Pretreatment of flax fibers with low-frequency ultrasound for enzymatic refining treatments
Résumé
Flax fibers are a natural resource used in many applications, such as textiles and materials, notably thanks to their mechanical properties. Fiber extraction involves an initial stage in the field after the plant has been harvested, involving biological and pedoclimatic phenomena (retting) followed by mechanical treatment of the straw (scutching). Combined with the genetic and agricultural factors involved in flax production, this complex process results in variability in fiber quality, making it more difficult to use on an industrial scale. The main cause of variability in mechanical properties is associated with the highly heterogeneous morphology of the fibers found in different forms at the end of the extraction process: elementary fibers, fiber bundles, and assemblies of fiber bundles. Mechanical treatments such as carding or combing are generally applied to homogenize and refine the fibers but are likely to generate mechanical defects. This study aimed to reduce the morphological heterogeneity of flax fibers while minimizing the introduction of defects. For this purpose, low-frequency ultrasound (22 kHz) was used to provide high mechanical effects, upstream of the action of enzymes (pectinases) acting on the pectic matrix responsible for the cohesion of elementary fibers into bundles. Spectroscopic, morphological, and mechanical analyses were carried out to observe the effect of the different treatments. The mechanical action of acoustic cavitation enabled attrition of the fiber bundles without the use of chemical inputs, while enzymatic treatment led to refining. As the surface finish and fineness of flax fibers are important characteristics for their valorization, the combination of ultrasonic and enzymatic treatments could be a way of improving their quality.