Biopolymer Foams Composed of Hydroxypropyl Cellulose: Fabrication, Aqueous Stability, and Mechanical Integrity

We describe the fabrication of biopolymer foams formed from aqueous solutions of hydroxypropyl cellulose, whereby freezing-induced phase-separation and solvent removal yields robust foam structures that are elastic in air and when wet, and that are stable to repeated compression when fully saturated with water. Through mechanisms of phase-separation, pore formation, and covalent crosslinking, we discovered effective methods to prepare microporous HPC foams that resist gelation even when exposed to water for long time frames (at least months). Employing multifunctional carboxylic acid crosslinkers allowed the foams to maintain their integrity when dry or wet, while the presence of α-cellulose as an additive further augmented their mechanical integrity and provided a means to adjust elasticity. The amount of crosslinker employed in the foaming process significantly impacted foam stability and water uptake, while polymeric crosslinkers enabled insertion of sulfobetaine zwitterionic moieties into the foams. Notably, the thermal transition characteristic of HPC solutions and gels proved operative in foam form, as seen in release of water from a saturated HPC foam using a combination of compressive and thermal mechanisms.