Effect of microstructure on the tensile and fracture properties of sisal fiber/starch based composites

V. ALVAREZ, A. VÁZQUEZ AND C. BERNAL

Buenos Aires, Argentina

Conferencia; COMAT 2005; 2005

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In this work, the tensile and fracture behavior of biocomposites consisting on starch based matrix and short sisal fibers was investigated. Composites were manufactured by injection molding using 5, 10 and 15 wt.% of sisal fibers. Tensile tests were carried out on samples of longitudinal (L) and transverse (T) directions with respect to the melt flow direction. Irrespectively of sample orientation, an increasing trend on Young’s modulus and tensile strength with fiber content was found. However, this reinforcing was more pronounced for L samples with most of the fibers oriented longitudinally to the loading direction. Quasi-static fracture tests were performed on SENB specimens with cracks propagating both, parallel and perpendicular, to the mold flow direction. KIC values increased with the addition of sisal fibers due to the operating failure mechanisms derived from the fibers. In addition, fracture toughness values were higher for samples with fibers preferentially aligned transverse to the crack propagation direction. Under dynamic conditions composites exhibited higher values of total fracture energy than neat matrix. This parameter also increased with fiber content due to the circumferential shear-cracking phenomenon that appeared with the fiber incorporation. Models used in this work were able to predict mechanical properties and orientation of these composites. Keywords: fracture toughness, biodegradable polymers, natural fibers, polymer-matrix composites, short-fiber composites, orientation, injection molding.