Effects of fibre surface treatment on fracture-mechanical properties of sisal-fibre composites

Sisal fibre reinforced composites, one class of a broad range of eco-composite materials, were studied in connection with the effects of fibre surface treatment on their fracture-mechanical properties. Previous investigations on sisal fibre and its composites have been fully reviewed [1], which provided an impetus for this research. Two fibre surface treatment methods, chemical coupling based on silane and oxidization based on permanganate and dicumyl peroxide, together with untreated sisal fiber composites were used to set up different levels of interface bonding strength. The interface effects on the mechanical properties and fracture toughness of sisal fibre reinforced vinyl-ester composites were completely assessed based on the test results obtained and theoretical analyses. Many aspects of studies reported in this paper are original, such as single fiber pull-out tests and toughness evaluation of sisal composites aided by scanning electron microscopy. The results showed that fibre surface treatment could improve interfacial bonding properties between sisal fibre and vinylester resin. These in turn influenced the fracture-mechanical characteristics of this class of ecocomposites.     

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.     

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.     

In situ near infrared evanescent wave examination of surfactant adsorption on silica optical fibers

The use of composite materials has increased considerably in the past 30 years. However, many of the molecular level processes occurring in the interfacial region have yet to be investigated. In this regard, an in situ Fourier transform near infrared technique has been demonstrated herein. This technique utilizes a seven-fiber bundle to examine monolayer and sub-monolayer level surfactant adsorption at the silica optical fiber/solution interface. It is felt that this technique will greatly increase the knowledge of the processes involved in the improvement of mechanical properties of silane treated composites.     

Surface Modification of Ultrahigh-molecular-weight Polyethylene Fibers with Coupling Agent during Extraction Process

Ultrahigh molecular weight polyethylene (UHMWPE) fibers were treated with a coupling agent following the extraction of gel fibers, resulting in modified fibers after subsequent ultra-drawing. The structure and morphology of the modified UHMWPE fibers were characterized and their surface wetting, interfacial adhesion, and mechanical properties were investigated. It was found that the coupling agent was absorbed into the UHMWPE fiber and trapped on the fiber surface. Compared with unmodified UHMWPE fibers, the modified fibers had smaller contact angle, higher crystallinity, and smaller crystal size. The interfacial adhesion and mechanical properties of UHMWPE fibers were significantly improved with increasing coupling agent concentration and gradually reached a plateau value. After treatment with 1.5 wt% solution of a silane coupling agent (γ -aminopropyl triethoxysilane, SCA-KH-550), the interfacial shear strength of the UHMWPE-fiber/epoxy composites was increased by 108% and the tensile strength and modulus of modified UHMWPE fibers were increased by 11% and 37% respectively.     

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.     

Influence of Fiber Surface Treatment on Mechanical Properties of CF/PET Composites

Carbon fiber (CF) / poly (ethylene terephthalate) (PET) composites were prepared with various contents (2–15wt%) of short carbon fibers. To investigate the effect of surface treatment of the CF on the mechanical properties of the composites, three specimens were prepared; those with short carbon fibers (called SCF), short carbon fibers oxidized with nitric acid (called NASCF) and the fibers oxidized with nitric acid and treated with silane coupling agent (called SCSCF). Flexural, tensile and impact tests were performed to observe mechanical behavior of the specimens. The morphology of the specimens was also studied with a scanning electron microscope (SEM). SCSCF composite had better mechanical properties than the other composites with the same content of carbon fibers since the coupling agent resulted in better interfacial adhesion between the fiber and the matrix.     

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.     

Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.     

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.     

A comprehensive review on surface modification,structure interface and bonding mechanism of plant cellulose fiber reinforced polymer based composites

Abstract

Plant cellulose fiber polymer composites are readily applied in wide range of applications due to ecological and economical alternative to traditional materials. The considerable amount of residues and organic wastes from agricultural process are still employed as lower energy resource. Organic materials are generally disposed in composting, landfilling or anaerobic digestion. The utilization of these wastes in plant fiber composites shows significant alternative and environmental friendly in nature. The production of plant cellulose fiber composite with higher structural properties is optimized by interfacial bonding between polymer and reinforced fiber. The interface plays a vital role in regulating mechanical properties by distributing bonds and stress transferring, which is one of least understood element of composites. This paper presents the comprehensive review of fiber structures, different modification techniques to reduce the incompatibility between matrix and fiber, assessment of structure interface and bonding, clarifies the interfacial adhesion of cellulose fiber composites.     

Jute fiber-reinforced chemically functionalized high density polyethylene (JF/CF-HDPE) composites with in situ fiber/matrix interfacial adhesion by Palsule Process

Jute fiber-reinforced chemically functionalized polyethylene high density (JF/CF-HDPE) composites have been processed, by Palsule process without using any compatibilizer and without any fiber modification, by using chemically functionalized maleic anhydride grafted polyethylene (MAPE) as matrix, in place of polyethylene. Fiber/matrix interfacial adhesion generated in situ, due to interactions between jute fiber and the maleic anhydride of the CF-HDPE matrix, has been established by Fourier transform infrared spectroscopy and scanning electron microscope micrographs. Mechanical properties of the JF/CF-HDPE composites developed with in situ fiber/matrix interfacial adhesion in this study have been found to be higher than those of the CF-HDPE matrix and increase with increasing amounts of jute fibers in the JF/CF-HDPE composites, and are better than properties of literature reported and laboratory processed jute fiber/polyethylene composites with and without MAPE compatibilizer. Measured tensile modulus of JF/CF-HDPE composites compares well with values predicted by rule of mixtures, inverse rule of mixture, Hrisch Model, Halpin-Tsai equations, Nielsen equations, and with Palsule equation. The feasibility of developing natural fiber/maleic anhydride grafted polyolefin composites by Palsule process without using any compatibilizer and without any fiber treatment is demonstrated.     

Improving the interfacial strength of PMMA resin composites by chemically grafting graphene oxide on UHMWPE fiber

Controlling interfacial microstructure and interactions between (ultra high molecular weight polyethylene) UHMWPE fiber and matrix is of crucial importance for the fabrication of advanced polymer composites. In this paper, (UHMWPE fiber-g-graphene oxide [GO]) was prepared. GO nanoparticles distributed onto the ?ber surface uniformly, which could increase surface polarity and roughness. Increases of interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of UHMWPE fiber-g-GO composites were achieved. These enhancements can be attributed to the existent of GO interface with providing chemical bonding and strong mechanical interlocking between the ?ber and matrix. Moreover, impact resistance of UHMWPE fiber-g-GO composites was enhanced.     

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.     

A study of advances in characterization of interfaces and fiber surfaces in lignocellulosic fiber-reinforced composites

This article deals with the aspects of interfacial and surface characterization of natural fibers and their composites. Vegetable fibers and their composites have attracted the attention of scientists worldwide because of their favorable properties. The different chemical modifications of natural fibers and characterization aspects have been discussed. The adhesion between fiber and matrix is a major factor in determining the response of the interface and its integrity under stress. Therefore characterization of the interface is of utmost importance. Both fiber surface and polymer matrix surface can be modified to obtain a strong interface. Various treatments being used for the lignocellulosic surfaces and the characterization techniques have been illustrated. The four main techniques of interfacial characterization that are enumerated in this article are the micromechanical techniques, spectroscopic, microscopic and swelling techniques. The micromechanical techniques like fiber pull-out and fragmentation have been dealt with giving emphasis to experimental aspects. Recent studies dealing with interfacial study of different lignocellulosic fiber reinforced composites have also been cited.     

Correlations among micro- and macromechanical properties of composite materials based on the interphase concept

In this paper an attempt was made to define microstructural properties of carbon fiber/PP composites, with respect to fiber surface chemistry and morphology. In order to define the effects of the fiber surface sizings and morphology on the polymer microstructure, the interphase and mechanical properties of the composites, carbon fibers with similar, but not identical surface chemistry (CH and CT) were used. Characterization was performed by several techniques: SEM, POM, reflection microscopy, DSC, FTIR, XPS, contact angle measurements. For microstructural analysis, the geometrical method, method of intercept and DIF method were used. It was found that both carbon fibers have a strong influence on the nucleation mechanism and crystallization as well as on the microstructural parameters in the model and macro composites. Nucleation efficiency of the fibers has been confirmed by the nucleation parameter Q, measured by Muchova–Lednicky method and by the interfacial energy parameters. Microstructural analysis based on the photographs obtained by POM, SEM and reflection microscopy has shown that in the CH/PP model and macrocomposites the sieve-grain network was formed, which indicates better mechanical properties. The results obtained for the macromechanical properties of PP composites reinforced with CH and CT have confirmed the prediction based on micostructural analysis.     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

The role of interactions at interfaces of glass-fiber reinforced composites

The performance of glass-fiber reinforced composite materials is strongly dependent on adhesion at the fiber-matrix interface. This study has considered the effect of parameters such as wettability, mechanical interlocking due to diffusion, and specific interactions on adhesion. The surface characteristics of treated and untreated glass fibers were studied by inverse gas chromatography. Donor/acceptor concepts were used to calculate a specific (acid/base) interaction parameter for fiber/matrix pairs. Tensile strengths of composites with Nylon-6,6 and polyethylene correlated with both acid-base and dispersive interactions. Initial attempts were made to separate and quantify contributions to interfacial bonding from dispersive forces, acid/base forces, diffusion and the mechanical interlocking of constituents. Findings were supported by scanning electron microscopy of the fracture surfaces of composite samples.     

Mechanical Properties and Morphology of Polypropylene/Polypropylene-g-Maleic Anhydride/Long Glass Fiber Composites

Long glass fiber (LGF)-reinforced polypropylene (PP) was prepared using a self-designed impregnation device. The effect of dicumyl peroxide (DCP) and maleic anhydride (MA) content on the compatibilizer, PP grafted with maleic anhydride (PP-g-MA), was investigated by means of scanning electron microscopy (SEM) and mechanical properties. The experimental results demonstrated that the increase of DCP and MA could effectively improve the interfacial interaction between PP and GF. Good interfacial adhesion between PP and GF in PP/ PP-g-MA /LGF composites was observed from SEM studies for the higher contents of MA. The best mechanical properties of PP/ PP-g-MA /LGF(30%) composites were obtained when the content of DCP and MA were 0.4 and 0.8 wt%, respectively. The storage modulus of the PP/PP-g-MA/LGF composites increased and then decreased with the content of MA. When the content of MA was 0.8 wt%, tan δ had the lowest value, indicating that the corresponding composites had the best compatibility.     

Discontinuous basalt and glass fiber reinforced PP composites from textile prefabricates: effects of interfacial modification on the mechanical performance

Spun and blown basalt fibers and their PP matrix composites were investigated. The composites were manufactured by hot pressing technology from carded and needle punched prefabricate using PP fiber as matrix material. Glass and blown basalt fibers were treated with reaction product of maleic acid-anhydride and sunflower oil while spun basalt fibers had a surface coating of silane coupling agent. Fibers were investigated with tensile tests while composites were subjected to static and dynamic mechanical tests. The results show that blown basalt fibers have relatively poor mechanical properties, while spun basalt fibers are comparable with glass fibers regarding geometry and mechanical performance. The static and dynamic mechanical properties of glass and spun basalt fiber reinforced composites are similar and are higher than blown basalt fiber reinforced composites. Results were supported with SEM micrographs.