Weak interaction, marginal miscibility, and ring-band spherulites in blends of poly(vinylidene fluoride) with polyesters

Fourier transform infrared (FTIR) spectroscopy, optical microscopy (OM), and differential scanning calorimetry (DSC) techniques were used to probe phase behavior and interactions in blends of poly(vinylidene fluoride) (PVDF) and polyesters [poly(trimethylene adipate) (PTA) and poly(pentamethylene adipate) (PPA)] of relatively low crystallizability, DSC thermal analysis and OM characterization proved that PVDF was miscible with PTA and PPA with a low lower critical solution temperature. Small negative values of the interaction parameters (x₁₂ -0.13 for a PVDF/PPA blend) were obtained with the meltingpoint depression method. FTIR spectroscopy results revealed that interactions between -CF₂ of PVDF and the -C=O group of the polyester were weak, in agreement with the thermal analysis results. An increase in the coarseness and/or ring-band spacing further provided supportive evidence that miscibility did exist between the polyester and PVDF constituents in the blends. Pattern changes in ring-band spherulites of the miscible blends further substantiated the favorable, though weak, interactions between the PVDF and polyester constituents.