Investigation of CO2 interactions with cellulose dissolved in the NaOH(aq) system
Cellulose derived from wood can be used as raw material for production of textile fibres, making it a renewable alternative to fossil oil. One of the key steps in this process is dissolution of the cellulose. The sustainable solvent NaOH(aq) has shown great potential for dissolution of cellulose, but its narrow dissolution window is still a limiting parameter for large scale implementation. The knowledge about the molecular interactions occurring during dissolution of cellulose in NaOH(aq) plays an important role in order to expand the dissolution window why further research in this field is needed.
In this thesis, the specific interactions that occurs between cellulose and CO2 (e.g from air) in NaOH(aq) solutions are investigated.
Using ATR-IR and NMR spectroscopy it was shown that CO2 from air chemisorbs on cellulose when dissolved in 8 wt% NaOH(aq) at -5°C and regenerated with ethanol. The chemisorption of CO2 was found to be reversible when water was used instead as the regenerating agent. Furthermore, a difference in molecular interactions was discovered for CO2 added to NaOH(aq) prior or after dissolution of the model substrate methyl α-D-glucopyranoside (MeO-Glcp). The post-dissolution addition of CO2 was shown to affect the chemical shifts (NMR spectroscopy) of MeO-Glcp more than the pre-dissolution addition of CO2; the same effect was observed for regenerated materials in ATR-IR spectroscopy. Moreover, in the cellulose solutions aged for two weeks, a gel formation was observed when CO2 was added after the dissolution of the cellulose substrate, pointing out specific interaction between the dissolved and deprotonated cellulose and freshly added CO2.