Preparation Of Layered Double Hydroxide And Its Application In Poly(Vinyl Alcohol)

In this work, Poly(vinyl alcohol) (PVA)/Layered Double Hydroxides (LDH) nanocomposite films were fabricated via a novel solution blending method by directly dispersing PVA particles into LDH aqueous suspension. The structure, morphology and properties of PVA/LDH nanocomposites were characterized by X-ray diffraction, rheological methods, mechanical tensile test and electron microscopies. Since water was the only used solvent, the method is a promising way to develop environmentally-friendly and high-performance PVA/LDH nanocomposites.(1) LDH was synthesized by hydrothermal, constant-pH and urea-hydrolysis methods, respectively. The structure and morphology of LDH could be controlled by the metal ion concentration, aging time and so on. LDH particles obtained in hydrothermal method exhibited the smallest size of 50-100 nm and best dispersity in aqueous medium.(2) Different from general polymer solutions, PVA aqueous solutions showed distinctive rheological behaviors relating to the inter chain hydrogen bonding between PVA chains. The steady shear curve of PVA aqueous solution with the concentration of 10 wt% indicated four regions with increasing shear rate, the first plateau, the first shear thinning region, the second plateau and the second shear thinning region. During dynamic frequency scanning, the storage modulus was higher than loss modulus in lower frequency region while the loss modulus was higher than the storage modulus in higher frequency region, which is contrary to the general polymer solution. In addition, changes in alcoholysis degree, shearing history, aging time and addition of LDH all could make different rheological responds for PVA aqueous solutions.(3) Exfoliated structures and uniform dispersion of LDH nanoplatelets were observed when ΦLDH= 1.0 wt%, the corresponding PVA/LDH nanocomposite films showed excellent mechanical properties, where the tensile strength and Young’s modulus of the nanocomposite films increased by 93% and 144%, respectively, compared with those of a neat PVA film. In addition, the PVA/LDH nanocomposite films exhibited water resistance, thermal stability and high transparency.(4) With ion-exchange ability, LDH was an ideal adsorbent to treat the organic dyes wastewater. The adsorption capacity of methyl orange (MO) was up to 1231 mg/g under 30℃. PVA/LDH nanocomposites fibers was prepared through electrospinning. Although the fibers showed lower diameter and rougher surface, their adsorption abilities need to be improved further.