Influence of Temperature and Humidity on Flax Fiber-Reinforced Composites for Helicopter Structures Using Protective Coatings

With the aim of investigating whether sustainable and environmentally friendly flax fiber reinforced composites can meet the high technical requirements of aeronautical structures, this paper presents the influence of temperature and humidity on their structural-mechanical properties using protective coatings. Four coatings, two of which are partially bio-based, are tested on unidirectional flax fibers reinforced with bio-epoxy and polyfurfuryl alcohol resin. To simulate environmental conditions, coated and uncoated test panels are conditioned for two weeks in a climatic chamber at different temperature and humidity levels before their tensile specimens are tested and evaluated for moisture absorption, tensile strength, Young's modulus and fracture strain. The results show that higher temperatures lead to an increased moisture absorption rate and a lower maximum uptake. Higher relative humidity results in an increased maximum moisture uptake. A fossil-based coating could significantly reduce and retard moisture uptake at 30° C and 95 % relative humidity.