Poly(vinly alcohol)/nano-sized layered double hydroxides nanocomposite hydrogels prepared by cyclic freezing and thawing

Abstract

In this paper, nano-sized MgAl-layered double hydroxides (LDH) were synthesized via a very fast nucleation and slow aging method that can be suspended in water. Poly(vinyl alcohol) (PVA)/LDH nanocomposite hydrogels were then prepared using a cyclic freezing/thawing method. The mechanical properties of PVA hydrogels were significantly enhanced by incorporation of LDH nanoplatelets. After 7, 9, and 11 freezing/thawing cycles, the tensile strength of PVA nanocomposite hydrogels containing 0.5 wt% LDH was remarkably increased by 100%, 100%, and 300%, respectively, while the Young’s modulus was increased by 25%, 22%, and 149%, respectively. More interestingly, the nanocomposite hydrogels exhibited larger elongation at the break than neat PVA hydrogels. However, after addition of the LDH nanoplatelets, the water-swelling ability of PVA hydrogels decreased. The microstructures and morphologies of PVA/LDH nanocomposite hydrogels were further investigated by scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. The results showed that well-dispersed LDH nanoplatelets played an important role in increasing physical cross-linking density by inducing PVA crystallization and the formation of more uniform polymer networks. As a result, the mechanical properties of PVA hydrogels were greatly improved, even at very low LDH loading levels.