Generation of hydroxyl radicals and effective whitening of cotton fabrics by HO under UVB irradiation.

Chemically crosslinked cotton fabrics may show yellowish appearance, especially citric acid (CA) crosslinked ones. Hydrogen peroxide (HO) bleaching under alkaline condition could improve the whiteness of the CA-crosslinked cotton fabrics but sacrificing certain crosslinking performance of the products due to alkaline hydrolysis of ester connections. Regular HO and UV irradiation (HO/UV) system can destroy color but also damage fibers due to the use of very short wavelength of UVC such as 254nm or shorter. Now, it was found that longer wavelength UV such as 312nm performed better in HO/UV systems on CA-crosslinked cotton fabrics. The reaction mechanism and potential product of the oxidation reaction on CA-crosslinked cotton were proposed and demonstrated. UV-vis spectrophotometer and Fourier transform infrared spectroscopy provided key evidence. Whiteness, wrinkle recovery angle and tensile strength of the fabrics were evaluated, and the results support the mechanism. The process is environmentally friendly and highly efficient.