Natural Fibers

Obtaining high-quality long hemp fibres for flax spinning: a chemical approach

Saal B
Donnerstag, 12.09.2024, 09:25 - 09:50 Uhr

Reducing bundle thickness is crucial in generating high-quality hemp yarns using the flax wet-spinning system. The chemical approach reported here had a positive impact on the separation of scutched hemp fibre bundles, obtaining a reduction of more than 50% in their diameter. The chemical analysis validated the removal of waxes, pectin, and lignin, and the treatments resulted in a decrease in tenacity when compared to the control hemp fibres, which was also reported in the literature.

VĂ¢nia Pais (Fibrenamics)
Hemp fibres have received significant attention in recent years from textile industry stakeholders due to their potential to be used as an alternative to traditional natural fibres like cotton, wool, and silk. When the aim is to spin hemp using the flax wet-spinning system, hemp stems and bundles must undergo several mechanical processes, such as scutching and hackling, to reduce bundle thickness and produce high-quality yarns. However, hemp is more rigid and difficult to operate than flax, which leads to the necessity of having procedures to effectively separate the bundles while generating a reduced amount of tow fibres and by-products during the hackling. To accomplish this, degumming treatments can be applied to scutched fibres to maximize the quality of hemp long fibres, resulting in a higher degree of separation and disintegration of the fibre bundles, improving the subsequent hackled process, and allowing for the spinning of thinner and higher quality yarns. In this work different chemical treatments using sodium hydroxide (NaOH) and ethylenediamine tetraacetic acid (EDTA) were applied to hemp scutched fibres, adjusting the temperature, time, and ratio parameters to lower the environmental impact of these approaches. After every treatment, several characterizations were performed, such as: optical and scanning electron microscopy; X-ray diffraction Analysis (XRD); evaluation of colour through a spectrophotometer; length and linear mass density; Fourier-transform infrared spectroscopy (FTIR); and tenacity. The results showed that the treatments had a positive impact on the separation of the fibre bundles, with a reduction of more than 50% in their diameter. This chemical approach also contributed to increasing the crystallinity of hemp fibres through the removal of amorphous aggregates. According to the CIELAB colour system, it was also observed a decrease in the yellowing index and an increase in the white index due to the removal of lignin. Furthermore, chemical characterization confirmed the removal of waxes, pectin, and lignin. Similarly to what is reported in the literature, when it comes to the mechanical properties, the treatments led to a decrease in tenacity when compared to the control hemp fibres. This was to be expected and is connected to the removal of non-cellulosic compounds.