Effects of roughness on interfacial performances of silica glass and non-polar polyarylacetylene resin composites

The influence of roughness on interfacial performances of silica glass/polyarylacetylene resin composites was investigated. In order to obtain different roughness, silica glass surface was abraded by different grits of abrasives and its topography was observed by scanning electron microscopy and atomic force microscopy. At the same time, the failure mechanisms of composites were analyzed by fracture morphologies and the interfacial adhesion was evaluated by shear strength test. The results indicated that shear strength of silica glass/polyarylacetylene resin composites firstly increased and then decreased with the surface roughness of silica glass increased. The best surface roughness range of silica glass was 40-60 nm. The main mechanism for the improvement of the interfacial adhesion was physical interlocking at the interface.     

Enhancing the interfacial strength of glass/epoxy composites using ZnO nanowires

This paper investigated the application of ZnO nanowires (ZnO NW) to enhance the interfacial strength of glass/epoxy composites. ZnO NW were grown on glass fibers by hydrothermal method, tensile properties of bare and ZnO NW coated fibers were measured by single fiber tensile testing, wettability of fiber with resin was studied by contact angle measurements and finally the interfacial strength and mechanisms were determined by single fiber fragmentation testing of glass/epoxy composites. The surface coverage of ZnO NW on glass fibers was fairly uniform without formation of major clusters. The coating of ZnO NW slightly reduced the tensile strength and improved the tensile modulus of fibers. Wettability tests showed reduction in contact angles for ZnO NW coated fibers because of enhanced wetting and infiltration of epoxy resin into nanowires. In fragmentation testing of microcomposites, smaller and concentrated interfacial debonding zones for ZnO NW coated fibers indicated good stress transfer and strong interfacial adhesion. A new form of crossed and closely spaced stress patterns were observed for nanowires of high aspect ratios. The interfacial strength of ZnO NW coated fibers increased by at least 109% and by 430% on average, which was attributed to the increased surface area and mechanical interlocking provided by ZnO NW.     

Surface Modification of Ultrahigh-molecular-weight Polyethylene Fibers with Coupling Agent during Extraction Process

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated with a coupling agent following the extraction of gel fibers, resulting in modified fibers after subsequent ultra-drawing. The structure and morphology of the modified UHMWPE fibers were characterized and their surface wetting, interfacial adhesion, and mechanical properties were investigated. It was found that the coupling agent was absorbed into the UHMWPE fiber and trapped on the fiber surface. Compared with unmodified UHMWPE fibers, the modified fibers had smaller contact angle, higher crystallinity, and smaller crystal size. The interfacial adhesion and mechanical properties of UHMWPE fibers were significantly improved with increasing coupling agent concentration and gradually reached a plateau value. After treatment with 1.5 wt% solution of a silane coupling agent (γ -aminopropyl triethoxysilane, SCA-KH-550), the interfacial shear strength of the UHMWPE-fiber/epoxy composites was increased by 108% and the tensile strength and modulus of modified UHMWPE fibers were increased by 11% and 37% respectively.     

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.     

Influence of interfacial reaction on interfacial performance of carbon fiber and polyarylacetylene resin composites

The influence of interfacial reaction on interfacial performance of carbon fiber/polyarylacetylene resin composites was studied. For this purpose, vinyltrimethoxysilane containing a double bond was grafted onto the carbon fiber surface to react with the triple bond of polyarylacetylene resin. The reaction between polyarylacetylene resin and vinyltrimethoxysilane was proved by reference to the model reaction between phenylacetylene and vinyltrimethoxysilane. Surface chemical analysis by XPS, surface energy determination from the dynamic contact angle, and the interfacial adhesion in composites was evaluated by interfacial shear strength test as well. It was found that vinyltrimethoxysilane, which can react with polyarylacetylene resin, had been grafted onto the carbon fiber surface. Furthermore, because the reaction between polyarylacetylene resin and vinyltrimethoxysilane took place at the interface, the interfacial adhesion in composites was significantly increased, and the improvement of interfacial adhesion was all attributed to the interfacial reaction.     

Interface and its effect on the interlaminate shear strength of novel glass fiber/hyperbranched polysiloxane modified maleimide-triazine resin composites

Interface is the key topic of developing advanced fiber reinforced polymeric composites. Novel advanced glass woven fabric (GF) reinforced composites, coded as GF/mBT, were prepared, of which the matrix resin was hyperbranched polysiloxane (HBPSi) modified maleimide-triazine (mBT) resin. The influence of the composition of the matrix on the interfacial nature of the GF/mBT composites were studied and compared with that of the composite based on GF and BT resin using contact angle, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and dielectric properties over wide frequency and temperature ranges. Results show that the interfacial nature of the composites is dependent on the chemistries of the matrices, mBT matrices have better interfacial adhesion with GF than BT resin owing to the formation of chemical and hydrogen bonds between mBT resin and GF; while in the case of mBT resins, the content of HBPSi also plays an important role on the interfacial feature and thus the macro-performance. Specifically, with increasing the content of HBPSi in the matrix, the interlaminate shear strength of corresponding composites significantly improves, demonstrating that better interfacial adhesion guarantees outstanding integrated properties of the resultant composites.     

Influence of Grafting Density of Diblock Copolymers on Interfacial Assembly Behavior and Interfacial Shear Strength of Glass Fiber/Polystyrene Composites

To investigate the influence of the grafting density and the molecular structure of block copolymers on the interfacial assembly behavior and interfacial shear strength, macromolecular coupling agents, hydroxyl-terminated poly(n-butyl acrylate-b-styrene) (HO-P(BA-b-S)) were synthesized by atom transfer radical polymerization, and then chemically anchored on the glass fiber surfaces to form a well-defined monolayer. The phase separation and 'hemispherical' domain morphologies of diblock copolymer brushes at the polystyrene/glass fiber interface were observed. The interfacial assembly morphology differs with changes in the grafting density of diblock copolymers. When the grafting density is greatest, the highest height difference of the hemispherical domain and the largest surface roughness are achieved, as well as the best interface shear strength. It was also found that the copolymer brush with a PBA block of the polymerization degree (Xn) about 77 is the optimal option for the interfacial adhesion of PS/GF composites. Thus, the grafting density and molecular structure of diblock copolymers determines the interfacial assembly behavior of copolymer brushes, and therefore the interfacial shear strength.     

Characterization of the surface and the interphase of PVC-copper amine-treated wood composites

Contact angles and surface energy of wood, as well as interfacial shear strength between wood and polyvinyl chloride (PVC) were investigated and used to monitor the modifications generated on the surfaces of wood treated with a copper ethanolamine solution. An increase in surface energy of wood after treatments promotes wetting of PVC on wood surfaces. Improved interfacial shear strength between treated wood and PVC matrix can be attributed to the formation of a stronger wood-PVC interphase. This suggests that treatment may be used to improve the adhesion between wood surface and PVC in the formulation of wood fiber composites to yield products with enhanced mechanical properties and better biological and physical performance against decay and insect destroying wood.     

Fiber-matrix adhesion mechanism of pitch-based carbon fiber composites

The fiber-matrix adhesion mechanism in high modulus pitch-based carbon fiber-epoxy matrix composites has been studied. The surface morphology and chemistry of the carbon fibers were examined by microscopic (SEM, STM), thermodynamic and spectroscopic (XPS, Raman) techniques. The interlaminar shear strength and transverse tensile strength of the composites made from surface-treated and untreated fibers were also obtained. In the microscopic analysis, there was no difference in the surface roughness between the surface-treated and untreated fibers. In the thermodynamic and spectroscopic analyses, surface treatment of the carbon fibers increased the amount of surface oxygen. The results indicated that the major role of the surface treatment on the carbon fiber-epoxy resin adhesion is not the mechanical interlocking effect by the surface roughness. The formation of surface oxygen-containing functional groups is assumed to account for the increase in fiber-matrix interfacial adhesion.     

Tensile properties of styrene-butadiene rubber/silica composites with mercapto functional silane coupling agents: influences of loading method and alkoxy group number

The influences of alkoxy group number and loading method of silane coupling agents on the mechanical properties of a styrene-butadiene rubber/silica composite were investigated. Mercapto functional silane coupling agents with dialkoxy and trialkoxy structures were used. The pre-treatment method and the integral blend method were compared. Both the fracture stress and modulus at 200% strain were higher in the pre-treatment than in the integral blend for dialkoxy type composites. However, they were higher in the integral blend than in the pre-treatment for trialkoxy-type composites. The interaction between the silane chains on the silica surface and the rubber molecular chains at the interfacial region was estimated by ¹H pulse nuclear magnetic resonance spectroscopy using an unvulcanized silica/rubber mixture. It was found that the binding of rubber molecular chains by the silane chains was higher in the pre-treatment system for dialkoxy-type composites, whereas it was higher in the integral blend for trialkoxy-type composites. The reason is proposed as follows: in the pre-treatment for dialkoxy type, a linear silane chain formed in the case of multi-layer coverage. The silane chain entangled with the rubber chain in the interfacial region and improved the reinforcement effect. For the trialkoxy type, a network structure formed using the pre-treatment method, lowering the amount of entanglement. However, in the integral blend for trialkoxy type, the formation of the silane network and the entanglement progressed simultaneously during the preparation process. A well-entangled interfacial region was formed.     

Weibull analysis of microbond shear strength at sisal fibre–polyester resin interfaces

An analysis has been made of the tensile strength of sisal fibres and the interfacial adhesion between fibres and polyester resin droplets. Density and microscopy methods were used to determine the cross-sectional area of the sisal fibres. The average tensile strength of treated sisal fibres decreased by a modest amount following treatment with 0.06 M NaOH. However, this treatment resulted in a substantial increase in the interfacial shear strength at the sisal fibre to polyester resin interface. Weibull analysis has been used successfully to analyse variability in tensile strengths and interfacial shear strength using probability of failure plots. Scanning electron microscopy has revealed the shape of resin droplets on the surface of treated and untreated sisal fibres and contact angles are much lower for droplets on treated fibres. Damage to the surface of fibres has been examined following shear testing. Weibull analysis is an effective tool for characterising highly variable fibre properties and evaluating the level of adhesion between polymer resin and the fibre surface.     

A Fiber-Bundle Pull-out Test for Surface-Modified Glass Fibers in GF/Polyester Composite

The development of high-performance polymer composites is tightly bound with the functional surface modification of reinforcements. A new method, based on the principle of the fiber-bundle pull-out test, is proposed to analyze the interfacial properties between the long fibers in the form of a bundle and the polymer matrix. Specimen geometry and a test fixture were designed using finite element analysis. The method was verified for unsized and sized glass fibers embedded in polyester resin to demonstrate its applicability for a wide range of adhesion between fibers and the polymer matrix. The pull-out test can be used for a relative comparison of different surface modifications if the bundle geometry is unknown. The results of high reproducibility and sensitivity for interfacial properties make the method attractive.     

Effect of the molecular weight of sizing agent on the surface of carbon fibres and interface of its composites

The influence of different molecular weight sizing agent on the performances of carbon fibres and carbon fibres composites were studied. Three different kinds of molecular weight sizing were used. Surface composition of the fibres modified with aqueous sizing and topographies of carbon fibres surface were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscope (SEM). The interlaminar shear strength and hygrothermal ageing test have been used to study the effect of fibres coatings on the adhesion of surface. The results of the study indicate that the molecular weight of sizing agent has an important influence to the carbon fibres and carbon fibres composites. The high and low molecular weight sizing agent decreased the interfacial shear strengths and hygrothermal ageing of carbon fibres composite. The moderate molecular weight of sizing agent showed an improvement of the interfacial adhesion and hygrothermal ageing.     

Interfacial adhesion and micro-failure phenomena in multi-fiber micro-composites using fragmentation test

Statistical fragments and micro-failure modes in the multi-fiber-reinforced micro-composites were investigated by fragmentation test. The specimen consisted of three fibers using carbon fibers (CFs) and glass fibers (GFs), embedded in the epoxy resin with three-dimensional arrangement. Fracture morphology and micro-failure behavior from the progressive fragmentation of fibers and fiber/matrix interfacial adhesion were observed via polarized-light microscope. The interfacial shear strength of CF/epoxy micro-composites is higher than that of the GF/epoxy micro-composites measured by the single fiber fragmentation test. The results show that fragment number on monofilament demonstrates obvious differences between multi-fiber and single fiber systems, and the location of the breakpoint is determined by the CFs that fracture firstly, indicating clustering fracture modes. This is because stress concentration around the breakpoints influences the stress redistribution on the adjacent fibers. Distinct micro-failure modes were observed in three-fiber and the hybrid systems, where matrix cracks around the CFs and interfacial debonding occurs around the GFs. The mixture of CFs and GFs demonstrates distinctive hybrid effect by the changes of the fragment number and initial fracture strain of fibers in hybrid systems.     

Friction and Wear Behaviors of Surface-Modified Carbon Fabric/Epoxy Resin Composites

Carbon fabric (CF) was pretreated by air-plasma bombardment and then further modified by deposition of polydopamine on the surface of the pretreated CF. Epoxy resin composites reinforced by unmodified or surface-modified carbon fabric were fabricated. The friction and wear behaviors of the resulting composites were evaluated in a ring-on-block contact mode. The flexural strength and Rockwell hardness of the composites were also evaluated. The morphologies of the worn surfaces of the unmodified and modified composites were analyzed by scanning electron microscopy. The surface treatment increased the surface roughness and changed the surface topography of the CF, which contributed to enhancing the interfacial adhesion of the composites and thus improved the mechanical properties and tribo-performance. The friction and wear properties of both the unfilled and filled composites were highly dependent on the load and sliding velocity. Moreover, the results were supplemented with scanning electron micrographs to help understand the possible wear mechanisms.     

Lignocellulosic composites with grafted polystyrene interfaces

The effects of surface grafting of a polymer onto lignocellulosic fiber surface and processing methods on both the interfacial interactions and the resulting composite properties of the fiber-reinforced thermoplastic composites were investigated. Chemithermomechanical pulp (CTMP) wood fiber was used as a reinforcement, which has been chemically modified by radical polymer grafting of styrene onto the fiber surfaces. The chemically modified CTMP fiber was then compounded with polystyrene (PS). Two different processing methods, both compression and injection moldings, were performed to prepare the wood-fiber-reinforced composites. Experimental results showed that surface modification of wood fiber leads to an obvious increase in mechanical properties of the fiber-reinforced composites as compared to the untreated fiber composites. The enhancement of mechanical properties is much greater through injection molding compared with compression molding owing to occurrence of orientation, and better mixing and interaction between the fiber and the matrix by injection molding. An improvement in fiber wetting properties and adhesion by the matrix was observed through scanning electron microscopy for the surface grafted fiber reinforced composites. Untreated wood fiber exhibited a smooth surface without adhered polymer, indicating poor adhesion, while polymer attached to the surface was seen on treated cellulose fiber due to the higher fiber-matrix interactions.     

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.     

Determination of interfacial material constants in plain glass woven fabric composites using finite element analysis

Numerical analysis with the finite element method (FEM) was used in order to identify interfacial material constants of plain glass woven fabric composites under mode I loading. Relations between strength, stress intensity factor, and modulus in the interphase which were correlated with the onset of unstable fracture were determined. As a result, it was reasonable that the interfacial moduli were between 2.8 and 8.4 GPa which corresponds to one to three times the resin modulus. It was suggested that the increase of concentration of silane coupling agent has led to an increase of the interfacial strength. Changing of fracture mechanisms from unstable to stable crack propagations was explained through the interfacial material constants.     

Influence of SiC Electron Acceptor–Donor Modification on Thermal and Physical Properties of Carbon Fiber/SiC/Epoxy Composites

In this work, the effects of electron acceptor–donor modification on the surface properties of SiC were investigated in the mechanical interfacial properties of carbon fibers-reinforced SiC-impregnated epoxy matrix composites. The surface properties of the SiC were determined according to acid/base values and FT-IR, and contact angle measurements. The thermal and mechanical interfacial properties of the composites were evaluated using a thermogravimetric analysis, critical strain energy release rate mode II (G _IIC), and impact strength testing. As a result, the electron acceptor-treated SiC had a higher acid value and polar component in surface free energy than did the untreated SiC or the electron donor-treated SiC. The G _IIC and impact strength mechanical interfacial properties of the composites had been improved in the specimens treated by acidic solutions due to the good wetting and a high degree of adhesion with electron donor characteristic epoxy resins.     

The effect of interface on fracture mechanism of GF/PP composites using O2 plasma treatment

Polypropylene sheets are treated with oxygen plasma for the interfacial control of GF/PP composites. The interfacial strength between glass fabric and PP resin is estimated by the T-peel test method. The evaluation of T-peel test data is done by both the T-peel strength method and the T-peel amplitude method. The T-peel strength value and T-peel amplitude value were respectively increased to about 50% and 120% compared with each value of non-treated specimens. The T-peel strength relates to the surface energy on the PP-sheet and the T-peel amplitude relates to the fracture pattern of the delamination surface. From SEM observations on the delamination surface, many voids in the space enclosed with fiber bundles are observed in the case of non-treated specimen and no void and fiber bridging are observed on the plasma treated specimens. It is found that interfacial properties between fiber and resin are improved by this plasma process.