Andrzej K. Bledzki

Possibilities for improving the mechanical properties of jute/epoxy composites by alkali treatment of fibres

Abstract The aim of this paper is the improvement of the mechanical properties of natural-fibre-reinforced thermosets, as a result of optimization of the properties of tossa jute fibres by the use of an NaOH treatment process. By this process shrinkage of the fibres during treatment had significant effects on fibre structure and, as a result, on the mechanical properties of the fibres. The highest fibre strength and stiffness were reached by using isometric conditions (shrinkage=0%). The fracture mechanism of the fibre was also affected by the shrinkage state. Regarding fibre/matrix adhesion, the rougher surface morphology after NaOH treatment did not lead to any improvement. Composite strength and stiffness generally increased as a consequence of the improved mechanical properties of the fibres by NaOH treatment under isometric conditions. The Youngs modulus of the composites was linearly dependent on fibre content for both untreated and treated fibre composites. The Youngs moduli of composites with treated and untreated fibres were approximately 30% and 50%, respectively, lower than for comparable glass-fibre/epoxy composites. The improvement in dynamic modulus (measured in an increasing-load test) of the composites as a result of the use of treated fibres was similar to that observed for Youngs modulus. Furthermore, the use of treated fibres and of higher fibre contents, both led to a decrease in fatigue behaviour and progress in damage in the composites. Impact damping was distinctly affected by the shrinkage state of the fibres during the NaOH treatment because of its influence on yarn toughness. A good correlation was found between composite impact damping and yarn toughness for the jute/epoxy composites investigated.

The influence of fiber-surface treatment on the mechanical properties of jute-polypropylene composites

This article concerns the effectiveness of MAH-PP copolymers (graft copolymer of PP and maleic anhydride) as coupling agents in jute-polypropylene composites. The fiber treatment time and the MAH-PP concentration influenced the mechanical properties of the composites. Flexural strength of the composites with MAH-PP treated fibers was higher than that of unmodified fibers, and increased with fiber loading. The cyclic-dynamic values at an increasing load indicated that the coupling agent reduces the progress of damage. Dynamic strength (dynamic failure stress at load increasing test) of the MAH-PP modified composites is therefore raised by about 40%. SEM investigations confirm that the increase in properties is caused by improved fiber-matrix adhesion. There was less inclination for fibers to pull out of the matrix.

Alkali treatment of jute fibers: Relationship between structure and mechanical properties

The mechanical properties of tossa jute fibers were improved by using NaOH treatment process to improve the mechanical properties of composites materials. Shrinkage of fibers during this process has significant effects to the fiber structure, as well as to the mechanical fiber properties, such as tensile strength and modulus. Isometric NaOH-treated jute yarns (20 min at 20°C in 25% NaOH solution) lead to an increase in yarn tensile strength and modulus of ∼ 120% and 150%, respectively. These changes in mechanical properties are affected by modifying the fiber structure, basically via the crystallinity ratio, degree of polymerization, and orientation (Hermans factor). Structure–property relationships, developed for cellulosic man-made fibers, were used with a high correlation factor to describe the behavior of the jute fiber yarns.

Creep and impact properties of wood fibre–polypropylene composites: influence of temperature and moisture content

Abstract Wood fibre reinforced polypropylene composites of different fibre content (40, 50 and 60% by weight) have been prepared and wood fibres (hard and long fibre) were treated with compatibiliser (MAH-PP) to increase the interfacial adhesion with the matrix to improve the dispersion of the particles and to decrease the water sorption properties of the final composite. Results indicated that impact properties were affected by moisture content. The Charpy impact strength decreased and maximum force was increased with increasing of moisture content. With the addition of MAH-PP (5% relative to the wood fibre content), damping index decreased around 145% for hard wood fibre–PP composites at 60 wt.% wood fibre content. Long wood fibre–PP composites showed more impact resistance than hard wood fibre–PP composites. Short term flexural creep tests were conducted to investigate the creep behaviour of wood fibre–PP composites. Three experimental parameters were selected: the addition of compatibiliser, temperature and wood fibre content. The addition of MAH-PP, increased creep modulus that means reduced the creep. The extent of creep resistance (creep modulus and creep strength) decreased with increasing temperature. It was also found that wood fibre content has a great effect on creep resistance which is increased with increasing wood fibre content.

Wood Fibre Reinforced Polypropylene Composites: Effect of Fibre Geometry and Coupling Agent on Physico-Mechanical Properties

Wood fibre reinforced polypropylene composites at fibre content 50% by weight have been prepared and different types of wood fibres (hard wood fibre, soft wood fibre, long wood fibre and wood chips) were treated with coupling agent (MAH-PP) to increase the interfacial adhesion with the matrix to improve the dispersion of the particles and to decrease the water sorption properties of the final composite.The present study investigated the tensile, flexural, charpy impact and impact properties of wood fibre reinforced polypropylene composites as a function of coupling agent and fibre length and structure.From the results it is observed that wood chips-PP composites showed better tensile and flexural properties comparative with the other wood fibre-PP composites with the addition of 5%MAH-PP, which is around 65% and 50% for tensile strength and flexural strength respectively. Hard wood fibre-PP composites showed better impact characteristic values comparative to other wood fibre-PP composites with the addition of 5%MAH-PP and damping index decreased about to 60%. Charpy impact strength also increased up to 60% with the addition of 5%MAH-PP for long wood fibre-PP composites. Water absorption and scanning electron microscopy of the composites are also investigated.

Physico-mechanical studies of wood fiber reinforced composites

Wood polypropylene composites (WPC) of different compositions (30, 40, and 50%) have been prepared using maleic anhydride–polypropylene copolymer of different percentage (5 and 10% relative to their wood fiber content). Tensile, flexural, fracture toughness, and impact test of the prepared WPC were carried out. From the results, it is observed that the hard wood fiber–polypropylene composites, by using maleated polypropylene (MAH-PP), show comparatively better performance to soft wood fiber–polypropylene composites. Tensile strength and charpy impact strength have been increased to a maximum of 50 and 20%, respectively. The damping index has been decreased by 60% when 10% of MAH-PP has been used. Water absorption and scanning electron microscopy of the composites are also investigated.

Calculation of elastic properties of natural fibers

This article deals with the calculation of the elastic properties of cellulose based natural fibers by using two different types of idealization and assumptions. One model (model A) bases on antisymmertrical laminated structure, while the second one (model B) bases on a thick laminated composite tube model. Model B is able to take into account the elliptic geometry, the hollow based structure of the cross section of the fiber cell. The calculated relationships between spiral angle and modulus in fiber axis by model A fits successful experimental data for holocellulose fibers which were published elsewhere. In general, modulus in fiber axis decreases with increasing spiral angle as well as the degree of anisotropy, while shear modulus reaches a maximum for a spiral angle of 45°. Fiber cell modulus increases linear with increasing cellulose content for both, the calculated (model A) and measured values. The correlation between experimental data and calculation ones was not as high as in the case of modulus versus spiral angle. The discrepancy between model A and a more real cross section is calculated (model B) with roughly 30%.

Natural-fibre-reinforced polyurethane microfoams

Polyurethane-based composites reinforced with woven flax and jute fabrics were prepared with an evenly distributed microvoid foam structure. The relationship between the resin-filled grade and the microvoid content and the density was described. The influence of the type of reinforcing fibre, fibre and microvoid content on the mechanical properties was studied. The investigation results for the static mechanical properties of the composites were described by approximate formulae. It was found that the specific data were only slightly dependent on microvoid content. Increasing the fibre content induces an increase in the shear modulus and impact strength. However, increasing the microvoid content in the matrix results in a decreased shear modulus and impact strength. The woven flax fibre results in composites with better mechanical strength than the woven jute fibre composites.

Possibilities to Improve the Properties of Natural Fiber Reinforced Plastics by Fiber Modification – Jute Polypropylene Composites –

The influence of the fiber-matrix adhesion in jute fiber-reinforced polypropylene on the materials behavior under fatigue and impact loadings was investigated throughout this study. It was shown that a strong interface is connected with a higher dynamic modulus and reduction in stiffness degradation with increasing load cycles and applied maximum stresses. The specific damping capacity resulted in higher values for the composites with poor bonded fibers. Furthermore, the stronger fiber-matrix adhesion reduced the loss-energy by non-penetration impact tested composites with roughly 30%. Tests which were performed at different temperatures, showed higher loss energies for cold and warm test conditions compared with room temperature. Post-impact dynamic modulus after 5 impact events was roughly 40% and 30% lower for composites with poor and good fiber-matrix adhesion, respectively.

Method for identification of elastic properties of laminates based on experiment design

Abstract A numerical-experimental method for the identification of mechanical properties of laminated composites from the experimental results is developed. For the first time it is proposed to use the experiment design to solve the identification (inverse) problems. The basic idea of the proposed approach is that simple mathematical models (response surfaces) are determined only by using the finite element solutions in the reference points of the experiment design. Therefore, a significant reduction (about 50–100 times) in calculations of the identification functional can be achieved in comparison with the conventional methods of minimization. Numerical examples of identification of elastic properties of different laminates from the measured eigenfrequencies of plates are discussed.