Jute fibre/epoxy composites: Surface properties and interfacial adhesion

Jute fibres were surface treated in order to enhance the interfacial interaction between jute natural fibres and an epoxy matrix. The fibres are exposed to alkali treatment in combination with organosilane coupling agents and aqueous epoxy dispersions. The surface topography and surface energy influenced by the treatments were characterized. Single fibre pull-out tests combined with SEM and AFM characterization of the fracture surfaces were used to identify the interfacial strengths and to reveal the mechanisms of failure.     

Characterization of the aramid/epoxy interfacial properties by means of pull-out test and influence of water absorption

Single fiber pull-out tests were carried out to investigate the influence of water absorption on the interfacial properties of aramid/epoxy composite. The fiber/matrix interfacial strength was severely decreased between 4 and 7 week immersion time in deionized water at 80 °C, and thereafter showed a plateau. This change with immersion time did not correspond with that of the water gain of the pull-out specimens, because the water gain did not reflect the one in the fiber/matrix interface. As a result of the degradation of the fiber/matrix interfacial strength, the pulled-out fiber surfaces of 7, 10 and 13 week wet specimen were smooth. In situ observations of interfacial crack propagation by a video microscope and an analysis of acoustic emission (AE) signals showed that AE signals obtained during the pull-out process were classified into four types according to fracture modes. AE signals detected at final unstable crack propagation and fiber breakage had high amplitude and long duration.     

The effect of surface treatment on the interfacial properties in carbon fibre/epoxy matrix composites

Carbon fibres with different degrees of surface oxidation, as well as epoxy-sized fibres, were used to prepare epoxy composites in order to compare the effects of the fibres surface chemistry on the interfacial properties. X-ray photoelectron spectroscopy, water vapour adsorption measurements and contact angle examination were applied to characterize the carbon fibre surfaces. A correlation was found between the content of primary adsorption sites on the fibre surface and interlaminar shear strength (ILSS) of the composites. Higher values of ILSS obtained for the oxidized fibres containing composites are proposed to be due to the higher concentration of carboxylic groups created on the oxidized fibres surface and to the creation of chemical bonds at the fibre/epoxy matrix interface. Enthalpy of cure, reaction peak temperature and glass transition temperature of the composites were determined by differential scanning calorimetry.     

The study of model polydiacetylene/epoxy composites

Raman spectroscopy and conventional mechanical testing have been employed to study a range of polydiacetylene fibre composite specimens with varying volume fractions cured at either room temperature for a week or at 100 C for 24 h. The high-temperature cured composites were found to contain thermal stresses sufficient to cause twinning in the polydiacetylene fibres which affected the mechanical response of the bulk composite. A simple modification to discontinuous fibre reinforcement theory which accounts for the effect of thermal stresses in the material has been presented, giving good agreement with the experimental data. Small cracks were found to be produced at the end of the fibres by thermal stresses.     

The study of model polydiacetylene/epoxy composites

A mode composite system consisting of one polydiacetylene single crystal fibre in an epoxy resin matrix has been subjected to tensile strain parallel to the fibre direction. The strain at all points along the length of the fibre was determined by resonance Raman spectroscopy while that of the matrix was measured by conventional techniques. Comparison of the fibre and matrix strain showed two distinct regions. Below about 0.5% matrix strain the composite followed Reuss-type behaviour with equal stress in the fibre and the matrix. At higher matrix strain the composite followed Voigt-type behaviour with any increase in matrix strain matched by an equal increase in fibre strain. In this region the strain distribution along the length of the fibre could be approximately described by the shear-lag model of Cox. The critical length of the fibre was found to increase linearly with fibre diameter as predicted by that model. Good qualitative agreement was found with the predictions of a calculation based on finite element analysis over the full range of applied stress.     

The interfacial properties of fibrous composites

The dependence of the magnitude of the interfacial parameters for a glass-fibre-reinforced polypropylene on the thickness of the applied silane layer on the glass-fibre surface was investigated. The interfacial parameters studied included the interfacial-shear strength, the interfacial coefficient of friction, the interfacial-frictional stress and the shrinkage pressure. These parameters were evaluated from pull-out data using a recent model. The results indicate that the maximum interfacial-shear strength is obtained at a critical thickness of the silane layer on the treated fibre. Both the interfacial-frictional stress and the interfacial coefficient of friction decreased with increased thickness of the silane coat.     

The effect of polybutadiene interlayer on interfacial adhesion and impact properties in oxygen-plasma-treated UHMPE fiber/epoxy composites

In order to improve the interfacial adhesion and impact properties of ultra-high modulus polyethylene (UHMPE) fiber/epoxy composites at the same time, the fiber coating technique was combined with the oxygen plasma treatment. The UHMPE fiber was treated with oxygen plasma and thin polybutadiene (PB) coating was introduced. PB coating decreased the interfacial adhesion and increased the impact property of the oxygen-plasma-treated UHMPE fiber/epoxy composites. However, oxygen-plasma-treated and PB-coated UHMPE fiber/epoxy composites show improved interfacial adhesion, flexural properties and impact property in comparison with the untreated control UHMPE fiber/epoxy composites. Oxygen plasma treatment introduces micro-pittings on the UHMPE fiber surface. These micro-pittings improved interfacial adhesion and flexural properties and decreased impact properties through mechanical interlocking. Thin PB coating cannot exclude this mechanical interlocking effect completely and there are imperfect wetted UHMPE fiber surface regions in which effect mechanical interlocking can occur. Stress transfer through the viscous PB interlayer also contributes to the interfacial adhesion and flexural properties of PB-coated UHMPE fiber/epoxy composites. The impact property of PB-coated UHMPE fiber/epoxy composites is due to low modulus PB interlayer.     

石墨烯/环氧树脂复合材料的介电性能研究

通过Staudenmaier法制备了完全氧化的氧化石墨(GO),并通过高温热膨胀制备了单层石墨烯(graphene)。用FT-IR和TG对GO的氧化程度、含氧官能团进行了表征,用SEM和TEM对天然石墨(NG)、GO和graphene的微观结构进行了分析。利用超声共混法制备了graphene/环氧树脂介电纳米复合材料,介电性能的测试表明,graphene的加入使环氧树脂介电常数大幅提高,当graphene添加量为0.25%(质量分数)时,材料介电常数达到25,是纯环氧树脂的4倍,介电损耗0.11。这为石墨烯在介电储能方面的应用和低成本介电复合材料的制备提供了新思路。     

Thermomechanical behaviour of interfacial region in carbon fibre/epoxy composites

A study of the thermomechanical stability of the fibre-matrix interphase in carbon/epoxy composites has been carried out. The thermodynamic work of adhesion has been evaluated at room temperature by wetting measurements. The interfacial shear stress transfer level τ for sized and desized carbon fibre has been measured as a function of temperature by means of a single-fibre fragmentation test. As the test temperature increased τ values were found to decrease, with values being higher for the desized carbon fibre. The dependence of interfacial shear stress transfer on bulk matrix mechanical properties (modulus and shear strength) has also been discussed. Dynamic mechanical measurements performed on single-bundle composites confirmed the better thermomechanical stability of the desized fibre interphase.     

Study of model polydiacetylene/epoxy composites

A model composite has been prepared consisting of a polydiacetylene single-crystal fibre in an epoxy resin matrix. The strain at points along the length of the fibre has been measured, using Raman spectroscopy, as a function of matrix strain and the post-cure temperature of the matrix. Good quantitative agreement has been found between the behaviour of the cold-cured system and the shear-lag model of Cox. The critical length of the fibres was measured as a function of fibre diameter and compared with recent calculations using finite difference methods. Higher post-cure temperatures have been shown to lead to compressive deformation of the fibres due to matrix shrinkage on cooling. The deformation is manifest as twinning, which disappears reversibly during tensile deformation. The amount of matrix shrinkage was determined by measuring the level of strain required to remove the twins. This was found to be in good agreement with the shrinkage determined from the linear thermal expansivity of the matrix.     

Fabrication and mechanical properties of aramid/nylon plain knitted composites

The presence of fibre/matrix interfaces strongly influences the overall mechanical properties of composites. In order to produce fully recyclable fiber reinforced composites with improved adhesion properties, polyethylene and polypropylene materials were previously used as single-polymer composite materials. In this paper, another breed of single-polymer composite material has been defined as the ‘one-unity’ composite. Polyamide materials were chosen and combined with aramid fibre in an attempt to achieve better interfacial bonding. Weft-knitting technique was used to produce textile reinforcements for aramid/nylon composite processing. Aramid/epoxy knitted composites were also fabricated to compare them with aramid/nylon thermoplastic composites. Mechanical properties of aramid/nylon and aramid/epoxy composites and their relationships to the fibre/matrix interfacial adhesion and interactions have been investigated. With the increase in processing time, tensile modulus and strength of aramid/nylon composites have increased and decreased, respectively. Furthermore, scanning electron microscopic observations clearly indicated that longer molding time has resulted in stronger adhesion property between fiber and matrix. Aramid/nylon knitted composites have revealed comparable strength property in the course direction, albeit they have inferior tensile strength in the wale direction when compared to that in aramid/epoxy composites. In aramid/nylon knitted composites, while tensile modulus exhibited an increasing trend, there were clear drops in tensile strengths with longer molding time. This indicates that there could be an optimum molding condition at which maximum tensile properties can be obtained. Aramid/nylon knitted composites exhibited relatively better interfacial bonding properties than Aramid/epoxy composites, which suffered fibre/matrix debonding.     

短切芳纶纤维/聚硅氧烷-甲基丙烯酸锌复合材料的结构与性能

为提高聚硅氧烷-甲基丙烯酸锌(ZDMA)树脂材料的性能,采用短切通用型芳纶纤维与聚甲基乙烯基硅氧烷-ZDMA复合并在高温下交联固化,得到短切芳纶纤维/聚硅氧烷-ZDMA复合材料.采用SEM、FTIR、拉伸和压缩试验方法、霍普金斯压杆试验方法,表征了短切芳纶纤维/聚硅氧烷-ZDMA复合材料的结构和静态力学性能,研究了芳纶...     

Flame and silane treatments for improving the adhesive bonding characteristics of aramid/epoxy composites

A fast and cost-effective surface treatment with flame and silane coupling agent treatments has been developed for the surface treatment of aramid/epoxy composite faces to improve the adhesive bonding characteristics of lightweight sandwich stealth radome structures. The flame treatment was performed with propane gas, and the silane treatment was performed with γ-methacryloxypropyltrimethoxy silane (γ-MPS) and γ-aminopropyltriethoxy silane (γ-APS) under different treatment conditions. The contact angles of the flame-treated aramid/epoxy composites and the single-lap shear strengths of the adhesive joint composed of the aramid/epoxy composite adherend and epoxy adhesive were measured and compared with those treated with argon plasma and mechanical abrasion. In addition, the surfaces were analyzed with atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to characterize the mechanical and chemical interactions of the aramid/epoxy composite with the epoxy adhesive.     

Improved interfacial properties of carbon fiber/epoxy composites through grafting polyhedral oligomeric silsesquioxane on carbon fiber surface

Carbon fibers were grafted with a layer of uniform octaglycidyldimethylsilyl POSS in an attempt to improve the interfacial properties between carbon fibers and epoxy matrix. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and dynamic contact angle analysis were performed to characterize the carbon fibers. AFM results show that the grafting of POSS significantly increased the carbon fiber surface roughness. XPS indicates that oxygen-containing functional groups obviously increased after modification. Dynamic contact angle analysis shows that the surface energy of modified carbon fibers is much higher than that of the untreated ones. Results of the mechanical property tests show that interlaminar shear strength (ILSS) increased from 68.8 to 90.5 MPa and impact toughness simultaneously increased from 2.62 to 3.59 J.     

Preparation and study of aramid/epoxy prepregs

Solid epoxy resin compounds were studied for their suitability as matrices for the preparation and curing of prepregs containing aramid fibres. Acid anhydrides were shown to be incompatible to the epoxy resin, producing a dispersed crystalline phase upon drying, whereas o-phenylenediamine is a miscible cross-linking agent. Also, diamine is safer because it reacts with the epoxy at temperatures considerably higher than the anhydrides. Composite specimens prepared by these prepregs display similar tensile strength and lower modulus than those derived from the one-step process, by the use of conventional liquid epoxy systems.     

Tailoring of the interfacial properties of polymeric single fibre-reinforced epoxy composites by non-oxidative plasma treatments

The interfacial properties of epoxy composites reinforced with a single, plasma-treated fibre of either poly(p-phenyleneterephthalamide) (PPTA) or poly(p-phenylenebenzobisoxazole) (PBO) have been investigated with a focus on evaluating the effect of two non-oxidative (He and N₂) microwave plasma treatments on interfacial adhesion properties. Tensile testing of single filaments revealed that their tensile strength does not diminish with the plasma treatments, despite the fact that their surface properties have been both physically and chemically modified. Interfacial characterisation by Raman spectroscopy indicated that the quality of adhesion was substantially enhanced following exposure of the fibres to microwave plasma treatment in either pure helium or pure nitrogen flows for just one minute. Such improvement was higher than that attained when O₂ was used for blowing the plasma, under the same operational conditions. Moreover, no swelling effect was observed by AFM after exposure of the He or N₂ plasma-treated fibres to ambient conditions for as much as 24 h.     

三向编织玻璃/环氧复合材料刚度性能

通过实验研究了三向编织玻璃/环氧复合材料的刚度性能 , 并考虑编织角和试件宽度参数的影响 , 探讨了拉伸和压缩刚度性能的差异。实验结果表明 : 在同一纤维体积分数条件下 , 随着编织角的增大 , 试件的纵向弹性模量有所减小 , 泊松比 (在编织角约大于 35° 时) 也有所减小 ; 宽度为两倍和三倍单胞宽度的试件的刚度性能基本相同; 试件的纵向弹性模量和泊松比远大于横向弹性模量和泊松比; 拉伸和压缩时试件的弹性模量和泊松比基本接近 ; 在横向拉伸和压缩时试件的应力2应变曲线具有明显的非线性特征。实验结果为编织复合材料结构设计提供了数据参考。