POLY(VINYL ALCOHOL) POLY(ACRYLIC ACID) BLENDS - MISCIBILITY STUDIES BY DSC AND CHARACTERIZATION OF THEIR THERMALLY-INDUCED HYDROGELS

Binary blends of poly (vinyl alcohol) (PVA) with poly (acrylic acid) (PAA) and polyacrylamide (PAAm) were characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and infrared spectroscopy (IR). Molecular weight, blend composition, and heating time at 150-degrees-C were the variables used. Results obtained by DSC indicated that PAA/PVA blends are miscible in the full range of composition. Similarly, TGA traces showed that thermal stability was higher for blends than for pure polymers. Blends of PVA with high molecular weight PAA exhibited a hydrogel behavior after drying at relatively low temperature (100-degrees-C), whereas blends containing low molecular weight PAA behaved as hydrogels only after they were heated at 150-degrees-C. Hydrogel character was increased for these two PVA/PAA blends with the heating time at higher temperature (150-degrees-C). IR spectra revealed that esterification took place in these blends after thermally treated at this temperature. In contrast, addition of glyoxal in combination with heating was necessary to produce hydrogels from PAAm/PVA blends. Furthermore, the cross-linking degree of these hydrogels was estimated from their absorbency values by applying the Flory-Rehner equation. (C) 1993 John Wiley & Sons, Inc.