CHEMICAL-MECHANICAL TREATMENTS FOR NATURAL FIBERS AND INNOVATIVE COMPOSITE APPLICATIONS

ARIEL L. STOCCHI

Durban

Conferencia; First International Conference on Composites, Biocomposites and Nanocomposites (ICCBN); 2013

Durban University of Technology

PLENARY SPEAK:CHEMICAL-MECHANICAL TREATMENTS FOR NATURAL FIBERS AND INNOVATIVE COMPOSITE APPLICATIONS The increasing trend of using composite materials in many structural and semi-structural applications, as a good alternative to conventional materials, makes necessary the knowledge of their load-bearing capabilities. Mechanical properties of composite materials depend on several factors, such as fiber content, fiber orientation, fiber/matrix interaction and mode of testing. Thus, specific methodologies and a complete understanding of the characteristics of these materials are required. During the last decades, there has been an increasing interest in the use of natural fibers as a substitute of glass fibers mainly due to their low specific gravity, the workable specific modulus, the low cost, and the non-abrasive, renewable and biodegradable nature of cellulosic fibers. All this factors make them attractive to use as reinforcements in composite materials. Therefore, novel applications for natural-fiber reinforced materials were developed. However, poor properties of natural fibers such as their low stiffness and poor environmental resistance still limit some uses. In order to overcome these disadvantages, several treatments have been proposed. In the case of natural fibers, in addition to the matrix/fiber interface modification, different changes on the interphase between elementary fibers, as well as on the roughness and density of the technical fibers could be also induced by chemical treatment. Furthermore, other factors such as the orientation of microfibrils of cellulose within each elementary fiber which changes the fiber crystallinity play an important role. A novel fiber treatment consisting on a traditional alkali treatment with superimposed biaxial tensile stress was successfully applied to woven jute fabric/vinylester laminates. Irrespectively of the time of treatment, the composites with fibres treated with alkali under stress were always stronger than the composites with untreated fibres or with fibres treated with traditional methods. For treatment times shorter than 4 h, the treatment appeared to be less effective to induce the structural changes on the fibres partially responsible of the improvement of the composites tensile properties. A significant improvement in stiffness was achieved by the composite treated with alkali under stress for 4 h. From the results of fabrics tensile 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 in the case of the strength. The work in our group not only involves the developing of natural fiber reinforced composites. Novel applications for these materials were explored. For example honeycomb cores made of thermoset polymer matrix and reinforced with jute fabrics were manufactured. The analysis comprises the fabrication methods, the experimental elastic characterization of the composites materials, the mechanical characterization of the cores including their failure mechanisms, and the estimation of the effective elastic properties of the cores via computational homogenization procedures. Other applications developed such natural fiber reinforced wind blades are shown.