Oxidized Starch vs Native Starch: Key Differences
SEVAGRAM EXCIPIENTS
Ask a mill superintendent why they switched from native starch to an oxidized grade for surface sizing, and the answer is rarely about chemistry — it is about a tank of starch gelling overnight and clogging a pump the next morning. The chemistry explains why that happens; the practical difference is what mills actually care about.
Viscosity and Retrogradation
Native starch, cooked and cooled, thickens further over time as the starch chains realign and partially re-crystallize — a process called retrogradation. Held in a tank for a few hours, it can gel hard enough to need re-cooking or even mechanical clearing of pipework.
Oxidation breaks down chain length, which lowers viscosity at the same cooking concentration and slows retrogradation considerably. Mills can hold an oxidized starch slurry through a shift without the same gelling risk.
Film Clarity and Strength
Native starch films are generally more opaque and slightly stronger per unit of starch applied, since the longer polymer chains form a denser network. Oxidized starch trades some of that raw film strength for clarity and flow — the shorter chains form a clearer, smoother film, which matters where coating appearance or print quality is being judged.
When to Use Which
- Use native starch when raw strength matters more than flow behaviour, and the starch will be used quickly after cooking — typically wet-end or internal addition.
- Use oxidized starch for surface sizing and coating, where consistent, lower viscosity, holding stability, and film clarity matter more than maximum strength per kilogram.
Frequently Asked Questions
Is oxidized starch weaker than native starch?
Per kilogram, slightly — the shorter chains form a less dense film. In practice this rarely matters for surface sizing, where flow and clarity are the priority over raw bonding strength.
Can a mill switch from native to oxidized starch without changing equipment?
Usually yes for surface sizing applications, since oxidized starch is generally easier on pumps and nozzles than native starch, not harder.
Does oxidized starch cost more than native starch?
Typically yes, since it requires an additional chemical processing step, but the handling and consistency benefits often offset the price difference at the size press.