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 Sodium bicarbonate is typically the chemical used to raise alkalinity, when required, in the sizing process. The AKD process works best at 150 ppm of bicarbonate alkalinity. Precipitated CaCO3 contributes about 60 ppm of bicarbonate alkalinity. Therefore, supplemental sodium bicarbonate is required in plants with process water of 90 ppm alkalinity or less. Sodium bicarbonate is also used in neutral starch sizing by adjusting the pH to 7-8 at the final starch sizing press. Paper in which alkaline sizing has been used is generally stronger, brighter and more resistant to aging. The alkaline sizing process also allows for more filler to be used in the manufacture of the paper, and improves the operating efficiency of the paper-making machine. | |||||||||||||||||||||||||