Quantitative evaluation of interfacial adhesion between fiber and resin in carbon fiber/epoxy composite cured by semiconductor microwave device

Interfacial adhesion between carbon fiber (CF) and epoxy resin in carbon fiber-reinforced epoxy composite, which was prepared by different heating process such as semiconductor microwave (MW) device and conventional electric oven, has been evaluated quantitatively. The interfacial shear strength (IFSS) between CF and epoxy resin, which was an indicator of adhesion on the interface, was measured by a single fiber fragmentation test. The single fiber fragmentation test showed that the IFSSs of the prepared specimens were different by heating methods. In the case of MW process, the curing reaction of epoxy resin on the CF interface would be progressed preferentially due to the selective heating of CF, resulting that the IFSSs of specimens prepared by MW irradiation were increased by enhancing the output power of MW. However, the IFSSs of the specimens were decreased by excessively high output power because the matrix resin on the CF interface was thermally degraded. As results, by optimizing the MW conditions of output power and irradiation time, the IFSS of the sample cured by MW was increased by 21% as compared to oven-heated one. It was found that the interfacial adhesion between CF and epoxy resin would be improved by the MW-assisted curing reaction on the surface of CF.     

Carbon fiber/epoxy composite materials cured thermally and with microwave irradiation

In this paper, composite materials of short carbon fibers (CFs) and a thermosetting epoxy were prepared in three different ways: without curing, thermal curing, and thermal curing followed by microwave irradiation. Mechanical properties of the three kinds of CF reinforced plastic (CFRP) composites were studied to explore the effect of microwave irradiation. Microscopic study with the aid of a scanning electron microscope (SEM) was performed on fractured composite surfaces to identify the principle features of failure. Degree of polymerization of the epoxy resin in the three CFRP composites was evaluated by infrared (IR) spectroscopy. The microwave irradiated CFRP exhibited mechanically ductile behavior even though its highest degree of polymerization. Use of microwaves and resultant stronger physico-chemical linkage at the interface between CF and epoxy resin are the main feature of this study.     

The effect of interphase modification on carbon fiber/polyarylacetylene resin composites

Interfacial modification for carbon fiber (CF) reinforced polyarylacetylene (PAA) resin, a kind of non-polar, was investigated. The high carbon phenolic resin was used as coating to treat the surface of CF after oxidation. Atomic force microscopy (AFM) with force modulation mode was used to analyze the interphase of composite. The interlaminar shear strength (ILSS) and mechanical properties of CF/PAA composites were also measured. It was found that the CF/PAA composites treated with oxidation and coating after oxidation had transition area between carbon fiber and PAA resin. The existence of transition area led to the improvement of interfacial performance of composites. Specially, the thickness and stiffness of interphase of composite treated with coating after oxidation were more suitable for CF/PAA composites. Thus, the composite treated with coating after oxidation had the highest value of ILSS and the best mechanical properties.     

Thermal and Mechanical Properties of Epoxy/Carbon Fiber Composites Reinforced with Multi-walled Carbon Nanotubes

Multi-scale hybrid composite laminates of epoxy/carbon fiber (CF) reinforced with multi-walled carbon nanotubes (MWCNTs) were fabricated in an autoclave. For laminate fabrication, 0.5 wt% of pristine MWCNTs or silane-functionalized MWNCTs (f-MWCNTs) were dispersed into a diglycidyl ether of bisphenol-A epoxy system and applied on the woven carbon fabric. The neat epoxy/CF composite and the MWCNTs-reinforced epoxy/CF hybrid composites were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), tensile testing, and field emission scanning electron microscopy (FE-SEM). A significant improvement in initial decomposition temperature and glass transition temperature of epoxy/CF composite was observed when reinforced with 0.5 wt% of f-MWCNTs. The coefficient of thermal expansion (CTE), measured by TMA, diminished by 22% compared to the epoxy/CF composite, indicating an improvement in dimensional stability of the hybrid composite. No significant improvement in tensile properties of either MWCNTs/epoxy/CF composites was observed compared to those of the neat epoxy/CF composite.     

新型腰果酚基不饱和树脂的结构及其紫外光固化行为的红外光谱研究

以天然产物腰果酚为原料,利用其酚羟基与环氧基的反应活性,通过开环醚化反应制备了两种腰果酚基不饱和树脂单体。通过傅里叶红外光谱研究了合成过程中主要活性基团的变化,结合核磁共振氢谱及凝胶渗透色谱分析进一步确定了合成树脂单体的分子结构,并利用红外光谱法对树脂单体的紫外光固化行为进行了研究,且对其光固化物进行了热重分析。研究表明：分子结构分析确认了目标产物的成功合成,树脂单体的分子结构以及不饱和双键含量对树脂的固化速度和固化物的热稳定性有着重要影响,两种单体在30 s内均已基本达到最高固化水平,光固化物的主分解初始温度均可达到350 ℃以上。     

Enhanced interfacial adhesion between PMMA and carbon fiber by graphene oxide coating

The purpose of this study is to increase the interfacial properties in PMMA/carbon fiber (PMMA/CF) composites Graphene oxide (GO) and brached polyethyleneimine were coated onto the surface of carbon fiber by layer-by-layer assembly in this work. Compared with the origin PMMA/CF composite, the composites reinforced by PMMA/CF–GO showed significant enhancement in interFacial shear strength (IFSS). The improved fiber–matrix adhesion was proved by fracture morphology observation of scanning electron microscopy and almost unaffected mechanical properties of the fiber itself during the coating process. The optimal assembly time was found to be 10 for enhancing the overall composite mechanical performance.     

两种含硅炔基树脂的固化行为研究

综合采用红外光谱（FTIR）、核磁碳谱 (13C NMR)、差示扫描量热（DSC）,热失重测试(TGA)等多种表征手段,研究了聚硅芳炔（PAR）和聚硅乙炔（PMR）两种含硅炔基树脂的固化行为,讨论了树脂固化物的结构与热稳定性的关系。结果表明：PAR和PMR树脂的固化机理不同,PAR主要通过炔基间的加成和Diels-Alder反应实现分子间的固化交联,并最终形成由苯环和稠芳环组成的芳构网络;PMR则主要通过硅氢基、炔基、烯基之间的加成反应实现固化,并成形饱和的碳硅Si—C(sp3)网络结构。固化成型的芳构网络和Si—C(sp3)网络结构分别赋予了PAR和PMR树脂固化物良好的热稳定性能,它们的热分解温度T_d5均大于600 ℃,900 ℃残重率均达到85%以上。     

Maintenance of highly interfacial shear strength by diblock copolymer between carbon fiber and epoxy resin in hostile environment

The environmental resistance properties of carbon fiber (CF), with various surface modifications, reinforcing epoxy resin composites have been studied by a microbond test. The results of cooling–heating cycling between ?40 and 95?°C indicate that the introduction of the flexible poly(n-butyl acrylate) (PnBA) blocks into the interface can effectively decrease the interfacial degradation rate, induced by interfacial thermal stress. After 50 cooling–heating cycles, the interfacial shear strength between CF and epoxy resin was still as high as 32.69?±?2.13?MPa. The results of hygrothermal treatment by immersing the composites in hot water show that assembly morphology of the diblock copolymer hydroxyl-terminated poly(n-butyl acrylate-b-glycidyl methacrylate) (OH-PnBA-b-GMA) at the interface can decrease the interfacial water absorption and thus increase the hygrothermal resistance of the composite. Besides, the length of PnBA block in the diblock copolymer influenced the interfacial properties of the composite in a hygrothermal environment.     

用布喇格光纤光栅传感器测定口腔复合树脂材料光固化收缩与温度演化特性

复合树脂材料已成为重要的牙齿美容修复材料.本文利用两种布喇格光纤光栅传感器测定了口腔复合树脂材料在光固化过程中的收缩与温度演化特性.一种为普通的光纤布喇格光栅,另一种为经过了化学镀镍的光纤布喇格光栅,同时埋入复合树脂样品中,用光照射使其固化,测得光纤布喇格光栅在固化过程中温度和应力随时间的演化曲线.实验结果表明,在光固化过程中,因为聚合反应,树脂产生了强烈的收缩应力和温度变化.掌握复合树脂的光固化收缩特性和温度变化特性对不断改良材料性能以及优化口腔材料的治疗效果具有实际意义.     

The effect of surface treatment of carbon fiber on the flexural property of thermoplastic polyimide composite

Rare earth solution (RES) surface modification and air-oxidation methods were used to improve the interfacial adhesion of the carbon fiber reinforced polyimide (CF/PI) composite. The flexural property of the PI composites reinforced by the carbon fibers treated with different surface modification methods was comparatively investigated. Results showed that the flexural strength of CF/PI composite was improved after RES treatment. The improvement of impact and flexural property of the CF/PI composite was mainly due to the improvement in interfacial adhesion after RES treatment. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RES treatment. The increase in the amount of organic functional groups increased the interfacial adhesion between CF and PI matrix.     

Identification des propriétés thermiques de composites fibres de verre/résines thermodurcissables: Application à l'optimisation des procédés de moulage

Identification of glass fiber/thermosetting resins composites thermal properties. Application to the optimization of molding processes. A procedure has been developed to optimize molding processes of thermosetting composite materials. Three stages have been distinguished. In the first one, some thermal and kinetic properties have been measured by differential scanning calorimetry. Thermal conductivities have been identified afterwards in thick instrumented pieces, placed in a thermally regulated press. High dependences of thermal conductivities on temperature and transformation degree have been shown. Secondly, coupled heat transfers have been numerically simulated and results have been satisfactorily compared with experimental thermograms. Finally, optimization technics based on effective inverse methods have been used.These points have been illustrated with two examples : glass fiber/epoxy resin and glass fiber/polyester. Sufficient mechanical characteristics of the first one, which is cured in oven, and good surface aspect of the second, that is made by injection in heated and closed molds, had to be obtained. The results let foresee real improvement of the corresponding molding processes.     

微米水合氧化铝/环氧复合材料脉冲真空闪络影响因素

 研究了微米Al₂O₃·3H₂O/环氧复合材料的脉冲真空闪络影响因素。分别给出了固化剂、分散方法、偶联剂对复合材料闪络特性的影响和纯环氧表面抛光前后的脉冲真空闪络特性。实验结果表明:酸酐固化的试样比胺类固化试样闪络电压要高;高速分散方法与超声波分散方法相比,采用前者制备的复合材料有更好的分散特性;使用偶联剂处理填料比不使用时得到的环氧复合材料闪络电压高;抛光后的纯环氧试样有较高的闪络电压。     

Effect of pre-heating resin composite and light-curing units on monomer conversion

The purpose of this study was to evaluate the effect of pre-heating resin composite photo-cured with light-curing units (LCU) by FT-IR. Twenty specimens were made in a metallic mold (4 mm diameter × 2 mm thick) from composite resin—Tetric Ceram® (Ivoclar/Vivadent) at room temperature (25°C) and pre-heated to 37, 54, and 60°C. The specimens were cured with halogen curing light (QTH) and light emitted by diodes (LED) during 40 s. Then, the specimens were pulverized, pressed with KBr and analyzed with FT-IR. The data were submitted to statistical analysis of variance and Kruskal-Wallis test. Study data showed no statistically significant difference to the degree of conversion for the different light curing units (QTH and LED) (p > 0.05). With the increase of temperature there was significant increase in the degree of conversion (p < 0.05). In this study were not found evidence that the light curing unit and temperature influenced the degree of conversion.     

Plasma treatment of carbon fibers: Non-equilibrium dynamic adsorption and its effect on the mechanical properties of RTM fabricated composites

The effect of oxygen plasma treatment on the non-equilibrium dynamic adsorption of the carbon fabric reinforcements in RTM process was studied. 5-Dimethylamino-1-naphthalene-sulfonylchloride (DNS-Cl) was attached to the curing agent to study the change of curing agent content in the epoxy resin matrix. Steady state fluorescence spectroscopy (FS) analysis was used to study this changes in the epoxy resin at the inlet and outlet of the RTM mould, and XPS was used to study the chemical changes on the carbon fiber surfaces introduced by plasma treatment. The interlaminar shear strength (ILSS) and flexural strength were also measured to study the effects of this non-equilibrium dynamic adsorption progress on the mechanical properties of the end products. FS analysis shows that the curing agent adsorbed onto the fiber surface preferentially for untreated carbon fiber, the curing agent content in the resin matrix maintain unchanged after plasma treatment for 3 min and 5 min, but after oxygen plasma treatment for 7 min, the epoxy resin adsorbed onto the fiber surface preferentially. XPS analysis indicated that the oxygen plasma treatment successfully increased some polar functional groups concentration on the carbon fiber surfaces, this changes on the carbon fiber surfaces can change the adsorption ability of carbon fiber to the resin and curing agent. The mechanical properties of the composites were correlated to this results.     

Temperature dependence of the stress transfer for thermal resistance polymer composites by X-ray diffraction

Temperature dependence of the stress transfer from the matrix resin to the incorporated fiber has been measured for poly(p-phenylene benzobisoxazole) (PBO) fiber/bismaleimide (BMI) resin composite by a novel X-ray diffraction method. At 120°C, stress transfer and tensile strength of the PBO/BMI composite are superior to that of the PBO/epoxy composite, due to the excellent thermal resistance and good mechanical property of BMI resins. The PBO/BMI composite possesses good adhesion and excellent mechanical properties at high temperature, which are suitable for thermal resistance applications.     

Preparation and Properties of Novel Inherent Flame-Retardant Cyclotriphosphazene-Containing Epoxy Resins

A novel flame-retardant cyclotriphosphazene-based epoxy resin (CPEP) was successfully prepared by epoxidation of bis-(4-hydroxyphenylsulfonylphenoxy) tetraphenoxycyclotriphosphazene with epichlorohydrin, and was characterized by ¹H nuclear magnetic resonance (NMR), Fourier transform infrared, and gel permeation chromatography (GPC). Then the blends of CPEP and diglycidyl ether of bisphenol A (E51) with different mass ratios were cured using 4,4′-diaminodiphenylmethane as a curing agent. The curing behaviors and the glass transition temperatures of the resulting thermosets were studied by differential scanning calorimetry. The thermal stabilities and flame-retardant properties of the cured resins were studied by thermogravimetric analysis and UL94 tests, respectively. In addition, mechanical, hydrophobic, and electrical properties were also characterized. Compared to the corresponding E51-based thermosets, the cured resins with a mixture of CPEP and E51 showed better thermal stabilities, higher char yields, and greatly improved flame-retardant properties. Furthermore, relatively good mechanical properties, hydrophobicity, and electric resistance were maintained. The cured resins of CPEP/E51 (mass ratio 1:1) achieved UL94 V-0 rating, indicating that the epoxy resin prepared in this study could be used as a flame-retardant coating material.     

长亚甲基链段改性固化剂的制备与性能

采用二官能度环氧树脂对己二胺进行改性,得到了含多段长亚甲基链段的柔性固化剂。利用红外光谱表征其基本结构。采用环氧树脂E-44与之进行固化,通过不同温度下固化时间对力学强度影响的分析,初步确定其最佳固化条件为80 ℃,6 h。通过热重分析检测不同固化比例下固化产物的热稳定性,并采用差示扫描量热法研究该固化剂的固化动力学参数、反应活性、最佳固化温度及时间。对其固化物拉伸剪切强度进行测试,测试结果表明:在固化比例为1:0.5时,在-196 ℃、室温、60 ℃下的拉伸剪切强度分别为16.84,14.73和13.52 MPa,基本满足实际应用的需求。     

Effect of Carbon Fiber Surface Oxidation on Tribological Properties of PTFE Composite under Oil-Lubricated Conditions

Air-oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil-lubricated conditions was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF/PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy (XPS) study of the carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen-containing groups on CF surfaces were increased greatly. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix, and large scale rubbing-off of PTFE was prevented; therefore, the tribological properties of the composite were improved.     

Strain energy effects on the ordering process in diblock styrene-butadiene copolymer

The technique of time-resolved small-angle x-ray scattering is used to monitor the disorder-order transformation occurring in asymmetric, diblock styrene-butadiene. A rapid thermal quench is applied to drive the system from its initial high-temperature disordered state to a low-temperature ordered structure, a body-centered cubic lattice of styrene spheres characterized by a series of concentric Debye rings in the two-dimensional scattering profile. At relatively late times in the microdomain ordering process, the uniform Debye rings were seen to rapidly develop nonuniformities indicating the existence of preferred orientation with a fiber texture, the 110] axis of the bcc structure defining the fiber axis. These results are interpreted in the context of a developing transformation strain energy during the ordering process and shown to be consistent with accompanying changes in lattice spacing as well as earlier observations of apparent fluctuations in the ordering process.     

Friction and wear of rare earths modified carbon fibers filled PTFE composite under dry sliding condition

Carbon fibers (CF) were surface treated with air-oxidation and rare earths (RE), respectively. The friction and wear properties of polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under dry sliding condition, were investigated on a block-on-ring M-2000 tribometer. Experimental results revealed that RE treatment largely reduced the friction and wear of CF reinforced PTFE (CF/PTFE) composites. The RE treated composite exhibited the lowest friction and wear under dry sliding. Scanning electron microscopy (SEM) investigation of worn surfaces and transfer films of CF/PTFE composites showed that RE treated CF/PTFE composites had the smoothest worn surface under given load and sliding speed, and a continuous and uniform transfer film formed on the counterface. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RE treatment, and more carboxyl groups were introduced onto CF surfaces after RE treatment. The increase in the amount of oxygen-containing groups increased the interfacial adhesion between CF and PTFE matrix, and accordingly increased the tribological properties of the composite.