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.     

Anisotropic orientation of the carbon fiber/liquid crystalline epoxy resin composites

Anisotropic orientation of carbon fiber (CF)/liquid crystalline epoxy (LCE) resin composite was readily induced during curing on a CF surface along a long molecular axis of CF. Orientation of LCE was confirmed with polarized optical microscope (POM) and wide angle X-ray diffractometer (WAXD). In addition, anisotropic ordering of LCE was correlated with curing rate, dynamic mechanical properties and thermal expansion behaviors of CF/LCE composite. Curing of LCE was accelerated in the presence of CF and the rubbery modulus of the CF/LCE composites cured at low temperature was enhanced by long-range, long axis orientational ordering of the LCE resin along a CF surface. Fully cured CF/LCE composite showed a negative coefficient of thermal expansion in the fiber direction. These results obtained in this study are interpreted in terms of structural changes occurring during curing.     

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.     

The Effect of Triethylene-Tetramine Treatment of Carbon Fibers on Performance of Composites

Amino groups can be introduced to the surface of carbon fibers (CF) by triethylene-tetramine (TETA) treatment. Carbon fibers coated with triethylene-tetramine (TETA) were treated at 400°C for 30 s in an oxidizing furnace. Differential scanning calorimetry studies showed that the surface functional groups of CF reacted with TETA. The changes of the surface composition and structure of CF were tested by X-ray photoelectron spectrometry (XPS). The interfacial interaction between the resulting CF and an epoxy matrix was also characterized by scanning electron microscopy (SEM) and three-point short-beam shear testing. The XPS results indicate that the number of amino groups on the surface of the CF was significantly increased after being treated with TETA. The interlaminar shear strength (ILSS) of TETA-treated CF-reinforced resin composites (CFRP) was increased by 30% compared with untreated ones, and in the treated CF fracture sections, CFRP pores and carbon fiber pullout were seldom observed. The failure of composites reinforced by treated CF shows a cohesive failure effect in the interface layer.     

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.     

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.     

Changes in the temperature of a dental light-cured composite resin by different light-curing units

The purpose of this study was to evaluate the temperature increase during the polymerization process through the use of three different light-curing units with different irradiation times. One argon laser (Innova, Coherent), one halogen (Optilight 501, Demetron), and one blue LED (LEC 1000, MM Optics) LCU with 500 mW/cm² during 5, 10, 20, 30, 40, 50, and 60 s of irradiation times were used in this study. The composite resin used was a microhybrid Filtek Z-250 (3M/ESPE) at color A₂. The samples were made in a metallic mold 2 mm in thickness and 4 mm in diameter and previously light-cured during 40 s. A thermocouple (Model 120–202 EAJ, Fenwal Electronic, Milford, MA, USA) was introduced in the composite resin to measure the temperature increase during the curing process. The highest temperature increase was recorded with a Curing Light 2500 halogen LCU (5 and 31°C after 5 and 60 s, respectively), while the lowest temperature increase was recorded for the Innova LCU based on an argon laser (2 and 11°C after 5 and 60 s, respectively). The temperature recorded for LCU based on a blue LED was 3 and 22°C after 5 and 60 s, respectively. There was a quantifiable amount of heat generated during the visible light curing of a composite resin. The amount of heat generated was influenced by the characteristics of the light-curing units used and the irradiation times.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

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.     

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.     

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.     

激光辐照下复合材料热响应的轴对称数值分析

为了模拟激光辐照下碳纤维增强复合材料的瞬态热响应,建立了轴对称计算模型。模型考虑了激光辐照过程中基体热分解、质量迁移、比热容和热导率等物理量的变化情况。采用有限元方法求解控制方程,边界条件包含了激光辐照、对流换热以及辐射换热。在此基础上编写了计算程序,预测了激光辐照下碳纤维增强复合材料的瞬态温度场和基体热分解状况。为了校核模型,开展了激光辐照碳纤维复合材料试验。计算结果与试验数据比较表明,模型预测的复合材料温度-时间曲线与试验结果较好吻合,在较低功率密度激光辐照下复合材料热响应以基体热分解为主,与试验烧蚀形貌观察结果一致。     

Synthesis and Properties of Amine-Cured Epoxy/Organophilic Layered Silicate Nanocomposites

Epoxy-layered silicate composites have been prepared by dispersing an organically modified montmorillonite (Nanofil 919) in an epoxy resin and curing in the presence of an aromatic hardener. Dispersion of the layered silicate within the epoxy matrix was verified using X-ray diffraction and transmission electron microscopy revealing that interaction improves upon organic silicate modification. Flexural properties and toughness increase with the organic silicate loading whereas glass transition temperature decreases and thermal stability remains practically unmodified.     

Processing and properties of carbon nanofibers reinforced epoxy powder composites

Commercially available CNFs (diameter 30–300 nm) have been used to develop both bulk and coating epoxy nanocomposites by using a solvent-free epoxy matrix powder. Processing of both types of materials has been carried out by a double-step process consisting in an initial physical premix of all components followed by three consecutive extrusions. The extruded pellets were grinded into powder and sieved. Carbon nanofibers powder coatings were obtained by electrostatic painting of the extruded powder followed by a curing process based in a thermal treatment at 200 °C for 25 min. On the other hand, for obtaining bulk carbon nanofibers epoxy composites, a thermal curing process involving several steps was needed. Gloss and mechanical properties of both nanocomposite coatings and bulk nanocomposites were improved as a result of the processing process. FE-SEM fracture surface microphotographs corroborate these results. It has been assessed the key role played by the dispersion of CNFs in the matrix, and the highly important step that is the processing and curing of the nanocomposites. A processing stage consisted in three consecutive extrusions has reached to nanocomposites free of entanglements neither agglomerates. This process leads to nanocomposite coatings of enhanced properties, as it has been evidenced through gloss and mechanical properties. A dispersion limit of 1% has been determined for the studied system in which a given dispersion has been achieved, as the bending mechanical properties have been increased around 25% compared with the pristine epoxy resin. It has been also demonstrated the importance of the thickness in the nanocomposite, as it involves the curing stage. The complex curing treatment carried out in the case of bulk nanocomposites has reached to reagglomeration of CNFs.     

Modelling of the transverse strength of fibre reinforced epoxy composite at low and high temperature

Process-induced thermal residual stresses and matrix failure of unidirectional carbon fibre reinforced composites (CFRP) have been investigated by finite element analysis (FEA). We used a partial discrete FEA model based on a unidirectional composite consisting of a microscopic area of fibres and matrix surrounded by a homogenised composite area. The FEA provided information about the stress state in the matrix and the fibre–matrix interface. The transverse strength of the composite was calculated regarding matrix failure and fibre matrix debonding. The influence of the temperature on the Young's modulus, the non-linear stress–strain behaviour and the strength of the matrix were investigated in detail. Following this approach it was possible to incorporate the resulting microresidual stresses on the transverse strength of the composite. Tensile tests of the neat resin and of the composite were performed in the temperature range of ?40°C to 60°C. The results of the FEA modelling are in good agreement with the experimental results of the transverse tests.     

Preparation and Properties of Nano‐SiO2/Epoxy Composites Cured by Mannich Amine

Nano‐SiO₂/epoxy composites cured by Mannich Amine (type T‐31) were prepared and studied and the results are reported in this paper. The nano‐SiO₂ was pretreated by a silane coupling agent (type KH‐550) and mixed with epoxy resin (type E‐51) using an ultrasonic processor. Amounts of filler loading ranged from 1% to 5% of the weight of the epoxy resin. Some properties of the resulting composites were characterized by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of tensile tests and impact tests showed that the composite with 3% nano‐SiO₂ loading presented the best mechanical performances. The tribological performance and thermal stability of the materials were also improved with the addition of nano‐SiO₂.     

Effects of plasma surface modification on the mechanical properties of carbon fiber and carbon fiber/epoxy composite

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.     

Micromechanical Behavior of Carbon Nanotube-Covered SiC Fibers in Polymer Matrix Composites

The incorporation of nanotube-covered fibers in continuous fiber/epoxy composites has been shown to influence the mechanical, electrical, and thermal properties of the composite. Increased interlaminar shear stress, flexural strength and modulus have been reported in such composites over composites containing bare fibers. In this study, the microstructure and interfacial shear strength (ISS) of continuous silicon carbide fiber/epoxy composites with and without nanotubes grown from the SiC fiber surface were investigated with micro-Raman spectroscopy (MRS) and microscopy. The fibers with nanotubes grown from the surface were found to have a reduced ISS compared with the bare fibers. Electron microscopy showed good wetting of epoxy in the nanotube forests, but poor attachment of the nanotube forests to the fibers. These results suggest that the mechanism leading to improvements in bulk composite properties is not due to an improvement in the fiber/matrix ISS.     

Synergistic Effect of Polyhedral Oligomeric Silsesquioxane and Multiwalled Carbon Nanotubes on the Flame Retardancy and the Mechanical and Thermal Properties of Epoxy Resin

A novel polyhedral oligomeric silsesquioxane containing phosphorus and boron (PB-POSS) was synthesized. The resulting PB-POSS and multiwalled carbon nanotubes (MWCNTs) were incorporated into an epoxy resin (EP) to prepare PB-POSS/MWCNTs/EP composites through a solution mixing method. The synergistic effect of MWCNTs and PB-POSS on the thermal and mechanical properties and the flame retardancy of these flame retardant composites were studied. The experimental results showed that the introduction of PB-POSS or MWCNTs further improved the LOI values of the epoxy resin, and the highest LOI value (32.8%) was obtained for the formulation containing 14.6 wt% PB-POSS and 0.4 wt% MWCNTs. In addition, the incorporation of both PB-POSS and MWCNTs significantly improved the thermal and mechanical properties of the composites. The mechanical properties of composites containing 14.7 wt% PB-POSS and 0.3 wt% MWCNTs reached the maximum. The impact strength and flexural strength increased by 42% and 7%, respectively, compared to the neat epoxy resin. Thus, a combination of PB-POSS and MWCNTs in the appropriate ratio could effectively enhance the thermal and mechanical properties and the flame retardancy of the epoxy resin matrix.     

Investigation of the Kinetics of Curing Reaction for the Resin Matrix Polymer Composite Based on Near-Infrared Spectroscopy

Abstract

Near-infrared (NIR) spectroscopy is a rapid and nondestructive method for the simultaneous measurement of different constituents in resin matrix polymer composites. This strategy has been applied in the synthesis of resin matrix polymer composites. In this article, we mainly review the control of curing reaction kinetics of the phenolic, epoxy resin, polyester resin, polyurethane, and other polymer resin based on NIR spectra, which is important to control the quality of the resin matrix polymer composites during synthesis.