| Abstract | This work investigates the effect of extrusion parameters and formulation on the properties of polypropylene / short flax fibers composites. The parameters that were varied during the twin-screw extrusion process were screw configuration, screw rate, extrusion temperature and flow rate. The effect of the location of the feeding zone of flax fibers is also considered. Regarding the composite formulation, the effect of flax and hemp content, presence of coupling agent and of a reactive additive on composite properties were analyzed. Composites obtained with hemp fibers in the same extrusion process were also considered for comparison purposes. The materials were characterized in terms of morphological characteristics, fiber length distribution, rheological, thermal and mechanical properties. The variation of extrusion parameters showed that polypropylene / flax fibers composites have a large process window that can be considered as an advantage of PP/flax compounds. Tensile strength evaluated on injection molded parts increased up to 50% with flax fibers content when coupling and reactive agents are used. Due to their high flexibility, flax fibers are less oriented in the flow direction and the mechanical properties will be more isotropic. Furthermore, these composites showed a good recyclability using an injection molding process by keeping the integrity of their mechanical properties after five reprocessing cycles. The processability of these materials using a cast film line and the mechanical properties of obtained sheets are also presented. |
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