Nanocellulose Assembly In Aqueous Media: towards hybrid functional materials

: (Alternative Format Thesis)

Abstract

In the last decade, raising awareness towards the use of sustainable materials resulted in fast-expanding research on cellulose nanoparticles (CNP). The abundance of cellulose and the versatility of CNP to assemble in a myriad of different structures made CNP an interesting building block for a variety of soft materials. To enable the use of CNP in day-to-day soft materials, a fundamental understanding of the CNP assembly coupled with exploratory research, aimed to propose new strategies of assembly, is demanded. Thus, prediction and control of the structure-to-property relationship of CNP-based material can be achieved in industrially relevant conditions. This work aimed to extend the understanding of the structure-property relationship of the CNP assembly required for the production of capsules and hydrogels able to incorporate targeted components. As a starting point, oxidised cellulose nanofibrils (OCNF) and cationic cellulose nanofibrils (CCNF) dispersions were investigated as a function of time and temperature; crucial parameters to account for shelf-life and processing of materials. To ensure heat insensitivity while gaining rheological control upon addition of secondary species, zwitterionic cellulose nanofibrils (ZCNF) were produced through covalent grafting of a quaternary ammonium moiety onto OCNF. The assembly and the ow behaviour of the ZCNF dispersions were found to be strongly responsive upon addition of ionic surfactants due to electrostatic interactions. On the other side, the addition of non-interacting colloids into OCNF-based hydrogels was pursued with the aim to preserve charge accessibility of the OCNF surface whilst modulating mechanical properties of the dispersion. This enabled the formation of long-living millimetre-sized spheroidal hydrogels in water, able to incorporate coordination polymers.

Using the complexation of CCNF and an oppositely charged polymer, spheroidal hydrogels were further developed to have a core-shell structure, from which a proof-of-concept application in biocatalysis is provided. By analogy to the core-shell spheroidal hydrogels, the charge-driven complexation between OCNF and an oppositely charged surfactant was used to target the OCNF assembly, and gelation, at the interface between two immiscible fluids (water/oil). The interfacial gelation of OCNF and its mechanical properties were investigated to provide solid knowledge for the production of capsules.

This work combines individual investigations regarding the structure-property relationship of CNP in aqueous media, providing an insightful contribution towards the production of functional materials.

Date of Award	2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Janet Scott (Supervisor) & Karen Edler (Supervisor)