The production process of hydroxypropyl starch ethers (HPS) mainly consists of key steps including raw material preparation, alkalization, etherification reaction, neutralization and purification, and drying. The entire process is carried out under strict control of pH, temperature, and inert gas protection to ensure high substitution degree and stable performance of the product.
Typical Production Process of Hydroxypropyl Starch Ethers (Taking Solvent Method as an Example)
1. Raw Material Preparation
Main raw materials: natural starch (such as corn, potato, or cassava starch), propylene oxide (etherifying agent), sodium hydroxide (catalyst), ethanol or isopropanol (organic solvent).
The starch needs to be pre-dried to a moisture content of less than 15% and sieved to remove impurities to ensure uniform reaction.
2. Dispersion and Alkalization
Add the starch to an ethanol-water mixed solvent to prepare a suspension of approximately 30%–40%. Slowly add sodium hydroxide solution while stirring.
Maintain the system pH at 9.0–10.5 and the temperature at 40–50℃ for 1 hour to fully activate the starch granules and generate sodium starch (Starch-O⁻Na⁺), preparing for subsequent etherification.
3. Etherification Reaction
Under nitrogen protection, slowly add propylene oxide in batches, avoiding violent exothermic reactions.
Maintain the reaction temperature at 40–50℃ and continuously stir for 18–24 hours to allow propylene oxide to fully undergo ring-opening etherification with the starch hydroxyl groups, generating hydroxypropyl substituents (-OCH₂CHOHCH₃).
The degree of substitution (DS) can be precisely controlled by adjusting the amount of propylene oxide and the reaction time, typically targeting 0.1–0.3.
4. Neutralization and Termination of the Reaction
After the reaction, adjust the system pH to 5.0–5.5 with dilute hydrochloric acid to neutralize residual alkali and terminate the reaction.
5. Washing and Filtration
The product is washed multiple times with ethanol or water to remove unreacted propylene oxide, byproducts (such as propylene glycol), and inorganic salts, thereby improving product purity.
6. Drying and Grinding
After washing, the wet material is centrifuged to remove water, then spray-dried or vacuum-dried to control the final moisture content to ≤15%.
The dried powder is then ground to the required fineness (typically 80–120 mesh) using an air jet mill, sieved, and packaged to obtain a white, fine powder product.
