USE OF CHELATING AGENT EDTA WITH SODIUM THIOSULFATE AND SODIUM-BOROHYDRIDE IN BLEACHING TREATMENT

This article briefly reviews the use of chelating agent EDTA with sodi um thiosulphate and sodium borohydride in bleaching treatment. A rag p aper (1832) was chosen for experiments. Acid soluble iron and. copper were measured and compared to the results obtained by using EDTA Brigh tness and colour reversion were observed and il-le content of COOH and CHO groups were measured before and after the accelerated ageing of p aper, Ii is shown that the chelating agent nn be useful in the removal of iron and copper on cellulose fibres. The best approach seems to be the use of a reducing agent coupled with a chelating agent. If sodium thiosulphate is used the colour stability of the treated paper is imp roved, but (his is not the case with NaBH4. Altogether, the mechanisms of all reactions which take place in paper when EDTA is used are stil l not clear and need more detailed investigations.