Poly(vinyl alcohol) and poly(vinyl pyrrolidone) blends: Miscibility, microheterogeneity and free volume change

Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(vinyl pyrrolidone) (PVP) were studied by differential scanning calorimetry (d.s.c.). PVA with different degrees of hydrolysis (88 and 99 wt%) and PVP with different molecular weights (10 000 and 360 000 g mol(-1)) were used. The blends exhibited a single glass transition, as determined by d.s.c., suggesting the miscibility of the system over the whole composition range studied. The enthalpy of fusion (Delta H-f), as well as the glass transition temperature (T-g), heat capacity (Delta C-p) and glass transition width (Delta w), were also determined by d.s.c. These parameters changed with the degree of hydrolysis of PVA, PVP molecular weight and blend composition. The behaviour of Delta C-p vs blend composition was complex for the different pairs of blends, suggesting strong interaction between PVA and PVP. From the analysis of Delta w dependence on blend composition we concluded that blends containing PVP of 10 000 g mol(-1) exhibit a larger number of relaxations than blends containing high molecular weight PVP, indicating that the density of interactions is larger in the former. (C) 1997 Elsevier Science Ltd.