On the investigation of thermal/cooling-gel biphasic systems based on hydroxypropyl methylcellulose and hydroxypropyl starch

This work investigates the rheology, structure, and properties of novel thermal/cooling-gel biphasic systems formed by hybridization of hydroxypropyl methylcellulose (HPMC) as a thermal gel and hydroxypropyl starch (HPS) as a cooling gel. Due to the different gelation properties, HPS became the dispersed phase in the other continuous phase at low temperatures, and so did HPMC at high temperatures. However, the dispersed phase could play a dominant role in the viscosity, thixotropy, and gel properties of the blends, and subsequently affect the crystalline structure, fractal structure, mechanical properties, oxygen permeability, and thermal stability of the blend films. Moreover, the rheological properties and the film structure and performance could also be varied by the chemical modification of starch. Hydroxypropylation could break the starch intermolecular hydrogen bonding, disrupt its ordered structure, inhibit the molecular rearrangement, and result in a softer gel texture that was more compatible with HPMC. With a higher degree of hydroxypropyl substitution, the resultant blend films were more amorphous and flexible but exhibited decreased mechanical properties and oxygen permeability. The knowledge obtained from this work could provide guidance to further developing various thermal/cooling-gel multi-phasic systems with desired properties and functionality.