Interfacial improvement of carbon fiber/epoxy composites using a simple process for depositing commercially functionalized carbon nanotubes on the fibers

An aqueous suspension deposition method was used to coat the sized carbon fibers T700SC and T300B with commercially carboxylic acid-functionalized and hydroxyl-functionalized carbon nanotubes (CNTs). The CNTs on the fiber surfaces were expected to improve the interfacial strength between the fibers and the epoxy. The factors affecting the deposition, especially the fiber sizing, were studied. According to single fiber-composite fragmentation tests, the deposition process results in improved fiber/matrix interfacial adhesion. Using carboxylic acid-functionalized CNTs, the interfacial shear strength was increased 43% for the T700SC composite and 12% for the T300B composite. The relationship between surface functional groups of the CNTs and the interfacial improvement was discussed. The interfacial reinforcing mechanism was explored by analyzing the surface morphology of the carbon fibers, the wettability between the carbon fibers and the epoxy resin, the chemical bonding between the fiber sizing and the CNTs, and fractographic observation of cross-sections of the composites. Results indicate that interfacial friction, chemical bonding and resin toughening are responsible for the interfacial improvement of nanostructured carbon fiber/epoxy composites. The mechanical properties of the CNT-deposited composite laminate were further measured to confirm the effectiveness of this strategy.     

Interfacial studies on the surface modified aramid fiber reinforced epoxy composites

In this work, solutions of rare earth modifier (RES) and epoxy chloropropane (ECP) grafting modification method were used for the surface treatment of aramid fiber. The effect of chemical treatment on aramid fiber has been studied in a composite system. The surface characteristics of aramid fibers were characterized by Fourier transform infrared spectroscopy (FTIR). The interfacial properties of aramid/epoxy composites were investigated by means of the single fiber pull‐out tests. The mechanical properties of the aramid/epoxy composites were studied by interlaminar shear strength (ILSS). As a result, it was found that RES surface treatment is superior to ECP grafting treatment in promoting the interfacial adhesion between aramid fiber and epoxy matrix, resulting in the improved mechanical properties of the composites. Meanwhile, the tensile strengths of single fibers were almost not affected by RES treatment. This was probably due to the presence of reactive functional groups on the aramid fiber surface, leading to an increment of interfacial binding force between fibers and matrix in a composite system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4165–4170, 2006     

Studies of the effect of fiber surface and matrix rheological properties on nonwoven reinforced elastomer composites

The influence of fiber type and fiber-surface properties on matrix flow behavior was investigated using structural reaction injection-molding (SRIM). The influence of fiber type, fiber-surface properties, and matrix type on strength properties in elastomeric composites reinforced with nonwoven fibrous structures was investigated using tensile tests on elastomer composite samples from SRIM and latex coagulation (LC) fabrication methods and the microbond strength method on individual fibers. The fibers used were PET, LLDPE, and p-aramid. Fibers were treated with epoxy, styrene, and isocyanate derivatives, which make the surface chemically reactive. Treatments were also made with NaOH and a copolymer of polyester and polyol ether, causing a change in the fiber surface energy. The matrix types were polyurethane elastomer and natural rubber. The results show that the surface treatments which produced a change in the surface energy influenced the flow rate of the matrix polymer during the composite fabrication process. The treatments resulted in chemically reactive fiber surfaces which improved the fiber-matrix bond strength without affecting the Young's modulus of the composite material. Good correlation was found between bond strength and surface energy including the dispersive component of surface energy in the case of polyurethane elastomer and surface-modified PET fibers. The age of the polyurethane matrix has a marked influence on the bond strength. The fiber volume fraction in composites has a strong influence on the Young's modulus of the elastomer composite. © 1995 John Wiley & Sons, Inc.     

Effect of fiber chemical treatment of nonwoven coconut fiber/epoxy composites adhesion obtained by RTM process

In this work untreated and alkali treated nonwoven coconut fiber mats/epoxy resin composites were manufactured using the resin transfer molding process. The alkaline solution removes some impurities present on fibers superficial layers and the effect regarding fiber/matrix adhesion were investigated by thermogravimetric analysis, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), ultrasonic C‐scan, and quasi‐static flexural test. Results show a removing of some amorphous fibers constituents, mainly waxes, extractives, and hemicellulose, revealing the fiber roughness surface but no initial degradation temperature changing. Regarding the composites, a similar interfacial adhesion was observed in both one through the results of SEM, DMA and quasi‐static flexural tests. The conclusion is that chemical treatment conditions applied on the fiber surface was been suitable to improve fiber roughness but did not the adhesion between coconut fibers mat and epoxy resin. POLYM. COMPOS., 38:2518–2527, 2017. © 2015 Society of Plastics Engineers     

Carbon fiber reinforced melamine‐formaldehyde

New composites based on carbon fiber (cf) and melamine‐formaldehyde (MF) are presented. Composites were manufactured by pressing stacked planar random veils (webs) or unidirectionally (UD) arranged fibers, and MF impregnated thin cellulose sheets. Non‐vented pressing for 60 s was used. Also, planar random, UD and bidirectional fiber composites with or without alumina trihydrate (ATH) were manufactured by conventional compression molding using much longer times (up to 20 min). Tensile strength of about 500 MPa and stiffness of 60 GPa was obtained for the UD composite containing 23 vol% fiber, and no ATH. Practically the same strength was measured for the bidirectional composite containing 46 vol% fiber and no ATH. Tensile strength and modulus of 130 MPa and 28 GPa, respectively, was obtained for the random fiber composite containing 16 vol% fiber. Measurements showed that replacement of ATH with cellulose in a composite containing 6 vol% carbon fibers increased the strength (2.5 times) without any penalty on stiffness, and increased strain at break. Cf‐MF interfacial strength is low. This was estimated for clean fibers by means of transverse tensile testing and in‐situ scanning electron microscopy (SEM), and for fibers with an epoxy compatible coating by using the interlaminar shear strength (ILSS) test. The cf/MF/cellulose composite performed well up to 200°C. Within this temperature range it retained 80% of its stiffness compared to about 60% in the case of a representative epoxy with a higher content of carbon fibers.     

Effect of fiber surface modification on the mechanical properties of sisal fiber‐reinforced benzoxazine/epoxy composites based on aliphatic diamine benzoxazine

Sisal fibers were incorporated into a mixture of benzoxazine and bisphenol A type epoxy resins to form a unidirectionally reinforced composite. Surface modifications of the sisal fibers were carried out with sodium hydroxide, γ‐aminopropyltrimethoxysilane, and γ‐glycidoxypropyltrimethoxysilane. The surface treatments led to changes in the morphology, chemical groups, and hydrophilicity of the fibers. The effect of the fiber surface treatments on the fiber–matrix interfacial adhesion and mechanical properties of the composites were also studied. The results showed that surface treatments with sodium hydroxide and a silane coupling agent led to improved fiber–matrix adhesion; this could be seen in the scanning electron micrographs of the fractured surfaces from mechanical testing and the reduction in the impact strength of the composites made from treated fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Tensile properties of cellulose fiber reinforced hydroxypropylcellulose films

The tensile properties of cross-linked and uncross-linked composite films (thickness ∼20–35 μm) prepared from Hydroxypropylcellulose (HPC) with incorporation of microcrystalline cellulose fibers (Avicel) were studied. The concentration of fibers in the composites ranged from 0 to 30 w/w% and cross-linked composites were obtained by the reaction of HPC-Avicel mixtures with 1,4-butyldiisocyanate. It was demonstrated that the inclusion of fibers in a HPC matrix produces composites with enhanced mechanical properties that are improved by cross-linking. Mechanical results seem to indicate that the elastic deformation of the cross-linked composites is predominantly dominated by the fiber content while the cross-linking affects mainly the plastic deformation. Maximum values of the Young's Modulus, yield stress and tensile stress were observed at 10 w/w% for the cross-linked and 20 w/w% for the uncross-linked composites. Furthermore cross-linked films with 10 w/w% of fibers present values of yield stress and tensile stress that are in average 15 to 20% higher than those obtained for uncross-linked composites with 20 w/w% of fibers. Studies in Polarizing Optical Microscopy and Atomic Force Microscopy (AFM) seem to indicate that tensile properties of these composites are correlated to the packing of fibers. For the concentration of the utilized cross-linking agent, and for a fiber content of 10 w/w%, an optimal packing of fibers throughout the matrix has been correlated to the minimal difference between the roughness parameters obtained by AFM analysis of the top and bottom surfaces of the films.     

Relation of interfacial adhesion in Kevlar®/epoxy systems to surface characterization and composite performance

A central problem in composite materials is the poorly understood relation between the nature of the surfaces at the fiber/matrix interface, the actual interfacial bond strength, and interface-sensitive composite properties, in this study on the Kevlar®/epoxy composite system, the interface was varied chemically by fiber sizings. The sized and unsized fiber surfaces and the cured matrix surface were characterized by contact angle measurements. The interfacial shear strength was directly measured by single-filament pull-out tests of sized and unsized fibers in epoxy matrix. The shear strengths of the composites made with sized and unsized fibers were measured. The results from surface analysis, interfacial shear tests, and composite shear tests were consitent. This suggests that surface-contact-angle analysis and single-filament pull-out tests may be helpful in screening strength of the composite.     

Characterization of the interphase in carbon fiber/polymer composites using a nanoscale dynamic mechanical imaging technique

The interphase of fiber reinforced polymer composites is a narrow region around the fiber, and the mechanical performance of a composite strongly depends on the properties of the interphase. The interphase of carbon fiber reinforced polymer composites (CFRPs) is difficult to quantitatively characterize because of its nanometer dimension. To solve this problem, we present a nanomechanical imaging technique for mapping the dynamic mechanical property around the interphase region in CFRPs, and for providing nanoscale information of the interfacial dimension. The experimental results show that this method can determine the width and topography of the interphase with nanoscale lateral resolution, based on the storage modulus profile on the cross section of the composite. The average interphase thicknesses of a T300 carbon fiber/epoxy resin composite and a T700 carbon fiber/bismaleimide resin composite are 118 nm and 163 nm, respectively, and the size of interphase is uneven in width and “river-like”, which is consistent with the surface topography of the carbon fibers. Furthermore, the effect of water-aging on the interphase of the T300/epoxy composite was analyzed using the in situ imaging technique. An increase in the interphase width and interface debonding were revealed, implying a degradation in the interphase region.     

Study of nanoreinforced shape memory polymers processed by casting and extrusion

Multi‐walled carbon nanotubes (CNTs) and cellulose nanofibers (CNFs) reinforced shape memory polyurethane (PU) composite fibers and films have been fabricated via extrusion and casting methods. Cellulose nanofibers were obtained through acid hydrolysis of microcrystalline cellulose. This treatment aided in achieving stable suspensions of cellulose crystals in dimethylformamide (DMF), for subsequent incorporation into the shape memory matrix. CNTs were covalent functionalized with carboxyl groups (CNT‐COOH) and 4,4′‐methylenebis (phenylisocyanate) (MDI) (CNT‐MDI) to improve the dispersion efficiency between the CNT and the polyurethane. Significant improvement in tensile modulus and strength were achieved by incorporating both fillers up to 1 wt% without sacrificing the elongation at break. Electron microscopy was used to investigate the degree of dispersion and fracture surfaces of the composite fibers and films. The effects of the filler (type and concentration) on the degree of crystallinity and thermal properties of the hard and soft segments that form the PU sample were studied by calorimetry. Overall, results indicated that the homogeneous dispersion of nanotubes and cellulose throughout the PU matrix and the strong interfacial adhesion between nanotubes and/or cellulose and the matrix are responsible for the enhancement of mechanical and shape memory properties of the composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Composites of rigid polyurethane foam and cellulose fiber residue

Rigid polyurethane composite foams were prepared with cellulose fibers as a filler. The cellulose fibers were an industrial residue of blanched cellulose pulp production. The influence of the cellulose fiber concentration on the structural, thermal, mechanical, and morphological properties of the foams was investigated. We also studied the influence of the cellulose fibers on the foam's resistance to fungal attack by placing a suspension of known fungus in contact with the surface of the foam and following the morphological evolution as a function of time (for 60 days). The increase in the cellulose filler concentration in the foams, up to 16% w/w with respect to the polyol, changed their properties as follows: (1) the cell size decreased, (2) the thermooxidative stability and mechanical properties remained approximately constant, (3) the thermal conductivity decreased slightly, and (4) fungal growth was observed. Therefore, a cellulosic fibrous industrial residue was rationally valorized as a filler in classical rigid polyurethane foams; this yielded materials with mechanical resistance and a susceptibility to fungi in a wet environment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on the effect of woven sisal fiber mat on mechanical and viscoelastic properties of petroleum based epoxy and bioresin modified toughened epoxy network

Sisal fiber reinforced biocomposites are developed using both unmodified petrol based epoxy and bioresin modified epoxy as base matrix. Two bioresins, epoxidized soybean oil and epoxy methyl soyate (EMS) are used to modify the epoxy matrix for effective toughening and subsequently two layers of sisal fiber mat are incorporated to improve the mechanical and thermomechanical properties. Higher strength and modulus of the EMS modified epoxy composites reveals good interfacial bonding of matrix with the fibers. Fracture toughness parameters K_IC and G_IC are determined and found to be enhanced significantly. Notched impact strength is found to be higher for unmodified epoxy composite, whereas elongation at break is found to be much higher for modified epoxy blend. Dynamic mechanical analysis shows an improvement in the storage modulus for bioresin toughened composites on the account stiffness imparted by fibers. Loss modulus is found to be higher for EMS modified epoxy composite because of strong fiber–matrix interfacial bonding. Loss tangent curves show a strong influence of bioresin on damping behavior of epoxy composite. Strong fiber–matrix interface is found in modified epoxy composite by scanning electron microscopic analysis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42699.     

Effects of novolac resin modification on mechanical properties of carbon fiber/epoxy composites

The epoxy resin matrix of carbon fiber (CF)‐reinforced epoxy composites was modified with novolac resin (NR) to improve the matrix‐dominated mechanical properties of composites. Flexural strength, interlaminar shear strength (ILSS), and impact strength were measured with unfilled, 7 wt% NR, 13 wt% NR, and 18 wt% NR filled to epoxy to identify the effect of adding NR on the mechanical properties of composites. The results showed that both interfacial and impact properties of composites were improved except for flexural property. The largest improvement in ILSS and impact strength were obtained with 13 wt% loading of NR. ILSS and impact strength were improved by 7.3% and 38.6%, respectively, compared with the composite without NR. The fracture and surface morphologies of the composite specimens were characterized by scanning electron microscopy. Intimate bonding of the fibers and the matrix was evident with the content of 7–13 wt% NR range. Decrease of crosslinking density and formation of NR transition layer were deduced with adding NR. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Hybridization effect of cellulose paper and postcuring conditions on the mechanical properties of flax fiber reinforced epoxy biocomposite

An ever-increasing rise in demand for sustainable materials has received significant attention in developing biocomposites for structural applications. In this regard, natural fibers replacing synthetic fibers as reinforcement in epoxy composite could be a significant gain toward sustainability, especially in automobile and structural applications. Herein, flax fiber/cellulose paper–reinforced epoxy biocomposite (FREC-X) was fabricated via a vacuum infusion process. The influence of postcuring conditions (time and temperature) and cellulose paper density on the mechanical properties of FREC-X was studied. The tensile strength and modulus of FREC-X increased by 37% and 64%, respectively, upon the integration of paper. Postcuring FREC-X further augmented the tensile and flexural properties of the composite, which could be attributed to the increase in cross-linking of the epoxy and yields a strong polymer network. Fractography analysis confirmed that the composites integrated with paper showed fewer defects with improved interfacial adhesion. In addition, the water absorption and thickness swelling results revealed that the presence of cellulose paper marginally increased the water uptake and thickness swelling of FREC-X. Furthermore, there was no significant change in the tensile and flexural properties of FREC-X observed even after immersing in water for >200 h. Such properties of FREC-X seen as a fascinating alternative to synthetic fibers and petroleum-based epoxy and are promising material for sustainable development.     

Unsaturated polyester‐toughened epoxy composites: Effect of sisal fiber on thermal and dynamic mechanical properties

In the present study, the mechanical and thermal properties of sisal fiber‐reinforced unsaturated polyester (UP)‐toughened epoxy composites were investigated. The sisal fibers were chemically treated with alkali (NaOH) and silane solutions in order to improve the interfacial interaction between fibers and matrix. The chemical composition of resins and fibers was identified by using Fourier‐transform infrared spectroscopy. The UP‐toughened epoxy blends were obtained by mixing UP (5, 10, and 15 wt%) into the epoxy resin. The fiber‐reinforced composites were prepared by incorporating sisal fibers (10, 20, and 30 wt%) within the optimized UP‐toughened epoxy blend. Scanning electron microscopy was used to analyze the morphological changes of the fibers and the adhesion between the fibers and the UP‐toughened epoxy system. The results showed that the tensile and flexural strength of (alkali‐silane)‐treated fiber (30 wt%) ‐reinforced composites increased by 83% and 55%, respectively, as compared with that of UP‐toughened epoxy blend. Moreover, thermogravimetric analysis revealed that the (alkali‐silane)‐treated fiber and its composite exhibited higher thermal stability than the untreated and alkali‐treated fiber systems. An increase in storage modulus and glass transition temperature was observed for the UP‐toughened epoxy matrix on reinforcement with treated fibers. The water uptake behavior of both alkali and alkali‐silane‐treated fiber‐reinforced composites is found to be less as compared with the untreated fiber‐reinforced composite. J. VINYL ADDIT. TECHNOL., 23:188–199, 2017. © 2015 Society of Plastics Engineers     

Effect of Compound Surface Treatment on the Performance of Poly(butylene succinate)/Chemithermomechanical Pulp Fiber Composites

Chemithermomechanical pulp fiber was pretreated by alkali solution to alter the surface characteristics of fibers. The untreated and treated fibers were used to prepare poly(butylene succinate)/chemithermomechanical pulp fiber composites with or without the incorporation of cellulose fatty acid ester (hydroxyethyl cellulose lauric acid ester). X-ray photoelectron spectrum analysis shows that the O/C ratio on the fiber surface increased after alkali treatment, indicating that part of lignin was removed during alkali treatment process. Scanning electron microcopy images indicate that the fiber surface was changed to rough after alkali treatment. The modification effect of hydroxyethyl cellulose lauric acid ester reflects as the improvement of fiber order in matrix, together with the enhancement of interfacial bonding, whereas, the modification effect of alkali treatment is mainly due to the enhancement of interfacial bonding. The integrated mechanical properties of composite prepared by alkali-treated fibers are superior to those of composite prepared by hydroxyethyl cellulose lauric acid ester-treated fibers. The combination of these two modification methods favors the enhancement of tensile and impact strengths of composite. However, in comparison with the composite prepared only by alkali treatment, the flexural strength and modulus would be despaired in a certain degree. When fibers were alkali treated, the shear viscosity of composite exhibited a larger increase, whereas the shear viscosity of composite prepared fibers with hydroxyethyl cellulose lauric acid ester treatment exhibits a slight decrease.     

Thermal and mechanical characterization of EVA/banana fiber-derived cellulose composites

Composite films based on poly(ethylene-co-vinyl acetate) (EVA) and cellulose derived from banana plant waste have been prepared and characterized. Cellulose whiskers isolated from, banana fibers, by an acid hydrolysis method and were incorporated into the EVA matrix by solution casting technique. The composite films were subsequently examined by scanning electron microscopy, thermogravimetry, differential scanning calorimetry, and FTIR spectroscopy. Compared with pure EVA and cellulose, the EVA/cellulose composite systems showed superior thermal stability. The mechanical testing of the composite films revealed that the tensile strength and elastic modulus were increased after cellulose incorporation into EVA. Among the EVA/cellulose composites, 7.5% cellulose loaded EVA showed the highest tensile strength. The percentage strain at break of the EVA/cellulose composite systems was found to be decreased which has been attributed to the restricted mobility of the polymer matrix by the presence of cellulose. X-ray diffraction studies showed that the EVA/cellulose composites were more crystalline than EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

环氧树脂对玻璃纤维/水泥复合材料界面性能的影响

在细观单纤维拔出实验基础上,利用ANSYS有限元程序,结合生死单元方法,对环氧树脂接枝处理的玻璃纤维/水泥基复合材料纤维拔出行为进行数值模拟,获得了界面理想结合/界面非理想结合下的拔出荷载-位移曲线。讨论了环氧树脂光滑接枝与粗糙接枝对玻璃纤维/水泥基复合材料界面强度的影响,研究表明,环氧树脂接枝不仅具有良好的界面结合性,还具有良好的机械嵌合性。     

Mechanical properties of carbon fiber composites modified with graphene oxide in the interphase

The surface topographies of carbon fibers treated by sizing agents with different graphene oxide (GO) content were investigated by scanning electron microscopy. The surface elements compositions of carbon fibers were determined by X‐ray photoelectron spectrometer. The interfacial properties of composites were studied by interfacial shear strength. The thermo‐mechanical properties of two typical specimens (CF‐G0 and CF‐G1 composites) were investigated by dynamic mechanical thermal analysis. The results showed the introduction of GO sheets on carbon fibers surfaces effectively improved the mechanical properties of carbon fibers/epoxy composites. POLYM. COMPOS., 38:2425–2432, 2017. © 2016 Society of Plastics Engineers     

Influences of liquid elastomer additive on the behavior of short glass fiber reinforced epoxy

In this study, improvements in mechanical and thermal behavior of short glass fiber (GF) reinforced diglycidyl ether of bisphenol-A (DGEBA) based epoxy with hydroxyl terminated polybutadiene (HTPB) modification have been studied. A silane coupling agent (SCA) with a rubber reactive group was also used to improve the interfacial adhesion between glass fibers and an epoxy matrix. 10, 20, and 30 wt% GF reinforced composite specimens were prepared with and without silane coupling agent treatment of fibers and also HTPB modification of epoxy mixture. In the ruber modified specimens, hardener and HTPB were premixed and left at room temperature for 1 hr before epoxy addition. In order to observe the effects of short glass fiber reinforcement of epoxy matrix, silane treatment of fiber surfaces, and also rubber modification of epoxy on the mechanical behavior of specimens, tension and impact tests were performed. The fracture surfaces and thermal behavior of all specimens were examined by scanning electron microscope (SEM), and dynamic mechanical analysis (DMA), respectively. It can be concluded that increasing the short GF content increased the tensile and impact strengths of the specimens. Moreover, the surface treatment of GFs with SCA and HTPB modification of epoxy improved the mechanical properties because of the strong interaction between fibers, epoxy, and rubber. SEM studies showed that use of SCA improved interfacial bonding between the glass fibers and the epoxy matrix. Moreover, it was found that HTPB domains having relatively round shapes formed in the matrix. These rubber domains led to improved strength and toughness, due mainly to the “rubber toughening” effect in the brittle epoxy matrix.