Interfacial Stabilization of Multiphase Systems with (Ligno)cellulosic (Nano)materials and Surfactants

Abstract

This thesis explores the interactions between (ligno)cellulosic (nano)materials and surfactants and evaluates their impact on interfacial activities relevant to multiphase systems, namely, foams and emulsions. The main plant-based components consider supramolecular constructs of cellulose, wood fibers, nanofibrils, cellulose carrying residual cell-wall molecules as well as non-cellulosics that are leached from fibers. The presented discussion focuses on phenomena relevant to the gas/liquid and liquid/liquid interfaces, the synergism between an anionic surfactant (sodium dodecyl sulfate, SDS) and like-charged (nano)cellulosic materials (wood fibers and cellulose nanofibrils, CNF). SDS is found to induce the leaching of non-cellulosics from wood fibers or CNF, which form surface-active aggregates with SDS. They effectively lower the gas/liquid interfacial tension and enhance foamability and foam stability, mainly by reducing drainage, coalescence, and coarsening. As an extension of the work with foams, they were used to produce wood fiber networks (foam-laying) from a wide selection of fibers and surfactant types. The cause-effect relations, the structuring mechanisms and the physico-mechanical properties of the fiber networks are revealed. The major drawback of typical foam-laid materials, namely, the loss of in-plane and out-of-plane strength, is addressed by replacing synthetic surfactants with an alternative surface active substance, carboxymethylated lignin. As an extension to foams and based on the uncovered interactions between cellulose and surfactants, the study turned to cellulose nanocrystals (CNC), which were considered in the formulation of food-grade emulsions. The synergism between an oppositely-charged surfactant (food-grade ethyl lauroyl arginate, LAE) and CNC is found to provide Pickering emulsions with outstanding stability. Taken together, the incorporation of plant-based components in the formulation of foams and emulsions is presented as an option in the framework of the future bioeconomy. The findings presented contribute to the effective and efficient utilization of natural resources for growing areas pertaining to multiphase systems.