Synthesis of a new kind of macroporous polyvinyl-alcohol formaldehyde based sponge and its water superabsorption performance

Abstract

Novel superabsorbents based on hydrophilic and macroporous polyvinyl alcohol-formaldehyde (PVF) sponges are prepared through the grafting polymerization of hydrophilic acrylamide (AM) monomer on the PVF and PVF–GA (pre-crosslinked with glutaraldehyde) network and through subsequent partial hydrolysis under alkaline conditions. The grafting percentage (GP) increases with the feed ratio of [AM]/[OH] and can reach up to 160%. The hydrolysis degree ranges between 60% and 70%. As-prepared polyacrylamide grafted PVF (PVF-g-PAM) and PVF–GA (PVF-g-GAM), and corresponding hydrolyzed samples (PVF-g-PAA and PVF-g-GAA) present average pore sizes ranging from 60 μm to 90 μm and a high porosity of 90%. Scanning electron microscopy (SEM) images reveal an interconnected pore structure, macroscopically rough surface, and pore size ranging from several micrometers to 200 μm. As-prepared sponges also exhibit rapid absorption kinetics and they can reach absorption equilibrium in both deionized water and saline solution in 1 min. The absorption procedure described in this study is consistent with the pseudo second-order rate kinetic equation. Notably, the PVF-g-PAA sponges can absorb deionized water as high as 320 g g⁻¹ within 60 s and can also absorb saline solution at a maximum capacity of 97.3 g g⁻¹ in 30 s. As-prepared PVF-g-PAM sponges with an absorption capacity less than 50 g g⁻¹ exhibit excellent reusability for at least 20 cycles. And the absorption mechanism is also discussed. Results show that these sponges with rapid absorption kinetics and high capacity can be considered as new superabsorbents for medical and sanitary applications.