Ionic liquid and ultrasound-assisted extraction of chestnut shell pigment with good hair dyeing capability

To effectively extract the pigment from chestnut shell in a green and efficient way, an eco-friendly and efficient method based on ionic liquid ultrasonic assisted extraction (IL-UAE) was established. The effect of a series of 1-alkyl-3-methyl imidazole ionic liquids on the yield was investigated. The results indicated that the chain length of ionic liquids and the properties of anions and cations had a significant impact on the extraction, and 1-butyl-3-methylimidazolium acetate ([Bmim]OAc) had the best extraction effect. In addition, the concentration of bond breaking agent (sodium dodecyl sulfate, urea), concentration of [Bmim]OAc, liquid-solid ratio, extraction power, time, temperature and other parameters were tested by single factor. Sodium dodecyl sulfate (SDS), urea concentration and liquid-solid ratio were optimized by response surface methodology (RSM). The optimal process conditions were as follows: SDS concentration of 0.44% (w/v), urea concentration of 2.87% (w/v), [Bmim]OAc concentration of 1.07 mol/L, liquid-solid ratio of 36.26 mL/g, ultrasonic power of 350 W, ultrasonic time of 50 min, and ultrasonic temperature of 80 °C, respectively. Under these conditions, the yield was 71.60 mg/g. Compared with the conventional reflux extraction with organic solvents (sodium hydroxide, ethanol), the optimized method improved the yield by 42.24% and 38.70% in a shorter time (50min versus 120min), respectively. The physico-chemical properties of hair dyed with chestnut shell pigment extracted by IL-UAE were compared with those extracted by conventional organic solvents. The results showed that the former showed excellent color intensity, smooth hair surface morphology and low internal damage than the latter. Our results helped to accelerate the high-value applications of chestnut wastes.