title: Stabilizing nanocellulose-nonionic surfactant composite foams by delayed Ca-induced gelation.
abstract: Aggregation of dispersed rod-like particles like nanocellulose can improve the strength and rigidity of percolated networks but may also have a detrimental effect on the foamability. However, it should be possible to improve the strength of nanocellulose foams by multivalent ion-induced aggregation if the aggregation occurs after the foam has been formed. Lightweight and highly porous foams based on TEMPO-mediated oxidized cellulose nanofibrils (CNF) were formulated with the addition of a non-ionic surfactant, pluronic P123, and CaCO3 nanoparticles. Foam volume measurements show that addition of the non-ionic surfactant generates wet CNF/P123 foams with a high foamability. Foam bubble size studies show that delayed Ca-induced aggregation of CNF by gluconic acid-triggered dissolution of the CaCO3 nanoparticles significantly improves the long-term stability of the wet composite foams. Drying the Ca-reinforced foam at 60 °C results in a moderate shrinkage and electron microscopy and X-ray tomography studies show that the pores became slightly oblate after drying but the overall microstructure and pore/foam bubble size distribution is preserved after drying. The elastic modulus (0.9-1.4 MPa) of Ca-reinforced composite foams with a density of 9-15 kg/m(3) is significantly higher than commercially available polyurethane foams used for thermal insulation.
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden. Electronic address: korneliya.gordeyeva@mmk.su.se.
authors.forename: Korneliya S
authors.initials: KS
authors.lastname: Gordeyeva
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden. Electronic address: andreas.fall@mmk.su.se.
authors.forename: Andreas B
authors.initials: AB
authors.lastname: Fall
authors.affiliation: Division of Solid Mechanics, Lund University, Lund 22100, Sweden. Electronic address: stephen.hall@solid.lth.se.
authors.forename: Stephen
authors.initials: S
authors.lastname: Hall
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden. Electronic address: bernd@icmm.csic.es.
authors.forename: Bernd
authors.initials: B
authors.lastname: Wicklein
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden. Electronic address: lennart.bergstrom@mmk.su.se.
authors.forename: Lennart
authors.initials: L
authors.lastname: Bergström
keywords: Foams; Gelation; Multivalent-ion; Nanocellulose; Strength; Surfactant; X-ray tomography