Freeze-Drying-Promoted Effect of Sorbitol Plasticization for Melt Processing of Poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) is an environmentally friendly polymer with excellent mechanical properties, biocompatibility, and biodegradability; nevertheless, thermal processing is very difficult because its melting point is close to its decomposition temperature. Herein, a synergistic plasticizing strategy based on solid plasticizing and freeze-drying technologies was proposed to effectively reduce the crystallinity of pristine PVA and destroy the intrinsic inter- and intramolecular hydrogen bonds, realizing the thermal processing of PVA. Specially, the sorbitol plasticizers were incorporated into a PVA aqueous solution to achieve the homogeneous mixing of the two components at the molecular scale, weakening the intrinsic hydrogen bonding network by forming additional hydrogen bonds with hydroxyl groups of PVA. Subsequently, the freeze-drying process was conducted to restrict the molecular mobility and PVA crystallization. The underlying plasticizing mechanism was revealed based on wide-angle X-ray diffraction (WXRD), differential scanning calorimetry (DSC), and temperature-dependent FTIR spectra. As a result, the modified PVA materials with a widened processing window up to 70 °C were successfully prepared, and the rheology behaviors were investigated comprehensively to guide the actual melt processing.