THERMOPLASTIC COMPOSITES BASED ON FLAX FIBERS AND POLYPROPYLENE - INFLUENCE OF FIBER LENGTH AND FIBER VOLUME FRACTION ON MECHANICAL-PROPERTIES

Natural-fibre-mat-reinforced thermoplastic (NMT) composites based on f lax fibre mats and a Polypropylene (PP) matrix were manufactured using (i) a film-stacking method and (ii) a paper making process. The influ ence of fibre length and fibre content on stiffness and strength is re ported and compared with data for glass-mat-reinforced thermoplastic ( GMT) composites, including the influence of using maleic-anhydride gra fted PP. The data is also compared with existing micromechanical model s like Kelly-Tyson and Cox-Krenchel for strength and stiffness, respec tively. A good agreement was found between theory and experiment in ca se of stiffness while in case of strength the experimental values fall well below the theoretical predictions. Results indicated that NMTs a re of interest for low-cost engineering applications and can compete w ith commercial GMTs, especially when a high stiffness per unit weight is desirable. Results also indicated that the key area for future deve lopment lies not only in improved adhesion but mainly in improving the fibre strength.