WHY AND WHAT DO WHEN WHITE AKD DEPOSITS OCCUR

摘要

Alkyl ketene dimer (AKD) is a typical internal sizing agent widely used today. When the stability of AKD emulsion is poor, AKD is likely to turn into the undesirable deposit and contaminate the papermaking process. This study was carried out to investigate the formation phenomenon of deposits originated from AKD and to find an effective way to control the deposits. It was found that the unhydrolyzed AKD tends to contaminate the papermaking process because the surface of AKD floes are hydrophobic to attach to air bubbles. Retention of AKD should be increased to control of deposits originated from AKD. AKD retention was measured by using UV/Vis spectroscopy. Based on this method of measuring AKD retention, the effect of raw materials and drainage condition on the AKD retention was evaluated. The results indicated that the major factors for AKD retention were the filtration effect of wet web, electrostatic attraction of raw materials and drainage conditions. AKD retention decreased significantly depending upon the operating conditions of the vacuum element of the paper machine. It was shown that the dosage of retention aids was the most influential factor in AKD retention. Also the type of AKD and fixing agent played important roles for AKD retention. Mill trial results showed that the complete control of the deposit originated from AKD could be achieved by increasing the AKD retention, which increased the productivity of the paper machine and improved paper quality. This research contributed to reduce sheet breaks and shutdown of the paper machine.