Hydroxypropyl starch ether (HPS) is a non-ionic modified starch obtained by etherification modification of natural plant starch. It features cold water solubility, high transparency, strong acid and alkali stability, excellent electrolyte resistance, and anti-aging properties, and is widely used in construction, food, medicine, oil drilling, and other fields.
Preparation Methods and Processes
The synthesis of hydroxypropyl starch ethers is mainly achieved through an etherification reaction between starch and propylene oxide under alkaline conditions, replacing the hydroxyl groups in the starch molecule to generate hydroxypropyl substituents. Depending on the reaction medium, there are three main processes:
Wet Process: This process is carried out in an aqueous system using 35%–45% starch slurry. Sodium sulfate is added to inhibit gelatinization, and NaOH is used as a catalyst. The reaction temperature is controlled at 40–50°C, and the reaction time is 10–20 hours. This method is safe to operate and produces high-purity products, but the degree of substitution is low (typically DS < 0.1), making it suitable for producing low-substituted products.
Solvent-based process: Starch is dispersed in organic solvents such as methanol and ethanol, and then reacted with an alkaline catalyst and propylene oxide. This method offers mild reaction conditions, high degree of substitution, and easy control, yielding highly substituted products. However, the solvent cost is high, and recovery is challenging.
Dry process: This is a gas-solid phase reaction. Starch and a catalyst are mixed in a closed container, and then propylene oxide gas is introduced. The reaction is carried out at 85°C and 0.3 MPa pressure. This method yields highly substituted products, but is prone to side reactions, requires high safety standards, and is rarely used industrially.
