Vacuum-Bag-Only (VBO) Molding of Flax Fiber-reinforced Thermoplastic Composites for Naval Shipyards

This article presents an alternative manufacturing process for unidirectional tape natural fiber Polypropylene with Maleic Anhydride grafted PolyPropylene (PP + MAPP) thermoplastic composites that could enable large high performance parts to be built, while being recyclable at end of life. The performance target is flax/epoxy composites that are currently manufactured in shipyard. A parametric analysis (time and temperature) of vacuum-bag-only molding of flax unidirectional tapes-reinforced PP + MAPP matrix is conducted to find the best configuration regarding the final composite tensile properties, as no standard procedure exists. The physical phenomena induced by temperature, water sorption/desorption, and pressure during the manufacturing step are investigated. The best parameters for temperature and time are found to be at 180 °C during 45 min, resulting in a fiber volume fraction of 42.2 ± 1.5%, and between 1.9 ± 0.7% and 8.2 ± 1.8% of porosity, depending on the method of determination. Interestingly, tensile properties are in the same order of magnitude as conventionally manufactured continuous flax fiber-reinforced thermoset or thermoplastic composites. The article ends with a discussion of the accessibility and technical concerns of vacuum-bag-only molding, material selection, design, mechanical performance, and end of life.