Formation of liquid crystals and behavior of LCST upon addition of xanthan gum (XG) to hydroxypropyl cellulose (HPC) solutions

Abstract

This study investigates liquid crystalline (LC) formation and lower critical solution temperature (LCST) of HPC solutions upon the addition of XG in various ratios. The LC region of HPC/H2O/H3PO4 tertiary system was significantly enlarged at low XG/HPC blending ratio of 1–10 wt%. The addition of well oriented 2-D XG molecules to HPC polymer induced easy orientation of linear HPC molecules to synergistically form a stable anisotropic phase. The LCST point of HPC solutions initially decreased with adding a little amount of XG and then increased with XG/HPC ratio of over 50/50. In HPC-rich medium, XG helices easily attracted H2O molecules at high temperature owing to their hydroxyl groups. Consequently, the formation of intermolecular hydrogen bonds and the phase separation of HPC molecules proceeded at a lower temperature. In XG-rich medium, the upper critical solution temperature (UCST) behavior of XG obstructed the LCST behavior of HPC, the LCST point of HPC therefore increased and the boundary shrinkage of HPC binodal curve occurred.