Effect of nano-SiO2 modified emulsion sizing on the interfacial adhesion of carbon fibers reinforced composites

The influence of nano-SiO₂ modified epoxy emulsion sizing on the interfacial adhesion properties of carbon fibers reinforced composites was investigated. The interfacial interaction between carbon fibers and the matrix was characterized by X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM) and three-point short-beam shear testing. The results showed that the amount of hydroxyl groups was slightly increased on the carbon fibers surface after treatment with nano-SiO₂ modified sizing. Compared to the unsized composites, the interlaminar shear strength (ILSS) values for the composites with unmodified sizing and nano-SiO₂ modified sizing were increased by 9% and 14%, respectively. The holes and carbon fibers pullout were not observed in their fracture sections. Surprisingly, the fracture section of the composites with nano-SiO₂ modified sizing was more compact and the fiber debonding was more difficult.     

水性上浆剂对碳纤维表面及碳纤维/环氧树脂复合材料界面性能的影响

以4,4'-亚甲基双(异氰酸苯酯)(MDI)为扩链剂, 将Triton X-100(TX-100)引入到双酚A二缩水甘油醚(DGEBA) 中, 设计合成水性碳纤维上浆剂(DGEBA-MDI-TX-100), 并利用合成的水性上浆剂对碳纤维表面进行改性。在此基础上, 以环氧树脂为基体, 制备碳纤维/环氧树脂复合材料, 研究了水性上浆剂改性碳纤维对碳纤维表面性能及其复合材料界面性能的影响。结果表明:与未经处理的碳纤维相比, 经过上浆剂改性后的碳纤维润湿性能得到了较大的提高, 与环氧树脂的接触角下降了 9.1%;与环氧树脂复合后制备的复合材料的界面剪切强度提高了64.7%。      

碳纤维/TiO2改性树脂复合材料的制备及力学性能

针对环氧树脂脆性大、与碳纤维形成的界面性能较差等问题,本文选用纳米TiO₂对5284环氧树脂进行改性,并以角联锁机织物为增强体制备了碳纤维/环氧树脂复合材料。使用FT-IR、旋转流变仪、表面张力仪等设备对TiO₂/环氧树脂进行表征,并研究了树脂改性对复合材料压缩与层间剪切性能的影响。研究表明：TiO₂的羟基与环氧树脂的环氧基和羟基发生了反应;经1wt.%TiO₂改性的树脂复数黏度为0.066 Pa·s,纤维与树脂间接触角为28.85°,浸润效果较好;相较于未改性复合材料,树脂改性的复合材料纵向压缩强度与模量分别提高了7.46%和11.03%,横向压缩强度与模量分别提高了6.99%和4.96%,纵向、横向的剪切强度分别提高了6.88%和4.65%。TiO₂改性环氧树脂提高了复合材料的承载能力,改善了界面结合强度。     

纳米SiO2改性炭纤维乳液上浆剂的性能评价

采用纳米SiO₂改性环氧树脂乳液上浆剂和未改性乳液上浆剂对聚丙烯腈(PAN)基炭纤维进行表面上浆。通过静置沉淀法和光学显微镜评价了两种乳液的稳定性。利用扫描电子显微镜(SEM)、 X射线能谱仪(EDS)、 原子力显微镜(AFM)和动态接触角测试仪(DCAA)研究了未上浆、 未改性和改性上浆炭纤维的表面性能, 并用单纤维碎裂法探讨了上浆剂对炭纤维与环氧树脂界面黏结的影响。结果表明: 未改性和经纳米SiO₂改性的两种乳液粒径较小, 稳定性较好, 而前者优于后者。上浆后, 炭纤维表面的粗糙度和表面能都增大, 而且最大值出现在改性乳液上浆炭纤维的表面。改性乳液上浆单纤维复合材料拥有最大的界面剪切强度(IFSS), 比未改性上浆的高出27.2%; 改性上浆炭纤维与基体的调和平均黏结功(W(h)_a )和几何平均黏结功(W(g)_a )也分别高出未改性上浆的12.7%和11.7%。      

碳纳米管纤维/环氧树脂复合材料的界面剪切强度及微观结构

研究了碳纳米管纤维的微观结构和拉伸性能,并进一步分析了其与环氧树脂形成界面剪切强度及微观结构。采用单丝断裂试验测试了碳纳米管纤维/环氧树脂复合材料体系的界面剪切强度,结合单丝断裂过程中的偏光显微镜照片、复合材料的拉曼谱图和断口扫描电镜照片,研究了碳纳米管纤维/环氧树脂复合材料界面的微观结构。结果表明: 碳纳米管纤维/环氧树脂复合材料的界面剪切强度约为14 MPa;在碳纳米管纤维和环氧树脂形成界面的过程中,环氧树脂可以浸渍纤维,形成具有一定厚度的复合相,这种浸渍过程和界面相的形成都有利于碳纳米管纤维与基体之间的连接。     

聚乙二醇改性环氧乳液碳纤维上浆剂的研制

用聚乙二醇(PEG)在催化剂过硫酸钾作用下与环氧树脂反应, 制得自乳化环氧树脂乳液。通过红外光谱表征改性环氧的结构, 并比较不同实验方案下乳液的稳定性, 探讨了反应原料、合成工艺等因素对实验结果的影响, 确定了最佳实验方案; 用热分析实验表征上浆剂的热稳定性, 接触角测试表征上浆剂乳液的浸润性, 单丝碎裂实验测定界面剪切强度。结果表明, 使用双酚A环氧树脂及PEG1000在80~120 ℃反应制得的乳液稳定性最好, 上浆剂的热稳定性和浸润性良好。用实验制得的乳液对碳纤维上浆, 单丝界面剪切强度比上浆前提高33.48%, 碳纤维毛丝量减少。      

氧化石墨烯改性玄武岩纤维及其增强环氧树脂复合材料性能

为了改善玄武岩纤维/环氧树脂复合材料的界面性能,通过偶联剂对氧化石墨烯进行改性,并将改性后的氧化石墨烯引入到上浆剂中对玄武岩纤维进行表面涂覆改性,同时制备了氧化石墨烯-玄武岩纤维/环氧树脂复合材料.采用FTIR表征了氧化石墨烯的改性效果;运用SEM分析了改性上浆剂处理对玄武岩纤维表面及复合材料断口形貌的影响和作用机制.结果表明:偶联剂成功接枝到氧化石墨烯表面;玄武岩纤维经氧化石墨烯改性的上浆剂处理后,表面粗糙度及活性官能团含量增加,氧化石墨烯-玄武岩纤维/环氧树脂界面处的机械齿合作用及化学键合作用增强,界面黏结强度得到改善,玄武岩纤维的断裂强力提高了30.8%,氧化石墨烯-玄武岩纤维/环氧树脂复合材料的层间剪切强度提高了10.6%.     

电子束固化复合材料界面

电子束固化复合材料界面粘结性能较低是急待解决的问题。利用阳极氧化技术和偶联剂涂层对碳纤维表面进行处理。处理前后的碳纤维表面性能利用SEM、XPS和接触角测试方法进行分析,通过层间剪切强度表征电子束固化复合材料界面粘结性能,并且与热固化复合材料进行对比。结果表明: 当碳纤维在酸性电解液中进行阳极氧化时,有利于提高电子束固化复合材料界面粘合性能,在碱性电解液中进行阳极氧化时, 则导致较低界面粘接性能。阳极氧化与偶联剂双重增效作用能够提高电子束固化复合材料界面粘合性能。     

Multiple effects of nano-SiO2 and hybrid fibers on properties of high toughness fiber reinforced cementitious composites with high-volume fly ash

This article explores multiple effects of nano-SiO₂ and hybrid fibers on the flowability, microstructure and flexural properties of high toughness fiber reinforced cementitious composites. Only a little negative influences of nano-SiO₂ and hybrid fibers on the flowability are observed. SEM and MIP analysis reveal that nano-SiO₂ results in much smaller pore size in the composites. However, the porosity increases gradually with nano-SiO₂ addition. Three-point bending test results show that nano-SiO₂ increases the flexural strength of the composites with nearly equivalent deformability, but higher strength of the matrix leads to wider cracks. Due to larger volume fraction and higher modulus, hybrid fibers effectively mitigate this adverse influence on crack width and further enhance the flexural strength. The composites reinforced with 1.4% steel fiber and 2.5% polyvinyl alcohol (PVA) fiber exhibit the best flexural properties in the test. Finally, a simplified model is proposed to illustrate the reinforced mechanism of steel-PVA fibers.     

Grafting Low Contents of Branched Polyethylenimine onto Carbon Fibers to Effectively Improve Their Interfacial Shear Strength with an Epoxy Matrix

The mechanical properties of carbon fiber (CF) reinforced composites are greatly dependent on the interfacial strength between the CFs and matrix. To improve the interfacial adhesion of carbon fiber/epoxy composites, branched polyethylenimine (PEI) is grafted onto the CFs treated in a mixed acid at optimized process time. The chemical compositions and bonds of functionalized CFs are characterized by thermal gravimetric analysis, Fourier‐transform infrared, and X‐ray photoelectron spectroscopy. The surface structures and morphologies of various CFs are analyzed by Raman spectroscopy and scanning electron microscopy, respectively. Microbond test is adopted to evaluate the interfacial shear strength (IFSS) between the CFs and epoxy matrix. The results show that the CFs modified by low molecular weight PEI are better than those modified by high molecular weight PEI. The IFSS of PEI modified CFs can reach a maximum of 107.2 ± 14.3 MPa at a low functionalization degree compared with 78.1 ± 11.6 MPa of unmodified CFs. The branched structure and high density of active amine groups on the PEI chains are responsible for the improved interfacial strength.     

Strengthening of basalt fibers with nano-SiO2–epoxy composite coating

Coatings, which were made from pure epoxy and SiO₂ nanoparticle modified epoxy composite, respectively, were applied onto the basalt fiber rovings. The SiO₂ nanoparticles were synthesized using a sol–gel method and modified using coupling agent. Fourier transform infrared spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC) analyses indicated the formation of modified SiO₂ nanoparticles. The SiO₂ nanoparticle–epoxy composite coating gave rise to a significant increase in the tensile strength of the basalt fibers as compared with the pure epoxy coating, and also the coating endowed the basalt fiber with a promising interfacial property in the basalt fiber reinforced resin matrix composite. The coating modification was an effective way in improving the mechanical properties of basalt fibers and the properties of basalt fiber/epoxy resin composites.     

单丝断裂能量法研究温度对碳纤维/环氧界面性能的影响

针对两种不同上浆剂碳纤维/高温固化环氧树脂体系, 采用基于WND(Wagner-Nairn-Detassis)能量模型的单丝断裂法, 测试分析了从室温到130 ℃范围内单丝复合体系界面断裂能的变化规律, 研究了碳纤维上浆剂对界面耐热性能的影响, 并结合复合材料层板的短梁剪切性能, 分析了微观和宏观界面性能的关联性。结果表明: 在测试温度范围内, 碳纤维/环氧体系的界面断裂能随温度升高呈先下降而后基本不变的趋势, 去除上浆剂后界面断裂能及其随温度的变化程度与未去除上浆剂的情况存在差异, 说明上浆剂对界面耐热性有重要作用。碳纤维/环氧树脂层板层间剪切强度随温度升高线性下降, 与界面断裂能的变化规律不一致, 这与两种测试方法的原理及界面破坏位置的不同有关。      

炭纤维乳液上浆剂

采用转相乳化法，选用不同的混合乳化剂对环氧树脂AG－80进行乳化。通过静置沉淀法，比较不同混合乳化剂对其乳化的影响，结果表明乳化效果最好的是乳化剂1601与NP－10的混合乳化剂。粒径分析结果显示乳液的最可几粒径为934．1nm时，乳液稳定性较好。上浆处理后，单纤维复合材料的界面剪切强度较未上浆时有所提高，说明用该上浆剂处理，不仅可达到保护炭纤维表面的目的，而且可以改善炭纤维与基体树脂间的界面粘结。     

Effect of interfacial adhesion and statistical fiber strength on tensile strength of unidirectional glass fiber/epoxy composites. Part I: experiment results

The effects of fiber surface treatment on ultimate tensile strength (UTS) of unidirectional (UD) epoxy resin matrix composites are examined experimentally. The interfacial shear strength (IFSS) and statistical fiber strength are significantly altered by five different kinds of surface treatments, which are: (a) unsized and untreated; (b) γ-glycidoxypropyltrimethoxysilane (γ-GPS); (c) γ-methacryloxypropyltrimethoxysilane (γ-MPS); (d) mixture of γ-aminoxypropyltrimethoxysilane (γ-APS), film former (urethane) and lubricant (paraffin); and (e) urethane-sized. The maximum UTS is obtained for the relatively strong interfacial adhesion (glass/γ-MPS/epoxy) but not for the strongest interfacial adhesion (glass/γ-GPS/epoxy). The governing micro-damage mode around a broken fiber and the interface region is matrix cracking for γ-GPS treated fibers, and a combination of interfacial debonding and matrix cracking for γ-MPS treated fibers. The micro-damage mode related to the interfacial adhesion strongly affects the fracture process, and thus the UTS of UD composites. The results also indicate that the interfacial adhesion can be optimized for effective utilization of fiber strength for fiber composites. A parameter called “efficiency ratio” of fiber strength in UD composites is proposed to examine and distinguish different effects of IFSS and fiber strength on the UTS of UD composites. The experimental results show that improved UTS of UD composites due to surface treatments mainly result from the increase in fiber strength but not from the modified interface.     

Electrodeposition of exfoliated graphite nanoplatelets onto carbon fibers and properties of their epoxy composites

Exfoliated graphite nanoplatelet (xGnP)/copper (Cu) coated carbon fibers were fabricated by electrophoretic deposition under different applied voltages. The electrical and mechanical properties of individual fibers and composites made from these fibers and epoxy resin were investigated. The electrical resistivity of xGnP/Cu coated single carbon fiber is lower than that of the uncoated control sample and decreases with increase in the applied voltage. The xGnP and metallic Cu were simultaneously deposited on the carbon fiber surface as a result of the electrochemical cell configuration. The interfacial shear strength decreases with applied voltage up to 30 V but increases with applied voltage of over 30 V. The interfacial shear strength for the coated samples except the 50 V treated sample is lower than that of control sample. The flexural strength and modulus of xGnP/Cu coated carbon/epoxy composites is higher than those of control sample due to the reinforcing effect of xGnP/Cu coated on the carbon fibers.     

Improving the interfacial property of carbon fiber/vinyl ester resin composite by grafting modification of sizing agent on carbon fiber surface

The poor interfacial adhesion between carbon fibers (CFs) and vinyl ester resin (VE) has seriously hampered the application of CFs/VE composites. In this work, the interfacial adhesion was efficiently enhanced by grafting acrylamide with epoxy sizing agent on CFs surface. The grafting reaction was feasible according to the thermodynamic calculation. The optimal grafting condition was 80 °C for 10 min based on the kinetic investigation by differential scanning calorimeter. Surface morphology and surface composition of modified carbon fibers (MCFs) were characterized, which indicated that acrylamide was grafted successfully on CFs surface and the surface roughness was increased slightly. After grafting, the interface shear strength of MCFs/VE composites was significantly improved by 86.96% and the interlaminar shear strength was enhanced by 55.61% due to the covalent bonds in interphase and the toughening effect of sizing gent. Moreover, the static and dynamic mechanical properties of composites with different interfacial adhesion were measured, which further confirmed the effect of the grafting modification.     

Role of a gradient interface layer in interfacial enhancement of carbon fiber/epoxy hierarchical composites

To improve the interfacial properties of carbon fibers/epoxy composites, we introduced a gradient interphase reinforced by graphene sheets between carbon fibers and matrix with a liquid phase deposition strategy. Interlaminar shear strength and flexural strength of the composites are both improved. The interfacial reinforcing mechanisms are explored by analyzing the structure of interfacial phase with linear scanning system of scanning electron microscope and atomic force microscope. Results indicate that carbon element shows a graded dispersion in the interface region and a gradient interface layer with the modulus decreasing from fibers and matrix is found to be built. To verify the effect of gradient interphase on the interfacial properties of composites, the mixture of carbon fiber/graphene/epoxy is sonicated before curing to disperse graphene sheets in matrix homogeneously. As a result, gradient interphase structures are disappeared and interfacial performance of composites is found to be weakened. The role of gradient interface layers in enhancing interfacial performances is further proved from a different angle.     

苯酚电聚合膜修饰炭纤维表面对环氧基复合材料性能的影响

将连续炭纤维束用自制的空气梳分散成单丝状长带后, 通过采用循环伏安法的电化学方法将单体苯酚在炭纤维表面聚合成膜, 对炭纤维进行表面修饰, 以提高复合材料中炭纤维与树脂基体的界面粘结性能。红外光谱分析表明, 苯酚电聚合膜能够增加炭纤维表面的羟基、 醚键等活性官能团, 从而提高炭纤维与环氧树脂基体的界面粘结强度。与未进行表面修饰的炭纤维增强环氧树脂复合材料相比, 以聚苯酚膜修饰的炭纤维单丝带增强的环氧树脂基复合材料横向拉伸强度最大提高了90%, 纵向拉伸强度最大提高了45%, 层间剪切强度最大提高了110%。实验也表明, 将炭纤维束分散成炭纤维单丝带后能够更有效地增强复合材料的各项力学性能。      

碳纤维水性杂化上浆剂的制备及其上浆后力学性能

以一定比例的甲基三乙氧基硅烷、正硅酸乙酯、对甲苯磺酸、γ-氨丙基三乙氧基硅烷、无水乙醇制备含硅溶胶,将含硅溶胶和聚醚型水性聚氨酯的水溶液以一定比例复合,制备碳纤维水性杂化上浆剂。研究了不同配比对上浆剂平均粒径和稳定性的影响,结果表明:当水性聚氨酯含量为0.02g/mL时,上浆剂乳液平均粒径为99.94nm,粒径分布较窄,稳定性较好;使用制备的杂化上浆剂对碳纤维进行上浆处理,结果显示:上浆后碳纤维单丝拉伸强度较商用碳纤维提高4.45%,较未上浆碳纤维提高11.04%;与环氧树脂复合后的复合材料界面剪切强度比商用碳纤维增强环氧树脂复合材料的提高了13.74%。     

上浆剂对国产T700级碳纤维复合材料界面性能的影响

采用扫描电镜(SEM)、原子力显微镜(AFM)、X射线光电子能谱(XPS)等测试方法表征了上浆/未上浆国产T700级(MT700)碳纤维的表面特性,并通过单丝断裂实验测试了单丝复合体系微观界面剪切强度(IFSS),在此基础上研究了碳纤维表面特性对单丝复合体系微观界面性能及其耐湿热性能的影响.研究表明:MT700碳纤维表面上浆剂改善了纤维/基体微观界面强度及其耐湿热性能;湿热环境对复合材料的微观界面性能影响显著,尤其是造成纤维/基体间的化学键合作用破坏,去湿后部分界面性能可恢复.