Effect of Na₂CO₃ on the Microstructure and Macroscopic Properties and Mechanism Analysis of PVA/CMC Composite Film

Polyvinyl alcohol (PVA)/carboxyl methyl cellulose sodium (CMC)/Na₂CO₃ composite films with different contents of Na₂CO₃ were prepared by blending and solution-casting. The effect of Na₂CO₃ on the microstructure of PVA/CMC composite film was analyzed by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and atomic force microscopy (AFM). Its macroscopic properties were analyzed by water sorption, solubility, and dielectric constant tests. The results show that the microstructure of PVA/CMC/Na₂CO₃ composite films was different from that of PVA and PVA/CMC composite films. In addition, compared to PVA and PVA/CMC composite films, the water sorption of PVA/CMC/Na₂CO₃ composite films relatively increased, the solubility in water significantly decreased, and the dielectric properties significantly improved. All these results indicate that the hydrogen bonding interaction between PVA and CMC increased and the crystallinity of PVA decreased after the addition of Na₂CO₃. This was also a direct factor leading to increased water sorption, decreased solubility, and enhanced dielectric properties. The reaction mechanism of PVA, CMC, and Na₂CO₃ is proposed to further evaluate the effect of Na₂CO₃ on the microstructure and macroscopic properties of PVA/CMC/Na₂CO₃ composite films.