Effect of Cobalt Oxide Nanoparticles on the Nano-scale Free Volume and Optical Properties of Biodegradable CMC/PVA Films

Chemically prepared cobalt oxide nanoparticles (NPs) were added to biodegradable carboxymethyl cellulose (CMC) (20%)/polyvinyl alcohol (PVA) (80%) blend films. The structural properties of these films were investigated by X-ray diffraction, Fourier transformation infrared spectroscopy (FTIR) and differential thermal analysis (DTA). Co3O4/(CMC + PVA) films show a semi-crystalline structure and the degree of crystallinity decreases with adding Co3O4 NPs. FTIR confirms the good interaction between the blend chains and Co3O4 NPs. The melting temperature T-m for CMC/PVA is about 212 A degrees C then decreased with increasing Co3O4 content, due to some decrease in the ordered association of the blend which results in a decrease in the blend crystallinity. Positron annihilation lifetime spectroscopy (PALS) measurements were carried out with a conventional fast-fast coincidence spectrometer. It was found that ortho-positronium lifetime tau (3) and free volume V-f increase while o-Ps intensity I-3 still constant as Co3O4 concentration increases. This is because adding Co3O4 NPs encourages the formation of o-Ps. The swelling ratio SR% as a function of Co3O4 concentration was also studied and its value increases with Co3O4 addition. The optical study illustrated the decrease of the transmittance T of the films from 87 to 35.5% with increasing Co3O4 content from 0 to 0.9 wt%. Also, both the direct and indirect optical band gaps of the films red-shifted from 4.05 to 3.75 eV and 3.3 to 2.75 eV, respectively. The influence of Co3O4 on the refractive index of the films is also reported.