Nanocellulose Oxidation - Fundamentals and Application in Hydrogels

Licentiate thesis, 2021

The adaptable surface chemistry of cellulose nanocrystals (CNCs) makes them outstanding; it provides colloidal stability, which is essential for engineering use, to commercially-available CNCs. Colloidal stability is achieved by the bulky negatively-charged sulfate half-ester groups on the surface that it manufactures itself via the use of sulfuric acid. The surface chemistry of CNCs can also be adapted into dialdehyde cellulose nanocrystals (DAC) by periodate oxidation in the presence of the sulfate half-ester groups. The oxidation extends the range of applications of CNCs. The objective of this thesis is to elucidate the role played by the sulfate half-ester groups on the oxidation reaction, both in the kinetics and its products. The results demonstrate that the oxidation reaction reduces the number of sulfate half-ester groups, which impacts on the colloidal stability, the size of the resulting product properties and, consequently, the DAC applications. A rheology study and a proof-of-concept demonstration are also performed to verify whether CNC derivatives could reinforce emulsions solidified by gelatin, as this could extend the range of CNCs in the field of microwave technology to be used as a fat phantom. The gelatin emulsions reinforced by CNC derivatives maintain the storage modulus above the loss modulus at temperatures above 40 ºC. The thermal stability of the reinforced emulsions could permit the successful implementation of these gels in the field of microwave technology. CNCs are possibly the better candidate than DAC for the reinforcement due to a combination of the ease of the phantom production and performance.