An Evaluation of Sodium Carbonate as a Replacement for Sodium Hydroxide in Hydrogen Peroxide Bleaching of CTMP

A series of experiments was performed to evaluate the effect of substituting sodium carbonate for the sodium hydroxide used in peroxide bleaching of spruce CTMP. Three peroxide levels were tested: I , 2, and 4% HzOz, and two levels of causticsubstitution; SO% and 80%. At both the 2% and 4% peroxide levels, substituting 50% of the caustic charge with sodium carbonate decreased the initial brightness gain by I point in TAPPI brightness. At the 80% caustic substitution level, the brightness gain decreased 1.5 points. Use of sodium carbonate as part of the alkali source in the bleaching process reduces the sensitivity of final bleached brightness to the alkali charge and should result in improved control. In all cases, sodium carbonate substitution was found to improve brightness stability and, in some cases, carbonate substituted samples gave higher reverted brightness than the caustic control.