Surface Functionality in Nanocellulose Processing and Composite Formulations

Onyianta, Amaka

Abstract

Cellulose nanofibrils (CNF) are cellulose nanomaterials with desirable properties and offer great potentials to be applied in diverse fields. While various pre-treatments have been studied with the aim of reducing the intensity of mechanical fibrillation process used during production, the overall energy demand of some of these processes still remain high. This study investigated the use of aqueous morpholine pre-treatment for CNF production and the effect of the resulting CNF on the properties of alginate-based hydrogels.
The study was carried out in three stages. The first stage of the project studied the swelling of cellulose in two intercrystalline swelling agents, piperidine and morpholine, at various aqueous concentrations. This was followed by the production of CNF using aqueous morpholine swelling of cellulose as a pre-treatment step. The surface chemistry, crystallinity, thermal properties, rheological properties, morphological properties and aspect ratio of the resulting morpholine pre-treated CNF (MCNF) were compared with the properties of carboxymethylated CNF (CMCNF) and TEMPO-oxidised CNF (TCNF). The effects of MCNF and CMCNF on the swelling, elastic modulus, compressive modulus and morphology of alginate-based hydrogels at various loadings of CNFs were studied during the second stage of the project. Finally, a proof of concept study on the use of the alginate-MCNF biocomposite for the adsorption of methylene blue dye from aqueous solutions was carried out.
Higher swelling was observed for morpholine in comparison to piperidine, hence its use in CNF production. The surface chemistry measurements revealed that MCNF remained unmodified at the end of the pre-treatment process. This led to a maintained crystallinity index and thermal stability relative to the starting material. Unlike the carboxymethylated and TEMPO-oxidised CNFs which had reduced crystallinity indices and thermal stabilities, because of the modification of the surfaces with anionic groups. The lack of ionic groups on MCNF led to a lower storage modulus in comparison to the other two CNFs.
Furthermore, the addition of MCNF and CMCNF to alginate-based hydrogels at 5 wt. %, relative to the dry mass of the alginate, led to a respective 36% and 17% increase in compressive modulus of the alginate-based hydrogels. Further increases in the amount of MCNF and CMCNF did not impact positively on the material properties of the alginate. This was attributed to the aggregation of fibrils, which led to the formation of imperfect networks within the ionically crosslinked hydrogels.
Proof of concept study on the adsorption of methylene blue dye from aqueous solution shows that the alginate-MCNF biocomposite can adsorb up to 1957 mg of methylene blue per gram of adsorbent in three hours. Thereby, indicating the potential of the biocomposite in wastewater remediation when fully optimised.

Citation

Onyianta, A. Surface Functionality in Nanocellulose Processing and Composite Formulations. (Thesis). Edinburgh Napier University. Retrieved from http://researchrepository.napier.ac.uk/Output/2025207

• Thesis Type: Thesis
• Deposit Date: Aug 3, 2019
• Publicly Available Date: Aug 29, 2019
• Public URL: http://researchrepository.napier.ac.uk/Output/2025207
• Award Date: Jul 4, 2019