Nanocellulose has received considerable interest during the last decade because it is renewable and biodegradable, and has excellent mechanical properties, nanoscale dimensions and wide functionalization possibilities. It is considered to be a unique and versatile platform on which new functional materials can be based. This thesis focuses on nanocellulose from wood (NFC) and from Cladophora algae (CNC), functionalized with surface charges or coated with the conducting polymer polypyrrole (PPy), aiming to study the influence of synthesis processes on structural and electrochemical properties of such materials and assess their biocompatibility. The most important results of the work demonstrated that 1) CNC was oxidized to the same extent using electrochemical TEMPO-mediated oxidation as with conventional TEMPO processes, which may facilitate easier reuse of the reaction medium; 2) NFC and CNC films with or without surface charges were non-cytotoxic as assessed by indirect in vitro testing. Anionic TEMPO-CNC films promoted fibroblast adhesion and proliferation in direct in vitro cytocompatibility testing, possibly due to its aligned fibril structure; 3) Rinsing of PPy-coated nanocellulose fibrils, which after drying into free-standing porous composites are applicable for energy storage and electrochemically controlled ion extraction, significantly degraded the PPy coating, unless acidic rinsing was employed. Only minor degradation was observed during long-term ambient storage; 4) Variations in the drying method as well as type and amount of nanocellulose offered ways of tailoring the porosities of nanocellulose/PPy composites between 30% and 98%, with increments of ~10%. Supercritical CO2-drying generated composites with the largest specific surface area yet reported for nanocellulose/conducting polymer composites (246 m2/g). The electrochemical oxidation rate was found to be controlled by the composite porosity; 5) In blood compatibility assessments for potential hemodialysis applications, heparinization of CNC/PPy composites was required to obtain thrombogenic properties comparable to commercial hemodialysis membranes. The pro-inflammatory characteristics of non-heparinized and heparinized composites were, to some extent, superior to commercial membranes. The heparin coating did not affect the solute extraction capacity of the composite. The presented results are deemed to be useful for tuning the properties of systems based on the studied materials in e.g. energy storage, ion exchange and biomaterial applications.

Nanocellulose is a nascent and promising material with many exceptional properties and a broad spectrum of potential applications; hence, it has drawn increasing research interests in the past decade.  A new type of nanocellulose -- with mono- or bi-layer cellulose molecular sheet thickness -- was synthesized through a combined chemical-mechanical process (TEMPO-mediated oxidation followed by intensive sonication), and this new material was named molecularly thin nanocellulose (MT nanocellulose).  The overarching objective of this study was to understand the formation and supramolecular structure of MT nanocellulose and contribute to the knowledge of native cellulose structure. The research involved four major bodies of study: preparation of MT nanocellulose, characterization of MT nanocellulose, modeling wood pulp-derived cellulose microfibril cross section structure, and a comparative life cycle assessment (LCA) of different nanocellulose fabrication approaches.  The results revealed that MT nanocellulose with mono- to bi-layer sheet thickness (~0.4-0.8 nm), three to six chain width (~2-5 nm), and hundreds of nanometers to several microns length, can be prepared through TEMPO-mediated oxidation followed by 5-240 min intensive sonication.  The thickness, width, and length of MT nanocellulose all decreased with extended sonication time and leveled off after 1 or 2 h sonication.  Crystallinity, hydrogen bonding, and glycosidic torsion angles were evaluated by XRD, FTIR, Raman, and NMR.  These experiments revealed systematic changes to structure with sonication treatments.  A microfibril "cross section triangle scheme" was developed for the microfibril supramolecular modeling process and a 24-chain hexagonal/elliptical hybrid model was proposed as the most credible representation of the supramolecular arrangement for wood pulp-derived cellulose I" microfibril.  Comparative LCA of the fabrication of nanocellulose indicated that nanocellulose presented a significant environmental burden markup on its precursor, kraft pulp, and the environmental hotspot was attributed to the mechanical disintegration process.  Yet, overall nanocellulose still presented a prominent environmental advantage over other nanomaterials like single-walled carbon nanotubes, due to its relative low energy consumption. Overall, this research developed a facile approach to produce a new type of nanocellulose, the MT nanocellulose, provided new insights about the supramolecular structure of cellulose microfibrils, and evaluated the environmental aspects of the fabrication process of nanocellulose. / Ph. D.

Over the past 10 years, growing concerns over the modification of fibers have led researchers to focus on enriching the carboxyl group content of fibers by chemical oxidation and topochemical grafting. The current series of experiments continues this line of research by investigating the carboxyl group content of fibers during kraft pulping, alkaline peroxide bleaching, and 2,2,6,6-tetrametyl-1-piperidinyloxy radical (TEMPO)-KBr-NaClO oxidation system. The first experiment characterizes changes in the carboxyl group content of fibers for two sets of kraft pulps: 1) conventional laboratory cooked loblolly pine kraft pulps, and 2) conventional pulping (CK) versus Lo-Solids pulping (LS) pulps. The results indicate that effective alkali (EA), temperature, and H-factor are the primary factors controlling fiber charge during kraft pulping. Another set of kraft pulps distinguished by conventional pulping and Lo-Solids pulping were investigated to determine the effect of H-factor and pulping protocol on fiber charge. The second experiment examines the influence of alkaline peroxide treatment on elementally chlorine-free (ECF) bleached softwood kraft pulp. The effect of increased fiber charge on refining, cationic starch adsorption, and hornification was examined. The final experiment investigates the effect of TEMPO-mediated oxidation of an ECF bleached softwood kraft pulp on carboxyl group content, carbonyl group contents, degree of polymerization, and water retention value of fibers. The results show that TEMPO-mediated oxidation is useful in enriching the carboxyl and carbonyl groups to fibers, as well as enhancing the property of water adsorption of fibers. These findings suggest that: (1) kraft pulping process can be modified to obtain the target carboxyl group content, (2) terminal peroxide bleaching provides higher fiber charge which can save energy and chemical charge of subsequent refining and wet-end processes, respectively, as well as reduce hornification during drying, (3) TEMPO-mediated oxidation of fibers is capable of improving the properties of fibers, including fiber charge and water adsorption, and enhancing final paper strength.