Increasing Sustainability of the Papermaking Process via Formulation of Cellulose Nanofibers and Polyelectrolyte Complexes
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The sustainability of paper-making is multifaceted. The paper industry is centered around the use of a renewable and biodegradable material: cellulose. However, the sustainability of paper is not only reliant on the material itself, but on the process used to produce paper. A trade-off when processing cellulose into paper, compared to production of materials from fossil fuel-based polymers, is the inherent hydrophilicity of cellulose and consequently the requirement of large amounts of energy to dry the water during production. More recent advancements introduce cellulose nanofibrils (CNFs) as additives in papermaking to improve properties and potentially replace plastics for multi-layer packaging applications. The trade-off, however, is that their micron and nanosized features require even greater amounts of energy to produce and to dry compared to typical cellulose fiber pulps. Therefore, to achieve greater sustainability of CNFs and products made from them, methods to reduce energy needed to dry are necessary and one strategy is to design the chemicals in the cellulose slurry to improve drainage prior to evaporative drying. This thesis explores formulation decisions to make paper manufacturing more sustainable through increasing percent solids with the use of CNFs and polyelectrolyte complexes (PECs). By increasing the percent solids of the wet paper web that enters the evaporative dryer, the sustainability and energy efficiency of the paper-making process can be improved. Going through the thesis we explore formulation decisions from small to larger scales, starting from studying molecular interactions between cellulose and polyelectrolytes and ending with consumer decisions and policy implications. At the molecular scale, this thesis aims to determine how electrostatic interactions and the selection of solid-like precipitate or liquid-like coacervate forming polyelectrolyte complexes (PECs) enhances the interactions of the PECs to cellulose fibers and how this improves water retention and increases percent solids. This work specifically studies the effects of mixing order and the selection of polyamine polycations of differing hydrophobicity on the rate of assembly, flocculation and morphology in suspension, and phase-dependent interactions of PEC and CNFs and how these affect the water retention values when they are added to CNF slurries. The findings are then applied to the formation of handsheets at a larger bench scale and realistic CNF and PEC loadings that are typically used in paper formulation with the overall aim to improve standard pulp and paper properties including: percent solids, tensile strength and opacity. Finally, the role of manufacturing decisions and consumer behavior on increasing sustainability through increasing the flow of CNF and CNF and polyelectrolyte packaging is explored. Because sustainability is becoming an increasingly important issue to consumers, who want to know that their actions, particularly through their purchasing decisions and disposition behaviors, are not negatively affecting the environment. Increasing solids in this case means achieving the highest useable post-consumer material through a circular economy with manufacturing and consumer behavior. The results of this thesis show how appropriate polyelectrolyte selection and experimental parameters give insights into molecular interactions and can be scaled up to useful properties and outcomes for the sustainability of papermaking.