Characterization of a coating layer on glass fibre used as reinforcing material in a polyepoxide matrix by means of FTIR spectroscopy and vapour phase interaction studies with monofunctional model compounds

Coatings on glass fibres, used to reinforce polyepoxide matrices, were examined by Fourier transform infra-red spectroscopy and by their reaction with styrene oxide, aniline, and also water in the vapour phase which was followed calorimetrically and gravimetrically. The coatings comprised an adhesive (of the DGEBA epoxy prepolymer type) applied on its own or together with a coupling agent (γ aminopropyltriethoxysilane). In all tests, these fibres were compared with untreated fibres of a similar type. The results of the studies indicate that the combination of the two coatings forms a reactive mixture within themselves which may inhibit uniform coating of the glass. It is also shown that the coating products on the glass control the process of water diffusion.     

玻璃纤维增强环氧基复合界面介电性能的研究

通过介电性能试验和理论计算研究了偶联剂对玻璃纤维／环氧复合界面层介电性能的影响。对玻璃纤维经偶联剂处理前后表面自由能和浸润活化能等进行了研究分析，探讨了偶联剂对玻璃纤维／环氧复合界面介电性能的影响机制。     

双氨基硅烷偶联剂在无碱玻璃纤维布后处理中的应用研究

将双氨基硅烷偶联剂KH-843尝试使用到无碱玻璃纤维布后处理中进行试验,与常见单氨基硅烷偶联剂KH-550和环氧基硅烷偶联剂KH-560对比,对比它们配制成水解溶液的表面张力,对比使用它们处理后的玻璃纤维布的浸透性;将双氨基硅烷偶联剂处理的玻璃纤维布浸胶制成半固化胶片后,压制成层压板,测试主要的电学性能和力学性能指标,表明双氨基硅烷偶联剂应用于玻璃纤维布的后处理,可以有效提高玻璃纤维布的浸透性,能够满足复合材料行业的需求。     

The Influence of Interfacial Structure on the Flexural Strength of E-glass Reinforced Polyester

Simultaneous mechanical and molecular characterization of a composite system has been attempted with respect to the interface. The mechanical properties of an E-glass cloth/ y-methacryloxypropyltrimethoxysilane (γ-MPS)/bisphenol-A-fumarate polyester resin composite system were studied as a function of the amount of γ-MPS coupling agent present on the glass fiber surface. Fourier transform infrared diffuse reflectance spectroscopy was used to determine the amount and structure of γ-MPS on the glass. This structure consists of two clearly distinguishable regions: physisorbed layers of γ-MPS which can be dissolved by organic solvents, and chemisorbed layers which are insoluble. The physisorbed layers of γ-MPS reduced the strength of the polyester composite. A polymer blend consisting of siloxane oligomer of γ-MPS and bisphenol-A polyester was also investigated as a model of the silane interphase. Results from this model study are in agreement with the polyester composite data.     

Deposition of Oxide Coatings on Fiber Cloths by Electrostatic Attraction

Electrostatic attraction has been used to deposit alumina and mullite coatings onto woven cloths of Nicalon fiber. This approach produced uniformly coated cloths while minimizing the dependence on the wetting relationship between the fiber and the coating precursor. The use of low sol concentrations (#1 g/L) facilitated the removal of excess sol from the cloth. Water was used to further displace excess aqueous sol from the cloth to give minimal fiberfiber bridging while maintaining uniform fiber coatings. The use of a polyelectrolyte enabled multiple deposition of coatings onto the fibers in the cloth. Multiple coating steps resulted in completely coated fiber surfaces; coverage was limited to 50% with only a single coating step. Vacuum infiltration was necessary to remove entrapped air from the cloths during coating. A discussion of wetting and infiltration of fiber cloths has been presented, which highlights issues that are critical for obtaining uniformly coated fibers and minimal fiber bridging in a woven-fiber cloth or preform.     

An NMR Imaging Study of the Interface of Epoxy Resin-Glass Fiber Reinforced Composites

NMR imaging was used to analyze E-glass fiber/epoxy composites. The NMR images revealed specific interactions between the glass fiber and epoxy, as indicated by the different degree of curing in the proximity of the fiber. When as-received glass fibers were used, an accelerated degree of curing in the proximity of the fibers as compared with the bulk was observed, whereas when heat-treated glass fibers were used the above trend was substantially inhibited. Finally, when E-glass fibers treated with an aminosilane coupling agent (γ-APS) were used, no variation in the degree of curing in the proximity of the glass fiber was observed. The above results suggest that physisorbed or chemisorbed molecular water present in the surface of the glass fiber assists in the opening of the epoxy ring by hydrogen bonding effects.     

The development of morphology during hot compaction of Tensylon high-modulus polyethylene tapes and woven cloths

The development of morphology in tapes and woven cloths of oriented melt-spun Tensylon polyethylene has been studied both before and after hot compaction over a range of temperatures below and above the optimum. For both the unidirectional fibres and the woven cloths, the optimum temperature was found to be where approximately 30% of the original structure was lost which, for Tensylon tapes, was ∼2 K below the point of major crystalline melting, giving a processing window roughly twice as wide as for other previously studied polyethylene materials. Transverse sections show a two-component morphology after etching of cratered ribbons emerging from a flat, relatively featureless landscape. This morphology disappears at the highest temperature studied when the longitudinal morphology consists of oriented walls from which transcrystalline units have grown during cooling. Morphological comparison with other polyethylenes and their compactions places Tensylon behaviour alongside Dyneema, Spectra and Tekmilon rather than the melt-spun Certran.     

The hot compaction behaviour of woven oriented polypropylene fibres and tapes. I. Mechanical properties

The aim of this work was to establish the important parameters that control the hot compaction behaviour of woven oriented polypropylene. Five commercial woven cloths, based on four different polypropylene polymers, were selected so that the perceived important variables could be studied. These include the mechanical properties of the original oriented tapes or fibres, the geometry of the oriented reinforcement (fibres or tapes), the mechanical properties of the base polymer (which are crucially dependant on the molecular weight and morphology), and the weave style. The five cloths were chosen so as to explore the boundaries of these various parameters, i.e. low and high molecular weight: circular or rectangular reinforcement (fibres or tapes): low or high tape initial orientation: coarse or fine weave.A vital aspect of this study was the realisation that hot compacted polypropylene could be envisaged as a composite, comprising an oriented ‘reinforcement’ bound together by a matrix phase, formed by melting and recrystallisation of the original oriented material. We have established the crucial importance of the properties of the melted and recrystallised matrix phase, especially the level of ductility, in controlling the properties of the hot compacted composite.     

EFFECT OF FILLER TREATMENT ON THE RHEOLOGICAL AND MECHANICAL PROPERTIES OF POLYETHYLENE COMPOSITES

Mechanical and Theological properties of a high density polyethylene (HDPE) filled with mica flakes, rutile and carbon black are investigated. Experimental results show that the Young modulus and the tensile strength of mica and rutile-HDPE composites are significantly enhanced by surface treatment of fillers with silane and titanate coupling agents. Surface treatments are shown to reduce the peak of the loss tangent (tan δ) and slightly increase the glass transition temperature (T_g). This is an indication of improved adhesion at the filler-matrix interface. The carbon black composites, however, hardly show any improvement by these treatments. The Theological properties are also effected by surface treatments, particularly at low shear rates. The low-shear rate viscosities (η _O) and characteristic time (λ ₀) of these systems are determined and compared. It is found that η ₀ and λ ₀ of carbon black composites are much higher than those of mica composites. This is probably due to the poor dispersion and/or agglomerates formation of the carbon black in the HDPE matrix. It is also suggested that the coupling agent, depending on its chemical structure and nature of the filler, may act as an adhesion promoter or as a lubricating agent.     

Compressibility and flow permeability of two-dimensional woven reinforcements in the processing of composites

The processing of composites under pressure is described by a viscoelastic model in which the pressure acts on the fibers in an elastic manner and on the liquid matrix in a viscous manner. Following a micro-mechanics approach, an analytical model has been derived for the nonlinear elastic compression of two-dimensional, orthotropic, plain woven fiber cloths, containing two empirical constants. The model is validated by experimental data and the empirical constants determined in the compression of a wet, plain woven, glass fiber reinforcement. The effects of the compression of woven cloths during processing are demonstrated by the change of their permeability.     

Physical properties of a bisphenol-F epoxy containing a silica filler treated with silane coupling agents

A model epoxy system consisting of a diglycidyl ether of bisphenol-F epoxy resin, 1,4-butanediol, and cured with 4-methyl-2-phenylimidazole has been investigated. Thermal analysis indicated that 3 parts per hundred resin (phr) is the optimum amount of curing agent for this system. The influence of silane-treated amorphous fumed silica fillers on properties of the cured epoxy was also examined. Silica particles were treated with 3-aminopropyldiethoxymethylsilane (APDS) and3-aminopropyltriethoxysilane (APTS) coupling agents. No change in glass transition temperatures was observed with the addition of the filler (with or without coupling agents) to the epoxy. Addition of the filler led to a slight increase in the activation energy for the glass transition; however, no change in activation energy was observed when using the coupling agent. Addition of either coupling agent to the filler surface led to an increase in cooperativity. Fumed silica also did not significantly affect moisture diffusion properties, but a small decrease was observed in the moisture saturation mass with the addition of silica particles treated with APDS.     

PHYSICAL PROPERTIES OF A BISPHENOL-F EPOXY CONTAINING A SILICA FILLER TREATED WITH SILANE COUPLING AGENTS

A model epoxy system consisting of a diglycidyl ether of bisphenol-F epoxy resin, 1,4-butanediol, and cured with 4-methyl-2-phenylimidazole has been investigated. Thermal analysis indicated that 3 parts per hundred resin (phr) is the optimum amount of curing agent for this system. The influence of silane-treated amorphous fumed silica fillers on properties of the cured epoxy was also examined. Silica particles were treated with 3-aminopropyldiethoxymethylsilane (APDS) and3-aminopropyltriethoxysilane (APTS) coupling agents. No change in glass transition temperatures was observed with the addition of the filler (with or without coupling agents) to the epoxy. Addition of the filler led to a slight increase in the activation energy for the glass transition; however, no change in activation energy was observed when using the coupling agent. Addition of either coupling agent to the filler surface led to an increase in cooperativity. Fumed silica also did not significantly affect moisture diffusion properties, but a small decrease was observed in the moisture saturation mass with the addition of silica particles treated with APDS.     

THE INFLUENCE OF SILANE COUPLING AGENT COMPOSITION ON THE SURFACE CHARACTERIZATION OF FIBER AND ON FIBER-MATRIX INTERFACIAL SHEAR STRENGTH

It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and γ-aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ×10 -3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis.     

Adhesive Bonding of Oil-Contaminated Steel Substrates

Durability of adhesive bonds formed by curing epoxies against oil-contaminated steel substrates using amidoamine curing agents was determined during exposure to boiling water. The most durable bonds were obtained using amidoamine curing agents with relatively low amine numbers and by blending silane coupling agents such as γ-glycidoxypropyltrimethoxysilane (γ-GPS) and N-(2-aminoethyl)-3-aminopropyltrimethoxy silane (AAMS) into the adhesives. When X-ray photoelectron spectroscopy (XPS) was used to characterize the failure surfaces of the adhesive joints after exposure to boiling water, it was determined that adhesives prepared using amidoamine curing agents with low amine numbers were able to displace the oil from the steel surface but adhesives prepared with amidoamine curing agents with high amine numbers were not. Results obtained from XPS also showed that the amino groups on the substrate fracture surfaces of joints prepared using curing agents with low amine numbers were protonated whereas the amino groups in the bulk adhesive were not, indicating that there was a chemical interaction between the curing agent and the hydrated surface of the substrate. It was also shown using infrared spectroscopy that the amidoamine curing agents formed salts with calcium compounds in the oil.     

Ionomer. I. The effect of woven glass mat reinforcement on tensile properties

An investigation was conducted on ionomer polymer. The ionomer pellets were molded into a thin sheet before fabrication into composites. The reinforcing agent used was woven glass mat. Before fabrication, the woven glass mat was treated with the following: 1. silane coupling agent for 5 min and dried at room temperature; 2. silane coupling agent for 5 min and dried in the oven at 110°C for 15 min; 3. Ultraviolet radiation for 5 min; and 4. silane (oven dried + ultraviolet). The composites were fabricated at various pressure, time, and temperature. An ideal processing condition was established, i.e., pressure = 5 MPa, temperature = 180°C, and the impregnation time = 30 min. The void contents of the composites were estimated using the ignition method and the tensile properties were measured. The results revealed that good impregnation of the matrix ionomer into the reinforcing agent can be achieved at 180°C. This was confirmed by low void content as compared with other test temperatures. Further clarification was through the tensile properties, which were higher than those at lower temperatures (120 and 150°C). The effect of fiber orientation was checked, and both 0 and 90° had identical strengths and moduli irrespective of the various fiber treatments. Apart from the void contents, the degree of impregnation was also checked based on the tensile strengths in 45, 25, and 60° fiber orientations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1395–1400, 2001     

WETTABILITY AND SURFACE ENERGETICS OF ROUGH FLUOROPOLYMER SURFACES

Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48 μm). Quasi-static advancing, θ_A, and receding, θ_R, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θ_V, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θ_A and θ_R is a good approximation for θ_V, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θ_A is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θ_V is a better representation of the average wettability of the surface (including the presence of defects).     

The structure of γ‐glycidoxypropyltrimethoxysilane on glass fiber surfaces: Characterization by FTIR,SEM, and contact angle measurements

The purpose of this article is to determine the structure of γ‐glycidoxypropyltrimethoxysilane (γ‐GPS) on glass fiber surfaces. The interfacial adhesion of glass fiber–polymer can be improved by the silane treatment of the glass fiber. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using a 10% (v/v) hydrochloric acid aqueous solution for different durations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with (γ‐GPS) were conducted at various time intervals. These fibers would be used to quantify the relationship between contact angle of glass fiber surface and the interfacial shear strength of the fiber–polymer interface. The effect of acid activation on glass surface and the interaction between glass fibers and silane coupling agent were examined using Fourier transform infrared spectroscopy. The experiments, in conjunction with electron photomicrographs of glass surfaces treated with coupling agent, are interpreted in an attempt to explain the stability of coupling agent‐glass interfaces. From SEM analysis, it was clearly observed that agglomerations of silane agent in the cavities among the heat cleaned fibers are available. However, this case was not observed for the silanization of acid activated glass fibers. In addition, contact angle measurements on glass fibers were performed to evaluate surface structure. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Properties of orthotropic glass–polypropylene composites manufactured by weaving of prepregtapes and other routes

Abstract

This paper reports a study of the melt impregnation and weaving of glass–polypropylene prepreg tapes into sheet for use as a precursor for pressed thermoplastic composite products and a comparison of the properties attainable with those achievable by other comparable routes. Melt impregnation has been used successfully to manufacture well impregnated tapes, with and without internal coupling agent. It appears that weaving could be an economically viable process for converting unidirectional tape into a conformable, press formable prepreg. The properties of glass–polypropylene laminates manufactured by pressing the tape woven product were compared with those of other glass–polypropylene composites, including crossply laminate made from Plytron and samples prepared by film stacking. Quasi-static mechanical properties were found to be comparable with those of Plytron and superior to those of the other materials. In the coupled samples, coupling was somewhat less effective than in Plytron. The impact behaviour of the pressed, tape woven products was impressive and superior to any of the other materials tested.     

On the Effects of Processing Conditions and Interphase of Modification on the Fiber/Matrix Load Transfer in Single Fiber Polypropylene Composites

The scope of this study was the investigation of the effects of both processing conditions (in terms of thermo-mechanical history) and interphase modification (fiber sizing and/or matrix coupling) on the interfacial shear strength (τ_i) of fiber reinforced isotactic polypropylene (iPP). Fiber/matrix load transfer efficiency was investigated by modified single fiber pullout and microdroplet pulloff test methods, respectively. It was established that τ_i of the neat microcomposite (unsized fiber/uncoupled matrix) is improved by quenching of the samples rather than by various spherulitic or transcrystalline supermolecular structures set under isothermal crystallization conditions. Enhanced interfacial shear strength for the quenched samples was attributed to a better wetting behaviour and a fine dispersion of the amorphous PP (aPP) fraction formed. An adhesion model was proposed based on which optimum τ_i is linked to both matrix strength and its wetting behaviour. It was demonstrated that the results from pullout and pulloff tests correlate very well with each other for the particular glass fiber/iPP model composite systems studied. It was shown further that matrix modification (coupling) or fiber sizing enhances τ_i practically to the same level, whereas a combination of matrix coupling and fiber sizing yields an even higher interfacial shear strength (synergistic effect).     

Effects of coupling agents on the rheological properties,processability, and mechanical properties of filled polypropylene

An experimental study was carried out to investigate the effects of coupling agents on the rheological properties, processability, and mechanical properties of highly filed polypropylenes (PP). Inorganic fillers used were CaCO₃ and glass beads, and coupling agents used were two silane coupling agents, N-octyl triethoxy silane and γ-aminopropyl triethoxy silane, and one titanate coupling agent, isopropyl triisostearoyl titanate. It was found that the addition of the coupling agents to the PP-CaCO₃ (50 wt percent) decreased the melt viscosity and increased the melt elasticity (first normal stress difference). However, the addition of the silane coupling agents to the PP-glass beads (50 wt percent) affected the rheological properties of the melts quite differently. The N-octyl triethoxy silane had relatively little effect on either the melt viscosity or the melt elasticity, whereas the γ-aminopropyl triethoxy silane increased the melt viscosity and decreased the melt elasticity. The CaCO₃- or glass bead-filled polypropylenes, with and without coupling agents, were injection-molded and the mechanical properties of the molded specimens were measured by the use of an Instron testing machine. It was found that the effect on the tensile strength and percent elongation of the filled polypropylenes depended upon the specific coupling agent utilized. A melt-spinning study was also carried out to investigate the effect of coupling agents on the spinnability (defined as the maximum draw-down ratio) of the PP-CaCO₃ system, and on the mechanical properties of the melt-spun fibers. It was found that the spinnability of the PP-CaCO₃ was enhanced considerably by the addition of the coupling agents, and that the tensile strength of the melt-spun fibers was also improved by their addition. Scanning electron micrographs were taken of the fracture surface of injection-molded specimens and an attempt was made, with the aid of photomicrographs, to explain the mechanical properties of molded specimens observed experimentally.