Khatha Wathakit 1, Sakaya Sombatpraiwan 1 and Khongdet Phasinam 2*
1The Center for Plant Genetic Conservation Project Under the Royal Initiative of Her Royal Highness Princess Maha Chakri Sirindhorn of Suranaree University of Technology, Nakhon Ratchasima, Thailand; 2Faculty of Engineering and Technology, Shinawatra University, Pathum Thani, Thailand
*Corresponding author: khongdet.p@siu.ac.th
This study investigated the phytochemical composition of different parts of Radermachera ignea and evaluated its potential as a natural colorant source for cotton and silk. Phytochemical screening of bark, leaves, and flowers was conducted using standard qualitative assays, while dye extraction from fresh and withered flowers was performed using aqueous and ethanol solvents at concentrations of 25–95%. Dyeing experiments incorporated natural and metal mordants, with Cu²?, Fe²?, and Al³? treatments standardized to 0.0001 mol of central metal ion per gram of fiber, followed by colorimetric evaluation using the L*, a*, and b* system. Wash fastness was assessed using simulated ultrasonic washing with sodium lauryl sulfate, and light fastness was evaluated under UVC irradiation as an accelerated comparative photodegradation stress test. Results showed significant differences (P<0.05) in L*, a*, and b* values among extraction methods and mordant treatments. Withered flower extracts obtained using 75% ethanol generally produced stronger coloration and higher redness (a*) in cotton and silk, whereas Cu²? and Fe²? mordants enhanced yellowness (b*) and relative color retention after washing and UVC exposure. Natural mordants, particularly tea leaves and banana sap, improved red-tone development, while copper-based mordanting was more effective in maintaining yellow tones under accelerated light exposure. The key methodological contribution of this study is the standardization of metal mordant comparisons based on equivalent central metal-ion concentrations rather than total metal-salt weight, enabling a more comparable assessment of Cu²?, Fe²?, and Al³? mordant effects. These findings provide practical guidance for selecting plant-based extracts and mordanting strategies for sustainable textile coloration. However, RI flower pigments, likely dominated by carotenoid-type compounds such as zeaxanthin, showed limited fixation and stability on textile fibers, suggesting that further stabilization strategies are required before practical textile application.