What is Starch
Starch is a natural carbohydrate polymer. The molecular formulae of starch is (C6H10O5)n. Mainly starch is used in paper mill to improve dry strength and surface. Its molecular weight is very high. Native starch has a very high viscosity. On the other hand modified starch has lower viscosity. The main sources of starches are regular corn, tapioca, waxy maize, wheat and potato. After cellulose fiber and mineral filler, starch is the third most widespread raw material in paper mill industries.
Molecular weight of starch is a factor for application of starch in paper mill industries. The maximum molecular weight (non-degraded) of starch is suitable for wet-end application. Because the non-degraded starches have huge dimensions, so the binding power is increased. On the other hand, reduced molecular weight (degraded) starches is suitable for surface application. This is the reason that degraded starches have lower viscosity.
Generally the starch is used in paper mill in three different stages for different function. The stages are wet end section for internal sizing, size press for surface sizing, and size press or off-machine application for coating. The most common wet-end starches are cationic starches or amphoteric starches or native starches while the surface starches are oxidized or hydroxyethylated.
Types of starches
Mainly starch is classified into two types. Native starch and modified starch.
Native starch: The most common native starches are corn starch, tapioca starch, waxy maize starch, potato starch, wheat starch and rice starch.
Modified starch: Cationic starch, amphoteric starch, oxidized starch etc.
Function of starches:
- Starch enhances the stiffness and bonding of paper sheet.
- Improve formation
- improve internal bond,
- Improve surface strength and wax-pick
- Increase tensile strength
- Improve fiber fines, filler and chemical retention.
- Improve drainage.
- increase dry strength properties
- better writing and printing surface
- reduce linting and dusting
- Reduce cost, because it is allowed to use more filler and more recycled fibers.
- Increase runnability and productivity. As breaks are lower.
- Energy consumption lower due to high binding power.