Electrospinning Nanofibres from Cellulose Dissolved in Ionic Liquid
This thesis investigates the electrospinning of cellulose nanofibres from ionic liquids. Cellulose nanofibres produced by an environmentally friendly process have the potential to replace synthetic nanofibres produced with volatile and harmful solvents.
The influence of a co-solvent was studied by investigating how three well-known co-solvents (DMSO, DMAc and DMF) affect spinnability. The solution parameters viscosity, surface tension and conductivity were investigated in detail and related to spinnability and fibre formation. To form fibres, regardless of co-solvent used, a certain degree of viscosity and surface tension was needed. The system with DMSO as co-solvent was found to give the best fibre formation, be spinnable at a lower EmimAc content, and show more pronounced shear thinning. Compared to DMSO, both DMAc and DMF have a molecular structure which can present a resonance form and consequently stronger interaction between ionic liquid and co-solvent.
The effect of the molecular weight of the cellulose and cellulose concentration on fibre spinnability has also been investigated. Cellulose was depolymerised with hydrochloric acid to yield fractions of cellulose with different molecular weight distributions. Size Exclusion Chromatography confirmed that the cellulose was degraded into different molecular weight fractions, where longer acid treatment time yielded more chain scission, hence a lower molecular weight. The dominant property for electrospun cellulose fibres from ionic liquids to be formed is solution viscosity, a property controlled by, e.g., polymer concentration or molecular weight.
molecular weight distribution.