Freeze-thawed humic acid/polyvinyl alcohol supramolecular hydrogels

Abstract Novel supramolecular hydrogels were prepared on the basis of polyvinyl alcohol loaded with different amounts of humic acid nanoparticles via a freezing-thawing method. The results showed the humic acid nanoparticles act as functional sites to aggregate the polyvinyl alcohol chains and result in the formation of three-dimensional supramolecular networks. It was shown that the humic acid nanoparticles can interact with the polyvinyl alcohol chains and interconnect the polymeric chains as functional crosslinkers. The results showed up to 3.4 % increase in the gel fraction value of polyvinyl alcohol hydrogel by incorporating humic acid nanoparticles. In addition, 2.5 and 5.7 °C increases in the glass transition temperature and the melting point of polyvinyl alcohol hydrogel were observed by incorporating 9 wt.% of humic acid, respectively. By incorporating the mentioned level of humic acid, up to 87 and 26 % increases were observed in the storage modulus at glassy state and crystallinity of polyvinyl alcohol hydrogel.