Bamboo fibers grafted with a soybean-oil-based monomer for its unsaturated polyester composites

A soybean-oil-based monomer, acrylated epoxidized soybean oil (AESO), was grafted onto bamboo fibers (BFs) using 1,6-diisocyanatohexane (DIH) as a linker to facilitate the formulation of a hydrophobic layer on the fiber surface and to impart the fibers with active functional groups that can form chemical connections with unsaturated polyester (UPE) resin. The reaction mechanism of BFs with AESO and DIH and its surface chemical characteristics were investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) analyses. These analyses confirmed that the AESO reacted with the DIH and then the resultant AESO-DIH oligomer was covalently bonded onto the BFs via urethane linkages. The grafting of BFs with AESO-DIH resulted in improved tensile and flexural properties, storage modulus, and thermal stability of the BF–UPE composite samples. There were also reductions in the water uptake rate and the diffusion coefficient due to the surface chemical changes of the fibers and thus the enhanced fiber-matrix interface of the composites.     

Stacking sequence effect of aramid–UHMPE hybrid composites by flexural test method: MATERIAL PROPERTIES

Aramid fibre–ultra-high modulus polyethylene (UHMPE) fibre interply hybrid composites were fabricated with changes in the stacking sequence. The flexural strength and modulus of hybrid composites were measured in order to investigate the effect of stacking sequence. Scanning electron microscopy (SEM) was used to examine the fracture surface of interply hybrid composites. When aramid fibre was at the compressive side and dispersion extent of fibers was small, the higher flexural strength and positive hybrid effect were observed. In addition, the different stacking sequence resulted in a change in flexural failure mechanism which had an effect on the flexural strength. As the dispersion extent of fibers decreased, the introduction of cohesive failure in aramid–aramid interface and PE–PE interface improved the flexural strength of hybrid composites.     

Modification of the surface of carbon fibers with multi-walled carbon nanotubes and its effect on mechanical characteristics of composites with epoxy resin

Effect of the catalyst composition on the structure of nanotubes layers obtained on the surface of carbon nanofibers was studied. We found the preliminary functionalization of the surface of carbon fibers to affect the coating uniformity and the thickness of synthesized nanotube layer. We determined the optimal surface concentration of the catalyst (Fe–Co) which provides uniform layer of nanotubes on the surface of carbon fibers. The effect of modification of the surface of carbon fibers with multi-walled carbon nanotubes on the mechanical properties of carbon fiber–epoxy resin composites was examined. The modification of the carbon fibers with multi-walled carbon nanotubes were shown to increase the flexural modulus and the flexural strength.     

Interface morphology and thermoplasticization behavior of bamboo fibers benzylated with benzyl chloride

In this study, benzylated bamboo flour (BBF) was synthesized using benzyl chloride under mild conditions. This material can be added to medium density polyethylene (MDPE) as a reinforcing filler material. The crystal structure and properties of the BBF and corresponding BBF/MDPE panels were investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy dispersive X‐ray spectroscopy, mechanical tests and surface hydrophobicity measurements, and the obtained results are in good agreement. According to the scanning electron microscopy and X‐ray diffraction investigations, the crystal structure of the bamboo material disappeared after the addition of benzyl chloride. The Fourier transform infrared spectroscopy analysis provided further evidence for the successful benzylation. The intensity of the bands attributed to the O—H stretching or deformation vibrations decreased, and the intensity of the bands attributed to the C = O and C—O bonds in the benzyl group increased, which was confirmed by the X‐ray spectroscopy analysis. The volume fraction of the dispersed phase increased dramatically, and the interfacial fusion between the BBF particles and the MDPE matrix improved. The tensile strength and flexural strength of the prepared BBF/MDPE panels were up to 24.21% and 26.73% higher, respectively, compared with panels fabricated from unmodified bamboo flour. Furthermore, the surface hydrophobicity was found to be higher, which confirmed the good interface fusion. The strengthening mechanism is discussed in this paper, and the overall results suggest that BBF is a promising candidate material for the substitution of traditional wood fibers and unmodified bamboo flour in wood plastic composites. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of fiber length and composition on mechanical properties of carbon fiber‐reinforced polybenzoxazine

The mechanical strength and modulus of chopped carbon fiber (CF)‐reinforced polybenzoxazine composites were investigated by changing the length of CFs. Tensile, compressive, and flexural properties were investigated. The void content was found to be higher for the short fiber composites. With increase in fiber length, tensile strength increased and optimized at around 17 mm fiber length whereas compressive strength exhibited a continuous diminution. The flexural strength too increased with fiber length and optimized at around 17 mm fiber length. The increase in strength of composites with fiber length is attributed to the enhancement in effective contact area of fibers with the matrix. The experimental results showed that there was about 350% increase in flexural strength and 470% increase in tensile strength of the composites with respect to the neat polybenzoxazine, while, compressive properties were adversely affected. The composites exhibited an optimum increase of about 800% in flexural modulus and 200% in tensile modulus. Enhancing the fiber length, leads to fiber entanglement in the composites, resulted in increased plastic deformation at higher strain. Multiple branch matrix shear, debonded fibers and voids were the failures visualized in the microscopic analyses. Defibrillation has been exhibited by all composites irrespective of fiber length. Fiber debonding and breaking were associated with short fibers whereas clustering and defibrillation were the major failure modes in long fiber composites. Increasing fiber loading improved the tensile and flexural properties until 50–60 wt% of fiber whereas the compressive property consistently decreased on fiber loading. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of surface treatment with potassium permanganate on ultra-high molecular weight polyethylene fiber reinforced natural rubber composites

The effects of surface treatment using potassium permanganate on ultra-high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were investigated. The results showed the surface roughness and the oxygen-containing groups on the surface of the modified fibers were effectively increased. The NR matrix composites were prepared with as-received and modified UHMWPE fibers added 0–6 wt%. The treated fibers increased the modulus and tensile stress at a given elongation. The tear strength increased with increasing fiber mass fraction, attained maximum values at 4 wt%. The hardness of composites exhibited continuous increase with increasing the fiber content. The dynamic mechanical tests showed that the storage modulus and the tangent of the loss angle were decreased in the modified UHMWPE fibers/NR composites. Several micro-fibrillations between the treated fiber and NR matrix were observed, which meant the interfacial adhesion strength was improved.     

A study of PP/PET composites: Factorial design,mechanical and thermal properties

Due to the economic importance of polypropylene (PP) and polyethylene terephthalate (PET), and the large amount of composites made with PP matrix and recycled PET as reinforcing material; an investigation was performed regarding the mechanical and thermal behavior of PP composites containing recycled polyethylene terephthalate fibers (rPET). Interfacial adhesion between the two materials was achieved by adding a compatibilizer, maleic anhydride grafted polypropylene, PP-g-MA. Mechanical behavior was assessed by tensile, flexural, impact and fatigue tests, and thermal behavior by HDT (Heat Deflection Temperature). Fractured surfaces and fiber were investigated by scanning electron microscopy. Multiple regression statistical analysis was performed to interpret interaction effects of the variables. Tensile strength, tensile modulus, flexural strength, flexural modulus and HDT increased after rPET fiber incorporation while strain at break, impact strength and fatigue life decreased. Addition of compatibilizer increased tensile strength, flexural strength and flexural modulus, fatigue life and HDT while tensile modulus, strain at break and impact strength decreased. However, at low fiber content, the impact strength increased, probably due to nucleation effects on PP.     

Synergistic effects induced by oxy-fluorination of carbon preforms to improve the mechanical and thermal properties of carbon-carbon composites

Oxy-fluorination of carbon preforms with various F₂:O₂ gas mixtures were examined to improve the mechanical and thermal properties of carbon fiber-reinforced carbon composites (C/C composites). The oxy-fluorination of the preforms introduced functional groups onto the preform surface, which improved their thermal properties. Oxy-fluorination also improved the interfacial adhesion of the C/C composites, resulting in increased flexural strength and anti-oxidation. Two synergistic effects of oxy-fluorination on the carbon preform are suggested. One optimizes interfacial adhesion by forming hard chemical bonds and soft electrophilic bonds between the surface functional groups of the oxy-fluorinated carbon preforms and the functional groups of the carbon precursors. The other improves anti-oxidation of the C/C composites by improving the thermal properties of the carbon preform itself and interfacial adhesion which resulted in reducing pores, voids, and interfacial cracks.     

Flexural behavior of unidirectional polyethylene–glass fiber–PMMA hybrid composites

Unidirectional hybrid laminates based on glass fibers (GF) and high performance polyethylene fibers (PEF) were prepared with a partially polymerized methyl methacrylate (MMA) matrix at room temperature followed by heating at 55°C for the stipulated time (well below the softening point of PEF). The ultimate flexural strength (UFS), flexural modulus (FM) and interlaminar shear strength (ILSS) of the composites were determined and analyzed. An interesting observation of the study was the change in flexural behavior, which was largely dependent on the position of GF and PEF ply/plies in the compression and tension sides. When the ply/plies of PEF were at the tension side, the UFS and FM showed a higher value than that when GF plies were in the tension side of the hybrid composites. The ILSS also follows the same trend regarding the position of the GF and PEF plies.     

Improved mechanical properties of epoxy composites reinforced with surface‐treated UHMWPE fibers

The surface treatment of ultra‐high molecular weight polyethylene fiber using potassium permanganate and the mechanical properties of its epoxy composites were studied. After treatment, many changes were happened in the fiber surface: more O‐containing groups (―OH, ―C═O, and ―C―O groups), drastically decreased contact angles with water and ethylene glycol, slightly increased melting point and crystallinity, and formed cracks. Different contents (0.1–0.5 wt%) ultra‐high molecular weight polyethylene fibers/epoxy composites were prepared. The results indicated that the surface treatment decreased the tensile strength of epoxy composites, but increased the bending strength. When the fiber content was 0.3 wt%, the above properties reached the maximum. At the same fiber content, the interlaminar shear strength of the composites was increased by 26.6% up to the as‐received fiber composites. Dynamic mechanical analysis of the composites suggested the storage modulus and tanδ were decreased due to the surface treatment. Fractured surface analysis confirmed that the potassium permanganate treatment was effective in improving the interface interaction.     

Improving the dispersion and flexural strength of multiwalled carbon nanotubes-stiff epoxy composites through β-hydroxyester surface functionalization coupled with the anionic homopolymerization of the epoxy matrix

Multiwalled carbon nanotubes (MWNTs) were functionalized in a two-step acid-epoxy functionalization process, in which suitable surface condition and reactivity compatible with the DGEBA epoxy resin was introduced. The use of (4-dimethylamino)-pyridine as an initiator for DGEBA homopolymerization produced covalent bonds between the functionalized MWNTs and the epoxy matrix through chain transfer reactions involving the secondary hydroxyls. This process yielded uniform MWNTs-stiff epoxy composites with significant enhancement in flexural strength without sacrificing the elastic modulus when compared to the neat resin.     

Mechanical and morphological properties of injection-molded rice husk polypropylene composites

In this work, the investigation of the physical, mechanical, and morphological properties of the rice husk flour/polypropylene composites was performed utilizing various filler loadings and coupling agent. Five levels of filler loading (35, 40, 45, 50, and 55 wt%) were designed. In addition, to help the interaction between fiber and polypropylene matrix, struktol coupling agent was added to the composites. All of tensile strength, Young's modulus, flexural strength, flexural modulus, and impact strength properties of the composites were carried out. Moreover, the 50 wt% filler-loaded composites had optimum tensile strength, flexural strength, and flexural modulus, whereas the 35 wt% of filler loading case was the best regarding Young's modulus, flexural strength, flexural modulus, and impact strength. Furthermore, the scanning electron microscope results demonstrate that as filler loading increases, more voids and fiber pullout occur.     

Recycled PP/EPDM/talc reinforced with bamboo fiber: Assessment of fiber and compatibilizer content on properties using factorial design

Thermoplastic composites reinforced with natural fibers have attracted the attention of many researchers, not only for environmental concerns, but also for economic reasons, recyclability, ease of processing, etc. One promising application is in the automotive industry due to their low cost and weight. This industry is increasingly pressured to produce vehicles that consume less fuel and are less polluting. Therefore, plastics reinforced with fibers are required to produce lighter parts to replace the much more abrasive glass fiber and mineral filled composites. One of the most widely used polymers in the automotive sector for manufacturing interior and exterior vehicle components is talc filled EPDM (ethylene-propylene-diene monomer) toughened polypropylene (PP). In this context, the aim of this study was to assess mechanical and thermal properties of bamboo fiber reinforced recycled talc filled PP/EPDM composites compatibilized with maleic anhydride grafted polypropylene (PP-g-MAH). Composites were prepared, according to a 2² factorial design with center point, in a Haake twin screw extruder with subsequent injection molding. Injected specimens were subjected to tensile, flexural, impact and fatigue testing. Morphological analyses were performed by scanning electron microscopy (SEM), and thermal analyses by thermogravimetry (TGA) and differential scanning calorimetry (DSC). Addition of bamboo fiber significantly increased tensile and bending strength, modulus and fatigue life, and decreased elongation at break and impact strength. On the other hand, addition of the compatibilizer had a positive effect only on tensile and flexural strength, and fatigue life whereas the effect was negative on elongation at break and impact strength. The addition of fiber and compatibilizer did not appreciably affect the matrix melting temperature, but slightly increased crystallization temperature and in some cases the degree of crystallinity.     

Cellulose nanofibril-reinforced biodegradable polymer composites obtained via a Pickering emulsion approach

Preparation of cellulose nanofibril (CNF)-reinforced, biodegradable polymer composites is challenging in that it’s hard to achieve good dispersion of the hydrophilic cellulose fibers in a hydrophobic polymer matrix. In this work, we developed a surfactant-free and efficient process to prepare CNF-reinforced poly (lactic acid) (PLA) composites from an aqueous dichloromethane Pickering emulsion self-emulsified by CNFs. CNF/PLA composites of homogeneous dispersion were obtained upon evaporation of CH₂Cl₂, filtration, drying and hot-pressing. Differential scanning calorimetry measurement revealed an enhanced crystallization capacity of the CNF/PLA composites. Thermogravimetric analysis indicated an increase of onset degradation temperature. The composites displayed an enhanced storage modulus compared with neat PLA throughout the testing temperature range, and especially in the high-temperature region (>70 °C). Enhancements of the flexural modulus and strength were also achieved.     

Investigation of microwave energy to cure carbon fiber reinforced phenylethynyl-terminated polyimide composites,PETI-5/IM7

The application of microwave energy to the processing of carbon fiber reinforced phenylethynyl-terminated polyimide composites (PETI-5/IM7) was investigated and evaluated with a variable-frequency microwave furnace. The thermal and physical properties of the composites were measured by dynamic mechanical thermal analysis, thermogravimetric analysis, thermomechanical analysis, and density and composition tests. The mechanical properties were determined by 3-point-bending and short-beam-shear tests at both room temperature and 177 °C. The shear failure surfaces of both microwave- and thermally cured composites were detected with environmental scanning electron microscopy. A comparison of the thermal and microwave processes was conducted to evaluate the advantage of the microwave process. Microwave-cured composites, fabricated under various pressures at the fixed process temperatures, also were investigated. From these studies, it was concluded that microwave energy successfully was used to fabricate PETI-5/IM7 composites with higher glass-transition temperatures (by 11–16 °C) and higher retention in flexural strength, flexural modulus, and shear strength at 177 °C than those fabricated by the thermal process. Furthermore, the microwave processes required only half the time used for the standard thermal process. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4616–4628, 1999     

Effect of Silane Coupling Agent and Compatibilizer on Properties of Short Rossells Fiber/Poly(propylene) Composites

Rossells fiber reinforced polypropylene composites were prepared by melt mixing. The fiber content was 20 wt%. Octadecyltrimethoxysilane (OTMS) and maleic anhydride grafted polypropylene (MAPP) were used to improve the adhesion between poly(propylene) (PP) and the fiber. The mechanical, rheological, and morphological properties, and heat distortion temperature (HDT) of the composites were investigated. Tensile strength, impact strength, flexural strength and HDT of MAPP modified PP composites increased with an increase in MAPP content. However, no remarkable effect of MAPP content on the Young's modulus of the composites was found. OTMS resulted in small decreases of tensile strength and Young's modulus, and increase in impact strength. Scanning electron micrographs revealed that MAPP enhanced surface adhesion between the fiber surface and PP matrix.     

Biocomposites based on Alfa fibers and starch‐based biopolymer

Biocomposite materials based on Alfa cellulose fibers (esparto grass plant) as reinforcing element and starch‐based biopolymer matrix were prepared and characterized in terms of mechanical performance, thermal properties, and water absorbance behavior. The fibers and the matrix were first mixed in the melted state under mechanical shearing using a plastograph and the obtained composites were molded by injection process. The tensile mechanical analysis showed a linear increase of the composite flexural and tensile modulus upon increasing the fiber content, together with a sharp decrease of the elongation at break. The fibers′ incorporation into the biopolymer matrix brings about an enhancement in the mechanical strength and the impact strength of the composite. Dynamic mechanical thermal analysis (DMTA) investigation showed two relaxations occurring at about ?30 and 35°C. The addition of Alfa fibers enhanced the storage modulus E′ before and after T_α, which is consistent with the reinforcing effect of Alfa cellulose fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of interfacial interactions on the mechanical behavior of hybrid composites of polypropylene / short glass fibers / hollow glass beads

Ternary composites of Polypropylene (PP)/Short Glass fibers (GF)/Hollow Glass Beads (HGB), with varying total and relative GF/HGB contents and using untreated and aminosilane-treated HGB compatibilized with maleated-PP, were prepared by direct injection molding of pre-extrusion compounded GF and HGB concentrates. The mechanical strength properties (tensile, flexural and Izod impact) were correlated with theoretical model predictions for hybrid composites, which identified synergistic gains over the rule of hybrid mixtures, depending upon the degree of interfacial interactions between the components of the hybrid composite. SEM analysis of cryofractured composites surfaces revealed that the presence of untreated HGB particles induces fiber-polymer interfacial decoupling under mechanical loading of the hybrid composites at much lower stress levels than in the presence of treated HGB particles. Higher storage modulus (E′) and lower mechanical damping (tan δ) from DMTA established the importance of strong polymer-hybrid reinforcement interfacial interactions in the development of lightweight/high strength PP syntactic foams.     

Influence of accelerated ageing on the physico-mechanical properties of alkali-treated industrial hemp fibre reinforced poly(lactic acid) (PLA) composites

30 wt% aligned untreated long hemp fibre/PLA (AUL) and aligned alkali treated long hemp fibre/PLA (AAL) composites were produced by film stacking and subjected to accelerated ageing. Accelerated ageing was carried out using UV irradiation and water spray at 50 °C for four different time intervals (250, 500, 750 and 1000 h). After accelerated ageing, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and mode I fracture toughness (K_Ic) were found to decrease and impact strength (IS) was found to increase for both AUL and AAL composites. AUL composites had greatest overall reduction in mechanical properties than that for AAL composites upon exposure to accelerated ageing environment. FTIR analysis and crystallinity contents of the accelerated aged composites support the results of the deterioration of mechanical properties upon exposure to accelerated ageing environment.     

Effect of Layering Pattern on the Mechanical Properties of Bark Cloth (Ficus natalensis) Epoxy Composites

The quest for sustainable materials as a consequence of a global drive to mitigate climate change has led to a focus on natural fiber–reinforced composite materials. In this study, skillful ply angle arrangement of bark cloth–reinforced laminar epoxy composites was carried out for the first time using vacuum-assisted resin transfer molding, and the composites fabricated were characterized for the effect of the layering pattern on their static and dynamic mechanical properties. Tensile strength and flexural strength were shown to be dependent on the ply angle arrangement. Dynamic mechanical analysis of the composites showed a glass transition temperature of 70°C, and the storage modulus and mechanical damping properties showed that the developed composites can withstand considerable loads and have excellent fiber-to-matrix adhesion.