Synthesis and Properties of Novel Polyvinyl Alcohol-Lactic Acid Gels

This 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 degrees C. The grafting process was carried out under nitrogen to avoid possible oxidation or other degradation of the process ingredients and product. Lower T(g) values were obtained for the PVA/LLA graft copolymers of higher LLA content suggesting some compatibility in the amorphous phase. Higher T, values were observed for PVA/LA graft copolymers that yielded tough polymer films. The structure of the copolymers was studied by solid-state (13)C-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 degrees C showed good swelling properties. The transport coefficient (n) values determined from the plot of log(M(t)/M(infinity)) 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 (W(b)), freezing (W(f)), and freezing bound (W(fb)), and water content (W(t))] 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. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113:2053-2061, 2009