Synthesis and properties of novel polyvinyl alcohol–lactic acid gels

Abstract

AbstractThis article describes a process for esterifying polyvinyl alcohol (PVA) with L‐lactide (LLA) and D,L‐lactic acid (LA), using ethyl acetate and N,N′‐dimethyl formamide at temperatures varying from 120 to 150°C. The grafting process was carried out under nitrogen to avoid possible oxidation or other degradation of the process ingredients and product. Lower Tg values were obtained for the PVA/LLA graft copolymers of higher LLA content suggesting some compatibility in the amorphous phase. Higher Tg values were observed for PVA/LA graft copolymers that yielded tough polymer films. The structure of the copolymers was studied by solid‐state 13C‐NMR, infrared spectroscopy, and differential scanning calorimetry (DSC). The PVA/LA films exhibited melt processability and good mechanical properties such as yield strength, tensile energy at break, modulus, and elongation at break. The polymer films produced through compression molding at 100°C showed good swelling properties. The transport coefficient (n) values determined from the plot of log(Mt/M∞) vs. log t indicate Fickian behavior, and they are consistent with the reported literature values for other PVA systems. The nature of water in gels [bound water (Wb), freezing (Wf), and freezing bound (Wfb), and water content (Wt)] was evaluated from DSC data. The results demonstrate that PVA/LA hydrogels with good combination of thermal, physicomechanical, and swelling properties can be prepared via the lactic acid esterification of PVA polymer process described. Besides being melt processable, the PVA/LA gels exhibit a melting point, which indicates possibly use of higher temperatures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009