The Role of Fiber Mechanical Treatment on the Retention of Cationic Starch

Cationic starches possess a positive or cationic charge. Because of this charge, they have found widespread use at the wet end of the papermachines. When applied properly, cationic starches have been found to increase filler and fines retention, improve interfiber bonding, increase pick resistance and reduce BOD in mill effluent. In order to obtain these benefits, it is first important to retain the cationic starch in the sheet. Several factors have been determined to affect cationic starch retention. These factors include - pH, starch molecular weight, starch charge density, rate of application, retention aid used, furnish type and degree of fiber mechanical treatment. It was discovered that a discrepancy existed in the role of fiber mechanical treatment on the retention of cationic starch. An experiment was designed and conducted to charify what effects fiber mechanical treatment had on the retention of cationic starch under conditions that simulate the wet end of a papermachine. It was found that as fiber mechanical treatment was increased, the retention of cationic starch increased to a maximum, then decreased as a greater amount of fines was lost in the white water. It was also found that in the absence of fines, fibers themselves retained more cationic starch because they were subjected to mechanical treatment