Spinning of cellulose fibres from ionic liquid solution

The goal of this master’s thesis was to study the solubility of nine different kraft pulp samples with different pre-treatments into a novel ionic liquid ([mTBNH][OAc]), and to find out how these pre-treatments affect the spinnability of dopes and mechanical properties of produced fibres. Samples were delivered in dried form, resulting in hornification of samples. Effect of hornification was reversed by kneading the pulp sample, combined with swelling in large amount of water and drying in draft cabinet was deemed the best method. Pulp samples were mixed into ionic liquid in room temperature, after which they were dissolved in temperature of approximately 85 ℃. It was concluded that there was no
correlation between solubility and pre-treatments pulp samples had undergone: Every sample had equally poor solubility before water activation, but solubilities were fully restored after treatment. Spinning of samples was conducted by dry-jet wet spinning process, utilizing custom-made spinning equipment. Samples were extruded through spinneret with eight 50 μm holes and drawn to godet through coagulating bath consisting of water. Efforts were made to improve the spinnability of dopes either by pre-heating of samples, heating samples during spinning, or lowering the cellulose concentration of dopes. Optimal concentration for spinnability was found to be 5 wt% of cellulose from total mass of dope.






From nine samples, six had sufficient spinnability to produce fibres for mechanical
testing. From these samples, SW3, SW5, and HW3 had clearly superior mechanical
properties compared to others. It was found that viscosity of dope was one of the most
important process parameters regarding spinnability of dopes, which was most effectively
decreased by treatment with endoglucanase and could caustic extraction in case of
samples SW5 and HW3, or with acid hydrolysis in case of sample SW3. Viscosity of
dope is increased by amounts of hemicelluloses and especially xylan, which makes their
removal beneficial for reduction of dope viscosity. With sample SW3, viscosity was
lowered by depolymerization of cellulose.

Samples were also studied with optical microscope. Surface structure and thickness had
clear correlation with spinnability: Good spinnability of dope caused produced fibre to
have clearly smoother surface structure compared to samples with inferior spinnability.
It was noted that high amounts of hemicelluloses might cause uneven surface
morphology, which also explains the smooth structure of samples with better
spinnabilities.