Colorant extraction from turmeric (Curcuma Longa L) and optimization of its application on chrome-free tanned paiche (Arapaima gigas) leather

Abstract

The tanning of paiche skins represents an opportunity to give added value to waste generated in aquaculture. It requires clean technologies, as the substitution of highly-toxic chemicals. Basic chromium sulfate, a tanning agent used because of the physical-mechanical and thermal properties it imparts to leather, and synthetic dyes, including azo compounds, are among the most toxic but important products in the process. This research aimed to obtain a natural colorant from Curcuma Longa L. for dyeing paiche skins tanned with phenolic-syntans and glutaraldehyde compounds. Curcumin, the coloring principle, was extracted from turmeric rhizomes in aqueous medium, and characterized by HPLC-DAD and UV-visible spectrophotometry, and its response to variations in temperature, time, and mass of turmeric was evaluated at the laboratory level. Subsequently, a Box-Behnken design was established to optimize dyeing at the pre-pilot level. The factors studied were dyeing time (x1), turmeric colorant concentration (x2) and mordant concentration (x3), while response variable was the Color Intensity of dyed leather (y1). Through ANOVA analysis, the main effects and behavior of the response variable were determined. Process was scaled-up to the pilot level at the optimal point, evaluating chemical, mechanical, and colorfastness properties of leather. Results indicate the extraction of curcumin increases with temperature and the mass of turmeric. Optimal process values were 100.5 minutes, 5.06 % colorant, and 13.20 % mordant. Chemical and mechanical results suggest that leather is suitable to produce footwear, clothing, and leather goods; however, it is necessary to improve its lightfastness.