Bending of flax/polypropylene composites based on comingled fabric: feasibility study

Abstract

Plant fibers are increasingly being incorporated into composites, as they reduce the material’s environmental impact. As part of an eco-design approach, we studied the processing of a flax/polypropylene (PP) composite. The ability of companies to adapt to demand is also a key factor in the ecological transition. While the manufacture of this composite using the bending method has already been studied, the way in which it is shaped has received little attention. In this study, the feasibility of bending composite samples (size 100 × 15 × 3.4 mm) at an angle of 90 degrees is evaluated. For its thermoplastic properties, the PP has been chosen, so it can be transformed more than one time, contrary to the epoxy. As a result, the manufacturing and storage of flat plates upstream will then allow elements to be shaped on demand, since only the bending stage would remain. Flax fibers are found in large quantities in France and are natural fibers with interesting properties. Process conditions were experimented with to achieve external bending without detrimental damage to mechanical behavior. Those conditions are related to the process fabrication: tools temperature (die and punch up to 145 °C), preheating of the material (160 °C), heat flux around the sample (flow up to 0.115 m³/s), implementation process (holding time between 240 and 360 s and cycles), fold orientation (45° or 0°), … The influence of the various parameters on fold quality (visual and mechanical) is analyzed by experimental design and strength tests (threshold higher than 117.3 MPa). Operating conditions have been determined, that guarantee both aesthetic quality and robustness through reproducible experimental protocols. Such semi- finished products will play a role in tomorrow’s structural parts for various industrial applications, such as the automotive industry, as well as in the construction of boat parts, etc.