The non-stop use of petroleum-based materials such as plastics can generate significant environmental problems, including pollution of the oceans and increased CO2 levels, and cause diseases like cancer due to the starting monomers. Consequently, increased use of sustainable and non-toxic polymers and monomers is required to address these issues. Cellulose, generously supplied by Mother Nature, is the most abundant biopolymer on Earth. Nanocellulose is a sustainable polymer extracted from the cellulose inwood or produced by bacteria and algae. This biodegradable nanomaterialhas recently been receiving intense research attention, since it has great potential for use in a broad range of industrial and biomedical applications. However, it has limitations such as moisture sensitivity and incompatibility with hydrophobic materials due to its hydrophilic nature. Chemical modification is necessary for it to fulfill the requirements for applications that require high moisture resistance and water repellency. Unfortunately, several of the existing methods involve harsh and toxic conditions or reagents. In this thesis, together with my co-workers, I have employed the toolbox of organocatalysis for accomplishing eco-friendly and innovative surface modification of cellulose and nanocellulose. The organocatalysts we usedmost in our research are the naturally abundant and industrially relevantorganic acids tartaric acid and citric acid.

Direct catalytic esterification of cellulose nanocrystal (CNC) with thioglycolicacid was performed either in suspension or on solid surfaces such as films and foams. We found that the reaction was accelerated by tartaric acid but could also be autocatalytic with respect to the thioglycolic acid under certain conditions. The synthesized CNC-SH was further exploited as a heterogeneous reducing agent as well as a handle for further nanocellulose modifications. This was demonstrated by using CNC-SH as a heterogenous reducing agent of Cu(II) to Cu(I), which is essential for allowing the Cu to actas a catalyst for 2,3-dipolar cycloaddition reactions between azides andalkynes. We also showed that the thia-modified CNC could undergo further functionalizing via thiol-ene click chemistry reactions, for example, we attached fluorescent compounds such as TAMRA and quinidine.

Herein we provide a fluorine-free method to prepare superhydrophobic CNC film with excellent water-resistance properties by combining self-assemblyand organocatalysis. Self-assembly of CNC via vacuum filtration resulted in xa film with a specific roughness at the microscale. Next, the catalytic silylation with a variety of alkoxysilanes in the presence of natural organic acids such as tartaric acid and citric acid was performed. The successful implementation of our method resulted in a super-hydrophobic CNC film (water contact angleover 150°) with excellent water-resistance. Thus, the combination of the selfassembly of a rough surface with catalytic surface modification resulted in a phenomenon like the “lotus effect” as exhibited by the leaves of the lotus flower. An investigation of the oxygen permeability of the octadecyltrimethoxysilane-modified CNC film revealed that it significantly decreased at high relative humidity compared with unmodified CNC films.

In this thesis, the fabrication of hydrophobic and functionalized MTM/CNF nanocomposites using organocatalytic surface modification with a large variety of alkoxysilanes is also performed. The surface modifications are mildand the mechanical strength of the Nacre-mimetic nanocomposites is preserved. Elemental mapping analysis revealed that the silane modification occurred predominantly on the surface.

A combination of organocatalyst and biopolyelectrolyte complex was appliedfor surface engineering of chemi-thermomechanical pulp (CTMP) and bleached sulfite pulp (BSP). The reaction was performed using a synergistic combination of an organocatalyst with a polyelectrolyte (PE) complex. Using this method, the strength properties of CTMP and BSP sheets were significantly increased (up to 100% in Z-strength for CTMP). Further investigations of the distribution of the PE complex were then performed using TAMRA and quinidine labeling and confocal laser scanningmicroscopy. This revealed that an even distribution of the cationic starch component of the PE complex had occurred within the CTMP-based paper sheets, which follows its lignin distribution pattern.

Due to challenges such as sustainability and increasing carbon footprint, there is a growing demand to replace fossil-based materials with green sustainable alternatives like cellulosic materials. However, unmodified cellulosic materials often encounter issues like high wettability and low mechanical strength that limit their applicability. To overcome these drawbacks, functionalization and modification are crucial and inevitable. Reported methods often involve toxic/harsh conditions or reagents, and multi-step processes. The focus of this thesis is on the fabrication, functionalization, and modification of cellulosic materials through facile and eco-friendly approaches to enhance their properties and broaden their potential applications.

We started with immobilizing copper nanoparticles on controlled pore glass substrate and used it as a recyclable heterogenous catalyst for the copper-catalyzed alkyne-azide cycloaddition (CuAAC). Focusing on sustainability, we also employed cellulosic materials as catalyst supports. First, cellulose was functionalized using a mild organocatalytic approach. Then, copper or palladium nanoparticles were immobilized onto the functionalized cellulose and used as effective recyclable heterogeneous catalysts in different reactions.

Direct esterification of CNC materials with thioglycolic acid was performed enabling us to introduce thiol groups onto CNC materials. The reaction occurred under mild conditions using natural nontoxic organic acid as an organocatalyst. The method was applied on different CNC materials, producing the corresponding thiol-functionalized CNC materials. The thiol-functionalized CNC was used as a heterogeneous recyclable reducing agent to reduce Cu(II) to Cu(I), which is the active form of copper in CuAAC. The prepared thiol-functionalized CNC materials further functionalized with attaching UV active molecules via thiol-ene click chemistry.

Lactic acid (LA) functionalized CNFs were prepared by using an ecofriendly one-step reaction method in high yields. This was achieved by converting pulp fibers into nanofibrillated cellulose lactate under mild conditions, using LA as both reaction media and catalyst. The process was concurrent and involved an autocatalytic esterification reaction without using metal-based or harsh acid catalysts. Moreover, the LA media were recycled and reused in multiple reaction cycles. 

In the fourth study, strong hydrophobic cellulosic materials were prepared via a facile, scalable and eco-friendly method. The method involves a betulin treatment and hot-pressing processes. First, a water-based betulin formulation was developed and used for the treatment of cellulosic materials. The betulin-treated samples were then hot-pressed. Hot-pressing altered the morphologies and led to dense structures. Moreover, it caused a polymorphic transformation of the betulin particles. Water contact angle and tensile tests revealed that the applied betulin/hot-pressing treatment method noticeably enhanced the samples’ hydrophobicities as well as their tensile strengths. Furthermore, a synergistic effect was noticed between the hot-pressing, betulin treatment, and sulfonation during the pulping process.

Densified and strong large veneers were fabricated via a facile and scalable method. The method involves a combination of chemical modifications of aspen veneers followed by hot-pressing. The study showed that hot-pressing enhanced the tensile strengths. The chemical modifications further improved the efficiency of the hot-pressing, resulting in higher tensile strengths. The chemical modifications changed the wood’s composition promoting wood softening and increasing the bonding. Since the method uses convenient and mild treatments combined with continuous hot-pressing, it enables the processing of large samples. It can also lower time/energy consumption, production costs and the environmental impact.