Citric Acid-Modified Layered Double Hydroxides as a Green Reinforcing Agent for Improving Thermal and Mechanical Properties of Poly(Vinyl Alcohol)-Based Nanocomposite Films

Citric acid (CA) with one hydroxyl and three carboxyl groups exists widely in citrus fruits and pineapples, where it is the main organic acid. In this article, nanosized CA-modified ZnAl-layered double hydroxide (CA-LDH) was synthesized by coprecipitation method in aqueous media. Several nanocomposite (NC) films of poly(vinyl alcohol) (PVA) were prepared by casting through the dispersion of the CA-LDH into the PVA aqueous solution under ultrasonic irradiation. The structures of individual layers of CA-LDH and PVA/CA-LDH NC films were characterized by X-ray diffraction (XRD), Fourier transform infrared, field emission scanning electron microscopy, and transmission electron microscopy techniques. Uniform dispersion of LDH nanoplatelets in PVA matrix was observed. The thermal stability of the NC was study by thermogravimetric analysis technique, and the results show that the thermal properties were improved as compared with the original PVA. The mechanical properties of the PVA/CA-LDH NCs are obviously enhanced compared to that of neat PVA. Uniform distribution of clay due to intimate interaction between clay and polymer appears to be the cause for improved properties. The UV-Visible transmission spectra of the composite films exhibited that, the samples retained high optical clarity and they could be potentially used in the packaging industry. (C) 2016 Society of Plastics Engineers