Bonding Optimization on Composite Surfaces using Atmospheric Plasma Treatment

The effect of atmospheric plasma treatment (APT) on the bonding performance of a cyanate ester and an epoxy carbon fiber reinforced composite fabricated with a polyester peel ply was evaluated. A room temperature (RT) cured epoxy, an elevated temperature cured epoxy, and a cyanate ester resin, were used as the bonding adhesives. Only small increases in the carboxyl species concentration were observed for both composite systems as a function of increasing plasma treatment. Lap shear (LS) tests of the bonded composites showed that the APT resulted in a 30% strength improvement for the RT cured epoxy bonded specimens while the cyanate ester composite exhibited negligible increases due to the formation of a highly oxidized, weakly bonded ash. Contact angle measurements indicated that the temperature exposure associated with the curing of the elevated temperature adhesives also reduced the efficacy of APT. Modifications of the bonding surface of these composites by the incorporation of a plasma responsive (PR) layer resulted in significant LS improvements. After incorporating the PR layer, the improvement in adhesive strength was over 225% that of an untreated specimen and approximately 190% that of the equivalently treated unmodified system. Bond strengths correlated with corresponding increases in carboxyl concentrations after APT.     

Surface modification of aramid fibers via ammonia‐plasma treatment

In this article, aramid fibers III were surface modified using an ammonia‐plasma treatment to improve the adhesive performance and surface wettability. The surface properties of fibers before and after plasma treatment were investigated by X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle measurements. The interfacial shear strength of each aramid fibers III‐reinforced epoxy composites was studied by micro‐debonding test. The ammonia‐plasma treatment caused the significant chemical changes of aramid fibers III, introducing nitrogen‐containing polar functional groups, such as ? C? N? and ? CONH? , and improving their surface roughness, which contributed to the improvement of adhesive performance and surface wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40250.     

Effect of plasma treatment and electron beam radiations on the strength of nanofilled adhesive‐bonded joints

This investigation highlights the adhesion performance of carbon fiber‐ and glass fiber‐reinforced polyphenylene sulfide when joined by high‐performance neat epoxy adhesive and nanofilled epoxy adhesive. A significant increase in the surface energy of these materials is observed after the surface modification with atmospheric plasma treatment. An increase in surface roughness is observed after exposing the surface to plasma. Lap shear testing of untreated and plasma‐treated joints is carried out to correlate the improvement in adhesion properties with the joint strength. A considerable increase in joint strength is observed when the surfaces of these materials are modified by atmospheric pressure plasma. There is a further increase in joint strength when the composites are joined by nanofilled epoxy adhesive, and subsequent exposure to electron beam radiations results in minor increase in the joint strength. Finally, the fractured surfaces of the joints are examined and the analysis is performed. POLYM. ENG. SCI., 50:1505–1511, 2010. © 2010 Society of Plastics Engineers     

Synthesis and characterization of bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane/epoxy/glass fiber composites

Bis(4‐cyanato‐3,5‐dimethylphenyl)anisylmethane was prepared by treating CNBr with bis(4‐hydroxy‐3,5‐dimethylphenyl)anisylmethane and blended with commercial epoxy resin in different ratios and cured at 120°C for 2 h, 180°C for 1 h, and postcured at 220°C for 1 h using diamino diphenyl methane as curing agent. Castings of neat resin and blends were prepared and characterized. The composite laminates were also fabricated with glass fiber using the same composition. The tensile strength of the composites increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m², for neat epoxy resin, to 0.8615 kJ/m², for 9% cyanate ester‐modified epoxy system. The 10% weight loss temperature of pure epoxy (358°C) was increased to 390°C by the incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% in the epoxy resin increases the T_g from 143 to 147°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Simultaneous enhancements in the mechanical,thermal, and electrical performances of glass‐fiber‐reinforced cyanate ester/epoxy composites with plasma‐functionalized carbon nanotubes at different temperatures

Woven glass‐fiber‐reinforced cyanate ester/epoxy composites modified with plasma‐functionalized multiwalled carbon nanotubes (MWCNTs) were prepared. The mechanical, thermal, and electrical properties of the composites were investigated at different temperatures. The results show that the interlaminar shear strength, thermal conductivity, and electrical conductivity of the composites at room temperature and the cryogenic temperatures were enhanced simultaneously by the incorporation of MWCNTs, whereas the nonconductive behavior of the composites as electrical insulating materials was not changed. Meanwhile, the reinforcing mechanism was also examined on the basis of the microstructure of the composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41418.     

Synthesis and characterization of bis(4‐cyanato 3,5‐dimethylphenyl) naphthyl methane/epoxy/glass fiber composites

Bis(4‐cyanato 3,5‐dimethylphenyl) naphthylmethane was prepared by treating CNBr with bis(4‐hydroxy 3,5‐dimethylphenyl) naphthylmethane in the presence of triethylamine at −5 to 5°C. The dicyanate was characterized by FT‐IR and NMR techniques. The prepared dicyanate was blended with commercial epoxy resin in different ratios and cured at 120°C for 1 hr, 180°C for 1 hr, and post cured at 220°C for 1 hr using diamino diphenyl methane (DDM) as curing agent. Castings of neat resin and blends were prepared and characterized by FT‐IR technique. The morphology of the blends was evaluated by SEM analysis. The composite laminates were also fabricated from the same composition using glass fiber. The mechanical properties like tensile strength, flexural strength, and fracture toughness were measured as per ASTMD 3039, D 790, and D 5528, respectively. The tensile strength increased with increase in cyanate content (3, 6, and 9%) from 322 to 355 MPa. The fracture toughness values also increased from 0.7671 kJ/m² for neat epoxy resin to 0.8615 kJ/m² for 9% cyanate ester epoxy modified system. The thermal properties were also studied. The 10% weight loss temperature of pure epoxy is 358°C and it increased to 398°C with incorporation of cyanate ester resin. The incorporation of cyanate ester up to 9% loading level does not affect the T_g to a very great extent. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Amino‐functionalization of carbon fibers through electron‐beam irradiation technique

Amino‐functinonalized carbon fibers were achieved via electron‐beam (EB) irradiation in Diethylenetriamine (DETA) solution and triethylene tetramine (TETA) solution at 200 kGy. Different graft monomer concentrations were investigated to find the optimal concentration of each graft monomer. X‐ray photoelectron spectroscopy, scanning electron microscopy, and Raman spectroscopy were applied to investigate chemical composition and functional groups, topography and disorder degree of amino‐functionalized carbon fibers surface. Meanwhile, adsorption ability and interfacial adhesion between modified carbon fibers and epoxy resin were determined by TGA and interlaminar shear strength (ILSS). It is found that amino‐functionalized carbon fibers which had rougher and more active surface performed better adsorption ability on epoxy resin than untreated fibers. The optimal ILSS values of carbon fiber (treated with DETA and TETA) reinforced composites were 21.37 MPa and 18.28 MPa, which were much higher than that of untreated fiber reinforced composites. The comprehensive results demonstrated that in this condition, the optimal grafting concentrations of both DETA and TETA were 1.5 mol/L. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40274.     

Effect of using oxygen,carbon dioxide,and carbon monoxide as active gases in the atmospheric plasma treatment of fiber-reinforced polycyanurate composites

A study was undertaken to address the effect of using different active gases during the atmospheric plasma treatment of composite specimens for adhesive bonding. The effect of using oxygen, carbon dioxide, or carbon monoxide on the surface chemistry, morphology, and mechanical properties of cyanate ester composites was investigated. CO treatment resulted in a surface profile that could be tailored to create an oxygen/carbon ratio as high as 0.71 with a negligible degree of polymer degradation as verified by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. On the other hand, CO₂ and O₂ treatments resulted in a fairly high degree of chain scission and degradation using otherwise similar treatment conditions. However, significant bond strength improvement (>75%) over conventional abrasion surface preparation techniques was achieved for all three types of gases. XPS of CO-treated specimens showed a large increase in carbonyl species formation in comparison with the weakly bonded carbonates (ash) formed when treating the same composites with CO₂ and O₂ gas suggesting a different mechanism. These results present a method by which sensitive carbon-based, hydrophobic surfaces can be modified without damaging the underlying substrate as well as improving bond performance over conventional surface preparation methods. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of epoxy sizing of carbon‐fiber on the properties of carbon fiber/cyanate ester composites

The high modulus carbon fiber (M40J) sized by epoxy resin E51 and E20 reinforced bisphenol A dicyanate (2,2′‐bis(4‐cyanatophenyl) isopropylidene resin composite was prepared in order to investigate the influence of epoxy sizing of the fiber on the properties of the composite. Differential scanning calorimetry (DSC) and fourier transforms infrared (FTIR) analysis showed that epoxy resin have catalytic effect on cure reaction of cyanate ester. Mechanical properties of the composite revealed that M40J fiber sized by epoxy resin could improve the flexural strength and interlaminar shear strength of M40J/bisphenol A dicyanate composites. The micro‐morphology of the composite fractures was studied by means of scanning electron microscopy (SEM). Reduced flaws were observed in the M40J‐bisphenol A dicyanate interface when the sized fiber was used. Water absorption of the composites was also investigated. It was found that the water absorption descended at the initial boiling stage (12 h). POLYM. COMPOS, 27: 591–598, 2006. © 2006 Society of Plastics Engineers     

Ultraviolet surface treatment for adhesion strength improvement of carbon/epoxy composite

—As the applications of composite structures have increased, various techniques to join composite parts to the structures have been developed in order to meet the required adhesion strength. In this work, surface modification of carbon/epoxy composites was investigated using ultraviolet (UV) surface treatment to increase the adhesion strength between the carbon/epoxy composite and the epoxy adhesive. After UV surface treatment, X-ray photoelectron spectroscopy (XPS) analysis and contact angle measurements were performed to analyze the surface characteristics of the carbon/epoxy composites. From the results of XPS analyses and adhesion strength tests, it was found that the increase of C O bond density on the surface of carbon/epoxy composite caused the enhancement of adhesion strength. Also it was found that the UV-B (wavelength 280–315 nm) surface treatment resulted in a superior adhesion strength compared to the UV-A (wavelength 315–400 nm) surface treatment.     

CE/EP/CF复合材料的湿热性能研究

采用溶液预浸渍法分别制备了两种碳纤维(CF)增强环氧树脂(EP)改性氰酸酯树脂(CE)(CE/EP/CF)复合材料,研究了该复合材料的吸湿行为及湿热环境对其力学性能和微观结构的影响。结果表明,CE/EP基体具有比EP更小的吸湿能力;湿热环境对CE/EP/CF复合材料的纵向拉伸强度影响不大,但对其层间剪切强度的影响较为显著。     

Structures and properties of HMPBO fibers treated by oxygen plasma/polyhedral oligomeric silsesquioxane

The surface of high modulus poly(p‐phenylene‐2,6‐benzobisoxazole) (HMPBO) fibers were treated by the combination method of oxygen plasma/polyhedral oligomeric silsesquioxane (POSS). The chemical compositions and surface morphologies of HMPBO fibers were characterized by Fourier transform infrared, X‐ray photoelectron spectroscopy, thermogravimetric analyzer, and scanning electron microscopy. The interfacial shearing strength (IFSS) of the HMPBO/cyanate ester (HMPBO/CE) micro‐composites was measured by single fiber pull out test. Results showed that the POSS was grafted on the surface of HMPBO fibers, and the grafting amount was about 0.82 wt%. After the treatment, the HMPBO fibers became coarser and the diameter was also increased. Compared with that of pure HMPBO/CE micro‐composites, the IFSS of treated HMPBO/CE micro‐composites was increased by 20.7%. POLYM. COMPOS., 34:2026–2030, 2013. © 2013 Society of Plastics Engineers     

Investigation of optimal surface treatments for carbon/epoxy composite adhesive joints

Although an adhesive joint can distribute the load over a larger area than a mechanical joint, requires no holes, adds very little weight to the structure and has superior fatigue resistance, but it not only requires a careful surface preparation of the adherends but also is affected by service environments. In this paper, suitable conditions for surface treatments such as plasma surface treatment, mechanical abrasion, and sandblast treatment were investigated to enhance the mechanical load capabilities of carbon/epoxy composite adhesive joints. A capacitively coupled radiofrequency plasma system was used for the plasma surface treatment of carbon/epoxy composites and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the surface free energies of treated specimens. The optimal mechanical abrasion conditions with sandpapers were investigated with respect to the mesh number of sandpaper, and optimal sandblast conditions were investigated with respect to sandblast pressure and particle size by observing geometric shape changes of adherends during sandblast process. Also the failure modes of composite adhesive joints were investigated with respect to surface treatment. From the peel tests on plasma treated composite adhesive joints, it was found that all composite adhesive joints failed cohesively in the adhesive layer when the surface free energy was higher than about 40 mJ/m², because of high adhesion strength between the plasma treated surface and the adhesive. From the peel tests on mechanically abraded composite adhesive joints, it was also found that the optimal surface roughness and adhesive thickness increased as the failure load increased.     

Design,Realization, and Characterization of Advanced Adhesives for Joining Ultra‐Stable C/C Based Components

The aim of this work is to develop high‐performance adhesives to join carbon fiber reinforced composites (C/C) for use in aerospace applications; in order to guarantee sound mechanical strength, a low coefficient of thermal expansion, and ease of application on large components. Several different adhesive formulations, based on phenolic or cyanate‐ester resins (charged with the maximum experimentally feasible amount of carbon‐based fillers), are developed and tested. The measurements of the lap shear strength at room temperature of the C/C joined by means of one phenolic and one cyanate ester‐based resin demonstrates that these formulations are the most suitable for the given application. A complete characterization, by means of viscosimetry, dilatometry, and thermal gravimetric analysis, coupled with gas analysis by means of mass spectroscopy, confirms that the phenolic‐based formulation is the most promising joining material. A nano‐indenter is used to obtain its Young modulus and hardness, both inside the joint and as a bulk cured adhesive.     

The effect of surface treatment on graphite nanoplatelets used in fiber reinforced composites

Atmospheric plasma treatment (APT) was used to surface‐activate graphite nanoplatelets (GnP) as well as highly graphitic P100 fibers used to manufacture composites. X‐ray photoelectron spectroscopy showed an increase in the O/C ratio of the treated surfaces when using either CO or O₂ as the active gas, whereas CO exhibited less damage to the treated reinforcement carbon material. APT of P100 fibers resulted in a 75% increase in composite tensile strength when compared to composites using untreated fibers. Surface treatment of GnPs also resulted in GnP/epoxy composites with significantly higher glass transition temperatures (Tg's) and 50% higher flexural strengths than those with no surface treatment because of stronger particle‐to‐resin coupling, which was also evidenced by the fracture surfaces. The effect of GnP loading concentration and plasma treatment duration was also evaluated on the tensile strength of fiber‐reinforced composites. The addition of untreated GnP filler resulted in a decrease in strength up to the 1% loading. However, higher loading conditions resulted in a 20% improvement because of GnP orientation effects. Fracture surfaces suggest that the fibers provided a mechanism for the GnPs to orient themselves parallel to the fiber axis, developing an oriented matrix microstructure that contributes to added crack deflection. Incorporating surface‐treated GnPs in these composites resulted in tensile strengths that were as high as 50% stronger than the untreated systems for all loading conditions. Increased GnP‐to‐matrix bonding as well as enhanced orientation of the GnPs resulted in multifunctional composites with improved mechanical performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39994.     

Adhesive joints between carbon fiber and aluminum foam reinforced by surface‐treated aramid fibers

Short aramid fibers have been successfully used to reinforce the interface adhesive property between carbon fiber/epoxy composites and aluminum foam, and to form aramid‐fiber “composite adhesive joints.” In this study, to further improve the reinforcing effect of the aramid‐fiber‐reinforced adhesive joints, aramid fibers were ultrasonic treated to conduct different surface conditions. Critical energy release rate of the carbon fiber/aluminum foam sandwich beams with as‐received and treated interfacial aramid fibers were measured to study the influence of the surface treatment on aramid fibers. It was found that reinforcements in critical energy release rate were achieved for all samples with treated aramid fiber as measured under double cantilever beam condition. The interfacial characteristics of the short aramid fibers with different surface condition were investigated and discussed based on scanning electron microscopy observations. It is suggested that advanced bonding between aramid fibers and epoxy resin was conducted after surface treatment, and more energy was therefore absorbed through fiber bridging during crack opening and extension process. POLYM. COMPOS., 36:192–197, 2015. © 2014 Society of Plastics Engineers     

Properties of cyanate ester-cured epoxy/polyphenylene oxide blends as a matrix material for Kevlar fiber composites

Epoxy/polyphenylene oxide (PPO) blends were cured with multifunctional cyanate ester resin. The effects of the PPO content on the cure behavior in the cyanate ester-cured epoxy were investigated with Fourier transform infrared spectroscopy (FTIR). The cure reaction in the epoxy/PPO blends was faster than that of the neat epoxy system. FTIR analysis revealed that the cyanate functional group reactions were accelerated by adding PPO and that several co-reactions had occurred, such as cyanate-hydroxyl addition and epoxy-cyanate addition. This was caused by the reaction of cyanate ester with the PPO phenolic end-group and water yielding imidocarbonate and carbamate intermediate which can react with cyanate ester to form cyanurate. Then the cyanurate can react further with the epoxy resin. Thermal mechanical analysis showed that the thermal stability of the epoxy/PPO blends is improved by adding PPO. The morphology of the fiber-rich areas in the composite is different from that of the epoxy/PPO blend without Kevlar fiber. In the pure polymer blends with high PPO content (30 and 50 phr), phase separation and phase inversion were observed. In the composites, the majority of the epoxy resin migrates to the polar fiber surface, resulting in epoxy-coated fibers. So the interfacial shear strength (IFSS) between Kevlar fiber and the epoxy/PPO blends is almost the same as that between Kevlar fiber and neat epoxy. The presence of PPO does not affect the interfacial property in the epoxy/PPO/fiber composite. So the interlaminar shear strength (ILSS) increase with the PPO content is due to an increase in the composite's ductility or toughness.     

Foam sandwich composites with cyanate ester based syntactic foam as core and carbon‐cyanate ester as skin: Processing and properties

Foam sandwich composites were processed using cyanate ester‐based syntactic foam as core and carbon fabric‐cyanate ester composite as skin. They were processed by a one‐step compression‐molding technique. The mechanical performance of the sandwich composites was evaluated in terms of flatwise tensile strength (FTS), flatwise compressive strength, and edgewise compressive strength. The dependency of these properties on the core composition was investigated. FTS initially increased with the increase in resin content of the syntactic foam core. However, higher resin content in the core led to a diminution in FTS due to high void content. The flatwise compressive strength and edgewise compressive strength and the corresponding moduli values showed an increasing trend with increase in resin content of the core despite the presence of voids at high resin content. The failure modes of the composites under different loading conditions have been examined. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The effect of atmospheric‐pressure air plasma discharge power on adhesive properties of aramid fibers

After exposure to the atmospheric‐pressure air plasma at different discharge powers, the adhesion characteristics of Twaron aramid fibers were investigated. For the 12 s‐300 W plasma treatment, the interlaminar shear strength of Twaron fiber reinforced thermoplastic poly(phthalazinone ether sulfone ketone) was increased from 46.0 to 61.7 MPa by 34.1%, and the diffusion of water molecule into the resulting composites was proved to be effectively prevented. These results showed that surface adhesive properties of the plasma‐treated aramid fibers were improved. At the power level of 300 W, X‐ray photoelectron spectroscopy analysis revealed the increases in concentrations of oxygen and nitrogen polar groups on the fiber surface, and atomic force microscopy observations led to the conclusion that the fiber surface morphology was changed and the surface roughness was greatly increased. These new polar and irregular surface structures accounted for the better adhesion between the fiber and the matrix, while due to the reasonability of this discharge power level applied to the surface modification, the measured fiber tensile strength only decreased by 2.0%. POLYM. COMPOS., 37:620–626, 2016. © 2014 Society of Plastics Engineers     

耐高温改性氰酸酯发泡胶膜的制备与性能

为了满足现代高性能雷达天线罩结构粘接的要求,采用环氧树脂/氰酸酯树脂预聚物改性酚醛型氰酸酯树脂的方法,研制了耐高温改性氰酸酯发泡胶膜。通过加入贮存稳定剂T,改善了发泡胶膜的室温贮存期,室温贮存期大于15d。在380℃下的抗压强度大于1MPa。测试频率为9375MHz时,胶膜的介电常数为1.30,介电损耗tanδ为9.6×10^-4。