Effect of processing on the properties of polypropylene reinforced with short sisal fibers

The effect of several processing techniques-pressing, twin-screw extruder, two-roll mill, and injection-molding-on the properties of polypropylene composites reinforced with short sisal fibers were investigated. The composite's properties were studied by tensile strength, notched Izod impact resistance, flexural resistance, and scanning electron microscopy. Impact properties were significantly improved (e.g., from 22 to 54 J/m for silane-treated fibers (30% weight fraction)). Tensile and flexural resistance was not improved by the fiber treatment. Tensile and flexural modulus approximately doubled with the addition of 30 percent byweight of untreated fiber. Processing produces a great variation on the dimension and dispersion of the fiber within the composite. The composites processed by the twin-screw extrusion presented much better fiber dispersion with fibers dissociated into individual ultimates. The relationship between processing and properties of these composites is discussed.