Thermal and dynamic mechanical properties of hydroxypropyl cellulose films

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. DSC results were indicative of a semicrystalline material with a melt at 220°C and a glass transition at 19°C (T1), although an additional event was suggested by a baseline inflection at about 80°C (T2). Corresponding relaxations were found by DMTA. A secondary relaxation at −55°C was attributed to the interaction between hydroxyl groups of the polymer and residual diluent. The tan δ peak at T2 was found to arise from an organized phase, presumably from a liquid‐crystal mesophase formed while in solution. Crosslinking with a diisocyanate increased the peak temperature of the two primary relaxations, and resulted in a more clearly defined peak for the T2 transition. From this behavior it was concluded that both T1 and T2 are similar to glass transitions (Tg's) associated with an amorphous component and a more highly ordered phase (due to a residual liquid crystal superstructure) in the HPC bulk.