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.     

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。      

The influence of fibre microstructure on fibre breakage and mechanical properties of natural fibre reinforced polypropylene

The aim of the study was to investigate the influence of fibre morphology of different natural fibres on the composites mechanical properties and on the fibre breakage due to extrusion process. The composite materials were manufactured using LTF (long fibre thermoplastic) extrusion and compression moulding and the used fibres were sisal, banana, jute and flax, and the matrix was a polypropylene. The results showed that sisal composites had the best impact properties and the longest fibres after the extrusion. Generally, the composites flexural stiffness was increased with increased fibre content for all fibres, being highest for flax composites. The flexural strength was not affected by the addition of fibres because of the low compatibility. The addition of 2 wt.% maleated polypropylene significantly improved the composites properties. Unlike the other three fibres, flax fibres were separated into individual elementary fibres during the process due to enzymatic retting and low lignin content.     

Influence of alkali treatment on the interfacial and physico-mechanical properties of industrial hemp fibre reinforced polylactic acid composites

The focus of this work was to produce short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites by compression moulding. Fibres were treated with alkali to improve bonding with PLA. The percentage crystallinity of PLA in composites was found to be higher than that for neat PLA and increased with alkali treatment of fibres which is believed to be due to the nucleating ability of the fibres. Interfacial shear strength (IFSS) results demonstrated that interfacial bonding was also increased by alkali treatment of fibres which also lead to improved composite mechanical properties. The best overall properties were achieved with 30 wt.% long aligned alkali treated fibre/PLA composites produced by film stacking technique leading to a tensile strength of 82.9 MPa, Young’s modulus of 10.9 GPa, flexural strength of 142.5 MPa, flexural modulus of 6.5 GPa, impact strength of 9 kJ/m², and a fracture toughness of 3 MPa m^1/2.     

Dynamic mechanical and thermal properties of MAPE treated jute/HDPE composites

The present paper summarizes an experimental study on the mechanical and viscoelastic behavior of jute fibre reinforced high density polyethylene (HDPE) composites. Variations in mechanical strength, storage modulus (E′), loss modulus (E″) and damping parameter (tan δ) with the addition of fibres and coupling agents were investigated. It was observed that the tensile, flexural and impact strengths increased with the increase in fibre loading upto 30%, above which there was a significant deterioration in the mechanical strength. Further, the composites treated with MAPE showed improved properties in comparison to the untreated composites. Dynamic mechanical analysis data showed an increase in the storage modulus of the treated composites The tan δ spectra presented a strong influence of fibre content and coupling agent on the α and γ relaxation process of HDPE. The thermal behavior of the composites was evaluated from TGA/DTG thermograms. The fibre–matrix morphology in the treated composites was confirmed by SEM analysis of the tensile fractured specimens. FTIR spectra of the treated and untreated jute fibres was also studied to ascertain the existence of type of interfacial bonds.     

Jute/polypropylene composites I. Effect of matrix modification

Natural fibre-reinforced polymers can exhibit very different mechanical performances and environmental aging resistances depending on their interphase properties, but most studies have been focused on fibre surface treatment. Here, investigations of the effect of maleic anhydride grafted polypropylene (MAHgPP) coupling agents on the properties of jute fibre/polypropylene (PP) composites have been considered with two kinds of matrices (PP1 and PP2). Both mechanical behaviour of random short fibre composites and micro-mechanical properties of single fibre model composites were examined. Taking into account interfacial properties, a modified rule of mixture (ROM) theory is formulated which fits well to the experimental results. The addition of 2 wt% MAHgPP to polypropylene matrices can significantly improve the adhesion strength with jute fibres and in turn the mechanical properties of composites. We found that the intrinsic tensile properties of jute fibre are proportional to the fibre’s cross-sectional area, which is associated with its perfect circle shape, suggesting the jute fibre’s special statistical tensile properties. We also characterised the hydrophilic character of natural fibres and, moreover, humidity environmental aging effects. The theoretical results are found to coincide fairly well with the experimental data and the major reason of composite tensile strength increase in humidity aging conditions can be attributed to both improved polymer–matrix and interfacial adhesion strength.     

Jute-reinforced polyester composites

Raw jute fibre has been incorporated in a polyester resin matrix to form uniaxially reinforced composites containing up to 60 vol% fibre. The tensile strength and Young's modulus, work of fracture determined by Charpy impact and inter-laminar shear strength have been measured as a function of fibre volume fraction. These properties all follow a Rule of Mixtures relationship with the volume fraction of jute. Derived fibre strength and Young's modulus were calculated as 442 MN m^–2 and 55.5 GN m^–2 respectively. Polyester resin forms an intimate bond with jute fibres up to a volume fraction of 0.6, above which the quantity of resin is insufficient to wet fibres completely. At this volume fraction the Young's modulus of the composite is approximately 35 GN m^–2, the tensile strength is 250 MN m^–2, the work of fracture is 22 kJ m^–2 and the inter-laminar shear strength is 24 MN m^–2. The properties of jute and glass fibres are compared, and on a weight and cost basis jute fibres are seen in many respects to be superior to glass fibres as a composite reinforcement.     

Mechanical properties of poly(butylene succinate) (PBS) biocomposites reinforced with surface modified jute fibre

A biocomposite was originally fabricated with biodegradable polymer PBS and jute fibre, and the effects of fibre surface modification on characteristics of jute fibre and mechanical properties of the biocomposite were evaluated in this paper. The experimental results show that surface modification can remove surface impurities and reduce diameter of jute fibres. Regarding the mechanical properties of biocomposites, it is observed that the biocomposites with jute fibres treated by 2% NaOH, 2 + 5% NaOH or coupling agent, respectively, an optimum in mechanical properties can obtain at fibre content of 20 wt.%, which exhibit an obvious enhancement in mechanical strength and modulus compared to the ones with untreated jute fibre. Furthermore, surface modification also exhibits less effects on flexural properties compared to tensile properties and more on flexural or tensile modulus than on the strength.     

The mechanical properties of vinylester resin matrix composites reinforced with alkali-treated jute fibres

Jute fibres were subjected to alkali treatment with 5% NaOH solution for 0, 2, 4, 6 and 8 h at 30°C. The modulus of the jute fibres improved by 12, 68 and 79% after 4, 6 and 8 h of treatment, respectively. The tenacity of the fibres improved by 46% after 6 and 8 h treatment and the % breaking strain was reduced by 23% after 8 h treatment. For 35% composites with 4 h-treated fibres, the flexural strength improved from 199.1 to 238.9 MPa by 20%, modulus improved from 11.89 to 14.69 GPa by 23% and laminar shear strength increased from 0.238 to 0.283 MPa by 19%. On plotting different values of slopes obtained from the rates of improvement of flexural strength and modulus, against NaOH treatment time, two different failure modes were apparent before and after 4 h of NaOH treatment. In the first region between 0 and 4 h, fibre pull out was predominant whereas in the second region between 6 and 8 h, transverse fracture occurred with minimum fibre pull out. This observation was well supported by the SEM investigations of the fracture surfaces.     

Influence of alkali treatment and fibre length on mechanical properties of short Agave fibre reinforced epoxy composites

Composites based on short Agave fibres (untreated and alkali treated) reinforced epoxy resin using three different fibre lengths (3 mm, 7 mm and 10 mm length) are prepared by using hand lay up and compression mould technique. The materials were characterized in terms of tensile, compressive, flexural, impact, water absorption properties and machinability behaviour. All mechanical tests showed that alkali treated fibre composites withstand more fracture strain than untreated fibre composites. As evidenced by the dynamic mechanical analysis (DMA) tests, the thermo-mechanical properties of the composite with alkali treated Agave fibre were considerably good as alkali treatment had facilitated more sites of fibre resin interface. The machinability and atomic force microscope (AFM) studies were carried out to analyze the fibre–matrix interaction in untreated and alkali treated Agave fibre–epoxy composites.     

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.     

A novel fiber treatment applied to woven jute fabric/vinylester laminates

In this work, a novel fiber treatment consisting on an alkali treatment superimposed to biaxial tensile stress was successfully applied to woven jute fabric/vinylester laminates. The effect of treatment on the composites tensile properties was investigated at two different times of treatment. A significant improvement in stiffness was achieved by the composite treated with alkali under stress for 4 h. However, no significant differences between the stiffness of the untreated composite and the composites treated with alkali under stress for 24 h were found. On the other hand, irrespectively of the time of treatment, the composites with fabrics treated with alkali under stress showed the highest values of tensile strength. From results of fabrics tensile tests, compression shear tests and X-ray diffraction analysis, the improved tensile properties exhibited by the composites with treated fabrics could be attributed to structural changes of the fibers as well as to a change in the fiber/matrix interfacial properties.     

Mechanical behaviour of jute cloth/wool felts hybrid laminates

This experimental work is aimed at the characterization of new fibre reinforced composites based on epoxy resin with both protein (wool) and lignocellulosic (jute) natural fibres. Wool-based and hybrid (wool/jute) composites with two different stacking sequences (intercalated and sandwich) were developed. Their microstructure has been investigated through optical and scanning electron microscopy, whereas their quasi-static mechanical behaviour has been evaluated in tension and bending. In addition, the impact behaviour under low-velocity impact at three different impact energies, namely 6 J, 8 J and 9 J has been addressed. The tensile and flexural tests have been monitored using acoustic emission (AE) in order to elicit further information about failure mechanisms. AE monitoring showed that development of damage was due to nucleation of matrix microcracks and subsequent debonding and pull-out phenomena in wool fibre composites and that only in hybrid composites a sufficient stress transfer across the jute fibre/matrix interface was achieved. The results confirmed the positive role of hybridization with jute fibres in enhancing both the tensile and flexural behaviour of wool-based composites, though highlighting the need for an improved adhesion between wool fibres and epoxy matrix.     

Effect of alkali treated jute fibres on composite properties

Jute fibres were subjected to a 5% alkali (NaOH) solution treatment for 0, 2, 4, 6 and 8 h at 30°C. An improvement in the crystallinity in the jute fibres increased its modulus by 12%, 68% and 79% after 4, 6 and 8 h of treatment respectively. The tenacity of the fibres improved by 46% after 6 and 8 h treatment and the % breaking strain was reduced by 23% after 8 h treatment. For the 35% composites with 4 h treated fibres, the flexural strength improved from 199.1 MPa to 238.9 MPa by 20%, modulus improved from 11.89 GPa to 14.69 GPa by 23% and laminar shear strength increased from 0.238 MPa to 0.2834 MPa by 19%. On plotting the different values of slopes obtained from the rates of improvement of the flexural strength and modulus, against the NaOH treatment time, two different failure modes were apparent before and after 4 h of treatment. In the first region between 0 and 4 h, fibre pull out was predominant whereas in the second region between 6 and 8 h, transverse fracture occurred with a minimum fibre pull out. This observation was well supported by the SEM investigations of the fracture surfaces.     

Structure property relation of hybrid biocomposites based on jute,viscose and polypropylene: The effect of the fibre content and the length on the fracture toughness and the fatigue properties

In the present study, the extent of jute and viscose fibre breakage during the extrusion process on the fracture toughness and the fatigue properties was investigated. The composite materials were manufactured using direct long fibre thermoplastic (D-LFT) extrusion, followed by compression moulding. The fracture toughness (K_IC) and the fracture energy (G_IC) of the PP–J30 composites were significantly improved (133% and 514%, respectively) with the addition of 10 wt% viscose fibres, indicating hindered crack propagation. The addition of viscose fibres resulted in three times higher fatigue life compared with that of the unmodified jute composites. Further, with the addition of (2 wt%) MAPP, the PP–J30–V10 resulted in a higher average viscose fibre length of 8.1 mm, and the fracture toughness and fracture energy increased from 9.1 to 10.0 MPa m^1/2 and 28.9 to 31.2 kJ/m², respectively. Similarly, the fatigue life increased 51% compared with the PP–J30–V10, thus demonstrating the increased work energy due to hindrance of the propagation of cracks.     

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.     

Dynamic mechanical and thermal analysis of vinylester-resin-matrix composites reinforced with untreated and alkali-treated jute fibres

Vinylester-resin-matrix composites reinforced with untreated and 5% NaOH treated jute fibres for 4 and 8 h with different fibre loading were subjected to dynamic mechanical and thermal analysis to determine their dynamic properties as a function of temperature. For all the composites the storage modulus, E′, decreased with increase in temperature, with a significant fall in the temperature range 110°–170 °C. For the treated composites, the rate of fall, dE′/dT, had an inverse relationship with the defect concentrations in the composites. The lowest defect concentrations in the 4 h treated composites corresponded to the highest rate of fall. The glass transition temperature, T_g, of the unreinforced resin, corresponding to the loss modulus peak, was 101.2 °C, whereas that of the composites increased by nearly 28 °C on account of the restricted mobility of the resin molecules in the presence of the fibres. In the case of the treated composites, the T_g value showed a decreasing trend (128 to 125 °C). Unlike the plain resin, a tiny hump was observed in the loss modulus, E″, curves of all the composites around 166 °C, which became broader and more prominent with increase in the jute fibre content. The very high tanδ value of the resin decreased in the composites, indicating that the addition of the fibres lowered the damping capacity of the composites.     

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.     

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.     

Alkali treatment of coir fibres for coir-polyester composites

Coir fibres were subjected to alkali treatment with a view to improving the wettability of coir fibres by a commercially available resin such as polyester. Tensile strength of the fibres increases by 15% when the fibres are soaked in 5% aqueous solution of NaOH at 28±1° C for 72 to 76 h after which it shows a gradual decrease. This decrease is much more pronounced when the alkali is replenished after every 24 h. SEM observations showed the removal of cuticle and tyloses from the surface of coir as a result of alkali treatment, resulting in a rough fibre surface with regularly spaced pits. The debonding stress of alkali-treated fibres from polyester matrix was 90% higher than that of untreated fibres from the same matrix. Untreated fibres tended to float in the polyester whereas alkali-treated fibres were uniformly dispersed in polyester. Incorporation of 0.30 volume fraction of untreated and treated fibres in polyester resulted in composites having 11% and less 5% porosity, respectively. Flexural strength, modulus and impact strength of composites containing alkali-treated fibres were 40% higher than those containing the same volume fractions of untreated fibres. Longitudinal ultrasonic velocity and sound attenuation measurements indicated less fibre segregation and better fibre-matrix bonding in composites containing alkali-treated fibres.