The kinetics and reuse of spent liquor in the TEMPO-mediated oxidation of mechanical pulp have been studied. It was found that the oxidation reaction of the mechanical pulp by the 2,2,6,6-tetramethyl piperidine-1-oxyl radical (TEMPO)-NaBr-NaOCl system can be approximately described by first-order kinetics with respect to TEMPO and NaBr. In the concentration range used, the rate constant k is directly proportional to the concentration of TEMPO and NaBr, whereas the concentration of NaOCl determines the end of conversion of the primary alcohol groups on the mechanical pulp into carboxylic acid groups. It was also found that the spent reaction liquor can be recycled and reused with reinforced addition of NaOCl without additional TEMPO and NaBr and remains effective in generating carboxylic acid groups on mechanical pulp.
This work examined the effects of carboxyl content on the characteristics of TMP long fibers. The carboxyl groups on TMP long fibers were generated by a TEMPO-mediated oxidation using different amounts of sodium hypochlorite. In general, the increases in carboxyl content improved the tensile and burst indices but reduced the tear index and fines retention. It was also found that low carboxyl content on oxidized long fibers could adsorb part of the dissoluble substance (DS) and other substances, reducing the DS and total organic carbon (TOC) in whitewater; the adsorption capacity decreased with increasing carboxyl content. Addition of cationic polymer increased the retention of fines and decreased the DS and other substances in whitewater.
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