Cat-ionic Starch - Technical Papermaking

Paper makers hold starch in high regard as one of the most important papermaking chemicals in producing high quality paper.

Cat-ionic starch is made up of modified maize starch that now has a slight cat-ionic charge (positive charge). Cat-ionic starch is added at the wet end of the machine. The slight cat-ionic demand of the starch allows it to bond with the anionic (negatively charged) fibers, fillers, fines, and other small unusable materials to improve dry strength in the sheet and even improve the retention of the sheet.

Cat-ionic starch is produced when a reactant chemical is treated with slurry of partially swollen starch granules.

Typical starch addition points in a approach flow system occur either before the machine chest in the thick stock system or after the machine chest at the start of the thin stock flow to the head box, Arguably both addition points allow for high strength, depends on the grade and the dosing quantity of starch. 

The problem with adding too much is that it will exceed the adsorption capacity of the surface, based on either the surface area or the limited extent of negative charge of the surfaces of fibers and other solid surfaces in the furnish. Excess starch beyond what adheres to the fibers in likely to cause foam, high biological oxygen demand (BOD) levels in the effluent, and poor retention and drainage. The performance of cationic starch as a strength agent sometimes can be improved by raising the pH; this will tend to make the fibers slightly more anionic and better capable of interacting with the starch.

When adding cat starch in a system with a high level of anionic trash the starch strength qualities can be improved with pretreating the stock with a highly charged cationic material to neutralize the anionic trash.