Composite consisting of polypropylene reinforced with short sisal fibers were prepared by melt-mixing and solution-mixing methods. In the melt-mixing technique, mixing parameters were optimised by varying the mixing time, rotor speed and chamber temperature. A mixing time of 10 min, rotor speed of 50 rpm and a mixing temperature of 170°C were found to be the optimum mixing conditions. Tensile properties of melt-mixed and solution-mixed composites were compared. Under optimum mixing conditions melt-mixed composites showed better tensile properties than those of solution-mixed composites. The influence of fiber length, fiber loading and fiber orientation on the mechanical properties of PP/sisal composites has been evaluated. The fiber breakage and damage during melt-mixing were analysed from fiber-length distribution curves and optical photomicrographs. The effect of chemical treatment on the tensile properties of sisal/PP composites was investigated. Treatments with chemicals such as sodium hydroxide, maleic anhydride, urethane derivative of PPG, and permanganate were carried out to improve the bonding at the fiber/polymer interface. It has been observed that all the treatments enhanced the tensile properties of the composites considerably, but to varying degrees.

Effect of processing variables on the mechanical properties of sisal-fiber-reinforced polypropylene composites