Controllable Synthesis of Hydroxypropyl Starch and Its Application in Hollow Capsules

Hydroxypropyl starch (HPS) is widely used in various applications due to its unique functional properties, but optimizing its molecular characteristics for specific applications remains a challenge. This study aimed to optimize the process parameters for producing HPS capsules with desirable molecular and performance properties. The mass fraction of the etherification reagent, reaction pH, reaction temperature, and reaction duration were controlled to create HPS with varying degrees of substitution (DS). Acid solution degradation was used to prepare HPS of varying molecular weights (MW), and cold-gelation was employed to prepare hollow HPS capsules. A rigorous evaluation of performance indicators was conducted, and response surface methodology (RSM) was used to examine the effects of solid content, MW, and dipping temperature on capsule performance. Experimental results showed that these factors influenced performance in the following order: solid content > molecular weight > dipping temperature. Optimal parameters were identified as a solid content of 18%, an MW of 77 kDa, and a dipping temperature of 57 ℃, yielding capsules with a wall thickness of 0.086 mm, a disintegration time of 328 s, and moisture absorption of 8.594%. These findings provide valuable insights for the tailored design of HPS capsules, which could enhance their utility in industrial applications.