Effect of chemical treatment on dynamic mechanical properties of sisal fiber-reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of treated sisal fiber-reinforced polyester composites fabricated by resin transfer molding (RTM) have been studied with reference to fiber surface modifications, frequency and temperature. The sisal fibers have been subjected to various chemical and physical treatments like mercerization, heating at 100°C, permanganate, benzoylation and vinyl tris(2-ethoxymethoxy) silane to improve the interfacial bonding with isophthalic polyester resin. Results indicated that treatment changed the storage modulus (E′), loss modulus (E″) and damping factor (tan δ) drastically at a wide range of temperature. The E′ value increased for every treatment, and is maximum for the composites fabricated by benzoylated-treated fibers. The T _g value obtained from the E″value showed an increase as compared to untreated fiber-reinforced composites. The alkali-treated fiber-reinforced composites showed lower tan δ value. Using Arrhenius' equation the activation energy was calculated and found maximum for the composites fabricated by alkali-treated fiber, which shows good fiber/matrix interactions.     

Investigation on resin interphase produced near silane-treated glass fiber in vinyl ester resin

In order to investigate the reaction of silane-treated glass fiber with thermosetting resin, a set of spectra were measured near the interface between the glass fiber and vinyl ester resin using microscopic FT-IR spectroscopy. A thin-sliced sample was made from glass fiber/vinyl ester resin composite to be subjected to the spectroscopy. The spectra were obtained through a 20 × 40 μm of a mask window at each 20 μm step from the glass strand area to the matrix resin. The intensity at 1450 cm^-1 of the spectra decreased from the glass strand area to the matrix resin. It was noticed, however, that the intensity kept the same value even in the matrix at a distance of 80 μm from the glass strand area. This meant that the resin in such an area was denatured by the reaction of silane to resin at the surface. This mechanism was supported by the significant size of the denatured area, which increased with amounts of silane at the surface of glass fiber.     

Thermal behavior of chemically treated and untreated sisal fiber reinforced composites fabricated by resin transfer molding

Using thermogravimetric analysis (TGA), the thermal behavior of sisal fibers and sisal/polyester composites, fabricated by resin transfer molding (RTM), has been followed. Chemical treatments have been found to increase the thermal stability, which has been attributed to the resultant physical and chemical changes. Scanning electron microscopy (SEM) and infrared (FT-IR) studies were also performed to study the structural changes and morphology in the sisal fiber during the treatment. The kinetic studies of thermal degradation of untreated and treated sisal fibers have been performed using Broido method. In the composites, as the fiber content increases, the thermal stability of the matrix decreases. The treated fiber reinforced composites have been found to be thermally more stable than the untreated derivatives. The increased thermal stability and reduced moisture behavior of treated composites have been correlated with fiber/matrix adhesion.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Studies on interface in polyester/fly-ash particulate composites

Fly ash (FA)-general purpose unsaturated polyester resin (GPR) particulate composites have been made. The effect of surface treatment of FA with two different silane coupling agents (CAs) on the mechanical properties like tensile, flexural, impact strength and hardness, thermal properties like thermal stability and morphological properties (SEM) of FA-GPR composites are studied. The properties of FA-CA-GPR are also compared with that of GPR and CaCO₃ -GPR. An enhancement in the tensile, flexural, and impact strength and moduli are observed when FA is surface treated with CA. Hardness is also found to increase with CA-treated FA-filled GPR. A suitable mechanism for the chemical reaction taking place at the interface in the presence of CAs is proposed.     

Effect of clay silylation on curing and mechanical and thermal properties of unsaturated polyester/montmorillonite nanocomposites

This work focuses on the chemical modification of montmorillonite (MMT) (Cloisite® Na) with compatible silanes, vinyltriethoxysilane (CVTES) and γ-methacryloxypropyltrimethoxysilane (CMPS) in order to prevent agglomeration and to improve montmorillonite interaction with an unsaturated polyester resin matrix seeking to achieve a multifunctional composite. Clays were dispersed in the resin by mechanical stirring and sonication and the nanocomposites were prepared by resin transfer into a mold. The mechanical, morphological, thermal and flammability properties of the obtained composites were compared with those prepared using commercial Cloisite® 30B (C30B) and Cloisite® 15A (C15A) clays. Advantages of using silane-modified clays (CVTES and CMPS) as compared with organic-modified clays (C30B and C15A) can be summarized as similar flexural strength and linear burning rate but higher storage modulus and improved adhesion to the polyester resin with consequent higher thermal deflection temperature and reinforcement effectiveness at higher temperatures. However, organic modified clays showed better dispersion (tendency to exfoliate) and consequently delayed thermal volatilization due to the clay barrier effect.     

Unsaturated polyester resin (UPR) reinforced with flax fibers,untreated and cold He plasma-treated: thermal,mechanical and DMA studies

Hemp, jute, flax, bagasse, coconut and bamboo fibers are some of the natural fibers that have attracted attention for the preparation of composite materials because of their low cost compared with synthetics fibers (glass, carbon). The performance of a natural fiber as reinforcement in composite materials is linked to its ability in term of adhesion with the synthetic matrix. This depends mainly on the quality of the fiber surface. In order to improve this adhesion, a thin reactive coating is generally used. In this study, cold He plasma treatments have been carried out on reinforcing flax fiber. Composites with unsaturated polyester resin (UPR) have been used with untreated flax fibers and plasma-treated fibers. The data characterizing the thermal, mechanical (dynamic and static) will be presented in order to analyze the efficiency of the He plasma treatment on the composite performances.     

1H pulse NMR analysis of silane-treated layers on glass fiber surfaces

The surface treatment of a glass fiber using mercapto-functional silane coupling agent having a di- or trialkoxy group has been studied. The surface of silane-treated fiber is observed by scanning electron microscopy. The treated layer looks hard like glass for the trialkoxy silane-treated, whereas it looks soft for the dialkoxy silane-treated. Molecular mobility of the treated layer is analyzed by ¹H pulse nuclear magnetic resonance spectroscopy. The amount of silane loading increases with increased silane concentration in the treatment solution. The relaxation time for the surface layer is longer for the dialkoxy structure than for the trialkoxy structure. The silane chain is flexible in the dialkoxy structure, but is rigid for the trialkoxy structure, independent of the loading amount of silane. The relaxation behavior for the mixture of the di- and trialkoxy structures is between those of the pure dialkoxy and trialkoxy structures and depends on the mixing ratio. The network density of silane chains on the glass fiber can be controlled by varying the mixing ratio of the di- and trialkoxy compounds.     

Sorption characteristics of water,oil and diesel in cellulose nanofiber reinforced corn starch resin/ramie fabric composites

Nowadays, utilisation of biodegradable materials has become necessary in order to maintain global environmental and ecological balance. Fully biodegradable nano 'Green' textile composites have been prepared from cellulose nanofibers reinforced corn starch resin and ramie fabric. Nanofibers having dimensions of approximately 1 μm long and 20–30 nm in diameter are used in the study. The nanofibers were incorporated in corn starch resin via ball mill mixing using ceramic balls. Textile composites were fabricated by pasting the reinforced resin onto the ramie fabric and by hot compression molding technique. Interactions at the fiber–matrix interface and the compatibility between cellulose and corn starch resin molecules will affect the properties of the system. The well dispersed cellulose nanofibers contribute higher interfacial area and good fiber networking within the matrix resin. This will lead to better barrier properties. Sorption characteristics of water, oil and diesel in the textile composites were analysed and the influence of nano fibers and macro fibers on the transport phenomena was investigated. The kinetics of sorption-diffusion process was investigated. Kinetic parameters such as n, k, diffusion coefficient, permeability, solubility parameter, % swelling index, etc., were analysed. The presence of cellulose nanofibers influences the sorption mechanism. The water sorption mechanism in the nanocomposites was found to exhibit slight deviation from Fickian mode. Structure–property relationships of the nanocomposites were evaluated.     

Fiber optic flow and cure sensing for liquid composite molding

The Polymer Composites group at the National Institute of Standards and Technology has efforts in both on-line flow and cure sensing for liquid composite molding. For our flow program, a novel fiber optic real-time sensor system has been developed that can sense resin at various locations on a single fiber using long-period gratings and a polychromatic source. The sensor operation and characterization will be discussed along with sensor performance during mold filling with various types of reinforcement. The cure sensing program focuses on the interface-sensitive fluorescence response of a dye molecule grafted to a high-index glass fiber. The fluorescence emission of the fluorophore undergoes a blue shift as the resin cures. The fluorescence sensor is made by grafting a silane functional fluorophore onto the surface of the glass with close attention to layer thickness. Fluorescence emission of the grafted fluorophore film is shown to be sensitive to epoxy resin cure, co-silane, and layer thickness. The response of the grafted fluorophore to cure on a high-index fiber is demonstrated.     

Effect of Fiber Surface Modification on the Interfacial and Mechanical Properties of Kenaf Fiber-Reinforced Thermoplastic and Thermosetting Polymer Composites

The surfaces of kenaf fibers were treated with three different silane coupling agents. 3-glycidoxypropyltrimethoxy silane (GPS), 3-aminopropyltriethoxy silane (APS), and 3-methacryloxypropyltrimethoxy silane (MPS). Among them, the most effective one for the property improvement was GPS when it was applied to the kenaf fiber surfaces at 0.5 wt%. Thermoplastic polypropylene (PP) and thermosetting unsaturated polyester (UPE) matrix composites with chopped kenaf fibers untreated and treated at different GPS concentrations from 0.1 wt% to 5 wt% were fabricated using compression molding technique. The present study demonstrates that the interfacial, flexural, tensile, and dynamic mechanical properties of both kenaf/PP and kenaf/UPE composites importantly depend on the GPS treatments done at different concentrations. The greatest property improvement of both thermoplastic and thermosetting polymer composites was obtained with the silane treatment at 0.5 wt% and the mechanical properties were comparable with E-glass composites prepared the same polymer matrix under the corresponding fiber length and fiber loading. The results also agreed with each other with regard to their interfacial shear strength, flexural properties, tensile properties, storage modulus, with support of fracture surfaces of the composites.     

Plasma-polymerized organosilicones as engineered interlayers in glass fiber/polyester composites

The plasma polymerization technique was used to surface modify glass fibers in order to form a strong but tough link between the glass fiber and the polyester matrix, and enable an efficient stress transfer from the polymer matrix to the fiber. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane in a mixture with oxygen gas were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physico-chemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Young's modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the pp-TVS/O₂ interlayer was 32% higher than that with industrial sizing developed for fiber-reinforced composites with a polyester matrix.     

Electro-optical properties of a PDLC based on unsaturated polyester resin

An electro-optical characterisation of a polymer-dispersed liquid crystal (PDLC) based on unsaturated polyester (UP) resin, recently prepared in our laboratory, is presented. Transmittance and response times as a function of an electric field applied to the sample, have been measured taking into account also the morphological aspects of various samples. The experimental results confirm the theoretical data previously calculated on the base of the dimensions of the liquid-crystal droplets inside the polymeric matrix. Our analysis on this new material suggests the possibility of employing such a PDLC to realise electro-optical devices. Received: 9 October 1998 / Revised version: 12 May 1999 / Published online: 21 January 2000     

Effect of surface treatment on sand erosion behavior of glass beads-filled epoxy resin

Effects of the adhesion between filler particle and matrix on the erosion rate were studied in cured epoxy resin filled with glass beads having mean diameter 17 um. In order to observe the effect of adhesion on erosion rate. the filler particles were treated with silane coupling agent, silicone oil and washed by acetone as well. The filler content of the specimen was varied and also the specimens were attacked by different size angular particles. The comparison of each type of specimen shows that by using acetone and silicone oil for surface treatment, the erosion rate is relatively high. Whereas the specimen in which the filler was treated by silane have low erosion rate. The difference of erosion behavior is influenced by impacting particle size and filler content. Using small impacting particles and also low filler content, the erosion behavior between silane and acetone treated was quite different. On the other hand, using large impacting particles and high filler content, the erosion behavior between them was similar.     

树脂基复合材料在连续激光作用下的损伤

 采用热压工艺制备了碳纤维布和高硅氧纤维布增强的环氧树脂和酚醛树脂基复合材料,研究了不同功率密度连续激光辐照下,复合材料的破坏形式及其组织结构与力学性能的变化。结果表明：当激光辐照功率密度大于0.1 kW/cm²后,树脂基体产生燃烧,碳纤维没有明显的损伤,而玻璃纤维布开始熔融,复合材料的拉伸性能降低30%~40%;当功率密度达到1 kW/cm²以后,除基体燃烧外,碳纤维复合材料产生明显的鼓泡分层,表层碳纤维有少量破断,而高硅氧纤维产生明显的熔融烧损,复合材料的拉伸性能降低80%以上。采用有限元计算方法,对碳纤维增强环氧树脂复合材料在连续激光辐照下的温度场进行了研究,计算结果与实验中复合材料的损伤行为相吻合。     

Influence of interfacial reaction on interfacial performance of carbon fiber and polyarylacetylene resin composites

The influence of interfacial reaction on interfacial performance of carbon fiber/polyarylacetylene resin composites was studied. For this purpose, vinyltrimethoxysilane containing a double bond was grafted onto the carbon fiber surface to react with the triple bond of polyarylacetylene resin. The reaction between polyarylacetylene resin and vinyltrimethoxysilane was proved by reference to the model reaction between phenylacetylene and vinyltrimethoxysilane. Surface chemical analysis by XPS, surface energy determination from the dynamic contact angle, and the interfacial adhesion in composites was evaluated by interfacial shear strength test as well. It was found that vinyltrimethoxysilane, which can react with polyarylacetylene resin, had been grafted onto the carbon fiber surface. Furthermore, because the reaction between polyarylacetylene resin and vinyltrimethoxysilane took place at the interface, the interfacial adhesion in composites was significantly increased, and the improvement of interfacial adhesion was all attributed to the interfacial reaction.     

Studies on short isora fibre-reinforced polyester composites

This paper reports the use of a natural fibre, isora, as reinforcement in unsaturated polyester resin. Isora is a bast fibre separated from the bark of Helicteres isora plant by retting process. Properties like tensile strength, flexural strength etc. have been studied as a function of fibre length and fibre loading using treated and untreated fibre. The mechanical properties were found to be optimum at a fibre length of 30 mm and a fibre loading of 30% by volume. The effects of alkali treatment on the fibre properties were investigated by SEM, IR and TGA. The mechanical performance of the treated isora fibre-reinforced polyester composites has also been investigated. SEM studies were carried out to investigate the fibre surface morphology, fibre pull-out and fibre–polyester interface bonding. SEM gave evidence for the changes that had occurred on the fibre surface during chemical treatment. The properties were found to be superior for the composite reinforced with treated fibre compared to the untreated fibre.     

Effect of surface treatment of nanoclay on the mechanical properties of epoxy/glass fiber/clay nanocomposites

A new method of silane treatment of nanoclays is reported where in the clay is nanodispersed in hydrolyzed silanes. The surface functionalization of Cloisite^® 15A nanoclay has been carried out using two different silane coupling agents: 3-aminopropyltriethoxy silane and 3-glycidyloxypropyltrimethoxy silane using varied amounts of silane coupling agents, e.g. 10, 50, 200, and 400 wt% of clay. The surface modification of Cloisite^® 15A has been confirmed by Fourier transform infrared spectroscopy. The modified clays were then dispersed in epoxy resin, and glass fiber-reinforced epoxy clay laminates were manufactured using vacuum bagging technique. The fiber-reinforced epoxy clay nanocomposites containing silane modified clays have been characterized using small angle X-ray scattering, transmission electron spectroscopy and differential scanning calorimetry. The results indicate that the silane treatment of nanoclay aided the exfoliation of nanoclay and also led to an increase in mechanical properties. The optimized amount of silane coupling agents was 200 wt%. The nanocomposites containing clay modified in 200 wt% of silanes exhibited an exfoliated morphology, improved tensile strength, flexural modulus, and flexural strength. The improved interfacial bonding between silane modified nanoclays and epoxy matrix was also evident from significant increase in elongation at break.     

Fe2O3 nanoparticles dispersed unsaturated polyester resin based nanocomposites: effect of gamma radiation on mechanical properties

ABSTRACT

In this work, unsaturated polyester resin (UPR) matrix based nanocomposite was fabricated using synthesized Fe₂O₃ nanoparticle as reinforcement and methyl ethyl ketone peroxide as curing agent by solution casting method. The Fe₂O₃ nanoparticles were synthesized using the sol–gel method and the formation of nanoparticle was confirmed by X-ray diffraction, Scanning electron microscope, Energy dispersive spectrometry analysis. Interactions between metal oxide nanoparticles and polymer molecules in fabricated nanocomposite were investigated by Fourier transform infrared spectrometer analysis. Pure UPR and Fe₂O₃/UPR composite were irradiated with various gamma radiation doses (0–15?kGy). At the 0?kGy (without radiation), the nanoparticles loaded composite showed better mechanical properties (increased in tensile strength and Young’s modulus and decreased in elongation) compared to that of pure UPR sheet. At the 5?kGy radiation dose, the tensile strength and Young’s modulus were further increased; whereas, the elongation was decreased in both samples.     

Interphase formation of a resin transfer molded silica-phenolics composites subjected to dynamic impregnation process

In this study interphase formation of a resin transfer molded (RTMed) silica-phenolics composites subjected to dynamic impregnation process was investigated. The solvent effect on the interphase formation of silica fiber-phenolics composites was evaluated. UV-vis spectra, XPS and electron paramagnetic resonance (EPR) techniques were used to characterize the competitive adsorption of the components of phenolics solution onto silica reinforcement surfaces. Interlaminar shear strength (ILSS) and void content of silica-phenolics composites were also measured. It has been found that phenolics forms distribution gradient over RTM mold with respect to isomeric composition under the effect of solvent, which result, to varying extent, in the inhomogeneity of void content and thus ILSS of a final product. For the first time, it has been shown that the RTM process of silica-phenolics composites is highly solvent-dependent. Our work gives an insight into the role of organic solvent in a RTM solution impregnation processing and provides useful information and trends relating microscopic to macroscopic behavior.