Effect of sodium bicarbonate treatment on mechanical properties of flax-reinforced epoxy composite materials

This paper deals with the evaluation of the effect of an eco-friendly and cost-effective surface treatment based on the use of sodium bicarbonate on the mechanical properties of flax-reinforced epoxy composites. To this aim, unidirectional fabrics were soaked for five days in 5 and 10% in weight of sodium bicarbonate solution at 25℃. Quasi-static and dynamic mechanical tests were performed and the fracture surfaces of the composites were analyzed through scanning electron microscopy. Results evidenced that this treatment improves the fiber–matrix adhesion thus increasing the performances of the composites. Treating the fabrics with 10% w/w of bicarbonate solution leads to improvements of ∼20 and ∼45% in tensile strength and modulus of the composites, respectively, compared to untreated ones. Furthermore, by increasing the concentration, negligible changes in the glass transition temperature and reductions in the tanδ peak heights were found. The observation of the fracture surfaces confirmed the beneficial effect of the proposed treatment.