Comparison of infrared-, ultrasonic-, and microwave-assisted mordanting methods for the natural dyeing properties of hemp fabrics

This study examined the natural dyeing properties of hemp fabrics using a mixed mordant consisting of aluminum potassium sulfate (10 and 20 g/L) and tannic acid (5 and 10 g/L). The natural dye was derived from jackfruit wood (Artocarpus heterophyllus) and then processed into a powder via spray drying. The fabrics were dyed using 10% owf dye, at a pH of 5, temperature of 80 °C, for 50 min, with a liquor ratio (L:R) of 1:30. Prior to dyeing, mordanting was applied to improve dye uptake. The mordanting process compared three distinct heating techniques: infrared heating (IRH), ultrasonic heating (USH), and microwave heating (MWH). The X-ray diffraction results showed that MWH was the only heating technique that maintained the crystallinity index (\(CI\)) of the fibers. However, it produced slightly lower color strength (\(K/S\) of 1.01 ± 0.01) compared to IRH (\(K/S\) of 1.36 ± 0.04) and USH (\(K/S\) of 1.32 ± 0.04). IRH exhibited the most significant reduction in the \(CI\), followed by USH. The sample treated with IRH had the highest aluminum content (0.88 ± 0.02%), whereas the MWH-treated sample had the lowest (0.75 ± 0.02%), which is consistent with the results concerning \(CI\) and \(K/S\). The ratings for color fastness to washing, light, and rubbing were generally favorable. Mordanting enhanced both the color fastness and the color strength of the fabric, but it did not affect the tensile properties of the fabrics. Mordanting and dyeing slightly enhanced the ultraviolet protection efficiency of the fabrics. However, all samples, including the pristine hemp fabric, provided excellent protection against ultraviolet radiation.

Graphical Abstract