Natural Fiber-Polypropylene Composites Made from Caranday Palm

Composites made from polypropylene (PP) and local South American fibers traditionally used in yarnderived craftsmanships, Caranday Palm, were studied regarding the effect of fiber addition, concentration and characteristics of the coupling agent (molecular weight and percentage of grafted maleic anhydride), as well as type of processing. A laboratory-scale intensive mixing followed by compression, and pilot plant twin extrusion followed by injection, were the two processes investigated. The use of the first one allowed the selection of processable formulations with high fiber concentration and a percentage of coupling agent below the surface fiber saturation. In fact, it was found that there is a concentration of maleic anhydride moieties that saturates the surface of the fiber irrespective of the agent molecular weight. Increasing the concentration of the coupling agent above that value does not produce further improvement of the mechanical properties. The formulations selected from the results of the laboratory process were considered for the pilot plant (extrusioninjection) process. The use of the second process consisting of extrusion-injection molding showed that the high shear developed in this process leads to defibrillation of the fiber bundles. In the case of the Caranday Palm fibers, this defibrillation resulted in elemental fibers (micron size) being the effective reinforcement of the composite instead of the technical fibers (millimeter size) that were present in the composites prepared by compression. Better mechanical properties were achieved by using the latter method.