Defence of doctoral thesis: Katarzyna Mystek – Use of Cellulose for the Preparation of Capsules and Beads with Molecularly Tailored Properties
Opponent: Dr. Bernard Cathala, French National Institute for Agriculture, Food and Environment (INRAE)
Supervisor: Professor Lars Wågberg, KTH
The continuously increasing global production of petroleum-based polymers to meet the ever growing demand for plastics for use in a multitude of industrial sectors (e.g. packaging and textiles) has an impact on human health, climate change and the entire ecosystem. Therefore, there is a need to develop truly biodegradable, high-performance materials from renewable resources that can replace conventional plastics. These environmentally friendly alternative materials must possess similar properties to the materials they are replacing. The excellent mechanical properties, good chemical stability and straightforward functionalization of cellulose makes it an excellent candidate raw material that can initiate a transition away from petroleum-based plastics and toward more sustainable future.
This thesis investigates the use of native and partially modified cellulose for the preparation of hollow or liquid-filled capsules and solid beads with unique and well-controlled structural and mechanical properties. The shaping of materials was made possible by the dissolution of cellulose in a suitable solvent, followed by its regeneration. Two different methods for preparing these cellulose-based materials are proposed: a solution–solidification method that creates millimeter-sized hollow capsules and solid beads, and an emulsification-solvent-evaporation method that results in the formation of micrometer scale liquid-filled capsules. The partial conversion of cellulose to dialcohol cellulose and cellulose acetate introduced flexibility and thermoplastic features to the cellulose materials. This resulted in the formation of stimuli-responsive capsules with properties suitable for different industrial applications; for example, in the production of next-generation lightweight materials. The hollow dialcohol-modified cellulose capsules exhibit a tendency, when wet, to expand to almost double their volume when exposed to a decreased external pressure, whereas the dry liquid-filled cellulose acetate capsules show a thermal expansion up to 60 times their original volume. Apart from the chemical modifications, the work discusses a method of altering the properties of cellulose beads by inclusion of cellulose nanocrystals, creating an all-cellulose composite material.
The thesis also includes model studies focused on a better understanding of the evolution of the internal structure of regenerated cellulose beads during drying from different solvents. A combination of small-angle X-ray scattering, wide-angle X-ray scattering and atomic force microscopy indentation techniques allowed the monitoring of the macro- and micro-scale structural changes taking place within the beads, as well as a continuous evaluation of the mechanical properties of beads upon solvent evaporation. This work provides a fundamental understanding of the mechanisms and molecular interactions characteristic of the drying of cellulosic materials.