Characterization of polypropylene composites reinforced with flax fibers treated by mechanical and alkali methods

Flax is a type of natural fiber widely used as reinforcing materials for polymer composites. The commercially available flax fibers in Canada consist of a significant amount of shive and other impurities, which could act as stress concentration regions to negatively affect the mechanical property of composites. In this study, the shive was manually removed from the commercial flax fibers by screening and combing to obtain different shive contents from 0 to 30 wt%. By contrast, the obtained flax fibers were further treated with alkaline solution. The fibers obtained from mechanical and alkali treatment were compared on their thermal and mechanical properties. As expected, it was found that the thermal stability and mechanical properties of the flax reinforced polypropylene composites increased significantly with the removal of the shive content. However, the alkali treatment on flax fiber did not further improve the composites properties. The possible reason was that the proper mechanical treatment (screening and combing) prior to alkaline treatment effectively loosened the fiber bundles for better single fiber separation in matrix and significantly removed the impurities, thus the effect of alkaline treatment did not become obvious.