The effects of surface treatments of fibers on the interfacial properties in single-fiber composites

The interfacial properties between fibers and the matrix contribute to the overall properties in high performance composites. Plasma treatments (Ar, O₂, CF₄/O₂, N₂/H₂) have been performed on carbon fibers to improve the fiber-matrix interaction. The treatment efficiency was checked by the single-fiber technique, while the surface chemistry and morphology were characterized by X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS), and scanning electron microscopy (SEM). The O₂- and N₂/H₂-plasma treatments proved most effective both for introducing oxygen-containing functionalities at the fiber surface and for improving the interfacial shear strength of carbon fiber/epoxy composites. A relationship between the oxygen concentration at the fiber surface and the interfacial shear strength is demonstrated.     

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.     

Micromechanics prediction of the transverse tensilc strength of carobn fiber/epoxy composites: The influence of the matrix and interface

Currently, there is great interest in understanding and improving the bond between the fibers and matrix in high performcance composite materials. In many recently developed systems, fiber surface treatments have been developed to improve poor bonding. These treatments are often evaluated by measureing their effect on a composite property sensitive to the interfacial bond strength, typically the composite shear strength. This paper presents an evaluation of the influence of the matrix and interface properties on the transverse tensile strength. These effects were quantified by compring transverse flexural experimental data with results from a finite element micromechanics model. The results indicate that the transverse tensile strength is significantly more dependent upon sizing than is the shear strength. Finally, the transvere flexure test appears to provide an additional and complementary test for evaluating interface bond characteristics.     

Stress Transfer in Single Fiber/ Resin Tensile Tests

Microscale (25 mm gauge length) “dogbone” resin specimens with single carbon fibers embedded through the length of the specimen have been studied as a method for determining the fiber-resin interphase strength. The specimens are pulled in tension until the fiber fragments to a critical length, l_c. Evidence is presented here, based primarily on the relaxation of stress birefringence around the fiber fragment, that this test may not be an unambiguous measure of fiber-resin adhesion. Data obtained for various production lots of AS-4, AS-6, and IM-6 fibers indicate an increase in l_cd with laminate tensile strength. Although there is theoretical justification for this correlation, it requires that the interphase shear strength is relatively constant.

In those instances where interfacial adhesion was expected to be low, i.e., surface contamination or unsurface treated fiber, there was a significant increase in l_c/d and usually a distinct difference in stress birefringence compared to “good” adhesion. However, the distinction in stress birefringence was not always clear cut.     

Modification of Low-surface Energy Fibers used as Reinforcement in Cementitious Composites: A Review

This paper provides a review on the surface modification of low-surface energy fibers (polypropylene, polyethylene, and nylon) and discusses on the effects of these treatments toward the physical/mechanical properties of cement-based composite materials. These properties include the tensile, flexural, compressive strength and toughness, stress–strain behavior, modulus of elasticity, and workability. The effects of these treatments on the changes in the fiber/cement matrix interfacial properties are also presented. Studies have shown that various surface treatments have been used to improve the efficiency of the low-surface energy synthetic fibers in the cementitious composites. The modifications are on the basis of physical, chemical, and mechanical methods. The main achievements found have been the development of fibers with modified surface to optimize fiber–matrix adhesion. Moreover, the recently developed surface modifications will allow obtaining high-performance cementitious materials reinforced with the synthetic fibers.     

Plasma surface modification of carbon fibers: a review

The properties of the fiber/matrix interface in carbon fiber-reinforced composites play a dominant role in governing the overall performance of the composite materials. Understanding the surface characteristics of carbon fibers is a requirement for optimizing the fiber-matrix interfacial bond and for modifying fiber surfaces properly. Therefore, a variety of techniques for the surface treatment of carbon fibers have been developed to improve fiber-matrix adhesion as well as to enhance the processability and handling of these fibers. Many research groups have studied the effects of plasma treatments, correlating changes in surface chemistry with the interfacial shear strength. This article reviews the recent developments relative to the plasma surface modification of carbon fibers.     

苎麻纤维增强磷建筑石膏复合材料耐水性能和力学性能研究

通过吸水率、软化系数、抗折强度和抗压强度试验,并结合傅里叶红外光谱和扫描电子显微镜测试,探究不同长度和掺量的苎麻纤维对苎麻纤维增强磷建筑石膏复合材料耐水性能和力学性能的影响。研究结果表明,掺入适量苎麻纤维可改善苎麻纤维增强磷建筑石膏复合材料的耐水性能和力学性能,以及提高复合材料的延性。掺入0.5%(体积分数,下同)的10 mm苎麻纤维时,复合材料的软化系数达到最大,较空白组提高20.0%。苎麻纤维的掺入能有效提高复合材料的抗折强度,28 d时,掺入1.5%的10 mm苎麻纤维试样较空白组抗折强度提高39.5%。掺入小于20 mm的苎麻纤维会降低复合材料的抗压强度,掺入不超过1.5%的30 mm苎麻纤维可提高复合材料的抗压强度,28 d时,掺入1.5%的30 mm苎麻纤维试样较空白组抗压强度提高10.1%。苎麻纤维在复合材料基体内会发生水解,随龄期的增长水解程度加重,表面逐渐粗糙。     

Study on the mechanical properties of hybrid reinforced rigid polyurethane composite foam

The mechanical properties of hybrid reinforced rigid polyurethane (PU) foams were investigated with the reinforcing agent SiO₂ and fibers. The effect of content of SiO₂ and fibers and the effect of length of fibers on the properties of the PU composite foam were emphatically analyzed. The experiment results show that the tensile strength of the PU composite foam is optimal when the content of SiO₂ and glass fiber is 20 and 7.8%, respectively. Furthermore, the reinforcing effect of glass fiber, Nylon‐66 fiber, and PAN‐matrix carbon fiber were compared and the results show that the tensile strength of the PU composite foam reinforced with 3–5% carbon fiber is optimal. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1493–1500, 2004     

The Effect of Nitric Acid Oxidization Treatment on the Interface of Carbon Fiber-Reinforced Thermoplastic Polystyrene Composite

The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibers and the composition of the matrix. The composition of polystyrene was modified by the addition of maleic anhydride (MAH) grafted polystyrene. The surface properties of the various matrix formulations were characterised by contact angle. Carbon fibers were modified by oxidation in nitric acid. The surface composition of the carbon fibers was characterized. The interaction between modified polystyrene and the carbon fibers was studied by single fiber pull-out tests. The best adhesion behavior was achieved between polystyrene containing grafted MAH and nitric acid oxidation carbon fibers. The addition of MAH-grafted polystyrene to the unmodified polystyrene caused the interfacial shear strength to increase. The apparent interfacial shear strength of this fiber-matrix combination allowed for the utilisation of 100% of the yield tensile strength of polystyrene.     

环氧改性聚碳酸酯单向纤维复合材料研究

采用Ｅ－５１环氧树脂改性聚碳酸酯，研究其单向Ｅ－玻璃纤维、单向碳纤维Ｔ３００、Ｍ４０复合材料。结果表明，改性后的聚碳酸酯复合材料（ＰＣＣＭ）的层间剪切强度等性能明显提高，玻纤复合材料提高幅度最大。纤维－基体界面粘接良好。     

Comparative study of interlaminar fracture toughness of GFRP with different fiber surface treatments

This investigation is focused on the influence of glass fiber surface treatment on the interlaminar fracture toughness of unidrectional laminates. Three different fiber surface treatments were considered: polyethylene treated fibers to get poor adhesion, silance treated fibers to get good bond strength, and industrial fibers without special treatments with the coupling agents. The interlaminar fracture behavior of unidirectional glass fiber reinforced composites with different fiber surface treatments has been investigated in mode I, mode II, and for the fixed mixed mode I/II ratio 1.33. Double cantilever beam (DCB), end notched flexure (ENF), and mixed mode flexure (MMF) specimens were used. The data obtained from these tests were analyzed by using different analytical approaches and the finite element method. For the fibers treated with the silane coupling agent, a value about 2.5 times higher of mode II interlaminar fracture toughness for crack initiation was obtained in comparison with the polyethylene sized composite. For the composite made from the industrial fibers, a value about 2 times higher was obtained. Because of extensive fiber bridging and pullout in the composites with poor fiber/matrix adhesion, the results of mode I and mixed mode I/II tests did not characterize the interphase quality. In order to determine the interphase quality, the mode II tests are recommended.     

Effect of fiber treatment on the mechanical properties of LDPE-henequen cellulosic fiber composites

The degree of mechanical reinforcement that could be obtained by the introduction of henequen cellulosic fibers in a low-density polyethylene, LDPE, matrix was assessed experimentally. Composite materials of LDPE-henequen cellulosic fibers were prepared by mechanical mixing. The concentration of randomly oriented fibers in the composite ranged between 0 and 30% by volume. The tensile strength of these composite materials increased up to 50% compared to that of LDPE. There is also a noticeable increase in Young's modulus for the composite materials that compares favorably with that of LDPE. As expected, the addition of the fibers decreases the ultimate strain values for the composite materials. The thermal behavior of the LDPE-henequen cellulosic fibers materials, studied by differential scanning calorimetry, DSC, showed that the presence of the fibers does not affect the thermal behavior of the LDPE matrix; thus, the interaction between fiber and matrix is probably not very intimate. Preimpregnation of the cellulosic fibers in a LDPE-xylene solution and the use of a silane coupling agent results in a small increment in the mechanical properties of the composites, which is attributed to an improvement in the interface between the fibers and the matrix. The shear properties of the composites also increased with increasing fiber content and fiber surface treatment. It was also noted that the fiber surface treatment improves fiber dispersion in the matrix. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 197–207, 1997     

Effect of 60Co gamma radiation on the mechanical properties of epoxy blends and epoxy-graphite fiber interface

The effect of ⁶⁰Co gamma radiation of up to 100 Mrads on an IM6-G graphite fiber-epoxy interface was studied using the single-fiber-composite (SFC) technique. Flexible epoxy blends were formulated using diglycidylether of bisphenol-A (DGEBA) based and polyglycol diepoxide epoxies which were cured with aliphatic and aromatic curing agents. Bulk epoxy specimens and graphite fibers were tension tested to obtain their tensile properties. The fragment length distribution from SFC tests, single fiber strength data, and a Monte Carlo simulation of Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results indicate that while graphite fiber strength is not affected by radiation, the tensile properties of the epoxies used are adversely affected by the radiation. The interfacial shear strength, however, increases significantly with the radiation dose. The study also supports the earlier results of many workers that the interfacial shear strength for flexible epoxies is much higher than the shear yield strength of the epoxies.     

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     

Role of silanes in adhesion. Part II. Dynamic mechanical properties of silane-treated glass fiber/polyester composites

—Glass fiber/unsaturated polyester composites, prepared by impregnating glass braid with varying thickness coatings (from 200 Å up to 1600 Å thick) of polyester resin, were tested with a DuPont Dynamic Mechanical Analyzer. The effects of the polyester resin thickness and silane treatments on the dynamic mechanical properties of the composites were evaluated. The results are supported by Fourier transform infrared spectroscopy of the composite materials. It is shown that both the concentration and the organo-functional group of the silane coupling agent influence the damping, storage, and loss moduli as well as the glass transition temperature (T_g) of the matrix resin in the closest vicinity to the glass/resin bondline. In the absence of a silane inner layer, a low T_g, 'soft' boundary layer exists due to inhibition of the polyester resin cure by the glass surface. It is noted that a reactive silane, such as γ-methacryloxypropyltrimethoxysilane, promotes the formation of a 'soft' or 'rigid' (high T_g) boundary layer, depending on the concentration of the silane in the treating solution. On the other hand, a non-reactive silane, such as methyltrimethoxysilane, produces a 'rigid' interphase in the entire range of concentrations of the silane solution. An attempt was made to correlate the dynamic mechanical properties of the boundary layer with the fiber/polymer interfacial shear strength. Upon pretreatment of glass fibers with silane coupling agents, the relative magnitude of the loss modulus, E", and the nature of the boundary layer (T_g) seem to be better indicators of efficient stress transfer from the polymer to the glass fiber in the composite system than tan δ. Efficient stress transfer is characterized by a low value of E" and 'soft' boundary layers. The results suggest that the mere presence of glass/polyester chemical bonding is insufficient to ensure effective stress transfer. A strong bond results from the synergistic effect of glass/silane/polymer chemical bonding and a 'soft' boundary layer.     

短纤维层间增强碳纤维复合材料层板的力学研究

以斜纹3k T300碳纤维布、环氧树脂和0.3~0.5 mm短切碳纤维为主要实验原料,使用短切纤维铺放装置将短切碳纤维定量铺放在碳纤维布表面,并铺层得到5块层间短切纤维增强的预制体,每块预制体含8层碳纤维布且每块预制体层间短切碳纤维铺放面密度分别为5,10,20,30,40 g/m2,并增设一块层数为8层、层间不含短切纤维增强的预制体作为对照组。采用真空辅助树脂灌注成型方式浸渍预制体后高温固化,得到层间含不同面密度短切纤维的碳纤维复合材料层合板,研究了不同面密度短切纤维含量对碳纤维复合材料层合板拉伸、弯曲以及层间剪切强度的影响。研究结果表明,当短切碳纤维铺放面密度为5 g/m2时,复合材料层板的拉伸、弯曲强度最好,在5~40 g/m2范围内,复合材料层板的层间剪切强度随短切碳纤维铺放面密度的增大而增大。     

The Effect of Environmental Treatments on Fiber Surface Properties and Tensile Strength of Sugar Palm Fiber-Reinforced Epoxy Composites

Fiber glass has been used widely in manufacturing industries, especially marine industries, because of low cost and high strength. However, glass fiber can cause acute irritation to the skin, eyes, and upper respiratory tract. This study looked at the possibility of substituting glass fiber with natural fiber in composite materials. The surface properties of sugar palm fiber (Arenga pinnata) were modified using seawater and freshwater as treatment substances. This led to biological, chemical, and water degradation of the sugar palm fiber. Morphological and structural changes in the fibers were investigated using a scanning electron microscope (SEM). A series of tensile tests based on ASTM D638-99 was carried out on epoxy composites with 15% sugar palm fiber by volume. It was found that seawater and freshwater treatments improved the surface properties of the sugar palm fiber and thus resulted in better adhesion quality as compared to untreated fiber. An improvement in tensile strength also supported this finding. Treatment with seawater for 30 days proved to be the best, with 67.26% increase in tensile strength.     

Adhesion of Graphite Fibers to Epoxy Matrices: I. The Role of Fiber Surface Treatment

Adhesion between graphite fibers and epoxy matrices is a necessary and sometimes controlling factor in achieving optimum performance. Manufacturers' proprietary fiber surface treatments promote adhesion without providing a basic understanding of the fiber surface properties altered through their use. This study has combined fiber surface chemistry, morphology, interfacial strength measurements and fracture characterization in order to elucidate the role of surface treatments. The results of this investigation lead to the conclusion that surface treatments designed to promote adhesion to epoxy matrix materials operate through a two-part mechanism. First, the treatments remove a weak outer fiber layer initially present on the fiber. Second surface chemical groups are added which increase the interaction with the matrix. Increases in fiber surface area are not an important factor in promoting fiber-matrix adhesion. In some cases the upper limit to fiber-matrix interfacial shear strength is the intrinsic shear strength of the fiber itself.     

电子束辐射接枝对PAN基碳纤维的表面改性

采用电子束加速器辐射接枝方法对聚丙烯腈(PAN)基碳纤维进行表面改性,研究了接枝单体种类对接枝率及其环氧树脂基复合材料力学性能的影响,分析了辐射接枝前后PAN基碳纤维的表面形貌与化学结构以及其复合材料界面断口的形貌变化。结果表明:电子束辐射接枝改性的PAN基碳纤维表面粗糙度增加,表面活性官能团增多,与树脂的机械锲合作用增强,其树脂基复合材料断口表而较为平整;乙二胺/水溶液体系是辐射接枝改性的理想溶液,在200 kGy的电子束辐射下,PAN基碳纤维表面的接枝率为6.66%,复合材料的层间剪切强度提高了45.1%。     

Effect of surface treatment of ramie fiber on the interfacial adhesion of ramie/acetylated epoxidized soybean oil (AESO) green composite

Recently, many researchers have attempted to convert soybean oil into useful polymers. One of the ways to make soybean oil into a matrix of green composites is to modify its triglyceride structure to obtain the acrylated epoxidized soybean oil (AESO) through epoxidization and acrylation. In this study, the effects of ramie fiber surface treatments such as acetylation, silane, and peroxide treatments on the chemical, morphological, and interfacial adhesion properties of a ramie/AESO green composite were studied. Surface-treated fibers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and dynamic contact angle analysis. The crystallinity and thermal stability of chemically treated fibers were investigated by wide angle X-ray diffraction and thermogravimetric analyzer. It was demonstrated that surface treatments lead to several morphological changes, including the formation of micro-cracks and removal of impurities by acetylation and peroxide treatment as well as surface smoothing by silane treatment. Surface energy of acetylated fiber decreased with treatment time and showed the lowest value for silane treated fiber. The interfacial shear strength (IFSS) of a fiber/AESO composite was investigated through the microbond test. The IFSS of silane treated ramie was higher than that of others. The result indicates that silane treated fibers improve the interfacial property, which is the most important characteristic for the end use of green composites.