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.     

Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

The effect of surface treatment of carbon fiber on the flexural property of thermoplastic polyimide composite

Rare earth solution (RES) surface modification and air-oxidation methods were used to improve the interfacial adhesion of the carbon fiber reinforced polyimide (CF/PI) composite. The flexural property of the PI composites reinforced by the carbon fibers treated with different surface modification methods was comparatively investigated. Results showed that the flexural strength of CF/PI composite was improved after RES treatment. The improvement of impact and flexural property of the CF/PI composite was mainly due to the improvement in interfacial adhesion after RES treatment. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the oxygen concentration was obviously increased after RES treatment. The increase in the amount of organic functional groups increased the interfacial adhesion between CF and PI matrix.     

Effect of fiber surface treatments on the fiber–matrix interaction in banana fiber reinforced polyester composites

Cellulosic fibers have been used as cost-cutting fillers in plastic industry. Among the various factors, the final performance of the composite materials depends to a large extent on the adhesion between the polymer matrix and the reinforcement and therefore on the quality of the interface. To achieve optimum performance of the end product, sufficient interaction between the matrix resin and the cellulosic material is desired. This is often achieved by surface modification of the resin or the filler. Banana fiber, the cellulosic fibers obtained from the pseudo-stem of banana plant (Musa sepientum) is a bast fiber with relatively good mechanical properties. The fiber surface was modified chemically to bring about improved interfacial interaction between the fiber and the polyester matrix. Various silanes and alkali were used to modify the fiber surface. Modified surfaces were characterized by SEM and FTIR. The polarity parameters of the chemically modified fibers were investigated using the solvatochromic technique. The results were further confirmed by electrokinetic measurements. Chemical modification was found to have a profound effect on the fiber–matrix interactions. The improved fiber–matrix interaction is evident from the enhanced tensile and flexural properties. The lower impact properties of the treated composites compared to the untreated composites further point to the improved fiber–matrix adhesion. In order to know more about the fiber–matrix adhesion, fractured surfaces of the failed composites where further investigated by SEM. Of the various chemical treatments, simple alkali treatment with NaOH of 1% concentration was found to be the most effective. The fiber–matrix interactions were found to be dependent on the polarity of the modified fiber surface.     

Interfacial effects in short sisal fiber/maleated castor oil foam composites

In this study, bio-foam composites are produced using short sisal fiber as the reinforcement and modified castor oil as the matrix, respectively. The foam composites with an average cell size of 200 μm possess properties similar to those of commercial polyurethane foams. The effects of fiber loading, fiber length and foam density on the compressive properties of the foam composites are reported in relation to the interfacial interaction. It is found that the addition of chopped sisal alters cell structure of the foam. Surface pre-treatment of sisal by alkali or silane coupling agent helps to improve the mechanical properties and interfacial adhesion. The exposure of the fibers to the gas cells of the foam reduces the effectiveness of interfacial effect, which is different from the case of conventional bulk composites. As a result, the reinforcing ability of sisal fibers becomes a function of fiber length and so on.     

Study of impact properties and morphology of unidirectional bamboo strips–polyester composites: effect of mercerization

Composites were fabricated with alkali (10%, 15% and 20%) treated bamboo fibers incorporated to the extent of 50% (by volume) and polyester resin. Impact test was made on bamboo strips and composites samples. It was observed that the fracture energy undergoes an increase from untreated to alkali treated bamboo strips. Alkali treated bamboo fiber composites show higher fracture energy value than the untreated bamboo fiber composites. The phenomenal change was quite evident from scanning electron micrographs of the fractured surface. Considering the effects of all factors, the work of fracture shows maximum value in the case of 20% alkali treated bamboo strip composites. It was also observed that the rate of increase of work of fracture value is much higher in the case of composite samples than the bamboo sample. It was explained on the basis of synergism obtained by improved interfacial adhesion between fiber and matrix, and removal of hemicellulose from the bamboo itself, which was evident from the intermolecular H-bonding formation studied by FT-IR.     

Short sisal fiber reinforced polypropylene composites: the role of interface modification on ultimate properties

Sisal fibers have been used for the reinforcement of polypropylene matrix. The compatibilization between the hydrophilic cellulose fiber and hydrophobic PP has been achieved through treatment of cellulose fibers with sodium hydroxide, isocyanates, maleic anhydride modified polypropylene (MAPP), benzyl chloride and by using permanganate. Various fiber treatments enhanced the tensile properties of the composites considerably, but to varying degrees. The SEM photomicrographs of fracture surfaces of the treated composites clearly indicated the extent of fiber–matrix interface adhesion, fiber pullout and fiber surface topography. Surface fibrillation is found to occur during alkali treatment which improves interfacial adhesion between the fiber and PP matrix. The grafting of the fibers by MAPP enhances the tensile strength of the resulting composite. It has been found that the urethane derivative of polypropylene glycol and cardanol treatments reduced the hydrophilic nature of sisal fiber and thereby enhanced the tensile properties of the sisal–PP composites, as evident from the SEM photomicrographs of the fracture surface. The IR spectrum of the urethane derivative of polypropylene glycol gave evidence for the existence of a urethane linkage. Benzoylation of the fiber improves the adhesion of the fiber to the PP matrix. The benzoylated fiber was analyzed by IR spectroscopy. Experimental results indicated a better compatibility between benzoylated fiber and PP. The observed enhancement in tensile properties of permanganate-treated composites at a low concentration is due to the permanganate-induced grafting of PP on to sisal fibers. Among the various treatments, MAPP treatment gave superior mechanical properties. Finally, experimental results of the mechanical properties of the composite have been compared with theoretical predictions.     

Mechanical and tribological enhancement of polyoxymethylene-based composites with long basalt fiber through melt pultrusion

Abstract

The polyoxymethylene (POM)/basalt fiber composites were prepared by use of long fiber-reinforced thermoplastic technology through melt pultrusion. The mechanical and tribological properties, morphology, and thermal stability of the resulting composites were investigated. The composites exhibit significant improvements in tensile, flexural, and notched impact strength. These mechanical strength and toughness are dependent on the fiber content over the full range of the study. The residual fiber length and distribution in the injection-molded specimens were characterized. The prominent reinforcement effect of basalt fiber on POM is derived from the supercritical fiber length, which is much longer than that of the short fiber-reinforced ones and thus makes the composites take full advantage of the strength of the reinforcing fibers. The Kelly–Tyson model was used to predict the ultimate tensile strength of POM composites using the measured values of residual fiber length in the matrix, but the deviations were observed at the high contents of basalt fiber. The morphologic investigation indicates that the fiber pullout and fiber breakage both contribute energy dissipation to the tensile fracture of the composites. The tribological characterization indicates that the friction coefficients and specific wear rates of POM composites also decrease remarkably. Such an improvement of tribological performance is due to the presence of the high wear-resistant basalt fibers on the top of the worn surface bearing the dynamic loadings under sliding. Moreover, the dynamic mechanical analysis reveals that the storage moduli of the composites increase with increasing the fiber content, whereas the loss factors present an opposite trend.     

Hybrid Nanoparticle/Microfiber‐Filled Injection‐Molded Composites

The structure and some properties of hybrid injection‐molded polypropylene (PP) composites, containing carbon fibers (CF) and nanoparticles, were studied. The effects of nanoparticle type, size, and content were investigated. All studied hybrid composites exhibited unexpected fiber disorientation (oriented even transverse to the melt‐flow direction), disappearance of the typical skin/core structure in fiber‐containing moldings and, surprisingly, very low fiber length. Different types of nanoparticles resulted in different levels of fiber breakage: the shortest fibers were observed in composites containing nano‐TiO₂ and longer ones in composites containing nano‐Al₂O₃ and carbon black (CB). Moreover, smaller nanoparticles resulted in higher levels of fiber length attrition. Electrical conductivity of the composites was found to drop drastically upon incorporation of several volume percents of insulating nanoparticles, although the content of CF when by itself was above the percolation threshold. Tensile modulus values, in the melt‐flow direction, of hybrid composites were also inferior to those of the only–CF‐reinforced composites, while rheological properties were dominated by CF, being practically not affected by the presence of nanoparticles. Based on the present and previous studies, the effect of nanoparticles on fiber orientation and their length attrition in hybrid injection moldings could be generalized to systems containing combinations of brittle fibers and hard nanoparticles.     

Improving the performance of conventional glass fiber epoxy matrix composites by incorporating nanodiamonds

Multiscale glass fiber epoxy matrix composites containing nanodiamonds were fabricated using vacuum bagging technique. Three different loadings of nanodiamonds were incorporated in epoxy resin after their functionalization through ozone-treatment, i.e., 0.1, 0.3 and 0.5 wt%. The functionalization of nanodiamonds was confirmed by infrared spectroscopy, which improved the dispersion of nanodiamond in epoxy resin thus improving the mechanical properties. Tensile, compression, flexural and interlaminar shear properties of the composites were improved. The tensile, compression and flexural strengths improved up to 36, 56 and 30% by the addition of 0.5 wt% nanodiamonds while the corresponding moduli increased to 30, 125 and 46%, respectively. An improvement of 38% in interlaminar shear strength was observed. The microscopy of the composites was performed using optical and electron microscopy and proper impregnation of glass fibers and the absence of the agglomerates of nanodiamonds were ensured. The homogeneous dispersion of nanodiamonds and their adhering role at fiber/matrix interface improved the mechanical properties of the composites. The developed composites are ideal candidate materials for engineering applications demanding high specific mechanical properties.     

Micromechanical Behavior of Carbon Nanotube-Covered SiC Fibers in Polymer Matrix Composites

The incorporation of nanotube-covered fibers in continuous fiber/epoxy composites has been shown to influence the mechanical, electrical, and thermal properties of the composite. Increased interlaminar shear stress, flexural strength and modulus have been reported in such composites over composites containing bare fibers. In this study, the microstructure and interfacial shear strength (ISS) of continuous silicon carbide fiber/epoxy composites with and without nanotubes grown from the SiC fiber surface were investigated with micro-Raman spectroscopy (MRS) and microscopy. The fibers with nanotubes grown from the surface were found to have a reduced ISS compared with the bare fibers. Electron microscopy showed good wetting of epoxy in the nanotube forests, but poor attachment of the nanotube forests to the fibers. These results suggest that the mechanism leading to improvements in bulk composite properties is not due to an improvement in the fiber/matrix ISS.     

Effect of fiber content and surface treatment on the mechanical properties of natural fiber composites produced by rotomolding

In this study, natural fibers (agave, coir, and pine) were surface treated with maleated polyethylene (MAPE) with two main objectives: (1) to improve the mechanical properties of natural fiber composites produced by rotational molding and (2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30, and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (hardness, impact, tension, and flexion). The results showed that MAPE surface treatment was more successful for agave and coir than for pine fibers due to their respective chemical composition. In general, surface treatment led to better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved using treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher (about 160, 400, and 100% for impact, tensile, and flexural properties, respectively) than for UFC.     

Studies on interfacial adhesion in unidirectional isora fibre reinforced polyester composites

Unidirectional isora fibre reinforced polyester composites were prepared by compression moulding. Isora is a natural bast fibre separated from the Helicteres isora plant by a retting process. The effect of alkali treatment on the thermal properties of the fibre was studied using TGA, DTA and DSC in oxygen and nitrogen atmosphere. Mechanical properties like tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali-treated fibres have been studied as a function of fibre loading. The optimum loading for tensile properties of the composite containing untreated fibre was found to be 45% by volume and on alkalization of the fibre, the optimum loading increased to 66%. For flexural properties the loading was optimized at about 56% and 66%, for the composites containing untreated and alkali treated fibres, respectively. From DMA studies it was observed that the alkali-treated fibre composites have higher E′ and E″ values compared to untreated fibre composites. From swelling studies in styrene it was observed that the mole percent uptake of the solvent by the treated fibre composites is less than by the untreated fibre composites. From these results it can be concluded that in composites containing alkalized fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Correlation of the mechanical properties to the fiber–matrix adhesion of Nextel 312™ fiber/BN/Blackglas™ composites

Boron nitride (BN)-coated aluminoborosilicate (Nextel? 312) fibers, produced via ammonia nitridation, along with 'as-received' and 'desized' fibers, were composited in a silicon oxycarbide (Blackglas?) matrix. The mechanical properties, failure properties, and fiber–matrix interfacial chemistry of the composite were investigated. BN treated fiber composites show a 90% improvement in flexural strength and substantial increases in shear strength (short beam shear and Iosipescu) over the 'as-received' fiber composite. The composite fabricated with 'desized' fibers underwent spontaneous delamination during pyrolization, precluding mechanical testing. X-ray photoelectron spectroscopy of the starting materials and of composite fracture surfaces combined with scanning electron microscopy and energy dispersive X-ray spectroscopy indicate that the locus of failure of the BN-coated fiber composite occurs at the matrix/BN coating interface.     

Characterisation Studies and Impact of Chemical Treatment on Mechanical Properties of Sisal Fiber

The availability of natural fibers with their high performance and low cost contributes to a healthy ecosystem and fulfills the economic interests of the society. Sisal fiber, which is easily cultivated, is one of the most widely used natural fibers. For the present studies, characterisation of locally available sisal fiber of M.P. state in India was carried out with the investigation on the effect of alkali treatment with a wide range of different concentrations on the mechanical properties of sisal fiber. The physical and chemical properties of sisal fiber were analyzed with known methods and results were found to be similar to earlier reported values. Alkali treatment was carried out with different concentrations and mechanical properties were evaluated with Lloyd Fiber Testing Instrument. The results show that the chemical treatment enhances the mechanical properties of fiber up to a limit and is found to decrease with further increase in concentration. Scanning Electron Microscopy was used to investigate the morphology of untreated and alkali treated sisal fibers which indicated that the different concentrations of alkali alter the fiber surfaces with variations. Sisal fibers before and after alkali treatment were characterised further by thermogravimetry to establish their thermal stability, and measurements showed that alkali treated fiber became more thermal resistant than the untreated fiber and it was also noticed that thermal resistance decreases at higher concentration.     

Fabrication of continuous fiber-reinforced thermoplastic composites with structural gradient from sheath-core type bicomponent fibers

Sheath-core type bicomponent fibers of polypropylene (PP) as a sheath component and thermotropic liquid crystalline polymer (TLCP) as a core component were prepared by the highspeed melt spinning process. Continuous fiber reinforced thermoplastic composites, in which TLCP acts as a reinforcing fiber and PP as a matrix polymer, were fabricated by the compression molding of these fibers. In the melt spinning, the attainable highest take-up velocity of TLCP was improved by co-processing with PP. Tensile modulus and strength of the TLCP component in the PP/TLCP bicomponent fibers increased with an increase in the take-up velocity. Comparison of wide-angle X-ray diffraction patterns of starting bicomponent fibers and fabricated composites indicated that the orientation relaxation of TLCP did not occur in the compression molding process. Accordingly, the tensile modulus and strength of the PP/TLCP composites were similar to those of the bicomponent fibers. Continuous fiber reinforced thermoplastic composites with various types of fiber content distributions were fabricated from the bicomponent fibers in which sheath-core composition was changed gradually in the spinning process. In the three-point bending test, the composites with two different types of symmetric structural gradients, one with higher TLCP fiber content near the surfaces than in the center and the other with higher TLCP content in the center than near the surfaces, exhibited different flexural moduli even though the overall TLCP contents were comparable. In the three-point bending test of a composite with asymmetric structural gradient, the yielding behavior and maximum flexural load varied depending on the direction of load application although the initial flexural moduli were similar.     

Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

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.     

Modified flax fibers reinforced soy-based composites: mechanical properties and water absorption behavior

Flax fibers are often used in reinforced composites which have exhibited numerous advantages such as high mechanical properties, low density and biodegradablility. On the other hand, the hydrophilic nature of flax fiber is a major problem. In this study, we prepare the soybean oil based composites reinforced with protein coated and lipid acylated flax fibers and compare their water uptake properties. Results showed that water resistance properties of the composites are improved where treated flax fibers are used. The composite with lipid acylation of the flax fiber exhibited to enhance tensile strength and water resistance properties. Influences of fiber length, fiber loading and pressure on mechanical properties are also reported.     

The role of interface modification on the mechanical properties of injection-moulded composites from commingled polypropylene/banana granules

Commingled polypropylene (PP)/banana granules were fabricated from slivers by mixing PP fibers and banana fibers by textile equipment. By twisting the sliver, the reinforcing fibers were compacted and bonded with the molten matrix material. PP/banana composites were prepared from commingled PP/banana granules by injection moulding method with special reference to the effect of maleic anhydride modified polypropylene (MAH-PP) concentration. The mechanical properties of the composites were found to depend on the concentration of MAH-PP. The tensile and flexural properties of the composites increased with the addition of MAH-PP up to 2 wt%. After 2 wt% addition of MAH-PP, these properties tend to be stabilized. On the other hand the unmodified composites showed the maximum impact strength. Fourier transform infrared spectroscopic (FTIR) analysis of the MAH-PP modified composites showed evidence of a chemical bridge between the hydroxyl group of the banana fiber and maleic anhydride of the MAH-PP through an esterification reaction. The feature peak of the esterification occurred in the range ～ 1743 cm^?1. In order to confirm the esterfication reaction further, FTIR spectra of the banana microfibrils and MAH-PP modified PP/banana microfibril composites were taken and compared. The tensile fracture surfaces of the unmodified and MAH-PP modified PP/banana composites were studied by scanning electron microscopy (SEM). An improvement in adhesion between the fiber and the matrix was observed in the case of MAH-PP modified composites. Two different processing methods, both injection and compression mouldings were performed to prepare the PP/banana composites. Tensile properties of the composites prepared by these two methods were compared. The enhancement of tensile properties for injection-moulded composites compared to the compression-moulded composites is owing to the occurrence of orientation, better mixing and interaction between the fiber and the matrix during injection moulding. Finally, experimental results of the tensile properties of the injection-moulded composites have been compared with theoretical predictions.