Cationic Starch - Technical paper making

Cat-ionic Starch - Technical paper making

Starch is used to increase the strength properties of paper and improve the sizing by means of coating the sheet with starch slurry or adding starch at the wet end of the machine.

Starch much like cellulose is a chain made up of glucose molecules, bridged together by oxygen atoms called “glycosides”. This makes starch very soluble in water but also easily digestible by bacteria.

There are two types of starch used in paper making, Cat-ionic wet end starch, and oxidized starch.

Wetend Starch Cookers (Cationic maize starch)

Wetend starch is modified using a derivatized quaternary ammonium compound to add a cat-ionic charge to the starch. This allows the starch to naturally bond with the anionic fibers, Fillers and fines (all anionic).

In a way cat-ionic starch can help improve drainage as well as improving dry strength properties in the sheet.

Cat-ionic starch can be added to different locations in the machine approach flow or Thick stock loop. Dosing in different locations can influence the advantages you get from cat-ionic starch.

Adding starch to the Pulp storage chest of the machine acts like a Fixative. The cat-ionic starch binds to the anionic trash in the pulp, cleaning the water loop, improving Wetend retention and in some cases acts like a dry strength agent.

For the strength impact cat-ionic starch should be dosed close to the thick stock pump. The short dwell time prevent the starch from attracting only the anionic trash. The starch can form bridges between the fibres fillers and fines to create a stronger better formation sheet as well as  improving formation. 

Uncooked cat-ionic starch can be added between the layers of a multi ply machine. The starch is sandwiched between the ply’s. Its not until the sheet is passed through the drying section that the starch cooks and acts like an inter layer glue. This can be important if the paper has a specific ply bond strength parameter that needs to be adhered to.