What are the effects of pH and alkalinity on AKD sizing?
The paper machine sizing machine sizing performance of AKD has a great relationship with the pH value. It is generally believed that only under medium/alkaline conditions, the lactone ring of AKD can be opened and reacted with the hydroxyl group on cellulose.
When pH <6, AKD has almost no sizing effect. With the increase of pH, the sizing efficiency of AKD gradually increases, especially when the pH is between 6.5 and 7.5, the sizing degree of the paper increases the fastest; When >8.0, the increasing speed of sizing degree begins to slow down. Therefore, in actual paper production, the pH is generally controlled between 7.5 and 8.5.
Alkalinity refers to the concentration of HCO3- in the slurry,which is usually expressed in milligrams of calcium carbonate contained in 1kg of water.
Bicarbonate ions can improve the sizing effect of AKD, and bicarbonate ions can improve the retention of AKD on the surface of cellulose fibers, and can also enhance the swelling of fibers, so that the hydroxyl groups on the fibers are fully exposed, which is beneficial to The reaction of AKD, and adding calcium carbonate to the AKD sizing system can also adjust the pH value of the system to the optimal range.
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