Research on the Adhesive Properties of Flax Fiber in the Production of Composite Materials

The article presents the results of theoretical and experimental research into the adhesive properties of flax fiber and their impact on the scientific development of composite material production. The research established that combining natural fibers with a polymer material or matrix increases the complexity of the composite forming process and causes problems in the physicochemical processes of matrix–filler interaction. This is explained by the low wettability of flax bast (13.0–14.5 g). It was found that the presence of cutins on oil flax fibers determines their high degree of hydrophobicity. To improve the adhesive properties of the bast, it was chemically treated to remove cellulose companions and cutins, high-molecular-weight compounds. The bast was chemically treated using the oxidative method. After chemical treatment, a fiber enriched with cellulose and freed from waxy substances was obtained. Thus, the cellulose content increased from 47.67–53.33% to 90.01–97.68%, and the waxy substances were almost completely removed. Their content in the bast was 18.13–18.57%, but after chemical treatment, it decreased to 0.01–0.04%. After chemical treatment, the wettability of the fiber increased to the required levels −104.94–122.78 g, indicating that the adhesive properties were significantly improved. The results of studies on physical and mechanical indicators demonstrate the high quality of the obtained composites. In terms of fluidity, all samples were superior to the control sample reinforced with cotton fiber. The theoretical and experimental research enabled the collection of experimental samples of composite materials.