Mechanical properties of maleic anhydride treated jute fibre/polypropylene composites

Abstract

The effect of maleic anhydride (MA) modification of jute fibre on the mechanical properties of jute/polypropylene (PP) composites was studied. Jute fibre, an environmental friendly, low-density renewable material was chemically modified with MA before the incorporation with PP to improve interfacial adhesion between them. Fourier transform infrared (FTIR) study showed that the C=C groups of MA attached to jute cellulose reacted with the PP matrix. Jute fibre/PP composite treated with MA displayed higher Young's modulus and dynamic storage modulus owing to the enhanced interfacial adhesion between the fibre and PP matrix. A scanning electron microscopy (SEM) study showed evidence of the enhanced adhesion and bridging in the interfacial region of the composite as the result of MA modification of jute fibre.     

Mechanical properties of plasma-treated sisal fibre-reinforced polypropylene composites

In recent years, sisal fibres have become a promising reinforcement for composites because of their low cost, low density, high specific strength, high specific modulus, easy availability and renewability. However, the poor adhesion between the hydrophilic sisal fibre and the hydrophobic thermoplastic matrices has adversely affected the widespread use of these composites. In this study, argon and air-plasma treatments have been used to modify the fibre surfaces under suitable treatment parameters to improve the compatibility between sisal fibres and polypropylene (PP). Sisal fibres and PP fibres are blended together to form a random mat which is then vacuum hot-pressed into a preimpregnated composite sheet. Mechanical properties such as tensile strength and modulus, flexural strength and modulus, and the storage modulus of the composite sheets improve after the incorporation of plasma-treated fibres. Furthermore, scanning electron microscopy analyses reveal the increased surface roughness of sisal fibre. Surface characterisation has been performed by X-ray photoelectron spectroscopy, showing an increase in oxygen/carbon ratio of sisal fibres after plasma treatment.     

Influence of silane coupling agents on the surface energetics of glass fibers and mechanical interfacial properties of glass fiber-reinforced composites

The effect of various silane coupling agents on glass fiber surfaces has been studied in terms of the surface energetics of fibers and the mechanical interfacial properties of composites. γ-Methacryloxypropyltrimethoxysilane (MPS), γ-aminopropyltriethoxysilane (APS), and γ-glycidoxypropyltrimethoxysilane (GPS) were used for the surface treatment of glass fibers. From contact angle measurements based on the wicking rate of a test liquid, it was observed that silane treatment of glass fiber led to an increase in the surface free energy, mainly due to the increase of its specific (or polar) component. Also, for the glass fiber-reinforced unsaturated polyester matrix system, a constant linear relationship was observed in both the interlaminar shear strength (ILSS) and the critical stress intensity factor (K_IC) with the specific component, γ_S ^SP, of the surface free energy. This shows that the hydrogen bonding, which is one of the specific components of the surface free energy, between the glass fibers and coupling agents plays an important role in improving the degree of adhesion at the interfaces of composites.     

Biodegradable jute cloth reinforced thermoplastic copolyester composites: fracture and failure behaviour

Abstract

Jute cloth reinforced, fully biodegradable thermoplastic composites were produced by the film stacking technique, with a semicrystalline copolyester (Ecoflex) as the matrix material. The jute cloth content varied between 0, 20 and 40 wt-% in the sheets produced by hot pressing. Specimens cut from the sheets were subjected to in plane static and out of plane dynamic loading, and the related fracture and failure behaviours were studied. The jute cloth proved to be a useful reinforcement to enhance in plane mechanical properties. The J integral concept (J–R curve) was adopted to assess the fracture behaviour of the composites. Crack propagation in single edge notched tensile (SEN-T) loaded specimens was detected using position resolved acoustic emission (AE). Acoustic emission was also used to characterise the failure. Surprisingly, no beneficial effect of the jute cloth was observed in the out of plane, namely instrumented falling weight impact (IFWI) test. This could be explained by the characteristics of the jute cloth used (the large mesh size increases the tendency to disintegrate when stretched at high strain rates) and by its moderate adhesion toward the matrix.     

The Effect of Accelerated Weathering on the Mechanical Properties of Alkali Treated Hemp Fibre/Epoxy Composites

In this study, 65 wt% aligned untreated long hemp fibre/epoxy (AUL) and aligned alkali treated long hemp fibre/epoxy (AAL) composites cured at 70°C using compression moulding were subjected to accelerated weathering using an accelerated weathering chamber with UV-irradiation and water spray at 50°C for four different time periods (250, 500, 750 and 1000 h). After accelerated weathering, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and fracture toughness (K _Ic) were found to decrease and impact energy (IE) was found to increase for both AUL and AAL composites. AUL composite had greater overall reduction in mechanical properties than that for AAL composite upon exposure to accelerated weathering environment. FTIR, TGA and WAXRD analyses of the accelerated weathered composites support the results of the deterioration of mechanical properties upon exposure to accelerated weathering environment.     

Structures and properties of blown moulding LLDPE films

Abstract

The crystalline structures, mechanical properties, transparence and fracture behaviours of linear low density polyethylene blown moulding films with nucleating agents incorporated in were investigated. The results indicated that with the nucleating agents used, the melting temperature T _m, crystalline structures, general profile of the stress–strain curves, tensile yield strength σ _y and essential work of fracture parameters before yield of the films, were almost unchanged, while the strain hardening phenomenon, tensile fracture strength σ _b, elongation at break &epsi _b, transparence and fracture parameters w _e and βw _p were enhanced greatly. As the loading content of nucleating agent increasing, the crystallinity first decreased and then increased rapidly; the strain hardening phenomenon ? _b and σ _b increased to a maximum and then decrease to a stable value, while the T _m and σ _y were also unchanged; the haze decreased first and then reached a stable value; the w _e and w _e,y decreased remarkably first and then rapidly increased, even enormously exceeding the w _e of pure linear low density polyethylene, while βw _p and β _y w _p,y increased to a quite high value first and then dropped to a lower level.     

Modification of epoxy resin by polysulfone to improve the interfacial and mechanical properties in glass fibre composites. I. Study of processes during matrix/glass fibre interface formation

The rheology of epoxy resin-polysulfone blends and wetting at the blend/glass fibre interface have been studied. Measurements were made in a rotary viscometer and in a modified Wilhelmy apparatus. It was shown that none of the blends investigated revealed non-Newtonian behaviour in the range of shear rates used. The viscosity of the blends increased as polysulfone content increased. Introduction of hardener resulted in a significant increase of the blends viscosity up to 2-3 orders of magnitude. Rheological tests suggested that 15 wt% polysulfone was the highest concentration useful for obtaining composites by solvent-free impregnation technique. These tests suggested that the structure of the cured epoxy-polysulfone blends depended on the modifier concentration. The structures of the blends differed for the blends containing 5 wt% polysulfone and 10-15 wt% polysulfone. All the blends (with the hardener) required at least 30 min at 180°C to achieve final values of the mechanical properties such as storage and loss moduli, loss tangent and complex viscosity. For all epoxy resin-polysulfone/glass fibre systems a complete wetting of the fibres was observed. Surface tension vs. polysulfone content dependency was found to be nonadditive. Surface tension measured was minimal for epoxy resin-5% polysulfone blend, while for other systems the values were close to that of epoxy resin. Modification of epoxy resin by polysulfone did not change the kinetics of the fibres wetting by the blends.     

Physical and mechanical properties of nano-CaCO3/PP composites modified with acrylic acid

Abstract

Nano-CaCO₃/polypropylene (PP) composites modified by the reactive monomer acrylic acid (AA) with or without the initiator dicumyl peroxide (DCP) were prepared using a two-step method. The effects of nano-CaCO₃ and AA on the physical and mechanical properties of nano-CaCO₃/PP composites were investigated. Differential scanning calorimetry (DSC) results showed that the incorporation of nano-CaCO₃ increased the crystallisation temperature as a result of the heterogeneous nucleation effect of nano-CaCO₃ on PP, and induced the formation of β phase PP. The addition of AA further increased the crystallisation temperature of PP and the intensity of β phase PP. The mechanical tests indicated that nano-CaCO₃ could simultaneously reinforce and toughen PP, and the mechanical properties of nano-CaCO₃/PP composites were higher than those of micro-CaCO₃/PP composites. In addition, incorporation of AA further increased the mechanical properties of the composites. In the presence of DCP, a small amount of AA could increase markedly the mechanical properties of nano-CaCO₃/PP composites.     

Studies of the Mechanical Properties and Practical Coating Adhesion on PP Modified by Oxidized Wax

In this study, the influences of polarity and the amount of oxidized polypropylene wax (OPPW) in blends with polypropylene (PP) were investigated by studying their surface properties. OPPW was completely miscible with PP up to 10 wt%. The adhesive strength of a acrylic-based primer coating on PP sheets, containing different wt% of OPPWs, was evaluated by using a direct 'pull off' test method. The results showed that the adhesive strength of the coating improved with an increase of the amount of OPPW in the blend. However, the degree of polarity in the OPPW did not have a significant impact on its adhesive properties. These observations were also supported by the results of ATR–FT-IR spectroscopy and surface energy measurements of the substrate. Furthermore, the results of adhesion test on the coating panels showed a significant enhancement after exposing to heat in an oven prior to the application of coating, e.g., about 230% increase for the blend containing 8 wt% of OPPW. The TGA curves showed a maximum drop of about 10% in thermal stability in comparison with that of the unblended PP. The changes in the mechanical properties of the blends were explained by considering the morphology of the blends and were supported by the changes in blend crystalinity and melting behavior. The elastic modulus remained almost unchanged while elongation and stress to breakpoint experienced a sharp reduction at concentrations of wax content higher than 6 wt%. The study showed a good balance of substrate coatability with its bulk properties at a blend concentration of about 6 wt% of OPPW.     

Modification of epoxy resin by polysulfone to improve the interfacial and mechanical properties in glass fibre composites. III. Properties of the cured blends and their structures in the polymer/fibre interphase

Thermal and mechanical properties (linear expansion coefficient, glass transition temperatures, Young's modulus, tensile and bending strengths, and failure energies under quasistatic and impact loadings) of cured epoxy-polysulfone (PSF) blends, as well as their structures have been studied. It was shown that PSF incorporation did not lead to appreciable changes in the linear thermal expansion coefficients and glass transition temperatures of the cured blends. According to this observation, incorporation of PSF into the epoxy matrix should not result in a significant increase in the internal stresses in the system. No drop in the modulus and strength of the bulk blends was observed when compared with unmodified epoxy matrix. The failure energy of the epoxy-PSF matrices increased as the PSF content increased under all loading conditions, whereas the strength of the polymer blend matrices increased only under impact loading. Optimal PSF content was found to be 10 wt%. It was shown that all the blends investigated were homogeneous before curing and became heterogeneous after curing. For epoxy-PSF/fibre joints a mixed (interfacial-cohesive) failure mode was observed for all the samples investigated. The results from the rheology, wetting, thermal, mechanical and structural tests, described in a set of papers, are compared with each other to explain the reasons for the adhesion strength behaviour of epoxy-PSF/glass fibre joints. Based on the finding here, an epoxy-10% PSF matrix is recommended for composite production.     

Effect of alkali treatment on properties of unidirectional isora fibre reinforced epoxy composites

Abstract

Unidirectional isora fibre reinforced epoxy composites were prepared by compression moulding. Isora is a natural bast fibre separated from Helicteres isora plant by retting process. The effect of alkali treatment on the properties of the fibre was studied by scanning electron microscopy (SEM), IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties such as 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 fibre loading for tensile properties of the untreated fibre composite was found to be 49% by volume and for flexural properties the loading was optimised at ～45%. Impact strength of the composite increased with increase in fibre loading and remained constant at a fibre loading of 54·5%. Alkali treated fibre composite showed improved thermal and mechanical properties compared to untreated fibre composite. From dynamic mechanical analysis (DMA) studies it was observed that the alkali treated fibre composites have higher E' and low tan δ maximum values compared to untreated fibre composites. From swelling studies in methyl ethyl ketone it was observed that the mole percentage of uptake of the solvent by the treated fibre composites is less than that by the untreated fibre composites. From these results it can be concluded that in composites containing alkalised fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Mechanical properties of injection molded long fiber polypropylene composites,Part 1: Tensile and flexural properties

Innovative polymers and composites are broadening the range of applications and commercial production of thermoplastics. Long fiber‐reinforced thermoplastics have received much attention due to their processability by conventional technologies. This study describes the development of long fiber reinforced polypropylene (LFPP) composites and the effect of fiber length and compatibilizer content on their mechanical properties. LFPP pellets of different sizes were prepared by extrusion process using a specially designed radial impregnation die and these pellets were injection molded to develop LFPP composites. Maleic‐anhydride grafted polypropylene (MA‐g‐PP) was chosen as a compatibilizer and its content was optimized by determining the interfacial properties through fiber pullout test. Critical fiber length was calculated using interfacial shear strength. Fiber length distributions were analyzed using profile projector and image analyzer software system. Fiber aspect ratio of more than 100 was achieved after injection molding. The results of the tensile and flexural properties of injection molded long glass fiber reinforced polypropylene with a glass fiber volume fraction of 0.18 are presented. It was found that the differences in pellet sizes improve the mechanical properties by 3–8%. Efforts are made to theoretically predict the tensile strength and modulus using the Kelly‐Tyson and Halpin‐Tsai model, respectively. POLYM. COMPOS., 28:259–266, 2007. © 2007 Society of Plastic Engineers     

Surface preparation effect on performance of adhesively-bonded graphite/epoxy composites subjected to impact

The influence of pre-bond surface preparation on performance of adhesively-bonded composites subjected to impact was investigated in this study. Impact test was carried out on adhesively bonded graphite/epoxy composite specimens at different low impact energies ranging from 5 to 20 J using the drop-weight impact test. Post-impact ultrasonic evaluation was performed in order to determine the resulting internal damage due to impact on the adhesive bondline. The ultrasonic C-scan of the gated ultrasonic wave signal was acquired and the ensuing debond area in the adhesive bond was determined quantitatively for specimens made from substrates with different surface preparations such as paper peel ply, sandblasting, and sandpaper abrasion. In order to determine the flexural load bearing capacity and stiffness reduction after impact, a three-point bending test was conducted on unimpacted and impacted specimens. A comparative study was performed to evaluate the performance of adhesively-bonded composites with different surface preparations. The results revealed that paper-peel ply performed the best in terms of resistance to debond area formation in the adhesive layer, as well as in terms of retention of flexural load bearing capacity and stiffness after impact.     

Tensile properties of multilayered biaxial weft knitted fabric reinforced composite material

Abstract

The multilayered biaxial weft knitted (MBWK) fabric made of E-glass fibres and stitched with polyester yarns, which is a kind of non-crimp fabrics, has been impregnated with epoxy via resin film infusion technique to manufacture the composite plates. The tensile properties of the MBWK fabric reinforced composite are studied with the multidirectional tensile testing. The classical lamination theory is applied to evaluate both the tensile modulus and Poisson's ratio, which shows good agreements with the experimental results. Failure analyses are also available by means of sample debris examination to identify the failure modes and the scanning electron microscope to reveal the microscopic mechanism. Predictions of the tensile properties provide a way to estimate the mechanical behaviours of the MBWK composite structures. Elongation at break is independent of the testing directions, which can be used as the failure criterion of the composite.     

Physico-mechanical properties of particleboards bonded with pine and wattle tannin-based adhesives

This study investigated the physical and mechanical properties of particleboards made using two types of tannin-based adhesives, wattle and pine, with three hardeners, paraformaldehyde, hexamethylenetetramine (hexamine) and TN (tris(hydroxyl)nitromethane), by measuring the physical (thickness swelling, linear expansion and water absorption) and mechanical properties (bending strength and internal bond strength). The performance of the particleboards made using tannin-based adhesives was influenced by physical conditions such as press time and temperature as well as by chemical conditions, such as the chemical structure of the tannin and the hardener. Wattle tannin-based adhesive being a thermoset, the wattle tannin-based particleboards were more influenced by physical conditions, while the pine tannin-based particleboards were influenced by the chemical structure of the pine tannin nuclei, which include phloroglucinolic A-rings. The reactivity of the hardener toward the tannin was in the order: paraformaldehyde > hexamine > TN for wattle tannin, while for pine tannin the order was hexamine > paraformaldehyde > TN.     

Strength of CFRP open hole laminates made from NCF,TFP and braided preforms under cyclic tensile loading

Abstract

Tensile tests and tension–tension cyclic tests were performed on carbon fibre reinforced plastics open-hole laminates. Specimens made from non-crimp fabric preforms, tailored fibre placement preforms and braided preforms in three different lay-up configurations ([+45]_{8 s}, [+45/0/?45]_{6 s}, [0/90]_{8 s}) were investigated and compared. The laminates were manufactured using a vacuum assisted processing technology and Hexcel RTM6 epoxy resin. Tensile strength and residual tensile strength values were measured and compared with unnotched specimens in order to evaluate the notch sensitivity. To evaluate deterioration during cyclic testing a two-dimensional digital image correlation system was used to capture deformation images of the specimen surface in the open-hole area. Observed similarities and differences in deformation and in load–elongation graphs of the tested specimens are discussed.     

Mechanical properties,electrical resistivity and piezoresistivity of carbon fibre-based self-sensing cementitious composites

Carbon fibre (CF) is one of the most effective materials in improving the conductivity of the composites by developing a conductive network within the matrix, which also enhanced the piezoresistivity behaviour of the cementitious composites and has a potential application for structural health monitoring. A systematic study of the effect of sizing condition and fibre length on the piezoresistivity behaviour of cementitious composites by adopting unsized CF with the length of 3, 6 and 12 mm, and desized CF of 6 and 12 mm as functional fillers. Each type of CF was added at four different weight fractions of 0.1, 0.3, 0.5 and 0.7% to determine the optimal fibre content. Electrical resistivity and piezoresistivity tests were conducted for samples before and after drying treatment to evaluate the effect of water content on electrical properties. Besides, fresh properties of the fresh mixture, mechanical properties and microstructure of the composites were also investigated. Results showed that unsized CF is more effective in enhancing composites flexural strength and reducing the electrical resistivity, which also showed a stronger bonding with the cement matrix and also demonstrated a better dispersive ability. In terms of piezoresistivity behaviour, for a given fibre length, desized CF showed higher sensitivity and repeatability compared to unsized CF; however, the signals showed more noise. The best piezoresistivity behaviour was obtained for composites containing 3 mm CF at 0.7 wt%, which showed a fractional change in resistivity (FCR) value of approximately 70%. An equation was developed, which can successfully describe the relationship between the FCR of cementitious composites containing CF and the applied external stress.     

Effect of nitric acid surface treatment on tensile and tribological properties of thermoplastic polyimide composite filled with carbon fibre

Abstract

Polyacrylonitrile based carbon fibres were submitted to nitric acid oxidation treatments to improve the interfacial adhesion of the carbon fibre reinforced polyimide (CF/PI) composite. The carbon fibre surfaces were characterised by X-ray photoelectron spectroscopy. Nitric acid oxidation not only affects the oxygen concentration, but also produces an appreciable change in the nature of the chemical functions, namely the conversion of hydroxy type oxygen into carboxyl functions. Nitrogen concentration of nitric acid oxidation treated carbon fibre is ～1·2 times higher compared with untreated one. The mechanical and tribological properties of the CF/PI composites treated with nitric acid oxidation were investigated. Results showed that the tensile strength of the CF/PI composites improved remarkably due to nitric acid treatment along with enhancement in friction and wear performance.     

Effect of powder size on microstructure and mechanical properties of Ti(C,N) based cermets

Abstract

Effect of the particle size of TiC and TiN on the microstructure and mechanical properties of Ti(C,N) based cermets has been evaluated. Ti(C,N)–WC–Co cermets made from four groups of mixed raw powders of different sizes were manufactured by vacuum sintering. The microstructure and composition were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDX). The result shows that the four samples have the typical microstructures of 'black core/grey rim'. The mechanical properties of the cermet manufactured from submicron TiC and nano TiN are the best among the four samples.     

Surface energy characterization of modified carbon blacks and its relationship to composites tearing properties

The effects of three types of chemical treatments, i.e. as polar acidic, polar basic, and nonpolar oxidations, on virgin carbon blacks have been studied in terms of pH, acid-base surface values, specific surface area, X-ray diffraction analysis, and surface free energy. The acidic chemical treatment leads to significant changes in surface and adsorption properties, surface free energy, and microstructures. The increased acidic surface functional groups on carbon blacks result from reaction between the basic carbon and the acidic chemical solution. Also, based on the determination of surface free energy from contact angle measurements, a good correlation between the London dispersive component or apolar (γ^d _s) of surface free energy and specific surface area (S_BET) (or crystalline size S along the c-axis, L_C) is shown in this work. Particularly, it is found that the γ^d _s of the carbon blacks studied is highly correlated with the mechanical tearing test results based on hydrocarbon rubber compound composites.