Upgrading Cellulose Networks: Conquering Limitations in Fiber Foams

Licentiate thesis, 2023

The battle to create structural materials with low environmental impact demands the investiture of two champions: porous structures and cellulose substrates. The dominant solutions when constructing strong lightweight materials are plastic and metallic foams, while currently, cellulose fiber foams suffer from challenges which hamper their development. Cellulose foams are structurally promising, but are sensitive to humidity and fire, and often have an inferior mechanical performance compared to their plastic and metallic counterparts. In addition, standard foaming techniques for cellulose fiber foams use synthetic sodium dodecyl sulfate (SDS), a surfactant which weakens critical fiber-to-fiber contacts. In this work, two approaches were employed as solutions to strengthen cellulose foams: cross-linking of cellulose fibers, and controlling pore structure formation. Phytic acid (PA), a bio-based polyphosphate, was cross-linked to cellulose fibers with the goal of improving fiber-fiber bonding and generating flame-retardancy in SDS-based cellulose foams. Controlling pore structure formation was separately achieved by dispersing tert-butanol (TBA), a water miscible amphiphile, into cellulose-water suspensions. Addition of TBA induced the formation of hierarchical structures which vastly increased the surface area and mechanical performance of dried foams. The functionalities produced by the two presented solutions expand the potential applications for cellulose foams, and serve to encourage the development of these materials as lightweight competitors in the transportation, construction and packaging sectors.