Improvement of the interfacial shear strength of poly(p‐phenylene benzobisoxazole) fiber/epoxy resin composite via a novel surface coating agent

Poly(p‐phenylene benzobisoxazole) (PBO) fiber with a smooth surface exhibits limited interfacial interaction with resin matrix. One of the effective strategies to improve the adhesion between the fiber and resin matrix is through surface modification of the fiber. In this study, we have proposed a novel surface treatment agent based on phosphoester cross‐linked castor oil (PCCO) for effective surface treatment of PBO fibers. The surface treatment agent was prepared by a simple cross‐linking reaction between hydroxy phosphorylated castor oil (PCO) and epoxy resin, with alcohol as the solvent at 65°C. Once the PBO fiber was treated with this agent, the interfacial adhesion between the PBO fiber and the epoxy resin could then be improved. Systematic analyses suggest that the surface treatment with (PCO + epoxy)/alcohol solution improves the interaction of the PBO fiber with the epoxy resin matrix. The PCCO coated onto the surface of PBO fiber acts as a coupling agent, improving the interfacial shear strength (IFSS) of the PBO fiber/epoxy resin composite. Results indicate a 156% increase in IFSS without compromising the mechanical properties of the fiber. POLYM. COMPOS., 37:1198–1205, 2016. © 2014 Society of Plastics Engineers     

Carbon nanotubes grafting PBO fiber: A study on the interfacial properties of epoxy composites

To improve the interfacial performance of poly[p‐phenylene benzobisoxazole] (PBO) fiber and epoxy resin, a modified multiwalled carbon nanotubes (MWCNTs‐Ecp) were used to achieve this purpose through grafting onto PBO fiber surface using a gamma ray radiation method. Experimental results indicated that the equilibrium wetting rate and equilibrium adsorption amount of the modified PBO fiber for epoxy resin and acetone were all higher than that of as received PBO fiber. The interfacial shear strength (IFSS) of single fiber composite increased from 31.4 to 77.5 MPa after modification. The fracture models of composites are changed from pure interfacial failure to combination failure of interface and resin interlayer. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

氧气低温等离子体对PBO纤维的表面改性

采用氧气低温等离子体对聚对苯撑苯并双噁唑(PBO)纤维进行表面改性,讨论了处理时间、处理功率及气压对PBO纤维单丝强度、与环氧树脂基体的界面剪切强度(π_(IFSS))、形态结构、表面元素组成和亲水性的影响。结果表明:在处理时间为2.5 min,处理功率为30 W,处理气压为50 Pa的最佳工艺条件下,经氧气等离子处理后的PBO纤维与环氧树脂的π_(IFSS)比原丝提高60%,达9.38 MPa,与水的接触角也从105°下降到72°。     

Promoting the adhesion of high‐performance polymer fibers using functional plasma polymer coatings

Plasma‐copolymerized functional coatings of acrylic acid and 1,7‐octadiene were deposited onto high strength, high modulus, poly‐p‐phenylene benzobisoxazole (PBO) fibers. X‐ray photoelectron spectroscopy (XPS) with trifluoroethanol derivatization confirmed that the PBO fibers were covered completely with the plasma copolymer and that the coating contained a quantitative concentration of carboxylic acid groups. Microdebond single filament adhesion and interlaminar shear strength (ILSS) tests were used to evaluate the interfacial strength of epoxy resin composites containing these functionalized PBO fibers. Both the interfacial shear strength (IFSS) obtained from single filament tests, and the ILSS of high volume fraction composites were a function of the surface functionality of the fibers so that there was a good correlation between ILSS and IFSS data. The tensile strengths of single fibers with or without coating were comparable, demonstrating that the fiber surface was not damaged in the plasma‐coating procedure. Indeed, the statistical analysis showed that Weibull modulus was increased. Therefore, plasma‐polymerized coatings can be used to control the interfacial bond between PBO fibers and matrix resins and act as a protective size for preserving the mechanical properties of the fibers. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The effect of silica (SiO2) nanoparticles and ammonia/ethylene plasma treatment on the interfacial and mechanical properties of carbon-fiber-reinforced epoxy composites

A nanoparticle dispersion is known to enhance the mechanical properties of a variety of polymers and resins. In this work, the effects of silica (SiO₂) nanoparticle loading (0–2 wt%) and ammonia/ethylene plasma-treated fibers on the interfacial and mechanical properties of carbon fiber–epoxy composites were characterized. Single fiber composite (SFC) tests were performed to determine the fiber/resin interfacial shear strength (IFSS). Tensile tests on pure epoxy resin specimens were also performed to quantify mechanical property changes with silica content. The results indicated that up to 2% SiO₂ nanoparticle loading had only a little effect on the mechanical properties. For untreated fibers, the IFSS was comparable for all epoxy resins. With ethylene/ammonia plasma treated fibers, specimens exhibited a substantial increase in IFSS by 2 to 3 times, independent of SiO₂ loading. The highest IFSS value obtained was 146 MPa for plasma-treated fibers. Interaction between the fiber sizing and plasma treatment may be a critical factor in this IFSS increase. The results suggest that the fiber/epoxy interface is not affected by the incorporation of up to 2% SiO₂ nanoparticles. Furthermore, the fiber surface modification through plasma treatment is an effective method to improve and control adhesion between fiber and resin.     

Surface modification of PBO fibers by argon plasma and argon plasma combined with coupling agents

The methods of argon plasma and argon plasma combined with coupling agents were employed to modify the poly[1,4‐phenylene‐cis‐benzobisoxazole] (PBO) fiber surface. The interfacial shearing strength (IFSS) of PBO fibers/epoxy resin was measured by the single fiber pull‐out test. The surface chemical structure and surface composition of PBO fibers were determined by FTIR and X‐ray photoelectron spectroscopy respectively. The morphology of the fiber surface was investigated by scanning electron microscopy and the specific surface area of the fibers was calculated by B.E.T. equation. Furthermore, the wettability of PBO fibers was confirmed by the droplet profile analysis method. The results showed that the elemental composition ratio of the fiber surface changed after the modification. The IFSS increased by 42 and 78% when the fibers were treated by argon plasma and argon plasma combined with the coupling agents, respectively. Meanwhile, the specific surface areas of the treated fibers were improved. In addition, compared with the modification of argon plasma, the modification of argon plasma combined with the coupling agents inhibited the attenuation phenomena of the IFSS and the wettability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1428–1435, 2006     

Effect of silane coupling agents on basalt fiber–epoxidized vegetable oil matrix composite materials analyzed by the single fiber fragmentation technique

The fiber–matrix interfacial shear strength (IFSS) of biobased epoxy composites reinforced with basalt fiber was investigated by the fragmentation method. Basalt fibers were modified with four different silanes, (3‐aminopropyl)trimethoxysilane, [3‐(2‐aminoethylamino)propyl]‐trimethoxysilane, trimethoxy[2‐(7‐oxabicyclo[4.1.0]hept‐3‐yl)ethyl]silane and (3‐glycidyloxypropyl)trimethoxysilane to improve the adhesion between the basalt fiber and the resin. The analysis of the fiber tensile strength results was performed in terms of statistical parameters. The tensile strength of silane‐treated basalt fiber is higher than the tensile strength of the untreated basalt fiber; this behavior may be due to flaw healing effect on the defected fiber surfaces. The IFSS results on the composites confirm that the interaction between the fiber modified with coupling agents and the bio‐based epoxy resin was much stronger than that with the untreated basalt fiber. POLYM. COMPOS., 36:1205–1212, 2015. © 2014 Society of Plastics Engineers     

Temperature effect on graphene‐filled interface between glass–carbon hybrid fibers and epoxy resin characterized by fiber‐bundle pull‐out test

The overall mechanical performance of glass–carbon hybrid fibers reinforced epoxy composites depends heavily upon fiber–matrix interfacial properties and the service temperatures. Fiber‐bundle pull‐out tests of glass (GF) and/or carbon fiber (CF) reinforced epoxy composites were carried out at room and elevated temperatures. Graphene nanoplatelets were added in the interfacial region to investigate their influence on the interfacial shear strength (IFSS). Results show that IFSS of specimens with fiber‐bundle number ratio of GF:CF = 1:2 is the largest among the hybrid composites, and a positive hybridization effect is found at elevated temperatures. IFSS of all the specimens decreases with the increasing of test temperatures, while the toughness shows a contrary tendency. As verified by scanning electron microscopy observations, graphene nanoplatelets on fiber surface could enhance the IFSS of pure glass/carbon and hybrid fibers reinforced epoxy composites at higher temperatures significantly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46263.     

Effect of Halloysite Nanotube Incorporation in Epoxy Resin and Carbon Fiber Ethylene/Ammonia Plasma Treatment on Their Interfacial Property

Abstract

Effects of halloysite nanotube (HNT) loading of up to 2% in epoxy resin on its mechanical properties were characterized. The interfacial property of the resin with carbon fiber nanocomposite was also studied. Single fiber composite (SFC) technique was used to characterize the carbon fiber/epoxy resin interfacial shear stress. Carbon fibers were also coated with ammonia/ethylene plasma polymer to obtain a thin coating of the polymer with amine groups that could react with the epoxy and thus improve the interfacial property. The results indicated that the Young’s modulus of HNT containing nanocomposites increased slightly up to a loading of 0.25% after which it started to decrease. The tensile strength, however, steadily decreased with increasing of HNT loading although the fracture strain did not change significantly. This might be related to the nanotube shape, size and clustering. The interfacial shear strength (IFSS) was also increased slightly with HNT loading. The ethylene/ammonia plasma polymer coated fibers exhibited significantly higher IFSS by over 150%, independent of the HNT loading. The highest IFSS obtained was almost 79 MPa for plasma treated fibers. The results suggest that the carbon fiber/epoxy interface is not affected by the incorporation of up to 1.5% of HNT. Furthermore, the fiber surface modification through plasma polymerization is an effective method to improve and control the IFSS.     

Improvement of interfacial adhesion between PBO fibers and cyanate ester matrix

Poly(p‐phenylene benzobisoxazole) (PBO) fibers were activated by the horseradish peroxidases (HRP) and then treated by 3‐Glycidoxypropyltrimethoxysilane (KH‐560) to improve the wettability and the interfacial adhesion between PBO fibers and cyanate ester matrix. The chemical compositions of PBO fibers were characterized and analyzed by FTIR and XPS. Surface morphologies of PBO fibers were examined by SEM. The wettability of PBO fibers was evaluated by the dynamic contact angle analysis test. The mechanical properties were evaluated by tensile strength and interfacial shear strength, respectively. The results demonstrated that hydroxyl groups and epoxy groups were introduced onto the surface of PBO fibers during the treatments. These treatments can effectively improve the wettability and adhesion of PBO fibers. The surface free energy of PBO fibers was increased from 31.1 mN/m to 55.2 mN/m, and the interfacial adhesion between PBO fiber and cyanate ester resin was improved to 10.77 MPa. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40204.     

Surface ammonification of the mutual‐irradiated aramid fibers in 1,4‐dichlorobutane for improving interfacial properties with epoxy resin

The mutual irradiated aramid fibers in 1,4‐dichlorobutane was ammoniated by ammonia/alcohol solution, in an attempt to improve the interfacial properties between aramid fibers and epoxy matrix. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), dynamic contact angle analysis (DCA), interfacial shear strength (IFSS), and single fiber tensile testing were carried out to investigate the functionalization process of aramid fibers and the interfacial properties of the composites. Experimental results showed that the fiber surface elements content changed obviously as well as the roughness through the radiation and chemical reaction. The surface energy and IFSS of aramid fibers increased distinctly after the ammonification, respectively. The amino groups generated by ammonification enhanced the interfacial adhesion of composites effectively by participating in the epoxy resin curing. Moreover, benefited by the appropriate radiation, the tensile strength of aramid fibers was not affected at all. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44924.     

Mechanical properties of carbon fiber composites modified with nano-SiO2 in the interphase

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO₂ particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO₂ particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO₂ particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO₂, respectively, when the nano-SiO₂ content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO₂ containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO₂. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO₂-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO₂ to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy.     

Improvement of adhesion of Kevlar fiber to epoxy by chemical modification

Kevlar 149 fibers were surface-modified by chlorosulfonation and subsequent reaction of -SO₂O with some reagents (e.g. glycine, water, ethylenediamine, and 2-butanol) to improve the adhesion to epoxy resin. The mechanical properties and surface topography of the modified fibers were investigated at different reaction times and reagent concentrations. The surface functional groups introduced into the surface of the fibers were identified by X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (SIMS). The interfacial shear strength (IFSS) between the fibers and epoxy resin was measured by the microbond test. The results showed that the IFSS was markedly improved (by a factor of 2.25) by the chlorosulfonation/glycine treatment and that the fiber strength was not affected. Scanning electron microscopy (SEM) was also used to study the surface topography of fibers pulled from the epoxy resin. Furthermore, energy dispersive X-ray (EDX) spectroscopy was used to qualitatively examine the amount of sulfur in the fiber surfaces and in the fracture surfaces of fibers from microbond pull-out specimens. The results of EDX examination were consistent with a change of the fracture mode from the interface between the fiber and the epoxy resin to a location within the fiber and/or epoxy resin as observed by SEM.     

微脱黏法在碳纤维/环氧树脂界面性能评价中的应用

利用微脱黏法测定碳纤维/环氧树脂复合材料的界面剪切强度,并分析了造成测试结果分散的影响因素.结果表明:在脱黏过程中,最大脱黏力随碳纤维埋人环氧树脂内长度的增加而线性递增,当埋人长度超过一定值后最大脱黏力趋于稳定:碳纤维与环氧树脂间的接触角对复合材料界面剪切强度有一定影响,接触角越大,界面剪切强度越高;测试结果的分散性与树脂微球的半月板区域、钳口区等因素有关;未经表面处理的碳纤维增强环氧树脂复合材料的界面剪切强度仪为39.4 MPa,低于处理后的复合材料(60.6 MPa).     

Covalent functionalization of carbon fiber with poly(acrylamide) by reversible addition–fragmentation chain transfer polymerization for improving carbon fiber/epoxy interface

A novel method was developed for grafting poly(acrylamide) (PAAM) on to the carbon fiber (CF) surface via reversible addition–fragmentation chain transfer (RAFT) polymerization to improve the interaction between carbon fibers and epoxy matrix in the composites system. The carbon fibers were first treated with nitric acid and γ‐methacryloxypropyltrimethoxy silane (KH570). Then, the PAAM was grafting onto the carbon fiber surface via RAFT polymerization. The resulted carbon fibers functionalized with PAAM (CF‐PAAM) were characterized by FTIR, XPS, and TGA, and the results revealed that CF‐PAAM were synthesized successfully. The introduction of PAAM chains could make the fiber surface rougher and introduce a large numbers of –NH₂ groups, which can improve the interfacial adhesion in the composites. The microbond test results showed that the interfacial shear strength (IFSS) of the composites reinforced by CF‐PAAM has been enhanced about 107%. POLYM. COMPOS., 38:27–31, 2017. © 2015 Society of Plastics Engineers     

淀粉纳米晶对玻璃纤维的表面改性研究

采用自制的淀粉纳米晶(SNC)对玻璃纤维进行表面处理,增加其与环氧树脂基体的界面剪切强度(IFSS)。研究了处理方式、处理时间、SNC乙醇分散液浓度、热处理温度等工艺参数对SNC在玻璃纤维表面沉积情况的影响,以及对改性玻璃纤维与环氧树脂的界面性能的影响规律。采用扫描电子显微镜、单纤维强力仪对处理前后玻璃纤维进行表征,并采用微脱粘法测试玻璃纤维与环氧树脂的界面粘结情况。结果表明,当重力静置处理时间24 h,SNC乙醇分散液浓度为1 g/100 m L时,SNC在玻璃纤维表面均匀沉积,且能显著提高玻璃纤维与环氧树脂的IFSS,为27.29 MPa,较未处理的纤维增加29.3%。150℃热处理4 h后,X射线光电子能谱结果显示SNC与玻璃纤维形成化学键合,进一步增加纤维与环氧树脂的界面粘结,IFSS值达到32.30 MPa,较未处理的纤维增加53%,且纤维的拉伸强度得到较好的维持。     

Properties and microstructures of epoxy resin/TiO2 and SiO2 hybrids

Epoxy resin/TiO₂ and epoxy resin/SiO₂ hybrids were prepared by different procedures, and their mechanical properties were correlated to their microstructures, as indicated by small‐angle X‐ray scattering (SAXS) measurements. Epoxy resin/TiO₂ hybrids were prepared by mixing the epoxy resin (EP828) with N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (S320) in acetone, and then titanium‐n‐butoxide (TnBU) was added. In addition, epoxy/SiO₂ hybrids were prepared by mixing EP828 with a curing agent, a diamino heterocyclic compound (B002) in acetone, and an organo silica sol (silica nanoparticles dispersed in methylethylketone) was added. In the EP828/S320/TiO₂ hybrid systems, the TiO₂ component was attached to both of the chain ends of the epoxy matrix, hence leading to the formation of inorganic domains via the covalent bonds. SAXS profiles of these hybrids showed peaks at q = 2.3 nm^?1, caused by interference between the domains. The storage modulus increased with increasing TiO₂ content above the T_g, owing to the strong interactions between TiO₂ and the epoxy matrix. The tanδ peak position did not change, although the intensity decreased with increasing TiO₂ content. The SAXS profiles of the EP828/B002/SiO₂ hybrids were very different to those of the corresponding EP828/S320/TiO₂ hybrids, and indicated that SiO₂ particles with rough surfaces were randomly dispersed in the epoxy matrix. The storage moduli of the EP828/B002/SiO₂ hybrid systems increased only slightly with SiO₂ content, because of the weak interactions. These mechanical properties are well explained by the microstructures derived from the SAXS profiles. Copyright © 2004 Society of Chemical Industry     

Effect of Atmospheric Plasma Treatment on Carbon Fiber/Epoxy Interfacial Adhesion

In this work the effect of atmospheric plasma treatment on carbon fiber has been studied. The carbon fibers were treated for 1, 3 and 5 min with a He/O₂ dielectric barrier discharge atmospheric pressure plasma. The fiber surface morphology, surface chemical composition and interfacial shear strength between the carbon fiber and epoxy resin were investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the single fiber composite fragmentation test. Compared to untreated carbon fibers, the plasma treated fiber surfaces exhibited surface morphological and surface composition changes. The fiber surfaces were found to be roughened, the oxygen content on the fiber surfaces increased, and the interfacial shear strength (IFSS) improved after the atmospheric pressure plasma treatment. The fiber strength showed no significant changes after the plasma treatment.     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effects of triethylenetetramine grafting of multi‐walled carbon nanotubes on its dispersion,filler‐matrix interfacial interaction and the thermal properties of epoxy nanocomposites

This study describes the influence of triethylenetetramine (TETA) grafting of multi‐walled carbon nanotubes (MWCNTs) on the dispersion state, interfacial interaction, and thermal properties of epoxy nanocomposites. MWCNTs were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then TETA grafting was performed. Chemically grafted MWCNT/bisphenol‐A glycidol ether epoxy resin/2‐ethyl‐4‐methylimidazole nanocomposites were prepared. TETA grafting could establish the connection of MWCNTs to the epoxy matrix and transform the smooth and nonreactive MWCNT surface into a hybrid material that possesses the characteristics of both MWCNTs and TETA, which facilitates homogeneous dispersion of MWCNTs and improves nanotube‐epoxy interfacial interaction. Therefore, the impact property, glass transition temperature, thermal stability, and thermal conductivity of epoxy nanocomposites are enhanced. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers