Addition effect of poly(N-vinyl pyrrolidone) on the miscibility of cellulose acetate/poly(vinyl alcohol) blends

Uniform mixing of cellulose acetate (CA) of DS (degree of substitution) = 2.18 with poly(vinyl alcohol) (PVA) was attained, by taking into consideration the hydrogen-bonding formability of both components. Blend miscibility of CA/PVA binary blends was examined by differential scanning calorimetry (DSC) as a function of the degree of saponification (Sp) of PVA. Although as-cast films of the CA/PVA blends were mostly transparent to the naked eye (i.e., optically compatible), the DSC analysis showed that the CA of DS = 2.18 was immiscible with PVA, irrespective of the Sp value. On the other hand, poly(N-vinyl pyrrolidone) (PVP), capable of forming a miscible monophase with CAs of DS < 2.8, was judged to be miscible with the PVAs of Sp = 19–100 mol%. Therefore, an attempt was made to compatibilize the immiscible polymer pair of CA and PVA by employing PVP as an additional component. Miscibility of the CA/PVA/PVP ternary blend was assessed by comparing the glass transition temperature (Tg) estimated by DSC with the ideal Tg value calculated from a Kwei equation. It was observed that PVP acted as a good compatibilizer for the polymer mixture of CA and PVA. Particularly, when the attractive interaction between the CA and PVA components and that between the PVA and PVP components were balanced with each other in frequency, all the three components were able to mix uniformly (i.e., totally miscible). In addition, a PVP sample of a higher molecular weight (PVP-H, Mw = 360 000) was found to be more effective as the compatibilizer relative to that of lower molecular weight (PVP-L, Mw = 24 500), due to the higher probability of intermolecular interaction of the former (PVP-H) with both CA and PVA per one polymer chain. © 2019 The Society of Materials Science, Japan.