FORMATION OF PROPERTIES OF TECHNICAL HEMP FIBERS SUITABLE FOR MANUFACTURING TEXTILE FOOTWEAR

Abstract

The article develops hierarchical classification systems for the properties of hemp cotonin and yarn based on it, based on the principle of studying only those properties of semi-finished products that have a direct impact on the quality of the finished fabric for the manufacture of shoe uppers. To assess the unevenness of the length of hemp cotonin, the combined characteristics of fiber groups were used, which were divided into maximum, average and minimum lengths. It was determined that the majority of hemp cotonin fibers have an average length of 20–40 mm, which is close to the staple length of medium-fiber and long-fiber cotton varieties. It is proven that hemp cotonin can be suitable for the production of yarn using a pneumomechanical spinning system. As a result of the study of the chemical composition, physical, mechanical, and geometric properties of hemp cotonin, it was found that its high strength, characterized by the breaking load index of one fiber – 12.0 gs, is due to the high content of cellulose (up to 91.2%) and lignin (up to 8%) in the chemical composition, significantly higher than in other bast crops, which is proven by the example of the chemical composition of long-staple flax. It was also determined that the chemical composition of hemp cotonin has a significant impact on its physical and mechanical indicators. In particular, the chemical composition of hemp has the greatest impact on the relative breaking elongation index, which is quite high – 26.5%. With such a breaking elongation index, one hundred percent use of this raw material in yarn for the manufacture of shape-stable products is not recommended. In order to improve the qualitative properties of hemp cotonin, specially selected steaming modes were used, the application of which showed a significant improvement in the indicators of the studied fiber and its chemical composition. The absolute elongation indicator decreased by 1.5 mm, and the relative elongation at break indicator by 9%, which is a direct indicator of the decrease in mechanical properties. After steaming, the fiber became thinner and softer, as evidenced by a decrease in the linear density indicator by 1.3 tex. A decrease in the actual humidity by 3% brought hemp cotonin closer to the normalized actual humidity used in the pneumomechanical spinning method. The elongation at break indicator also decreased by 2.9 gs, which almost brought it closer to the normalized indicators of the fiber's spinnability. High-temperature steam under pressure destroyed pectin substances by 4%, which bind microfibrils. This led to a decrease in the ability of the fibers to elongate due to a decrease in the cohesion between the components. Hemicelluloses under the influence of steam underwent hydrolysis, became less elastic. Their reduced content (by the smallest indicators by 7%) makes the fiber more rigid and reduces its plasticity, but not critically, leaving a certain percentage (3.0–7.8%), which will provide the shoe fabric with the necessary quality indicators during operation. Also, lignin modification took place – a decrease by the smallest indicators by 1.1%. Lignin was partially destroyed or modified at high temperature, which positively affected the change in the mechanical properties of the fiber. The loss of waxy and fat-like substances by 1% affected the smoothness and sliding of hemp fiber, making it less susceptible to stretching. As a result of the conducted research, it was found that by using certain steaming modes (pressure: heating, boiling – 1.2–7.1 kgf/cm2; steaming – 1.8–2.3 kgf/cm2; washing – 0 kgf/cm2; temperature: heating, boiling – 90–160 0С; steaming – 140–121 0С; washing – 40 0С; duration of the operation: heating, boiling – 30 min.; steaming – 20 min.; washing – 10 min.) it is possible to obtain cottonized fiber with improved properties, suitable for the manufacture of potential high-quality footwear products from upper fabric based on technical hemp. In order to verify the relationship between the outlined steaming modes and the experimentally determined mechanical, geometric and physical properties of hemp cotton, which affect its spinning properties and are factors in the formation of the qualitative characteristics of the fabric suitable for the manufacture of potential footwear products, an additional study was conducted using the three-factor mathematical experimental design method. Analysis of the research results, namely the obtained regression equations and response surfaces, revealed that the most significant factors influencing the formation of the studied properties of cotton fiber in steaming modes are the steaming pressure and temperature, which was revealed during experimental and theoretical studies.