Effectiveness of Different Coating Treatments on the Durability of Flax Textiles

In recent years, there has been a growing interest in the study of natural fibers for their use in fiber reinforced cementitious matrix (FRCM) strengthening system. Natural fibers are a sustainable and renewable alternative to synthetic fibres with significant potential in civil engineering field. These fibers offer advantages, such as lightness and biodegradability, thus reducing environmental impact in terms of energy consumption and CO2 emissions. The use of these fibers can be considered an alternative to replace traditional fiber grids of the most common FRCM reinforcement systems, which employ textiles made of basalt, glass, carbon, aramid, PBO or steel fibers. The use of natural fibers as reinforcements in cementitious matrix composites is limited by an important factor: the durability of such materials, depending on the composition of these fibers in relation to the content of lignin and hemicellulose. In fact, in presence of aggressive environments the degradation of natural fibers involves the decomposition of lignin and hemicellulose. For this reason, coatings are normally used to protect fibers from the environment. Depending on the composition of these coatings, an increase in the mechanical properties of the coated fibers can be observed. In this paper, an experimental campaign was conducted to investigate the effects of different types of coating applied on two different flax textiles. Tensile tests were performed to compare the performances of uncoated fibers and of fibers coated with different treatments. To study the durability of the considered textiles, tensile tests were also performed after an exposure period of 20 days in an alkaline environment. The variations, in terms of mechanical properties, observed for the different textiles are discussed in the paper, trying to relate the results with the coating type and composition. For some coatings, a significant decrease of the mechanical properties was observed, while others were able to provide a good protection to the fibers against the alkaline environment, which did not experience an important strength reduction with respect to unconditioned samples.