Investigation of color change and moisture regain of naturally colored cotton
Kang, Sho Yeung
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Naturally colored cotton does not need to be dyed or bleached and does not require pesticide treatment, making the processing of colored cotton inexpensive and environmentally friendly. However, there are concerns about its unidentified pigment character and low moisture regain, which affect its commercialization. In this research, the characterization of pigments in three naturally colored (buffalo brown, coyote brown and green) cottons, and their moisture regain change during finishing and care processes were studied. An enzymatic scouring process using pectinase and cellulase did not significantly change color of naturally colored cottons. Two alkali scouring processes (CaCO3 and NaOH) decreased lightness, and chroma (a* and b*) of naturally colored cottons. With color changes of cottons toward dark colors, scouring solutions after scouring were also strongly colored. Wax extraction, light microscopy analysis, scanning electron microscopy (SEM), X-ray surface analysis, and inductively coupled plasma (ICP) were used to determine mechanism of color changes. Results show that after alkali scouring, cross-sections of fiber became swollen for green cottons, pigment in the fibers moved to outer surface, and potassium content of fiber decreased significantly. Enzyme treatment as detergent and UV exposure were used to simulate possible color change after care. Color of scoured cotton was stronger after enzyme treatment. Lightness of single enzyme treated cottons decreased after five hours UV exposure and then increased. Cottons treated with multiple enzymes showed continuous increase with UV exposure. The green cotton lost its green color and gained red color after UV exposure. The scouring process and enzyme treatment increased the weight of naturally colored cottons. Statistical analysis on change in present moisture regain showed that the weight increase was due to higher moisture regain (%) after processes.