Mid Sweden University

This work reveals the structural variations ofcellulose nanofibers (CNF) prepared from different cellulosesources, including softwood (Picea abies), hardwood (Euca-lyptus grandis × E. urophylla), and tunicate (Ciona intestinalis),using different preparation processes and their correlations tothe formation and performance of the films prepared from theCNF. Here, the CNF are prepared from wood chemical pulpsand tunicate isolated cellulose by an identical homogenizationtreatment subsequent to either an enzymatic hydrolysis or a2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxi-dation. They show a large structural diversity in terms ofchemical, morphological, and crystalline structure. Amongothers, the tunicate CNF consist of purer cellulose and have a degree of polymerization higher than that of wood CNF.Introduction of surface charges via the TEMPO-mediated oxidation is found to have significant impacts on the structure,morphology, optical, mechanical, thermal, and hydrophobic properties of the prepared films. For example, the film density isclosely related to the charge density of the used CNF, and the tensile stress of the films is correlated to the crystallinity index ofthe CNF. In turn, the CNF structure is determined by the cellulose sources and the preparation processes. This study providesuseful information and knowledge for understanding the importance of the raw material for the quality of CNF for various typesof applications.

Softwood fibers pretreated with a monocomponent endoglucanase wereused to prepare a series of cellulose nanofiber qualities using amicrofluidizer and 2 to 34 MWh ton-1 of energy input. The specific surfacearea was determined for the series using critical point drying and gasadsorption. Although the specific surface area reached a maximum of 430m2 g-1 at 11 MWh ton-1, the nanofiber yield and transmittance continued toincrease beyond this point, indicating that more energy is required toovercome possible friction caused by an interwoven nanofiber networkunrelated to the specific surface area. A new method for estimating thesurface area was investigated using xyloglucan adsorption in pure water.With this method it was possible to follow the disintegration past the pointof maximum specific surface area. The technical significance of thesefindings is discussed.

Nanocellulose is a recently developed form of cellulose that has the potential to be used in many different industries, ranging from food to high-performance applications. This material is commercially manufactured through the homogenization of chemical pulps, but the process is energy-consuming and is still an important subject for development. Simple, robust methods are required for the quality control and optimization of industrial nanocellulose production. In this study, a number of different methods, based on different principles of monitoring the manufacture of cellulose nanofibers were evaluated and compared for five different nanocellulose qualities, both for their resolution and robustness/ease. Methods based on microscopy, light scattering, centrifugation, and viscosity were examined and all appeared useful for observing the manufacturing process during its initial stage. However, only methods based on centrifugation, turbidity, and transmittance yielded reliable data for the entire manufacturing process. Of these methods, transmittance measurement may be the best candidate for routine use because the method is simple, rapid, and only requires spectrophotometer equipment.