What Is Oxidized Starch? How It Is Made and Used
SEVAGRAM EXCIPIENTS
Native starch out of the cooker is thick, stringy, and prone to retrogradation — it thickens again as it cools, which makes it awkward to handle in continuous coating or sizing operations. Oxidation solves that problem by breaking some of the long starch chains apart, producing a thinner, more stable paste that flows and coats more predictably.
What Is Oxidized Starch?
Oxidized starch is native starch that has been chemically treated, usually with sodium hypochlorite or hydrogen peroxide, to break down a portion of its molecular chains and introduce carboxyl groups onto the starch backbone. The result is a starch with lower paste viscosity at the same concentration, better film clarity, and far less tendency to thicken again on cooling compared to the native material.
Mills cook it, cool it, and apply it the same day without the gel-forming problems native starch causes in a holding tank.
How Oxidized Starch Is Made
The process starts with native starch slurried in water. An oxidizing agent is dosed in under controlled pH and temperature, and the reaction runs for a set period before being neutralized and the starch washed and dried. The degree of oxidation — essentially how much chain breakdown and carboxyl substitution occurs — determines the final viscosity and film properties.
A lightly oxidized starch retains more native film strength; a more heavily oxidized grade flows thinner and is easier to apply at higher solids, which matters for high-speed coating and sizing.
Why Paper Mills Use Oxidized Starch
- Lower, stable viscosity — flows consistently through size press nests and coating heads without the gelling native starch develops on standing.
- Better film clarity — produces a clearer, smoother surface film.
- Higher solids at workable viscosity — mills can run more starch solids through the same equipment.
- Consistent day-to-day handling — reduced retrogradation means less variation batch to batch.
Frequently Asked Questions
Is oxidized starch the same as native starch?
No. Oxidized starch starts as native starch but is chemically treated to break down chain length and reduce viscosity, changing how it cooks, flows, and films.
Why does oxidized starch have lower viscosity than native starch?
The oxidizing treatment breaks some of the long starch polymer chains, which reduces molecular weight and therefore the viscosity of the cooked paste at a given concentration.
What is oxidized starch typically used for in paper mills?
It is most commonly used in surface sizing at the size press and in coating formulations, where stable, lower viscosity and good film clarity are needed.