Enhancing the efficiency of hemp fiber dyeing with natural dyes: Indigo and lac

Hemp fibers dyed with natural dyes are environmentally sustainable, but it is typically difficult to achieve an intense shade and washing durability. In this study, mercerization and cationization using polyelectrolyte, Poly-diallyldimethylammonium chloride (polyDADMAC), were chosen to enhance the dyeing efficiency and mechanical properties. Indigo and lac were chosen as natural dyes due to their widespread use. SEM demonstrated that untreated fibers contained the non-cellulose boundary layer on the surfaces, but after mercerization, the surfaces were smoother, making them suitable for absorbing natural dyes. In agreement with the FT-IR, the spectra of non-cellulose disappeared after mercerizing. Following cationization, the FT-IR spectra confirmed the consequences of using poly-DADMAC. Tensile testing demonstrated that mercerized hemp yarns were 34.1% stronger compared to untreated hemp yarns due to the decrease in non-cellulose content and that the intermolecular attraction of cellulose was not disturbed. The color strength and fastness properties were described by the K/S value. Mercerization considerably affected the K/S of indigo dyeing, while cationization affected lac dyeing significantly. Besides that, both treatments improved fastness properties as well.