The stabilizer of macromolecular metal complexes for pearl bleaching

436

Journal of Inorganic Biochemistry

Abstracts

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THE S T A B I I J Z E R OF M A C R O M O L E C U L A R M E T A L COMPLEXES FOR PEARL BLEACHING

Zhang Bingjian a and Zhang Xiaoli b a Departmentof Chemistry, Zhefiang University, Hangzhou, Zhefiang 310027,China b Pearl Laboratory, Zhanjiang Fishery Collage, Zhanjiang 524025, China Most of the sea pearls obtained by cultivation possess an unfavorable color and cannot be made into various handicrafts unless the color was eliminated by bleaching treatment. The main composition causing the bleaching action is usually H202, that is the anion HO2-. The HO2-is very unstable and easy to decompose further.Therefore, application of stabilizer is the effective way to increase the bleaching efficiency of the pearls. In this work, the stabilizers of macromolecular metal complexes (SMMC) were selected and studied. A modified synthetic method was developed by dehydration of the reactants. A series of SMMC hve been synthesized Eli The bleaching formulation is: 30 °/~H202100 ml; surface active agent 5 ml; neutralizer 10 ml; H201000 ml and SMMC. Test conditions is: reaction temperature 35 ___3 *C; ilhlminating value 11000 Lx; reaction time 24 hr; the ratio between pearl and bleaching liquid 1:2. The iodimetry is applied to determine the concentration ofH202 EH202] . Elemental analysis, TG-DTA, UV-,IR-spctra of the process were investigated in detail. It has found that optimum amount of SMMC is 1 "~ 1.5 ml/1. [I-I:O4 1. EEl. Fig 1. shows the effect on inhibition of decomposition of with SMMC HO2-. When SMMC is applied during bleaching, the pearl bleaching rate increases by 20% and the bleaching cycle 302.0 ~ i ~ ~ _ _ _ shortens. At the same time the surface of the bleached pearls will be more bright and smooth. There are many hydroxyl groups, carboxyl groups and Mg 2÷ no SMMC etal metal ions on the macromolecular chain of the SMMC, 1.0 ~ which makes SMMC to dissolve in water easily and makes the intermolecular and intramolecular chelation to occur in the 4 8 12 16 20 24 solution. Time hr Elemental analysis, TG-DTA, UV-, IR-spetrctra of the bleaching process found some of the Mg 2+ on the rings were Fig. 1 Stabilizing Effect of SMMC replaced by Mn etal heavy metal ions. The complex stability of Mg chelate ring is less than that of the heavy metal chelate ring. Thus, the heavy meal ions lose their catalytic action on H 2 0 2 that action increase the decomposition rate of riO2-. On the other hand, Mg 2÷ is short of electron, the whole macromolecular chain forms an electron accepting colloid. HO2- is easy to adsorbed on the complex colloid. The active intermediate HO2- is in a controlled state owing to the adsorption by static electricity, but its oxidation characteristics is not changed ,the reaction still occur when HO2 encounters pigments .Thus , the original competing mechanism in bleaching liquid is changed, the ineffective decomposition reaction of H202 is inhibited. I

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Reference 1 Zhang Bingjian and Zhang Xiaoli, Chemical Journal of Chinese Universities, 17(7),1161(1996) 2 Zhang Bingjian and Zhang Xiaoli, World Chinese Workshop on Applied Chemistry, 1995,9,P89

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