Effects of alkali treatment and elevated temperature on the mechanical properties of bamboo fibre–polyester composites

Bamboo fibre reinforced composites are not fully utilised due to the limited understanding on their mechanical characteristics. In this paper, the effects of alkali treatment and elevated temperature on the mechanical properties of bamboo fibre reinforced polyester composites were investigated. Laminates were fabricated using untreated and sodium hydroxide (NaOH) treated (4–8% by weight) randomly oriented bamboo fibres and tested at room and elevated temperature (40, 80 and 120 °C). An improvement in the mechanical properties of the composites was achieved with treatment of the bamboo fibres. An NaOH concentration of 6% was found optimum and resulted in the best mechanical properties. The bending, tensile and compressive strength as well as the stiffness of this composite are 7, 10, 81, and 25%, respectively higher than the untreated composites. When tested up to 80 °C, the flexural and tensile strength are enhanced but the bending stiffness and compressive strength decreased as these latter properties are governed by the behaviour of resin. At 40 and 80 °C, the bond between the untreated fibres and polyester is comparable to that of treated fibres and polyester which resulted in almost same mechanical properties. However, a significant decrease in all mechanical properties was observed for composites tested at 120 °C.     

Mechanical property analysis of kenaf–glass fibre reinforced polymer composites using finite element analysis

Nowadays, natural fibres are used as a reinforcing material in polymer composites, owing to severe environmental concerns. Among many different types of natural resources, kenaf plants have been extensively exploited over the past few years. In this experimental study, partially eco-friendly hybrid composites were fabricated by using kenaf and glass fibres with two different fibre orientations of 0° and 90°. The mechanical properties such as tensile, flexural and impact strengths of these composites have been evaluated. From the experiment, it was observed that the composites with the 0° fibre orientation can withstand the maximum tensile strength of 49.27 MPa, flexural strength of 164.35 MPa, and impact strength of 6 J. Whereas, the composites with the 90° fibre orientation hold the maximum tensile strength of 69.86 MPa, flexural strength of 162.566 MPa and impact strength of 6.66 J. The finite element analysis was carried out to analyse the elastic behaviour of the composites and to predict the mechanical properties by using NX Nastran 9.0 software. The experimental results were compared with the predicted values and a high correlation between the results was observed. The morphology of the fractured surfaces of the composites was analysed using a scanning electron microscopy analysis. The results indicated that the properties were in the increasing trend and comparable with pure synthetic fibre reinforced composites, which shows the potential for hybridization of kenaf fibre with glass fibre.     

Investigation on mechanical properties of woven alovera/sisal/kenaf fibres and their hybrid composites

The go-green concept results in multipoint focus towards materials made from nature; easily decomposable and recyclable polymeric materials and their composites along with natural fibres ignited the manufacturing sectors to go for higher altitudes in engineering industries. This is due to the health hazard and environmental problems faced in manufacturing and disposal of synthetic fibres. This study was undertaken to analyse the suitability of new natural fibre as an alternative reinforcement for composite materials. In this paper, tensile, flexural and impact test is made for the woven alovera and kenaf (AK), sisal and kenaf (SK), alovera, sisal and kenaf fibre hybrid epoxy composites (ASK). The composite laminates are made through a hand-layup process. The surface analysis is studied through scanning electron microscopy. From the investigation the SK hybrid composite shows good tensile property, AK hybrid composite shows better flexural property and the best impact strength is observed for ASK hybrid composite. The natural fibres slowly replace the synthetic fibres from its environmental impact, marching towards a revolution in engineering materials.     

The potential of harakeke fibre as reinforcement in polymer matrix composites including modelling of long harakeke fibre composite strength

Mechanical properties of aligned long harakeke fibre reinforced epoxy with different fibre contents were evaluated. Addition of fibre was found to enhance tensile properties of epoxy; tensile strength and Young’s modulus increased with increasing content of harakeke fibre up to 223 MPa at a fibre content of 55 wt% and 17 GPa at a fibre content of 63 wt%, respectively. The flexural strength and flexural modulus increased to a maximum of 223 MPa and 14 GPa, respectively, as the fibre content increased up to 49 wt% with no further increase with increased fibre content. The Rule of Mixtures based model for estimating tensile strength of aligned long fibre composites was also developed assuming composite failure occurred as a consequence of the fracture of the lowest failure strain fibres taking account porosity of composites. The model was shown to have good accuracy for predicting the strength of aligned long natural fibre composites.     

The effects of alkali–silane treatment on the tensile and flexural properties of short fibre non-woven kenaf reinforced polypropylene composites

Kenaf fibre reinforced polypropylene composites were manufactured by compression moulding. The kenaf fibre was considered in three forms; untreated, treated with sodium hydroxide solution and treated with sodium hydroxide solution followed by three-aminopropyltriethoxysilane. The effects of these chemical treatments on the tensile and flexural properties of the composites were investigated. Mechanical test results show that alkali treatment followed by three-aminopropyltriethoxysilane treatment (alkali–silane treatment) significantly improves the tensile and flexural properties of short fibre non-woven kenaf polypropylene composites. In particular, the specific tensile and flexural strengths of alkali–silane treated kenaf composites with 30% fibre mass fraction are, respectively, only 4% and 11% lower than those of composites made using glass fibre. Scanning electron microscopy examination shows that the improvements in the tensile and flexural properties resulting from alkali–silane treatment can be attributed to better bonding between the fibres and matrix.     

Experimental and theoretical studies on the properties of injection moulded glass fibre reinforced mixed plastics composites

Recycled mixed post-consumer and post-industrial plastic wastes consisting of HDPE, LDPE and PP were injection moulded with short glass fibre (10–30% by weight) to produce a new generation composite materials. Intensive experimental studies were then performed to characterise the tensile, compression and flexural properties of glass fibre reinforced mixed plastics composites. With the addition of 30 wt.% of glass fibre, the strength properties and elastic modulus increased by as much as 141% and 357%, respectively. The best improvement is seen in the flexural properties due to the better orientation of the glass fibres in the longitudinal direction at the outer layers. The randomness and length of the glass fibre were accounted to modify the existing rule of mixture and fibre model analysis to reliably predict the elastic and strength properties of glass fibre reinforced mixed plastics composites.     

Factorial study of material and process parameters on the mechanical properties of extruded kenaf fibre/polypropylene composite sheets

Thin kenaf/polypropylene (PP) composite sheets were manufactured via extrusion. The effects of kenaf and maleated PP (MAPP) proportions, fibre length, PP melt flow index (MFI) and die temperature on tensile, flexural, in-plane and out-of-plane shear properties were analysed by conducting experiments through ‘design of experiments’ methodology. Higher kenaf content and lower die/barrel temperatures resulted in composite sheets with higher average mechanical properties in various modes of testing. Matrix MFI appeared to significantly affect all mechanical properties. It is interesting to note that the properties of the very short-fibre composites produced are comparable to those reinforced with longer discontinuous fibres and long-fibre mats.     

Mechanical properties of natural fibre reinforced polyester composites: Jowar,sisal and bamboo

In this paper, the experiments of tensile and flexural tests were carried out on composites made by reinforcing jowar as a new natural fibre into polyester resin matrix. The samples were prepared up to a maximum volume fraction of approximately 0.40 from the fibres extracted by retting and manual process, and compared with established composites like sisal and bamboo developed under similar laboratory conditions. Jowar fibre has a tensile strength of 302 MPa, modulus of 6.99 GPa and an effective density of 922 kg/m³. It was observed that the tensile strength of jowar fibre composite is almost equal to that of bamboo composite, 1.89 times to that of sisal composite and the tensile modulus is 11% and 45% greater than those of bamboo and sisal composites, respectively at 0.40 volume fraction of fibre. The flexural strength of jowar composite is 4%, 35% and the flexural modulus is 1.12 times, 2.16 times greater than those of bamboo and sisal composites, respectively. The results of this study indicate that using jowar fibres as reinforcement in polyester matrix could successfully develop a composite material in terms of high strength and rigidity for light weight applications compared to conventional sisal and bamboo composites.     

The effect of reprocessing on the mechanical properties of polypropylene reinforced with wood pulp,flax or glass fibre

Composites of polypropylene, substitutable for a given application and reinforced with: Medium Density Fibreboard fibre (MDF) (40 wt%); flax (30 wt%); and glass fibre (20 wt%), were evaluated after 6 injection moulding and extrusion reprocessing cycles. Of the range of tensile, flexural and impact properties examined, MDF composites showed the best mean property retention after reprocessing (87%) compared to flax (72%) and glass (59%). After 1 reprocessing cycle the glass composite had higher tensile strength (56.2 MPa) compared to the MDF composite (44.4) but after 6 cycles the MDF was stronger (35.0 compared to 29.6 MPa for the glass composite). Property reductions were attributed to reduced fibre length. MDF fibres showed the lowest reduction in fibre length between 1 and 6 cycles (39%), compared to glass (51%) and flax (62%). Flax fibres showed greater increases in damage (cell wall dislocations) with reprocessing than was shown by MDF fibres.     

Effect of resin system on the mechanical properties and water absorption of kenaf fibre reinforced laminates

The objective of this study is to compare the mechanical and water absorption properties of kenaf (Hibiscus cannabinus L.) fibre reinforced laminates made of three different resin systems. The use of different resin systems is considered so that potentially complex and expensive fibre treatments are avoided. The resin systems used include a polyester, a vinyl ester and an epoxy. Laminates of 15%, 22.5% and 30% fibre volume fraction were manufactured by resin transfer moulding. The laminates were tested for strength and modulus under tensile and flexural loading. Additionally, tests were carried out on laminates to determine the impact energy, impact strength and water absorption. The results revealed that properties were affected in markedly different ways by the resin system and the fibre volume fraction. Polyester laminates showed good modulus and impact properties, epoxy laminates displayed good strength values and vinyl ester laminates exhibited good water absorption characteristics. Scanning electron microscope studies show that epoxy laminates fail by fibre fracture, polyester laminates by fibre pull-out and vinyl ester laminates by a combination of the two. A comparison between kenaf and glass laminates revealed that the specific tensile and flexural moduli of both laminates are comparable at the volume fraction of 15%. However, glass laminates have much better specific properties than the kenaf laminates at high fibre volume fractions for all three resins used.     

Flexural properties of hemp fibre reinforced polylactide and unsaturated polyester composites

In this work, flexural strength and flexural modulus of chemically treated random short and aligned long hemp fibre reinforced polylactide and unsaturated polyester composites were investigated over a range of fibre content (0-50 wt%). Flexural strength of the composites was found to decrease with increased fibre content; however, flexural modulus increased with increased fibre content. The reason for this decrease in flexural strength was found to be due to fibre defects (i.e. kinks) which could induce stress concentration points in the composites during flexural test, accordingly flexural strength decreased. Alkali and silane fibre treatments were found to improve flexural strength and flexural modulus which could be due to enhanced fibre/matrix adhesion.     

Mechanical properties of 3D KD-I SiCf/SiC composites with engineered fibre-matrix interfaces

Three-dimensional (3D) silicon carbide (SiC) matrix composites reinforced with KD-I SiC fibres were fabricated by precursor impregnation and pyrolysis (PIP) process. The fibre-matrix interfaces were tailored by pre-coating the as-received KD-I SiC fibres with PyC layers of different thicknesses or a layer of SiC. Interfacial characteristics and their effects on the composite mechanical properties were evaluated. The results indicate that the composite reinforced with as-received fibre possessed an interfacial shear strength of 72.1 MPa while the composite reinforced with SiC layer coated fibres had a much higher interfacial shear strength of 135.2 MPa. However, both composites showed inferior flexural strength and fracture toughness. With optimised PyC coating thickness, the interface coating led to much improved mechanical properties, i.e. a flexural strength of 420.6 MPa was achieved when the interlayer thickness is 0.1 μm, and a fracture toughness of 23.1 MPa m^1/2 was obtained for the interlayer thickness of 0.53 μm. In addition, the composites prepared by the PIP process exhibited superior mechanical properties over the composites prepared by the chemical vapour infiltration and vapour silicon infiltration (CVI-VSI) process.     

Effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this study was to investigate the effect of pectin and hemicellulose removal from hemp fibres on the mechanical properties of hemp fibre/epoxy composites. Pectin removal by EDTA and endo-polygalacturonase (EPG) removed epidermal and parenchyma cells from hemp fibres and improved fibre separation. Hemicellulose removal by NaOH further improved fibre surface cleanliness. Removal of epidermal and parenchyma cells combined with improved fibre separation decreased composite porosity factor. As a result, pectin removal increased composite stiffness and ultimate tensile strength (UTS). Hemicellulose removal increased composite stiffness, but decreased composite UTS due to removal of xyloglucans. In comparison of all fibre treatments, composites with 0.5% EDTA + 0.2% EPG treated fibres had the highest tensile strength of 327 MPa at fibre volume content of 50%. Composites with 0.5% EDTA + 0.2% EPG → 10% NaOH treated fibres had the highest stiffness of 43 GPa and the lowest porosity factor of 0.04.     

Flexural strength of bidirectional hybrid epoxy composites reinforced by E glass and T700S carbon fibres

A study on the flexural properties of bidirectional hybrid epoxy composites reinforced by E glass and T700S carbon fibres in inter-ply configurations is presented in this paper. Test specimens are made by hand lay-up and their flexural properties are obtained by three point bend test in accordance with ASTM D790-07. For comparison, the flexural behaviour is also modelled numerically using finite element analysis (FEA), and analytically using the Classic Lamination Theory (CLT). It is shown from the results that in general, good agreement is found between the experimental data and the model predictions. The flexural strength decreases when partial laminas from a carbon/epoxy laminate are replaced by glass/epoxy laminas. No significant hybrid effects for the flexural strength are found from the experiments. However, simulation studies show that hybridisation can potentially improve the flexural strength.     

Mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane composites

A study on mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane (TPU) composites is presented in this paper. Kenaf bast fibre reinforced TPU composites were prepared via melt-mixing method using Haake Polydrive R600 internal mixer. The composites with 30% fibre loading were prepared based on some important parameters; i.e. 190 °C for reaction temperature, 11 min for reaction time and 400 rpm for rotating speed. The composites were subjected to soil burial tests where the purpose of these tests was to study the effect of moisture absorption on the mechanical properties of the composites. Tensile and flexural properties of the composites were determined before and after the soil burial tests for 20, 40, 60 and 80 days. The percentages of both moisture uptake and weight gain after soil burial tests were recorded. Tensile strength of kenaf fibre reinforced TPU composite dropped to ∼16.14 MPa after 80 days of soil burial test. It was also observed that there was no significant change in flexural properties of soil buried kenaf fibre reinforced TPU composite specimens.     

The effect of fibre content on the mechanical properties of hemp and basalt fibre reinforced phenol formaldehyde composites

In this study, mechanical properties such as tensile, flexural and impact strengths of hemp/phenol formaldehyde (PF), basalt/PF and hemp/basalt hybrid PF composites have been investigated as a function of fibre loading. Hemp fibre reinforced PF composites and basalt fibre reinforced composites were fabricated with varying fibre loading i.e. 20, 32, 40, 48, 56 and 63 vol%. The hybrid effect of hemp fibre and basalt fibre on the tensile, flexural and impact strengths was also investigated for various ratio of hemp/basalt fibre loading such as 1:0, 0.95:0.05, 0.82:0.18, 0.68:0.32, 0.52:0.48, 0.35:0.65, 0.18:0.82 and 0:1. Total fibre loading of the hybrid composites was 40 vol%. The results showed that the tensile strength and elongation at break increase with increasing fibre loading up to 40 vol% and decrease above this value for hemp fibre reinforced PF composite. Similar trend was observed for flexural strength and the maximum value was obtained for 48 vol% hemp fibre loading. Impact strength of hemp/PF composite showed a regular trend of increase with increasing fibre loading up to 63 vol%. Tensile strength, flexural strength and impact strength values of basalt/PF composites were found to be lower compared to hemp/PF composites. The tensile strength and elongation at break of basalt/PF composite increased by incorparation of basalt fibre up to 32 vol% and decreased beyond this value. Flexural strength of basalt/PF composite decreased linearly with fibre loading. However, the maximum impact strength was obtained for 48 vol% basalt fibre loading. For hemp/basalt hybrid PF composite, the tensile strength decreased with increasing basalt fibre loading. On the other hand, the flexural and impact strengths showed large scatter. The maximum flexural strength value was obtained for 0.52:0.48 hemp/basalt ratio. Corresponding value for impact strength was obtained for 0.68:0.32 hemp/basalt fibre ratio.     

Ductile unidirectional continuous rayon fibre-reinforced hierarchical composites

Endless rayon fibres (Cordenka®) were used to reinforce polyhydroxybutyrate (PHB) nanocomposites containing 2.5 wt.% nanofibrillated cellulose (NFC) to create truly green hierarchical composites. Unidirectional (UD) composites with 50–55% fibre volume fraction were produced using a solvent-free continuous wet powder impregnation method. The composites exhibit ductile failure behaviour with a strain-to-failure of more than 10% albeit using a very brittle matrix. Improvements at a model composite level were translated into higher mechanical properties of UD hierarchical composites. The Young’s moduli of rayon fibre-reinforced (NFC-reinforced) PHB composites were about 15 GPa. The tensile and flexural strength of hierarchical PHB composites increased by 15% and 33% as compared to the rayon fibre-reinforced neat PHB composites. This suggests that incorporation of NFC into the PHB matrix binds the rayon fibres, which does affect the load transfer between the constituents resulting in composites with better mechanical properties.     

Evaluation of mechanical and thermal properties of banana–flax based natural fibre composite

Hybrid materials of any kind are the keynote for today’s demands. This paper deals with one of such hybrid composite made of natural fibres namely, banana and flax fibres. The structural build-up is such that one layer of banana fibre is sandwiched between two layers of flax fibres by hand layup method with a volume fraction of 40% using Epoxy resin and HY951 hardener. Glass fibre reinforcement polymer (GFRP) is used for lamination on both sides. This lamination also increases the overall mechanical properties along with better surface properties. The properties of this hybrid composite are determined by testing its tensile, impact, and flexural loads using a Universal testing machine. Thermal properties are analysed and hybrid composites of flax and banana with GFRP have better thermal stability and flame resistance over flax, banana with GFRP single fibre hybrid composites. Morphological analysis is done using Scanning Electron Microscope (SEM). The result of test shows that hybrid composite has far better properties than single fibre glass reinforced composite under impact and flexural loads. However it is found that the hybrid composite have better strength as compared to single fibre composites.     

A comparison of the mechanical characteristics of kenaf and lyocell fibre reinforced poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) composites

Cellulose fibre-reinforced poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) composites have become increasingly interesting with regard to their biodegradability and mechanical characteristics. The use of different matrices leads to variable composite characteristics. This study provides a comparison of the mechanical characteristics of compression-moulded 30 mass% lyocell and 40 mass% kenaf fibre-reinforced PLA and PHB. The results of the tensile tests showed that 30 mass% lyocell/PLA composites reached the highest tensile and bending strength with 89 and 148 N/mm², respectively. The highest Young’s modulus was also measured for 30 mass% lyocell/PLA with 9.3 GPa, and the highest flexural modulus was measured for 40 mass% kenaf/PHB with 7.1 GPa. By far, the best impact strength was determined for lyocell/PHB with 70 kJ/m², followed by lyocell/PLA with 52 kJ/m². The investigation of the Shore D hardness resulted in a higher value for the PLA matrix with 81.5. PHB achieved a hardness of 67.5. By adding fibres as reinforcement, the Shore D hardness increased up to 83.6 for lyocell/PLA and 73.1 for kenaf/PHB. Density measurements showed lower densities for the composites with higher fibre loads (kenaf/PLA and kenaf/PHB) in comparison to the theoretical density. This speaks for a higher proportion of air inclusion in the composites which could negatively affect the mechanical composite characteristics.     

Hybridisation effect on diffusion kinetic and tensile mechanical behaviour of epoxy based flax–glass composites

This paper aims at investigating the hybridisation effect on the diffusion kinetic and the tensile mechanical behaviour of flax–glass fibres reinforced epoxy composites. For this purpose, hybrid composites composed of flax and glass fibre laminates with different stacking sequences were consolidated by compression moulding and subjected to environment ageing. The obtained results show that the water uptake and the diffusion coefficient are clearly reduced by the addition of glass fibre layers in flax laminate. The ageing conditions performed show that the flax–glass hybridisation presents a positive effect in a wet environment at low temperatures (∼20 °C) in the Young’s modulus and the tensile strength. For example, the Young’s modulus fell by 50% and 41% for hybrid laminates with 6% and 11% of glass fibres, and by 67% for the Flax laminate. However, the flax–glass hybridisation was not necessarily a relevant choice when the hybrid laminates were exposed in a wet environment at high temperatures. Indeed, at 55 °C, this hybridisation had a negative effect on the tensile strength and on the specific tensile strength.