Development of o-phthalic anhydride as a low-temperature activator in H₂O₂ bleaching system for cotton fabric

O-phthalic anhydride (PA) was developed as a low-temperature activator in the H₂O₂ bleaching system for cotton fabric. The performance of the H₂O₂/PA bleaching system was investigated by measuring the CIE whiteness index (WI) of the bleached cotton fabric, H₂O₂ decomposition rate and bursting strength, respectively. The effects of experimental conditions, including PA dosage, bleaching time, bleaching temperature and NaOH concentration, were discussed in the H₂O₂/PA bleaching system. Upon addition of PA, the WI and H₂O₂ decomposition rate increased significantly at 70 °C. The results showed that the bleaching system had a promising application prospect. Compared with the H₂O₂ system, the H₂O₂/PA system significantly promoted ¹O₂ generation under the same alkali condition by using 9,10-dimethylanthracene as a fluorescent probe for ¹O₂. And the generation of large amount of ¹O₂ did not obviously affect the bleaching performance in the H₂O₂/PA system. By using benzenepentacarboxylic acid as a fluorescent probe for HO· detection, it was found that the fluorescence intensity was enhanced 14 folds in the presence of PA, indicating that PA could strongly promote HO· generation. By using dimethyl sulfoxide as a scavenger to control HO· concentration, it was found that the WI of the fabric was closely related to the HO· concentration, revealing that the HO· could play an important role in the bleaching process. Phthalic acid was also added to the H₂O₂ bleaching system to investigate potential bleaching route of the H₂O₂/PA system. Based on these experimental results, a possible bleaching mechanism of the H₂O₂/PA system was proposed.