Tailoring Cellulose Nano- and Microstructures Through Chemical Functionalization and Alignment

Licentiate thesis, 2025

Cellulose, a major structural component of plant cell walls, is a renewable biopolymer known for its mechanical strength and chemical versatility. Traditionally used in the paper and textile industries, it is now drawing increasing attention for applications in emerging fields such as bioplastics, pharmaceuticals, optics, and nanotechnology. This thesis aims to summarize research on the chemical modification of both cellulose fibers and cellulose nanocrystals (CNCs), highlighting how tailored modifications can produce materials with distinct properties and diverse applications.

The modification of softwood based bleached kraft pulp (BKP) was made through the esterification of the hydroxyl groups found on the cellulose fibers using itaconic anhydride. Two methods were explored, mechanical kneading and gas-phase reactions, both gaining BKP-itaconate. The fibers were characterized by a variety of techniques, including Fourier transformed infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), titrations, powder X-ray diffraction (PXRD) and water absorption. Manuscript I explores fiber modification relative to chemical composition but also fiber confirmation and material properties. CNCs were studied in relation to the counterions and conjugation of azetidinium salts (Az-salts) to the sulfate groups.  Paper II investigated the influence of different counter ions and sample preparation, i.e. sonication and drying temperature, on the CNCs alignment in films, visualizing their chiral nematic structures with polarized optical microscopy (POM) and UV-Vis. Paper III investigated the effects of Az-salts, the effective introduction of alkyl chains to the CNC surfaces, in relation to the rheological properties of the CNC suspensions. Additional work conducted at the B23-Beamline at Diamon Light source (UK) is presented, where Mueller Matrix Polarimetry (MMP) was used to understand the structuring and aggregation of CNCs in films depending on different additives.