Moisture absorption and wet-adhesion properties of resin transfer molded (RTM) composites containing elastomer-coated glass fibers

Transient water sorption studies were carried out at constant temperature (45 °C) to assess the hydrolytic stability and wet-adhesion properties of glass fiber/epoxy composites having different sizings. Lower effective diffusivity values correlated with improved overall mechanical performance in relation to the control (unsized) samples, and revealed the importance of changing the surface energy characteristics of glass fibers by using distinctively hydrophobic pure polymers. Admicellar polystyrene and styrene-isoprene coatings formed over the inorganic reinforcement appear to create an interface with much higher resistance to moisture attack than the organosilane/matrix interface in composites with commercial sizing. This fact was corroborated by comparing their effectiveness in property retention, which showed the mechanical property (e.g. ultimate tensile strength, stiffness and interlaminar shear strength) increased with respect to the uncoated composites in the dry state as well as after water saturation. Poor wet-adhesion properties of commercial sizings in humid conditions could perhaps be attributed to higher contents of inert material present in these coatings. Fractography analysis was consistent with the previous observations regarding catastrophic failure in composites without coating, and suggested that interfacial debonding, extensive fiber pullout and matrix crazing were the major contributors to the overall failure mechanism. Failed surfaces of both commercial and elastomer-coated composites also showed areas with fiber pullout, but in this case, matrix residues remained on the fiber surfaces, yielding a much rougher appearance. Good fiber-matrix adhesion, particularly in admicellar-coated composites, was also revealed by the presence of hackles and more tortuous failure paths.     

Evaluation of fiber surfaces treatment and sizing on the shear and transverse tensile strengths of carbon fiber-reinforced thermoset and thermoplastic matrix composites

The mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is especially true for maximizing the strength of unidirectional composites in off-axis directions. The materials of interest in this study were PAN-based carbon fibers (XA and A4) used in combination with a thermoset (EPON 828 epoxy) and a thermoplastic (liquid crystal poymer) matrix. The effect of surface treatment and sizing were evaluated by measuring the short-beam shear (SBS) and transverse flexural (TF) tensile strengths of unidirectional composites. Results indicated that fiber surface treatment improves the shear and trasverse tensile strengths for both thermosetting and thermoplastic matrix/carbon fiber-reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing treated fibers for the epoxy composites. Scanning electron microscope photomicrographs were used to determine the location of composite failure, relative to the fiber-matrix interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transeverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are limited by the LCP matrix shear and transverse tensile strengths, respectively.     

Influence of different glass fiber sizings on selected mechanical properties of PET/glass composites

The properties of fiber-reinforced plastics are considerably influenced by fiber-matrix interaction. The aim of this study was to investigate the influence of glass fiber surface treatments on the morphology of poly(ethylene terephthalate) (PET) and on selected mechanical properties of unidirectional PET/glass fiber composites. The materials used here were E-glass fibers treated with model sizings including aminosilane as a coupling agent and polyurethane and epoxy resin dispersions as film formers and PET as the matrix. For identification of the degree of crystallinity of the PET matrix, differential scanning calorimetry (DSC) was used. To study the influence of the different sizings on the mechanical properties, the following tests were performed: interlaminar and intralaminar shear tests and a transverse tensile test. Dynamic-mechanical analysis (DMA) was used to characterize the behavior of the composites under dynamical load. The DSC results show that the overall crystallinity and the melting behavior of the PET matrix were hardly influenced by the glass fiber surface treatments used. The various strength properties of the composites are influenced not only by the silane coupling agent, but also by the type of film former. With an epoxy resin dispersion, the mechanical properties were enhanced compared with a polyurethane dispersion. These results were confirmed by characterization of the composites by DMA.     

Evaluation of surface treatments for glass fibers in composite materials

The thermomechanical stability of a number of organosilane surface treatments for glass fibers was evaluated for use in a fiber reinforced epoxy resin. All of the silane coatings were found to improve the tensile strength of E-glass filaments, particularly at large gauge lengths. A phenylamino silane and an amino silane were particularly effective in this regard. The fiber/matrix interface was evaluated as a function of temperature and after exposure to boiling water using a single-fiber composite test. All silane coatings transmitted a higher interfacial shear stress than obtained in composites with no coatings, and in all cases the shear stress transmission was considerably higher than would be expected from the yield properties of the resin. Measurements of the glass transition temperature of the epoxy resin, as well as Fourier-Transform Infra-Red analysis, indicated modification of resin properties in a zone around the glass fibers. Each of the silane coatings provided more stable thermomechanical properties than those obtained with uncoated glass, at least until the silanes were irreversibly degraded by boiling water. A phenylamino silane provided the most thermally stable properties. Finally, unidirectional E-glass fiber reinforced laminae were fabricated and the measured values of longitudinal strength were compared favorably to theoretical predictions.     

Influence of plasma treatment on properties of ramie fiber and the reinforced composites

In this research, 9 series of ramie fibers were treated under low-temperature plasma with diverse output powers and treatment times. By analysis of the surface energy and adhesion power with epoxy resin, 3 groups as well as control group were chosen as reinforced fibers of composites. The influences of these parameters on the ramie fiber and its composites such as topography and mechanical properties were tested by scanning electron microscopy (SEM), atomic force microscopy (AFM), tensile property and fragmentation test of single-fiber composites. Contact angle and surface free energy results indicated that with the increased treatment times and output powers, surface energy and adhesion work with epoxy resin improved. Compared with the untreated fibers, surface energy and adhesion work with epoxy resin grew 124.5 and 59.1% after 3 min-200 w treatment. SEM and AFM showed low temperature plasma treatment etched the surface of ramie fiber to enhance the coherence between fiber and resin, consequently fiber was not easy to pull-out. After 3 min-200 w treatment, tensile strength of ramie fiber was 253.8 MPa, it had about 30.5% more than that of untreated fiber reinforced composite. Interface shear stress was complicated which was affected by properties of fiber, resin and interface. Fragmentation test showed biggest interface shear stress achieved 17.2 MPa, which represented a 54.0% increase over untreated fiber reinforced composites.     

高能辐照对国产芳纶纤维/环氧复合材料界面性能影响

芳纶纤维因其表面惰性、光滑使其与树脂浸润性差,界面结合强度低。以环氧氯丙烷为介质1,采用60Coγ-射线辐照方法对国产芳纶纤维进行表面改性,以界面剪切强度（IFSS）和层间剪切强度（ILSS）表征芳纶/环氧复合材料界面结合性能。结果表明在400kGy辐照剂量下改性效果最好;经高能辐照处理的芳纶纤维表面能升高,并失去了原有的光滑表面,且纤维表面氧含量有大幅度提高,使得纤维表面活性增大。     

玻纤浸润剂组分对环氧基复合材料界面性能的影响

通过测定复合材料NOL环层间剪切强度,研究了增强型玻纤浸润剂中常用的几类成膜剂、润滑剂对玻纤增强环氧基复合材料界面层剪性能的影响。聚酯、环氧、聚氨酯成膜剂种类中,用于玻璃纤维增强环氧树脂基复合材料时,环氧成膜剂的复合材料界面性能最佳;不论干润滑剂,还是湿润滑剂,其复合材料的界面性能均较成膜剂弱,阳离子酰胺类润滑剂相对其他润滑剂略好。     

酸处理MWNTs对PBO／环氧界面性能的影响

多壁碳纳米管经过强氧化性酸的处理后,经XPS表征结果得出表面含有羧基的碳纳米管（MWNTs—COOH）。MWNTs—COOH经过超声处理后放入4,6-二氨基间苯二酚和对苯二甲酸的多聚磷酸体系中,原位聚合得到MWNTs—COOH／聚对苯撑苯并双嗯唑（PBO）复合材料,经液晶纺丝得到MWNTs—COOH／PBO纤维。用纤维界面分析仪测试MWNTs—COOH的加入对PBO纤维／环氧树脂界面剪切强度的影响。通过SEM和AFM对纤维的表面形貌进行观察,可看出MWNTs—COOH的加入改善了PBO与环氧树脂的界面强度。     

Effects of polyhedral oligomeric silsesquioxane coatings on the interface and impact properties of carbon‐fiber/polyarylacetylene composites

Two kinds of polyhedral oligomeric silsesquioxane (POSS) coatings were used for the modification of the interface in carbon fiber (CF) reinforced polyarylacetylene (PAA) matrix composites. The effects of the organic–inorganic hybrid POSS coatings on the properties of the composites were studied with short‐beam‐bending, microdebonding, and impact tests. The interlaminar shear strength and interfacial shear strength showed that the POSS coatings resulted in an interfacial property improvement for the CF/PAA composites in comparison with the untreated ones. The impact‐test results implied that the impact properties of the POSS‐coating‐treated composites were improved. The stiffness of the interface created by the POSS coatings was larger than that of the fiber and matrix in the CF/PAA composites according to the force‐modulation‐mode atomic force microscopy test results. The rigid POSS interlayer in the composites enhanced the interfacial mechanical properties with a simultaneous improvement of the impact properties; this was an interesting phenomenon in the composite‐interface modification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5202–5211, 2006     

Foreword

The effect of surface treatments and fiber sizings on the stress transfer characteristics and composite properties of AS-4 carbon/epoxy materials has been determined. Fiber surface chemistry was systematically varied from acidic to basic with RF glow discharge plasmas of CO₂ and NH₃ and characterized with ESCA techniques. Sizings applied to some of the treated fibers consisted of diglycidyl ether of bisphenol-A(DGEBA). Single fiber tension tests were used to measure the interfacial shear strength of samples made with DGEBA/metaphenylene diamine resin. Short beam shear and transverse flexure tests were used to examine the composite properties of modified materials.

Results showed that the plasma treatments were effective in altering the surface chemistry of the fiber but that changes in surface chemistry had surprisingly little effect on the critical stress transfer length. Sizing had a more significant effect on the transfer length. The interlaminar shear strength of the composites were unaffected by the treatments. Transverse flexure tests were more sensitive to the changes in surface characteristics. The work indicates that the interface properties of AS-4 fibers are close to optimal but that improvements in composite performance are possible through interphase formation.     

纳米TiO2对环氧树脂及碳纤维增强复合材料力学性能的影响

利用超声波技术将纳米TiO2在环氧树脂中进行分散,考察了纳米TiO2含量对环氧树脂及碳纤维/环氧复合材料力学性能的影响。研究表明,纳米TiO2可对环氧树脂固化物同时起到增韧增强的作用,冲击断口形貌显示为典型的韧性断裂。同时纳米粒子的加入可改善碳纤维和树脂基体的界面粘结性能,提高复合材料的层间剪切强度。     

Studies on surface energetics of glass fabrics in an unsaturated polyester matrix system: Effect of sizing treatment on glass fabrics

The surfaces of glass fibers were sized by polyvinyl alcohol (PVA), polyester, and epoxy resin types in order to improve the mechanical interfacial properties of fibers in the unsaturated polyester matrix. The surface energetics of the glass fibers sized were investigated in terms of contact angle measurements using the wicking method based on the Washburn equation, with deionized water and diiodomethane as the wetting liquids. In addition, the mechanical behaviors of the composites were studied in the context of the interlaminar shear strength (ILSS), critical stress intensity factor (K_IC), and flexural measurements. Different evolutions of the London dispersive and specific (or polar) components of the surface free energy of glass fibers were observed after different sizing treatments. The experimental result of the total surface free energies calculated from the sum of their two components showed the highest value in the epoxy‐sized glass fibers. From the measurements of mechanical properties of composites, it was observed that the sizing treatment on fibers could improve the fiber–matrix interfacial adhesion, resulting in improved final mechanical behaviors, a result of the effect of the enhanced total surface free energy of glass fibers in a composite system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1439–1445, 2001     

Surface energetics of carbon fibers and its effects on the mechanical performance of CF/EP composites

To exploit the reinforcement potential of the fibers in advanced composites, it is necessary to reach a deeper understanding on the interrelations between fiber surface chemical and energetic characteristics, wetting properties, and mechanical performance. In this study CF/EP was chosen as a model thermoset composite material, whereby a hot-curing epoxy (EP) system served as the matrix. The fibers selected were PAN-based high-tenacity carbon fibers (CF) of varying surface treatment level and/or coating. Surface free energies for the carbon fibers were determined by dynamic contact angle measurements in a variety of test liquids of known polar and dispersive surface tension utilizing a micro-Wilhelmy wetting balance and following the methods proposed by Zisman and Owens and Wendt, respectively. Surface treatment resulted in an increase of the polar fraction of the fiber surface free energy, whereas its dispersive part remained unaffected. The interfacial shear strength (IFSS) as determined in the microdroplet pull-off test was enhanced both by intensification of the surface treatment and sizing the CF with an EP component. A linear relationship between IFSS and the polar fraction of the fiber surface free energy γ^p_s was found. Further attempts were made to find correlations between surface free energy of the CF and laminate strengths measured in shear and transverse tension. © 1996 John Wiley & Sons, Inc.     

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.     

The effect of surface treatments on the mechanical properties of basalt‐reinforced epoxy composites

Basalt fiber is an emerging alternative reinforcement to glass or carbon depending upon the application. An important contributing parameter to ultimate performance of any composite is the fiber–‐matrix interface, to which toughness and compressive strength are intimately related. To better understand this matrix fiber interaction in controlling properties, we compared different modification strategies and the impact upon the properties of composites. Strategies focussing upon mechanical interlocking through increased surface roughness and covalent chemical bonding using sol/get methods were explored. Combined methods were also used to explore synergistic behavior as well as the use of aliphatic triethylenetetramine (TETA) to react with any covalently attached epoxy groups. Results from single ply composites showed that when the properties were fiber or fiber/matrix dominated, the sol/gel or epoxy silane method gave the largest improvement in ultimate tensile strength increasing 66% and 27% for uni‐weave 0° and 45° laminas. The combined surface modification methods exhibited increases of 45% and 13% for the same laminas. When properties were matrix dominated, the combined strategies produced the highest improvements in ultimate tensile strength of about 55% compared with 37% for sol/gel modification. For 16‐ply plain weave laminates, epoxy silane surface treatments produced the greatest improvements in compressive and interlaminar shear strengths, increasing 52% and 21%, respectively. This correlated with fiber‐ and fiber/matrix‐dominated results from single ply laminas. The combined treatment using TETA however decreased shear and compressive strength by about 20%, while scanning electron microscopy (SEM) evaluation and dynamic mechanical thermal analysis (DMTA) attributed this to increased resin ductility and plasticization. © 2013 Society of Plastics Engineers     

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     

表面处理对玻纤/碳纤增强橡胶基密封复合材料性能的影响

采用压延成张工艺制备碳纤维和玻璃纤维混杂增强非石棉橡胶基密封复合材料(NAFC),以横向抗拉强度作为表征混杂增强橡胶基密封材料中纤维与橡胶界面粘结性能的指标.通过扫描电镜(SEM)对材料横向拉伸试样断口进行形貌分析,及对材料的耐油、耐酸、耐碱性能进行测试,探讨了不同表面处理工艺对纤维与基体界面粘结效果的影响.研究结果表明,对玻璃纤维采用偶联剂KH-550浸渍后涂覆环氧树脂涂层,对碳纤维在空气氧化后涂覆环氧树脂涂层,可有效增强纤维、基体的界面粘结,所制得的混杂纤维增强复合材料具有较好的机械性能和耐介质性能.     

Fabrication of thermally conductive composite with surface modified boron nitride by epoxy wetting method

Boron nitride (BN) particles fabricated with different surface treatments were used to prepare thermally conductive polymer composites by epoxy wetting. The polar functionality present on the BN particles allowed the permeation of the epoxy resin because of a secondary interaction, which allowed the fabrication of a composite containing high filler concentration. The different cohesive energy densities of the synthesized material due to a functional-group-induced surface treatment effect on surface free energy and wettability determined the thermal and mechanical properties of the polymer. The results indicate that surface-curing agents interrupt the interaction between the filler and matrix, and do not always enhance thermal conductivity. Moreover, the composites showed maximum thermal conductivity at 30 wt% epoxy loading when the fixed-pore volume fraction reached in the filtrated BN film. The measured storage modulus was also enhanced by surface treatment because of the sufficient interface produced and interaction between the large amount of the filler and epoxy.     

Nanoscale toughening of carbon fiber‐reinforced epoxy composites through different surface treatments

Interests in improving poor interfacial adhesion in carbon fiber‐reinforced polymer (CFRP) composites has always been a hotspot. In this work, four physicochemical surface treatments for enhancing fiber/matrix adhesion are conducted on carbon fibers (CFs) including acid oxidation, sizing coating, silane coupling, and graphene oxide (GO) deposition. The surface characteristics of CFs are investigated by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, interfacial shear strength, and interlaminar shear strength. The results showed that GO deposition can remarkably promote fiber/matrix bonding due to improved surface reactivity and irregularity. In comparison, epoxy sizing and acid oxidation afford enhancement of IFSS owing to effective molecular chemical contact and interlocking forces between the fiber and the matrix. Besides, limited covalent bonds between silane coupling and epoxy matrix cannot make up for the negative effects of excessive smoothness of modified CFs, endowing them inferior mechanical properties. Based on these results, three micro‐strengthening mechanisms are proposed to broadly categorize the interphase micro‐configuration of CFRP composite, namely, “Etching” “Coating”, and “Grafting” modifications, demonstrating that proper treatments should be chosen for combining optimum interfacial properties in CFRP composites. POLYM. ENG. SCI., 59:625–632, 2019. © 2018 Society of Plastics Engineers     

Permeability and mechanical property correlation of bio based epoxy reinforced with unidirectional sisal fiber mat through vacuum infusion molding technique

The present investigation is focused to study the permeability of natural fiber during vacuum infusion (VI) process and the effect of the surface treatments of natural fiber, fiber loading direction, resin flow direction and process parameter on the tensile properties of developed composites (sisal/bio based epoxy). The bio based resin exhibits good flow characteristics in NaOH and isocyanate treated fibers which may be attributed to change in polarity. The surface treatments appear to provide an appreciable enhancement in tensile strength through enhanced bonding between fiber and matrix. The longitudinal tensile strength has been found to be higher than that of the transverse direction and the flow along the fiber provides maximum tensile strength. It has also been demonstrated that VI process provides improved mechanical properties as compared to hand‐layup process. Morphological studies of fractured developed composites were performed by scanning electron microscopy (SEM) to understand the de‐bonding of fiber/matrix adhesion. POLYM. COMPOS., 38:2192–2200, 2017. © 2015 Society of Plastics Engineers