Blends of polycaprolactone with polyvinylalcohol:: a DSC, optical microscopy and solid state NMR study

Blend films of polycaprolactone (PCL) and polyvinylalcohol (PVAl) have been obtained by evaporation of a solution of both components in hexafluoroisopropanol. The miscibility of the polymers in the amorphous part of the blend has been studied by conventional methods (optical microscopy. DSC and FTIR) and by solid state NMR. Phase separation is observed in the melt. The absence of any lowering of Tm and the presence of one low temperature Tg near that of pure PCL support the hypothesis of phase separation in the amorphous part of the blend. However, various experimental data suggest the presence of some type of physical interactions between components. These data are: the important decrease of PCL crystallinity in the blend, the morphology of PCL spherulites after crystallization at 45 degrees C and the absence upon annealing the blend at 50 degrees C, of any rearrangement of PCL crystallites into spherulites as observed in pure PCL. The measurement of proton spin-lattice relaxation time T-1 by solid state NMR using cross polarization ha, shown that the components are compatible at the scale of 60-90 nm and are thus very finely dispersed into each other. (C) 1999 Elsevier Science Ltd. All rights reserved.