Cross-linked poly(methyl vinyl ether-co-maleic acid)/poly(ethylene glycol)/nanocellulosics foams via directional freezing

Aligned micro- and nanoporous materials have gained tremendous interest since they provide great potential in organic electronics, absorbents, biomedicine and tissue engineering. Herein, cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) cross-linked with poly(methyl vinyl ether-co-maleic acid) (PMVEMA) and poly (ethylene glycol) (PEG) foams were prepared by both the directional and un-directional freezing techniques. Aligned three-dimensional porous structures were observed for the directional frozen foams after lyophilization via scanning electron microscope (SEM). As a result, these highly organized structures exhibited enhanced mechanical performance properties. Particularly, for the 25% CNF foams, the compression modulus increased 60% compared with the un-directional frozen samples. These nanocellulosics-based foams could absorb up to 10-fold water of their initial weight with excellent water stability when immersed in water for more than 48 h. Overall, this study describes a novel process combining cross-linking and directional freezing which successfully fabricates naturally derived foams with anisotropic structure.