Mechanism of H2O2/bleach activators and related factors
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A mechanism of H2O2/bleach activator bleaching systems was proposed by using H2O2/tetraacetylethylenediamine (TAED) system as a model. HO· concentrations of the system under different pH conditions was measured by using benzenepentacarboxylic acid as a fluorescent probe. Computational analysis of bond enthalpies of H2O2 and peracids revealed that HO· should be the most effective agent in bleaching process, and peracids formed in H2O2/bleach activator bleaching systems could more easily produce HO·. The formation of peracids in H2O2/TAED system depends on the pH values of bleaching solutions and a nucleophilic substitution of the acid derivative by peroxide anion (HOO−). Charge density on carbonyl carbons of bleach activators affects the formation of peracids as well, which was proven from these compounds of TAED, tetraacetylhydrazine, N-[4-(triethylammoniomethyl)-benzoyl]-caprolactam chloride, phthalimide, N-acetylphthalimide and nonanoyloxybenzene sulphonate. It is likely that the charge densities on carbonyl carbon of amide bleach activators should be larger than 0.185. For ester bleach activators, the results were also investigated by activation energy, Gibbs free energy and Hansen solubility parameters. In addition, the ecotoxicity of bleach activators has been evaluated by ECOSAR program. Potential bleach activators can be designed and explored according to these results instead of large amounts of experimental data.
KeywordsBleach activators Cotton Hydrogen peroxide Charge density Bleaching species
This work was supported by the Fundamental Research Funds for the Central Universities of Donghua University (Grant No. CUSF-DH-D-2017052). The authors gratefully acknowledge Dr. Xuan Zhang for the experimental equipment and statistical analyses. The first author thanks the scholarship support from China Scholarship Council (CSC).
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