THE EFFECT OF CONTACT TIME BETWEEN CATIONIC POLYMERS AND FURNISH ON RETENTION AND DRAINAGE

The effect of the contact time between cationic polymers (polacrylamid es and cationic starches) and stock on retention and dewatering has be en studied using a new type of equipment. Dewatering is carried out un der low pressure and the addition of chemicals and other operations ar e controlled by a microprocessor The retention often shows a maximum a fter a polymer contact time of 10-20 s. It is found that long contact times drastically reduce the effect of the added polymer. This is expl ained as being due to floc rupture, degradation of the polymer and poo r reflocculation. The dewatering time is extremely sensitive to the po lymer contact time and increases steadily with increasing contact time .