Cellulose-poly(vinyl alcohol) blends prepared from solutions in N,N-dimethylacetamide-lithium chloride

Blend films of cellulose with poly(vinyl alcohol) (PVA) were prepared from mixed solutions in N,N-dimethylacetamide (DMAc)--lithium chloride (LiCl) by coagulation in a nonsolvent. The state of miscibility of the clear films obtained over the entire composition range was characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical measurements. The WAXD and DSC results indicate that the crystallinity of PVA decreased drastically with increasing cellulose content and it exhibited no tendency to crystallize in the blends containing > 70 wt.% cellulose. The cellulose component showed a very low degree of crystallinity, even in homopolymer film prepared in the same way. In a detailed estimation of the glass transition temperature by dynamic mechanical analysis, the coagulated blends were not totally miscible, but showed a definite degree of partial miscibility in the composition range 0/100-60/40 of celluloses/PVA. Above 60 wt.% cellulose content, however, it was found that there was considerable miscibility in the amorphous regions. The relatively good miscibility in this composition range may be due to the increased capability of the two polymers, each with abundant hydroxyl groups, to interact mutually through hydrogen bonding. The presence of such an interaction was supported by a melting point depression of PVA observed in the DSC characterization of the blends. Systematic depressions were also noted more markedly in the melting and crystallization temperatures in the DSC experiment carried out on the blends once melt recrystallized. This suggests that thermodynamic interaction between the two polymers is enhanced above the melting point of PVA, although the possibility of the presence of some kind of morphological effect is admitted. 41 ref.--AA