Amphoteric starch is a modified starch that contains positively and negatively charged substituent groups. It is used as wet-end additives, surface sizing agent and coating agent in the paper mill industries.
In the paper making process several materials are anionic such as wood fibers, titanium dioxide, clay, expanders, pigment dispersant, black liquor, bleach chemicals etc, whereas some materials are cationic such as alum, poly aluminium chloride (PAC), cationic resin, some retention aids etc. So it is very significant to maintain a clean and ionically balance environment to attain efficient result, which is done by amphoteric starch.
Amphoteric starch at the same time contains cationic group and anionic group. Usually cationic groups can be amino, ammonium, sulphonium or phosphonium group whereas anionic groups may be phosphate, phosphonate, sulfate, sulfonate or carboxyl groups. Among these cationic groups quaternary ammonium group is more preferred by the papermakers. On the other hand among the anionic groups phosphate group is best choice. The position of the anionic groups and cationic groups may be at same position or different position in the starch. The effective raw material for producing amphoteric starch is waxy maize due to highly content amylopectin.
Function of amphoteric starch
The benefits of amphoteric starch are following; especially when alum and PAC are used in paper making process.
- enhances dry strength properties
- improve drainage which lead to better sheet formation.
- retention of fines and fillers
- Better print quality
Specification of amphoteric starch:
- Physical appearance: odorless white to off white dry powder
- Moisture Content % w/w (at 105°C-110°C): 14max
- pH value: 10% aqueous solution, 5-8
- Viscosity 2% Solution at 50℃: 60-80 CPS
- Whiteness: 85%min.
- Fineness (100mesh): 99% min
- Nitrogen content: up to 0.3%
- Ash (dry solid basis): less than 3.0%