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.     

Influence of fibre-surface treatment on structural, thermal and mechanical properties of jute fibre and its composite

Jute fibres (Corchorus olitorious), an environmentally and ecologically friendly product, were chemically modified and treated with 5% NaOH solution at room temperature for 2 h, 4 h and 8 h. The above samples were characterized and morphologically analysed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Instron 1185. Alkali treatment affects the supramolecular structure of the fibre as shown by XRD by improving the degree of crystallinity of the fibre. Surface chemistry of the fibre also altered as depicted by FT-IR studies. This chemical treatment was also found to alter the characteristic of the fibre surface topography as seen by the SEM. From the mechanical single fibre test it was found that the tenacity and modulus of the fibre improved after alkali treatment. This might be due to the improvement in the crystallinity. DSC data demonstrated that the thermal degradation temperature for the cellulose get lowered from 365·26°C to 360·62°C after alkali treatment led to the reduction in fibre thermal stability. Jute fibre reinforced composite were prepared with treated and untreated jute fibre (15 wt%) reinforced unsaturated polyester (UPE). Effectiveness of these composites was experimentally investigated through the study of the composites by DSC, Instron 1195 for mechanical property of composites, volume fraction of the porosity and hydrophobic finishing of the composite. From the DSC analysis it was found that thermal stability enhanced for treated fibre reinforced composite. This could be due to the resistance offered by the closely packed cellulose chain in combination with the resin. Flexural strength of the composite prepared with 2 h and 4 h alkali treated fibre were found to increase by 3·16% and 9·5%, respectively. Although 8 h treated fibre exhibited maximum strength properties, but the composite prepared with them showed lower strength value. Alkali treatment helped in the development of hydrophobicity and reduction in volume fraction of the porosity. This may be due to the better fibre matrix interface adhesion caused due to the fibre surface treatment by alkali.     

Cross-sectional area evaluation and tensile properties of alkali-treated kenaf fibres

A cross-sectional area evaluation method for multi-cell type natural fibres treated in a highly concentrated alkali solution was proposed using kenaf fibres. Cross-section of kenaf fibres was drastically changed by the alkali treatment compared to the untreated fibres. Conventional data-based approximation (DBA) method for evaluating cross-sectional area was not sufficient, because it was based on cross-sectional area data of the untreated fibres. DBA was modified on the assumption that the shape of each cell in the alkali-treated fibres was an ellipse, and again correlated with hexagonal cross-sectional area, which was approximated by measuring the projection widths on the fibre along 0°, 60° and 120° directions. This is the new data-based approximation method (DBA-AT). Results showed that the tensile strength was greatly improved, compared to the strength values estimated by untreated fibre-based DBA. Especially, tensile strength of alkali-treated fibre on the condition of 15 wt%NaOH for 1 h was comparable to untreated fibre.     

Effect of fibre content and alkali treatment on mechanical properties of Roystonea regia-reinforced epoxy partially biodegradable composites

The present paper investigates the effect of fibre content and alkali treatment on tensile, flexural and impact properties of unidirectional Roystonea regia natural-fibre-reinforced epoxy composites which are partially biodegradable. The reinforcement Roystonea regia (royal palm) fibre was collected from the foliage of locally available royal palm tree through the process of water retting and mechanical extraction. The poor adhesion between fibre and matrix is commonly encountered problem in natural-fibre-reinforced composites. To overcome this problem, specific physical and chemical treatments were suggested for surface modification of fibres by investigators. Alkali treatment is one of the simple and effective surface modification techniques which is widely used in natural fibre composites. In the present study both untreated and alkali-treated fibres were used as reinforcement in Roystonea regia epoxy composites and the tensile, flexural and impact properties were determined at different fibre contents. The alkali treatment found to be effective in improving the tensile and flexural properties while the impact strength decreased.     

Impact fatigue behaviour of vinylester resin matrix composites reinforced with alkali treated jute fibres

An impact fatigue study has been made for the first time on 35% jute/vinylester composites containing both untreated and alkali treated fibres. Longer alkali treatment removed the hemicellulose and improved the crystallinity and gave better fibre dispersion. The flexural strength properties of the composites made from treated fibre were superior. 4 h alkali treated jute fibres gave the optimum combination of improved interfacial bonding and fibre strength properties. However this was not reflected in their impact fatigue behaviour. On the contrary, the composites reinforced with 8 h alkali treated fibres displayed superior impact fatigue properties. Here, the fibres suffered catastrophic fracture with microfibrillar pull-out at some places and improved the fatigue resistance property of the composites as evident from SEM micrographs.     

Effect of soaking time and concentration of NaOH solution on mechanical properties of coir–polyester composites

The green husk coir fibres were treated with different levels of soaking time and concentration of alkali solution. As a result of alkali treatment, the surface modifications were done on the fibre surface and were studied using scanning electron micrographs. The coir?Cpolyester composites were fabricated using hand lay up process and the mechanical properties (tensile, flexural and impact strength) were evaluated as per ASTM standards. The effect of soaking time and concentration of NaOH solution were studied based on evaluated values of mechanical properties to find out optimum fibre treatment parameters.     

Influence of chemical surface modification on the properties of biodegradable jute fabrics—polyester amide composites

The chemical surface modifications of jute fabrics involving bleaching, dewaxing, alkali treatment, cyanoethylation and vinyl grafting are made in view of their use as reinforcing agents in composites based on a biodegradable polyester amide matrix, BAK 1095. The effect of different fibre surface treatments and fabric amounts on the performance of resulting composites are investigated. The mechanical properties of composites like tensile and bending strengths increase as a result of surface modification. Among all modifications, alkali treatment and cyanoethylation result in improved properties of the composites. The tensile strength of BAK is increased by more than 40% as a result of reinforcement with alkali treated jute fabrics. SEM investigations show that the surface modifications improve the fibre–matrix interaction. From degradation studies we find that after 15 days of compost burial about 6% weight loss is observed for BAK whereas cyanoethylated and alkali treated jute–BAK composites show about 10% weight loss. The loss of weight as well as the decrease of bending strength of degraded composites is more or less directly related.     

Development of kenaf-glass reinforced unsaturated polyester hybrid composite for structural applications

The main aim of this paper is to develop kenaf-glass (KG) fibres reinforced unsaturated polyester hybrid composite on a source of green composite using sheet moulding compound process. Unsaturated polyester resin (UPE) and KG fibres in mat form were used at a ratio of 70:30 (by volume) with treated and untreated kenaf fibre. The kenaf fibre was treated with 6% sodium hydroxide (NaOH) diluted solution for 3 h using mercerization method. The hybrid composites were tested for flexural, tensile and Izod impact strength using ASTM D790-03, ASTM D618 and ASTM D256-04 standards respectively. The highest flexural, tensile and impact strength were obtained from treated kenaf with 15/15 v/v KG fibres reinforced UPE hybrid composite in this investigation.Scanning electron microscopy fractography showed fibre cracking, debonding and fibre pulled-out as the main fracture mode of composites and kenaf treated 15/15 v/v KG reinforced hybrid composite exhibited better interfacial bonding between the matrix and reinforcement compared to other combinations.     

甘蔗渣的碱处理对其纤维增强全降解复合材料的影响

利用压制成型的方法制备了甘蔗渣纤维增强全降解复合材料, 探讨了碱处理对材料性能的影响。结果表明, 1 %碱液处理后材料的力学性能得到了提高。碱处理后纤维的分解细化和表面优化改善了纤维/ 基材的粘结性能, 从而使材料力学性能得到提高。而且, 处理后纤维拉伸强度和长径比的增大以及纤维缺陷的降低也会增强材料性能。      

Studies on fly ash/coir/sugarcane reinforced epoxy polymer matrix composite

In the past years studies were conducted on natural fibre reinforced polymer composites to observe their mechanical properties in order to decide their industrial applications. These composites have already been used in many applications from aerospace to sporting equipment. These green composites can be used as a replacement for synthetic composites. This is because the natural fibres are eco-friendly, biodegradable, renewable, etc. In this work, an attempt is made to reinforce fly ash, coir fibre and sugarcane fibre with epoxy polymer matrix. Central composite design under response surface methodology (RSM), one of the approaches of design of experiments (DOE) is used to determine optimum sample preparation conditions of fly ash, coir fibre and sugarcane fibre. Both tensile and flexural (three-point bending) tests are conducted on these fabricated composites to determine their materialistic characteristics. Analysis of variance (ANOVA) is carried out using Minitab software to find the influence of fly ash, coir fibre, sugarcane fibre on composites. Regression equations obtained from analysis of variance is used to calculate values. Experimental and calculated values are compared and their error % are calculated and tabulated. Response surface optimization study is carried to find the optimized parameters of composites. It is observed that, increase in wt.% of coir fibre and decrease in wt.% of fly ash and sugarcane fibre, increases yield stress and these parameters have mixed impact on ultimate tensile stress. The addition of fly ash, coir fibre and sugarcane fibre in low percentages increases Young's modulus. Increase in wt.% of fly ash and coir fibre and decrease in wt.% of sugarcane, increases flexural modulus and flexural stress.     

Plasma surface modification of advanced organic fibres

The interlaminar shear strength, interlaminar fracture energy, flexural strength and modulus of extended-chain polyethylene/epoxy composites are improved substantially when the fibres are pretreated in an ammonia plasma to introduce amine groups on to the fibre surface. These property changes are examined in terms of the microscopic properties of the fibre/matrix interface. Fracture surface micrographs show clean interfacial tensile and shear fracture in composites made from untreated fibres, indicative of a weak interfacial bond. In contrast, fracture surfaces of composites made from ammonia plasma-treated fibres exhibit fibre fibrillation and internal shear failure as well as matrix cracking, suggesting stronger fibre/matrix bonding, in accord with the observed increase in interlaminar fracture energy and shear strength. Failure of flexural test specimens occurs exclusively in compression, and the enhanced flexural strength and modulus of composites containing plasma-treated fibres result mainly from reduced compressive fibre buckling and debonding due to stronger interfacial bonding. Fibre treatment by ammonia plasma also causes an appreciable loss in the transverse ballistic impact properties of the composite, in accord with a higher fibre/matrix interfacial bond strength.     

The compression strength of composites with kinked,misaligned and poorly adhering fibres

Experiments carried out on pultruded fibre reinforced polyester resins show that, at moderate fibre volume fractions, the compressive strength of aligned fibre composites depends linearly on the volume fraction. The strength falls off when the fibre volume fraction,V _f=0.4 with Kevlar and high strength carbon fibres. The effective fibre strength atV _f<0.4 is much less than the tensile strength but it is close to the tensile strength with E-glass fibres and high modulus carbon fibres. Poor adhesion between fibres and matrix reduces the compressive strength, as does kinking the fibres when the fibre radius of curvature is reduced to below 5 mm. Misalignment of the fibres reduces the compressive strength when the average angle of misalignment exceeds about 10° for glass and carbon fibres. However, with Kevlar no such reduction is observed because the compression strength of Kevlar reinforced resin is only a very little better than that of the unreinforced resin.     

改性椰纤维增强聚乳酸复合材料力学性能

目的添加适量椰纤维(CF)改善聚乳酸(PLA)的力学性能,以适应产品的包装。方法采用熔融共混法制备不同CF含量的CF/PLA复合材料。通过力学性能测试、扫描电子显微镜观察和动态热力学性能测试,探讨添加不同含量的碱洗CF对复合材料力学性能的影响。结果与纯PLA相比,复合材料的拉伸强度降低,冲击强度增大,储能模量增大,玻璃化转变温度降低。当碱洗CF质量分数为3%时,复合材料的冲击强度比纯PLA增加了24%。结论添加CF有利于提高复合材料的力学性能,碱液浸泡更有利于改善CF和PLA基体的界面相容性。     

Copper coating on coir fibres

Conditions for obtaining continuous coatings of copper (thickness range 1.5 to 5μm) on coir fibres have been reported. Activation of the surface of coir fibres was achieved by treating the surface of the fibres with NaOH-HCHO/ammoniacal AgNO₃ solution. Copper was deposited on the activated surface of coir fibres from Fehling-formaldehyde solution. The effects of variation in formaldehyde and sodium hydroxide concentrations and pressures inside the coating vessel on deposition rates were determined. The minimum concentrations of NaOH and HCHO required for maintaining a maximum rate of deposition of copper from a solution contaning 10g l⁻¹ copper sulphate were found to be 6.6 g l⁻¹ and 2.5 to 3.5 g l⁻¹, respectively. Optical and scanning electron microscope studies show that relatively more uniform and non-porous copper coatings were obtained when deposition was carried out under reduced pressures. A 5μm thick copper coating on coir fibre prevents the propagation of flame as was shown by flammability tests. Copper coating on coir fibre decreases its electrical resistivity from 2.55×10⁶Ωcm to 4.68×10⁻³Ωcm with 1.5μm thick coating and 3.76×10⁻⁵Ωcm with 5μm thick coating. Reinforcement of polyester with copper-coated coir fibre leads to an increase of about 25% in tensile strength and flexural strength as compared to polyester reinforced with plain coir fibre.     

Improving the mechanical properties of glass-fibre-reinforced polyester composites by modification of fibre surface

Polyalkenyl-poly-maleic-anhydride-ester/amide type new experimental additives have been developed and used to achieve the better properties of glass-fibre-reinforced polyester composites. Two different commercial reinforcements have been investigated: a chopped glass fibre and a glass woven [0/90°] fabric materials. Based on their chemical structures, both were E-type. The surfaces of reinforcements have been treated with the dissolved form of polyalkenyl-poly-maleic-anhydride-ester, polyalkenyl-poly-maleic-anhydride-amide and polyalkenyl-poly-maleic-anhydride-ester-amide type experimental coupling additives then they have been used in fibre-reinforced thermoset. The coupling additives have had differences not only in their chemical structure and physical properties, but also in the fibre–matrix interaction that can also be affected by them. That is the reason why additives have resulted in numerous differences in the mechanical properties of the reinforced specimens. The most favourable effects have been found in the case when the glass-fibre surface was modified by polyalkenyl-poly-maleic-anhydride-ester-amide type additives. Moreover, results have referred to more favourable effects in case of chopped glass-fibre mat than in glass woven fabric composites. Tensile properties could be improved by 38.9% with that additive and flexure properties with 21.9% in those laminates. Tensile and flexure properties of glass woven [0/90°] fabric reinforced composites could be improved by 18.0%, and 40.1% comparing to the untreated glass fibres containing polyester composites with the same reinforcement. The polyalkenyl-poly-maleic-anhydride-ester type surface modifying additive has deteriorated the tensile and flexural properties of the laminates, but the dynamic properties have been more favourable than those of specimens with untreated glass fibres. Fibre–matrix interaction responsible for increased or decreased mechanical properties has been studied on SEM micrographs of the fractured face of composites. It has been found that the unfavourable results had been caused by the fibre slipping out the polyester matrix. Nevertheless, it has been supported by visual observation that the polyalkenyl-poly-maleic-anhydride-ester-amide additive managed to improve the adhesion between the fibres and the matrix.     

Plasma surface modification of advanced organic fibres

A marked improvement in the interlaminar shear strength and flexural strength of aramid/ epoxy composites is observed when the fibres are pretreated in an ammonia or ammonia/ nitrogen gaseous discharge (plasma) to introduce amine groups on to the fibre surface. Scanning electron and optical microscopic observations are used to examine the microscopic basis for these results. Scanning electron micrographs of shear fracture surfaces show clean fibre/matrix separation in composites made from untreated fibres, indicative of weak interfacial bonding. In contrast, shear fracture surfaces of composites containing plasma-treated fibres exhibit clear evidence of fibre fibrillation and matrix cracking, suggesting stronger interfacial bonding. Optical microscopic examination of flexure specimens shows that enhanced strength results mainly from reduced compressive fibre buckling and debonding, due to an increase in fibre/matrix interfacial bond strength. This increase is not accompanied by any significant change in the interlaminar fracture energy or flexural modulus of the composites, but there is an appreciable loss in transverse ballistic impact properties. These results are also examined in terms of the observed increase in fibre/matrix interfacial strength.     

Laccase and alkali treatments of cellulose fibre: Surface lignin and its influences on fibre surface properties and interfacial behaviour of sisal fibre/phenolic resin composites

This paper is an attempt to investigate the influences of enzyme (laccase) and alkali treatments on the surface lignin of single cellulose fibre. The fibre surface characteristics and the interfacial behaviour of the sisal fibre/phenolic resin composites were also studied by SEM, AFM, XPS. The surface lignin greatly affected the surface physical and chemical properties of single cellulose fibres. The surface lignin concentration was up to 35% for the raw fibre without any treatment, and then it decreased to 24%, 20% and 18% for the fibres with laccase treatment, alkali treatment and laccase/alkali treatment, respectively. The removal of lignin from fibre surface could enhance the interfacial strength of composites, and thus increase the tensile strength and internal bonding strength by 43% and 51%, respectively, for the composites obtained from laccase/alkali treated fibres.     

The impact strength of fibre composites

Two models have been developed which predict the crack initiation energy, notched impact strength and unnotched impact strength of fibre composites. One is applicable to composites containing short fibres and the other to composites containing long fibres. Data obtained with randomly oriented short fibre composites were consistent with the one model. The other model has been verified using composites containing uniaxially oriented long fibres and long fibres oriented randomly in a plane. The success of the model demonstrates that the high notched impact strength with long fibres is due to the redistribution of stress away from the stress concentrating notch, the extra stress that can be held by the fibre relative to the matrix and the work required to pull fibres out of the matrix during crack propagation. The parameters which have been shown to control the fracture energy are composite modulus, fibre length, fibre volume fraction, effective fibre diameter, fibre tensile strength and the coefficient of friction during fibre pull-out from the matrix. The matrix toughness on the other hand usually has no effect at all for composites containing fibres randomly oriented in two dimensions and only a minor effect in exceptional cases. The shear strength of the fibre-matrix bond has only an indirect effect in that it controls the number of fibres which pull out rather than fracture.     

Characterisation and utilization of natural coconut fibres composites

Two thousand fibres were randomly taken from a coir fibre stack, characters of the fibres were analysed. It was shown that length of the fibres was in the range between 8 and 337 mm. The fibres amount with the length range of 15–145 mm was 81.95% of all measured fibres. Weight of fibres with the length range of 35–225 mm accounted for 88.34% of all measurement. The average fineness of the coir fibres was 27.94 tex. Longer fibres usually had higher diameters.Composite boards were fabricated by using a heat press machine with the coir fibre as the reinforcement and the rubber as matrix. Tensile strength of the composites was investigated.     

Investigation of the effect of surface modifications on the mechanical properties of basalt fibre reinforced polymer composites

Unsaturated polyester-based polymer composites were developed by reinforcing basalt fabric into an unsaturated polyester matrix using the hand layup technique at room temperature. This study describes basalt fibre reinforced unsaturated polyester composites both with and without acid and alkali treatments of the fabrics. The objective of this investigation was to study the effect of surface modifications (NaOH & H₂SO₄) on mechanical properties, including tensile, shear and impact strengths. Variations in mechanical properties such as the tensile strength, the inter-laminar shear strength and the impact strength of various specimens were calculated using a computer-assisted universal testing machine and an Izod Impact testing machine. Scanning Electron Microscope (SEM) observations of the fracture surface of the composites showed surface modifications to the fibre and improved fibre–matrix adhesion. The result of the investigation shows that the mechanical properties of basalt fibre reinforced composites are superior to glass fibre reinforced composites. This work confirms the applicability of basalt fibre as a reinforcing agent in polymer composites.