Plasma‐graft polymerization of vinyl monomer with an acid amide group onto a surface of carbon fiber and its adhesion to epoxy resin

The mechanical properties of a fiber‐reinforced plastic are influenced by the adhesion between a reinforced fiber and a matrix resin. In this work it is shown how to obtain strong adhesion between a carbon yarn and an epoxy resin through the formation of covalent bonds. Acid amide groups reactive with epoxy groups were introduced onto a surface of the yarn by means of plasma‐graft polymerization of acrylamide. The density of active radicals formed on a surface of the yarn by the plasma irradiation was first increased with increasing discharge power and plasma irradiation time, and then the rates of the increase were largely decreased. The degree of grafting was linearly increased with increasing the surface density of active radicals. The yarn embedded in diglycidyl ether of bisphenol‐A/triethylenetetramine mixture was pulled out to obtain pull‐out force after curing. Pull‐out force was increased with increasing degree of grafting and the failure in pulling out of the yarn was cohesive. The covalent bonds formed in the graft layer will result in an increment of pull‐out force. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 284–290, 2000     

Plasma‐graft polymerization of a monomer with double bonds onto the surface of carbon fiber and its adhesion to a vinyl ester resin

Double bonds reactive with active radical species were introduced onto the surface of carbon yarn by the plasma‐graft polymerization of adipic acid divinyl ester and ethylene glycol dimethacrylate monomers to increase the adhesive strength in the interface between the carbon yarn and a vinyl ester resin. The degree of grafting increased with increasing polymerization time and polymerization temperature. The degree of grafting depended on both the solvent and the monomer species used in the polymerization, and a high degree was obtained with ethylene glycol dimethacrylate as the conjugated monomer and in a mixture of methyl isobutyrate and water. The grafted yarn, whose surface layer contained double bonds, was reacted with a vinyl ester resin containing benzoyl peroxide and N,N‐dimethylaniline. The pull‐out force of the yarn embedded in the resin increased with increasing degree of grafting. The failure in pulling out the yarn was cohesive. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2415–2419, 2003     

Waterborne oil‐modified polyurethane coatings via hybrid miniemulsion polymerization

As part of a wider effort to develop a new class of waterborne coatings, hybrid miniemulsion polymerization was carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of oil‐modified polyurethane resin. Latexes with different ratios of resin to acrylic monomers were synthesized. The monomer emulsions prepared for hybrid miniemulsion polymerization showed excellent shelf‐life stability (>5 months) and the polymerization was run free of coagulation. Solvent extraction indicated that the grafting efficiency of polyacrylics was greater than 29% for all the samples produced. A ¹³C solution NMR spectrum showed that a substantial fraction of the original carbon double bonds (>61%) in oil‐modified polyurethane remained after polymerization for film curing. Films obtained from the latexes presented good adhesion properties and fair hardness properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 105–114, 2000     

Grafting acrylate functionalities at the surface of carbon fibers to improve adhesion strength in carbon fiber–acrylate composites cured by electron beam

Acrylate functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix cured by electron beam. An isocyanate bearing aliphatic urethane acrylate was used as a coupling agent. As revealed by X-ray photoelectron spectroscopy, the isocyanate groups reacted with carboxylic acids and hydroxyl groups located at the surface of the fiber, leading to a covalent bonding of the acrylate groups. The adhesion strength was measured by a micromechanical test derived from the pull-out test. A significant improvement of the interfacial shear strength was obtained (+91%) with an electron beam curing. For comparison, an isothermal cure by UV was also investigated and led to the same level of adhesion strength. The improvement was also proved by an increase in the 90° flexural strength of unidirectional composites (+38%). Grafting functionalities that were compatible with the radical mechanism of the polymerization of the matrix appeared to be a promising strategy for the improvement of the mechanical properties of carbon fiber–acrylate composites cured by electron beam.     

Chain-extended bismaleimides. II. A study of chain-extended bismaleimides as matrix elements in carbon fiber composites

A series of chain-extended bismalemide resins as matrix elements in carbon fibers were cured and characterized in terms of their thermal and thermomechanical properties. The cured resins were stable up to 430°C and EDABMI/MDA has the highest T^g value and the lowest loss modulus value. To understand the compatibility and the degree of adhesion between the resin and the fiber, their surface properties were determined in terms of the surface energy component and single-fiber pull-out tests. The surfaces of the resins were found to have a basic character. The resins containing ether groups have a higher degree of basicity than does the resin containing methylene groups. Similarly, an increasing trend in the interlaminar shear strength (ILSS) and the work of adhesion values were observed with the increasing number of the ether groups in the resin structure. © 1996 John Wiley & Sons, Inc.     

Surface and interface characterization of untreated and SMA Imide-treated hemp fiber/acrylic composites

The hydrophilic nature of natural fibers adversely affects adhesion to a hydrophobic matrix, and consequently it may unfavorably influence the strength of the composite. Therefore, modifying the fiber or the matrix is essential to obtain optimum composite properties. In this work, hemp fibers were modified applying a paper sizing technique using SMA Imide resin (copolymer of styrene and dimethylaminopropylamine maleimide) as a surface modifying agent. The performance of the hemp/acrylic composite was improved significantly using the treated fibers. Inverse gas chromatography (IGC) and pull-out test were employed to study the hemp fiber/matrix interface and the surface characteristics of untreated and treated hemp fibers. The IGC results demonstrated that treated fibers had slightly higher dispersive force compared with untreated fibers. Moreover, modification of fibers with SMA Imide resin slightly decreased the basic character and significantly increased the acid character of hemp fibers. From the pull-out test, the average stress to pull the SMA-treated fibers out was 71% higher than that calculated for untreated fibers. The higher interfacial strength for the treated fibers shows that the SMA treatment had a beneficial influence on the adhesion of the acrylic resin to the hemp fibers. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Dispersion, interfacial interaction and re-agglomeration of functionalized carbon nanotubes in epoxy composites

The surface, interfacial and dispersion properties of carbon nanotubes (CNTs), and the mechanical properties of the CNT/epoxy composites affected by CNT functionalization are investigated. It is demonstrated that there exists strong correlations between amino-functionalization, dispersion, wettability, interfacial interaction and re-agglomeration behaviour of CNTs and the corresponding mechanical and thermo-mechanical properties of CNT/epoxy composites. The amino-functionalized CNTs exhibit higher surface energy and much better wettability with epoxy resin than the pristine CNTs, and the attached amine molecules arising from the functionalization effectively inhibit the re-agglomeration of CNTs during the curing of resin. These ameliorating effects along with improved interfacial adhesion between the matrix and functionalized CNTs through covalent bonds result in improved flexural and thermo-mechanical properties compared with those without functionalization.     

Synthesis and characterization of tall oil fatty acids-based alkyd resins and alkyd–acrylate copolymers

The polymerization and properties of environmentally friendly waterborne binders for wood coatings were studied. Conjugated and non-conjugated tall oil fatty acids-based alkyd resins were synthesized and further copolymerized via miniemulsion polymerization with acrylates (butyl acrylate and methyl methacrylate). The ratio between alkyd resin and acrylate monomers was varied and the effect on copolymerization and the copolymer binder properties, such as particle size, molecular weight, grafting of acrylate to alkyd resin and reaction of double bonds, were studied. It was observed that the use of MMA influenced on the degree of grafting of acrylate and monomer conversion because the steric hindrances prevent MMA to react with alkyd double bonds as eagerly as BA. The increasing amount of alkyd resin was noticed to decrease the polymerization rate. The research showed that it was possible to prepare stable hybrids, alkyd–acrylate copolymers, with varied chemical composition.     

Effects of compaction and UV exposure on performance of acrylate/glass‐fiber composites cured layer by layer

With an aim to reducing manufacturing costs, in general and specifically to provide a solution to the thick laminate curing depth issue for composite materials, UV curing technology was combined with a fiber placement process to fabricate acrylate/glass‐fiber composites. A novel layer‐by‐layer UV in situ curing method was employed in this article and interlaminar shear strength (ILSS) tests and SEM were used to evaluate the effect of processing parameters, including compaction force and UV exposure dose, on ILSS. The SEM images from short‐beam strength test samples and the results of ILSS showed that the fibers' distribution was uniform in the cured matrix resin resulting from the compaction forces and that beneficially influenced the ILSS of the composite greatly. However, the matrix resin produced large shrinkage stresses when it reached a high degree of conversion (DC) in one‐step, which resulted in poor interlaminar adhesion. In addition, the fast curing speed of UV on the composite resulted in poor wetting between fiber and resin, and accordingly resulted in lower ILSS. To overcome these problems and obtain high ILSS value composites, an optimized compaction force and UV exposure dose were determined experimentally. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of naphthyl curing agent having thermally stable structure on properties of UV-cured pressure sensitive adhesive

Pressure sensitive adhesives (PSAs) with higher thermal stability were synthesized by crosslinking acrylic copolymer with naphthyl curing agent. The acrylic copolymer was synthesized for a base resin of PSAs by solution polymerization of 2-ethylhexyl acrylate, ethyl acrylate, and acrylic acid with N,N′-azobisisobutyronitrile as an initiator. The acrylic copolymer was further modified with glycidyl methacrylate to have the vinyl groups available for UV curing. Thermal stability of acrylic PSAs was improved noticeably with increasing naphthyl curing agent content and UV dose mainly due to the extensive formation of crosslinked structure in the polymer matrix. Although the peel strength decreased with UV curing of acrylic polymer, a proper balance between the thermal stability and the adhesion performance of PSAs was obtained by controlling the UV curing with naphthyl curing agent content and UV dose.     

Experimental characterization of interfacial adhesion of an optical fiber embedded in a composite material

The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material. The present paper reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A simple system composed of optical fibers embedded in an epoxy vinylester resin was first studied to evaluate the influence of embedded length, curing temperature and curing time. Pull-out tests on optical fibers bonded in epoxy vinylester/glass fiber composite material were carried out to measure the effect of glass concentration on the fiber bonding. The pull-out results showed no effect of both embedded length and curing temperature. However, an increase of the interfacial debonding stress is reported with increased curing time. For the optical fiber/composite system, a linear evolution of interfacial debonding stress with increasing glass fiber concentration is reported.     

Effect of PVC on low-polar isobutylene polymerization in the presence of BCl3

Summary The low-polar polymerization of isobutylene (IB) in the presence of BCI₃ was carried out in CH₂Cl₂ ([IB]=7 mol/l) at -78, -20 and +20°C in the presence of vinyl chloride/2-chloropropene (VC/2CP) copolymer, representing PVC resin enriched in structures with chlorine atoms bonded to the tertiary carbons. The polymerization products consist of mixtures of polyisobutylenes (PIB) and grafted VC/2CP-g-PIB copolymer. Attention was focused on evaluation of the extent of the grafting reaction. VC/2CP-g-PIB was analyzed by GPC, ¹H-NMR and ¹³C-NMR spectroscopies and elemental analysis. The results obtained indicate that the rate of polymerization of IB decreases with increasing temperature but that the grafting efficiency increases. The experiments demonstrated that the VC/2CP copolymer induces strong grafting, compared with PVC, and that it might therefore be assumed that the C-Cl bonds with chlorine atoms bound to tertiary carbons directly initiate the polymerization of IB. The effect of the C-Cl bonds is discussed in terms of their catalytic and initiation activities.     

Photoinitiated surface grafting of synthetic fibers,I. Photoinitiated surface grafting of ultra high strength polyethylene fibers

Photoinitiated surface grafting of acrylic monomers has been carried out onto high strength polyethylene (HSPE) yarn by means of a continuous process. The grafting reaction is initiated by UV irradiation of the yarn after presoaking in an acetone solution of initiator and monomer. Four initiators, benzophenone (BP), 4-chlorobenzophenone (4-CBP), 2-hydroxy-2-cyclohexylacetophenone (HHA), and 2,2-dimethoxy-2-phenylacetophenone (DMPA), and two monomers, acrylic acid (AA) and acrylamide (AM), have been used. After short irradiation time (10 to 20 s) successful grafting is obtained, as shown by ESCA and IR-ATR spectra, dye adsorpotion from aqueous solution, and measurements of adhesion of single filaments to epoxy resin. Grafting efficiency of 74% has been reached for AA as monomer (26% is homopolymer). The tensile strength and modulus of the HSPE yarn are retained in the grafting process. The degree of surface grafting is mainly a function of structure and concentration of monomer and photoinitiator in the presoaking solution and of the irradiation conditions used. Increasing irradiation time gives increasing amounts of grafted polymer up to a certain limiting value. The reactivities of the four initiators have been compared showing the highest grafting yields of AA with BP and of AM with 4-CBP as photoinitiator. AA grafted HSPE yarn can be dyed to rather deep color by dipping in an aqueous solution of Crystal Violet. Increased dye absorption by a factor of up to seven has been measured for yarn grafted with AA to the maximum level obtained. The filaments of the grafted yarn show increased adhesion to epoxy resin by a factor of up to five compared with the ungrafted filaments.     

Curing of epoxy resin by ultrafine silica modified by grafting of hyperbranched polyamidoamine using dendrimer synthesis methodology

Hyperbranched polyamidoamine–grafted silica was prepared according to dendrimer synthesis methodology. The modified silica was dispersed uniformly in epoxy resin, and the curing of epoxy resin proceeded successfully by heating in the presence of the modified silica; the gel fraction of the epoxy resin cured by the hyperbranched polyamidoamine–grafted silica (grafting = 80.2%) reached 77% at 170°C after 48 h. The gel fraction increased with increasing terminal amino group content of the hyperbranched polyamidoamine–grafted silica. In addition, the curing ability of the silica increased by complexation of the terminal amino groups of the grafted polyamidoamine with boron trifluoride. The modulus of elasticity of the curing materials obtained using the modified silica as a curing agent was lower than that using conventional a curing agent such as ethylenediamine in the presence of untreated silica. On the other hand, the heat resistance of the curing product using the modified silica was superior to that using ethylenediamine, but no difference in glass‐transition temperature was observed. It is expected that hyperbranched polyamidoamine grafted‐silica is incorporated uniformly with chemical bonds in the matrix of the epoxy resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 573–579, 2001     

Modification of epoxy resin by polysulfone to improve the interfacial and mechanical properties in glass fibre composites. II. Adhesion of the epoxy-polysulfone matrices to glass fibres

Adhesion of epoxy-polysulfone (PSF) matrices to glass fibres of 12–30 μm in diameter was studied under both quasi-static and cyclic loadings. A pull-out technique was used for adhesion measurement. It was shown that incorporation of PSF into epoxy resin changed its adhesion to fibres. A maximum was observed in the adhesion strength vs. PSF content dependence at 10 wt% thermoplastic concentration. The results obtained were compared with the data on the epoxy-PSF matrices adhesion to thick steel wire (d = 150 μm) and Nylon-6 fibres (d = 250 μm). Similar values of the adhesion strength increase (22–25%) confirmed that all the changes at the interface were connected primarily with the matrix. A new preferably non-destructive cyclic loading technique was used to test the systems under cyclic loading at varying force amplitudes, frequencies and displacement amplitudes. In this technique the interphase behaviour is characterised by two variables: by the phase angle between the deformation applied to the matrix and the force transferred by the matrix to the fibre, and also by the amplitude of this force. Minimal force amplitudes were observed for the joints with 10 wt% polysulfone. Moreover, phase-angle values for epoxy-10% polysulfone joints were minimal among all the systems investigated. Increase in the number of loading cycles caused much more damage to unmodified epoxy matrix than that to epoxy-polysulfone matrices. Thus, modification of epoxy resin by polysulfone enhanced its adhesion to fibres under both quasistatic and cyclic loadings, especially for epoxy-10% polysulfone matrix. The possible mechanism of the phenomenon observed is discussed.     

接枝型水性环氧树脂乳液的合成与粘接性能研究

以过氧化苯甲酰为引发剂,丙烯酸为接枝单体,按自由基接枝聚合机理制得稳定的环氧树脂乳液。考查了环氧树脂分子质量、引发剂用量、丙烯酸用量、温度、时间对反应的影响,利用红外光谱对接枝产物的结构进行了表征。通过粘接性能测试,考查了不同固化温度和固化时间对乳液粘接性能的影响。实验结果表明,在环氧树脂上接枝了强亲水性基团-COOH,乳液稳定性较好,粘接力较高。     

Investigation of the Properties of Phthalocyanine Resin Containing Bismaleimide Groups

A bisphthalonitrile monomer containing bismaleimide groups was synthesized using 4,4′-bismaleimidodiphenylmethane and 4-aminophenoxyphthalonitrile. The structure of the monomer was confirmed by elemental analysis and IR spectroscopy. With this monomer, a phthalocyanine resin containing bismaleimide groups was obtained by catalytic thermal polymerization. The structure of the resin was confirmed by IR spectroscopy. The characteristic absorption peak of nitrile groups at 2200cm^-1 disappeared in the IR spectra, showing that polymerization of monomer was complete. Thermogravimetry of the resin in air and N₂ was investigated; the results show that this resin has excellent thermal and thermo-oxidative stabilities, and a high char yield in nitrogen (82·7%). In addition, a monomer solution in dimethylacetamide was flow-coated on a glass strip to form a resin film. The adhesion between film and glass strip was firm, and the resin film had strong resistance to saturated alkali solution. A solubility test showed that the resin possessed good chemical inertness. Copper and aluminium strips were bonded using monomer solution. The single-lap shear strength of samples was tested after curing. The results demonstrated that the adhesion between resin and copper strips was stronger than with aluminium strips. The resin can be used as a heat-resistant adhesive. © of SCI.     

Surface modification of Kevlar® fiber by a combination of plasma treatment and coupling agent treatment for silicone rubber composite

To improve the adhesion between poly(p-phenylene terephthalamide), PPTA, fiber and silicone rubber, the surface modification of PPTA was investigated. Combining plasma treatment and coupling agent treatment with the silicone adhesive was found to be effective in improving adhesion. The combination process made the pull-out force of the PPTA yarn/silicone rubber composite 2.5 times higher, compared with the plasma treatment or the coupling agent treatment alone. The plasma treatment led to the elimination of carbonized layer from the PPTA yarn surface and the formation of oxygen functionalities including C-O and C=O groups. The elimination of the carbonaceous deposits from the PPTA surface and the interaction between the silicone adhesive and the oxygen functionalities created by the plasma treatment contribute to the improvement of adhesion with silicone rubber.     

Graft polymerization of methyl methacrylate onto nylon 6 using pentavalent vanadium as initiator

Pentavalent vanadium ion (V^v)-induced graft polymerization of methyl methacrylate onto nylon 6 was investigated under a variety of conditions. Increasing the V^v-concentration up to 2 mmol/l was accompanied by an enhancement in grafting; the latter was not affected by further increase in V^v-concentration. Unlike grafting, the homopolymer and total conversion tended to increase by increasing V^v concentration. The graft yield enhanced significantly when the MMA-concentration was increased up to 3% further increase in MMA-concentration had no effect on grafting. Raising the polymerization temperature from 50° up to 70°C caused a significant increase in the rates of grafting, homopolymerization and total conversion. Using a solvent-water mixture as medium for polymerization affected considerably the magnitude of grafting. While using methyl alcohol, ethyl alcohol and acetone at any ratio in the solvent-water mixture resulted in decreased grafting, using an isopropyl alcohol-water mixture up to a ratio of 25 : 75 gave rise to increased grafting.     

Fiber-Matrix Interfacial Adhesion Improvement in Carbon Fiber-Bisphenol-A Polycarbonate Composites by Polymer Grafting

Fiber-matrix interfacial adhesion in thermoplastic composites is generally poor due to the lack of formation of strong covalent and/or ionic bonds between the generally inert thermoplastic resins and the surface of the reinforcing fiber. Adhesion can be improved by forming covalent linkages between the fiber and the matrix by grafting a polymer of appropriate compatibility, molecular weight, and sufficient density onto the surface of the fiber. We have grafted low molecular weight polycarbonate and polymethyl methacrylates onto the surface of carbon fibers and measured an improvement in the level of adhesion ranging from 25% to100% over the ungrafted composites. It was also observed that the level of improvement in adhesion appears to be independent of the molecular weight of the grafted polymer. Examination of the fracture surface of these composites reveals that the failure is cohesive in the matrix for the polymer grafted fiber composites, while it is adhesive for the ungrafted composites.