For comparison, vapor growth carbon nanofibers (VGCNFs) and graphite carbon nanofibers (GCNFs) were also studied for making nano-epoxy resins and hybrid multi-scale composites. Unlike VGCNFs and GCNFs that are prepared by bottom-up methods, ECNFs are produced through a top-down approach; hence, ECNFs are more cost-effective than VGCNFs and GCNFs. The results indicated that the incorporation of a small mass fraction (e.g., 0.1% and 0.3%) of ECNFs into epoxy resin would result in substantial improvements on impact absorption energy, inter-laminar shear strength, and flexural properties for both nano-epoxy resins and hybrid multi-scale composites. In general, the reinforcement effect of ECNFs was similar to that of VGCNFs, while it was higher than that of GCNFs.     

超细玻璃粉增强环氧树脂的研究

研究了玻璃粉/环氧树脂封接复合材料的制备与性能.利用激光粒度分析仪、电子多功能实验机、SEM、热分析仪等测试粉料粒径、结构形貌以及机械强度等性能.结果表明,在玻璃粉的制备过程中,加入适量的活性剂(硬脂酸盐),可以大大降低玻璃粉的粒径和粒径分布范围.将超细玻璃粉用偶联剂处理后,与环氧树脂混合制备成封接复合材料,比环氧树脂具有更好的力学性能和热稳定性.     

Hybrid composites made of carbon and glass woven fabrics under quasi-static loading

Experimental studies are presented on in-plane mechanical properties for two types of hybrid composites made using 8H satin weave T300 carbon fabrics and plain weave E-glass fabrics with epoxy resin. Results are also presented for 8H satin weave T300 carbon/epoxy and plain weave E-glass/epoxy. Studies are carried out under both tensile and compressive in-plane quasi-static loading. It is observed that for hybrid composites, placing glass fabric layers in the exterior and carbon fabric layers in the interior gives higher tensile strength and ultimate tensile strain than placing carbon fabric layers in the exterior and glass fabric layers in the interior. Quantitative data is given for different mechanical properties.     

Mechanical and electrical performance of Roystonea regia/glass fibre reinforced epoxy hybrid composites

The present paper investigates mechanical and electrical properties of Roystonea regia/glass fibre reinforced epoxy hybrid composites. Five varieties of hybrid composites have been prepared by varying the glass fibre loading. Roystonea regia (royal palm), a natural fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. Roystonea regia, E-glass short fibres were used together as reinforcement in epoxy matrix to form hybrid composites. It has been observed that tensile, flexural, impact and hardness properties of hybrid composites considerably increased with increase in glass fibre loading. But electrical conductivity and dielectric constant values decreased with increase in glass fibre content in the hybrid composites at all frequencies. Scanning electron microscopy of fractured hybrid composites has been carried out to study the fibre matrix adhesion.     

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two T_gs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.     

Investigations on the fabrication and the characterization of glass/epoxy,carbon/epoxy and hybrid composites used in the reinforcement and the repair of aeronautic structures

This paper reports the fabrication and the characterization of glass/epoxy, carbon/epoxy and hybrid laminated composites used in the reinforcement and/or the repair of aeronautic structures. These composites were manufactured by the hand lay-up process. Their physical, thermal and mechanical behaviors are discussed in terms of moisture absorption, thermal stability, tensile strength, elastic modulus, flexural strength, flexural modulus and abrasive wear resistance. The impact of hygrothermal aging on the mechanical properties of each composite group has been also investigated.The main results indicated that after water immersion, all composites showed significant moisture absorption especially for glass/epoxy composite. Thermogravimetric analysis showed that the hybrid composite presented the best thermal stability behavior while the glass/epoxy composite the bad behavior. The mechanical properties of the carbon/epoxy composites, in the bulk material, were considerably higher than those of the glass/epoxy; the hybrid structure presented intermediate mechanical properties. The same trend was also observed in terms of wear properties. Finally, a deleterious effect on the strength of all composites due to hygrothermal exposure was established. However, carbon/epoxy composites seem to be less susceptible to aging damage after 90 days at 90 °C.     

Evaluation of the mechanical behavior of epoxy composite reinforced with Kevlar plain fabric and glass/Kevlar hybrid fabric

In this study, composite plates were manufactured by hand lay-up process with epoxy matrix (DGEBA) reinforced with Kevlar fiber plain fabric and Kevlar/glass hybrid fabric, using to an innovative architecture. Results of the mechanical properties of composites were obtained by tensile, bending and impact tests. These tests were performed in the parallel direction or fill directions of the warp and in a 90° direction. FTIR was used in order to verify the minimum curing time of the resin to perform the mechanical tests, and scanning electron microscopy was used to observe reinforcement and matrix fractures. Composites with Kevlar/glass hybrid structure in the reinforcing fabric showed the better results with respect to specific mechanical strength, as well as bending and impact energy.     

表面官能团化多壁碳纳米管/环氧树脂复合材料的制备及性能

本文首先将多壁碳纳米管(MWNT)进行表面化学修饰,接入羧基、胺基等官能团,采用红外光谱进行了表征.以纯化后的MWNT和表面化学修饰的MWNT作为填料,制备了MWNT /环氧树脂复合材料,研究了MWNT的加入对环氧树脂的力学性能、电学性能、热稳定性和玻璃化转变温度等的影响,并利用场发射电镜观察了胺基化MWNT在环氧树脂基体中的分散情况.     

Optimum mixing ratio of epoxy for glass fiber reinforced composites with high thermal stability

The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through FT-IR instrument. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and T_g was conformed according to different epoxy mixing ratios. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.     

Strain rate sensitivity of glass/epoxy composites with nanofillers

It is understood that small amount of nanoclay in the neat epoxy and fiber reinforced epoxy composite system improves the mechanical properties. The mechanical properties of most of polymer matrix composites are rate sensitive. Most of the researches have concentrated on the behavior of the polymer composites at high strain rates. The present research work is to study the effect of clay on neat epoxy and glass/epoxy composites, at low strain rates. The clay in terms of 1.5, 3 and 5 wt% are dispersed in the epoxy resin using mechanical stirrer followed by sonication process. The glass/epoxy nanocomposites are prepared by impregnating the glass fiber with epoxy–clay mixture by hand lay-up process followed by compression molding. Characterization of the nanoclay is done by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Tensile stress–strain curves are obtained at strain rates of 10⁻⁴, 10⁻³, 10⁻² and 10⁻¹ s⁻¹ by a servo-hydraulic machine and the variation of modulus, strength and failure strain with strain rate are determined. The results show that, even at low strain rates, the longitudinal strength and stiffness increase as strain rate increases for all clay loadings. It is observed that the tensile modulus increases as the clay loading increases for both epoxy and glass/epoxy nanocomposites. Scanning electron microscopy is used to study the adhesion of composites in fracture surfaces.     

湿热老化对玻璃纤维/环氧树脂复合材料性能的影响

为研究玻璃纤维(GF)/环氧树脂复合材料湿热老化机制, 首先, 利用称重法、动态热机械分析仪(DMA)、SEM和矢量网络介电分析仪研究了湿热老化对GF/环氧树脂608(EP608)复合材料性能的影响;然后, 分析了复合材料的吸湿率、力学性能、介电性能与老化时间的关系, 并对其老化机制进行了探讨。结果表明:随老化时间延长, GF/EP608复合材料的力学性能和介电性能均有不同程度的下降;湿热老化对GF/EP608复合材料吸湿率的影响符合Fickian扩散定律;树脂基体的塑化、水解和基体-纤维界面的破坏是造成GF/EP608复合材料力学性能和介电性能下降的主要因素。所得结论可为GF增强环氧树脂基复合材料的应用提供科学依据。      

苎麻纤维布和玻璃纤维布混杂铺层复合材料的力学性能

利用真空吸注成型(vacuum resin absorbable molding,VRAM)工艺制备苎麻纤维布与玻璃纤维布混杂铺层的环氧树脂基复合材料。测定复合材料的损耗因子、储能模量的温度谱和力学性能;利用单悬臂梁共振实验测量复合材料的共振频率和自由振动衰减曲线并计算出了阻尼因子。用有限元软件对其共振频率和自由振动衰减实验进行仿真分析。结果表明:通过苎麻纤维布/玻璃纤维布的混杂铺层,能够实现材料阻尼性能和力学性能的可控调节,充分发挥复合材料可设计性强的优势。其中RGR铺层的复合材料的损耗因子比纯玻璃纤维板提高了1.4倍,而拉伸强度比纯苎麻纤维板提高了3倍多;自由振动的有限元模拟曲线和实验曲线基本吻合,表明可以通过模拟软件实现复合材料的虚拟振动测试,从而为材料性能预测和设计提供方便。     

The influence of heat treatment and finishing on the mechanical and dielectric properties of glass fabric-epoxy resin laminar composites

The aim of this investigation was to define the optimum conditions of obtaining glass fabric-epoxy resin laminar composites with mechanical and dielectric properties that satisfy the quality needed for production of printed circuit boards for microelectronics. Commercial materials: glass woven fabric, different types of silane finish and epoxy resin were the starting materials in obtaining composites. The conditions needed for the thermal removal of the original size from glass fabric were investigated. The optimal heat treatment should be performed at temperatures less than 550 °C, while cooling rates should be as low as possible. In this manner, the fabric has less than 0.1% of residual size, and the mechanical properties remain satisfactory. Different types of adhesion promoters based on silanes were applied on heat-treated glass fabric as finishes. The quality of the composite material made of thermally and chemically treated glass fabric and epoxy resin was controled by measuring the tensile and dielectric strength of the composite. Depending on which properties of composite are of primary concern, mechanical or dielectric, a finish with an amino functional group and lower heat-treatment temperature or epoxy-modified coatings and higher heat-treatment temperature should be used for obtaining glass-fabric epoxy resin laminar composites.     

Preparation and mechanical properties of carbon nanotube grafted glass fabric/epoxy multi-scale composites

In the present paper, carbon nanotubes (CNTs) were chemically grafted onto surfaces of the amino silane treated glass fabric by a novel chemical route for the first time to create 3D network on the glass fibers. The chemical bonding process was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The glass fabric/CNT/epoxy multi-scale composite laminates were fabricated with the CNT grafted fabrics using vacuum assisted resin infusion molding. Tensile tests were conducted on fabricated multi-scale composites, indicating the grafting CNTs on glass fabric resulted a decrease (11%) in ultimate tensile strength while toughness of the multi-scale composite laminates were increased up to 57%. Flexural tests revealed that the multi-scale composite laminates prepared with CNT grafted glass fabric represent recovering after first load fall. The interfacial reinforcing mechanisms were discussed based on fracture morphologies of the multi-scale composites.     

静电植绒法处理多壁碳纳米管改性玻纤织物/环氧树脂复合材料的制备及力学性能

为提高玻纤增强环氧树脂复合材料的力学性能,采用静电植绒法将多壁碳纳米管(MWCNTs)附着在玻纤织物表面,得到改性的玻纤织物。利用一种低黏度的环氧树脂和所制得的改性织物,采用真空辅助成型工艺(VARI)制备了MWCNTs改性格玻纤织物/环氧树脂复合材料层合板,表征了层合板的力学性能。对进行力学实验后的MWCNTs改性玻纤织物/环氧树脂复合材料试样断口进行了SEM和OPM观察。结果显示:与未添加MWCNTs的玻纤织物/环氧树脂复合材料层合板相比,添加了MWCNTs的层合板的拉伸强度降低了10.24%,弯曲强度降低了13.90%,压缩强度降低了17.33%,拉伸模量和弯曲模量分别提高了19.38%和16.04%,压缩模量提高了13%;MWCNTs与玻纤织物之间的结合较弱,在拉伸作用下,存在明显的脱粘和分层;将改性玻纤织物在200℃下热压处理2h后,制备的MWCNTs改性玻纤织物/环氧树脂复合材料层合板的力学性能均有所提高,热压处理后树脂与玻纤织物之间的界面结合得到改善。     

Epoxy-carbon nanotubes as matrix in glass fiber reinforced laminated composites

A manufacturing process using vacuum-assisted resin infusion molding was used to produce glass fiber-reinforced laminates with the epoxy matrix and with the 0.5 weight % NH₂ functionalized-MWCNT based epoxy matrix. Images obtained from the TEM and SEM indicates that MWCNTs are well dispersed into the epoxy matrix. Microstructures observations of the composites from SEM show the better interaction between CNTs and epoxy. The mechanical and thermo-mechanical behavior of the glass fiber-epoxy system and glass fiber-CNT/epoxy system was characterized through flexural test and Dynamic Mechanical Analysis (DMA).     

短玻纤增强丙烯腈-丁二烯-苯乙烯共聚物的制备及性能

以丙烯腈-丁二烯-苯乙烯共聚物(ABS)及短玻璃纤维(SGF)为原料, 以苯乙烯-马来酸酐共聚物(SMA)和环氧树脂(EP)为界面相容剂, 制备了SGF/SMA-EP-ABS复合材料。用扫描电镜(SEM)、 动态力学热分析(DMTA)等研究了界面相容剂对SGF增强ABS复合材料力学性能及界面粘结性能的影响。结果表明:加入SMA或EP, SGF增强ABS复合材料的力学性能明显提高; SMA与EP同时加入具有明显的协同效果, 使复合材料的性能更为优越。当SGF加入质量分数为30%时, SGF/SMA-EP-ABS复合材料的拉伸强度、 弯曲强度、 冲击强度较未添加界面相容剂时分别提高了56%、 42%、 79%。SEM和DMTA测试表明, 加入SMA和环氧树脂后, SGF与ABS基体之间的界面粘结性能得到很大改善。      

Effects of adhesion on the effective Young's modulus in glass slide/glue laminates

Bond-phase defects in laminates can affect the mechanical properties of laminate composites. In this study, the effects of adhesion area, number of glue spots, and bond thickness on the effective Young's modulus of adhered microscope glass slides have been investigated. Three different adhesive agents (super glue, epoxy cement, and epoxy resin) were used to explore the effect of bond-phase defects upon adhesion in laminates. The elastic moduli of single glass slides, unadhered glass slide pairs, glass slide/glue composite specimens and epoxy resin specimens were non-destructively determined by a sonic resonance technique. The change of Young's modulus of adhered glass slides was monitored while adhesion area per cent ranged from 0.35%–100%. Trends in the Young's moduli of glass slide/glue composite specimens have been analysed by a least-squares best-fit procedure to two empirical equations. Qualitative explanations for the observed trends are discussed in this paper.     

磨碎玻璃纤维增强环氧树脂复合材料的制备及力学性能研究

用硅烷偶联剂对磨碎玻璃纤维表面进行改性,并制备玻璃纤维/环氧树脂复合材料,采用超声分散对复合材料分散处理,探讨不同磨碎玻璃纤维粉质量比对环氧树脂基复合材料压缩、拉伸性能的影响。研究表明,添加磨碎玻璃纤维后,环氧树脂的强度和硬度显著增强。当磨碎玻璃纤维掺量在15%~25%之间时,复合材料的综合力学性能最好,其压缩强度、压缩模量、拉伸强度最高达到67.1 MPa、1.68 GPa、57.6 MPa,与纯环氧树脂相比提高了24%、35%、34%;断裂伸长率随着掺量的增加逐渐降低,当含量达到30%时比纯环氧树脂的降低了48%,表明添加玻璃纤维粉后环氧树脂脆性增强。目数小粒径较大的玻璃纤维粉对环氧树脂力学性能增强效果更优,但影响程度不如含量对复合材料力学性能的影响大。     

Organoclay effect on transverse compressive strength of glass/epoxy nanocomposites

This research focuses on the fabrication of glass fiber/epoxy nanocomposites containing organoclay as well as understanding the organoclay effect on the transverse compressive strength of nanocomposites. To demonstrate the organoclay effect, three different loadings of organoclay were dispersed, respectively, in the epoxy resin using a mechanical mixer followed by sonication. The corresponding glass/epoxy nanocomposites were produced by impregnating dry glass fiber with organoclay epoxy compound through a vacuum hand lay-up procedure. Unidirectional block specimens were employed for transverse compression tests on a hydraulic MTS machine. Experimental observations indicate that glass/epoxy nanocomposites containing organoclay exhibit higher transverse compressive strength than conventional composites. Furthermore, the failure mechanisms for all tested specimens were found to be fiber and matrix debonding. Therefore, results indicate that the increasing characteristic in transverse failure stress may be ascribed to the enhanced fiber/matrix adhesion modified by the organoclay.