Karoliina Junka

Modification of Cellulose Nanofibrils with Luminescent Carbon Dots

Films and hydrogels consisting of cellulose nanofibrils (CNF) were modified by covalent EDC/NHS coupling of luminescent, water-dispersible carbon dots (CDs). Quartz crystal microgravimetry with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) were used to investigate the attachment of CDs on carboxymethylated CNF (CM-CNF). As the first reported use of CD in nanocellulose products, we provide proof-of-concept for the synthesis of transparent and fluorescent nanopaper and for its tunable luminescence as confirmed by confocal microscopy imaging.

Titrimetric methods for the determination of surface and total charge of functionalized nanofibrillated/microfibrillated cellulose (NFC/MFC)

Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed.

Multilayers of cellulose derivatives and chitosan on nanofibrillated cellulose

The aim of this work was to study the effect of solution conditions and polysaccharide structure on their Layer-by-Layer (LbL) deposition on nanofibrillated cellulose (NFC). Multilayer build-up of cellulose derivatives and chitosan on NFC model surfaces was studied using Quartz Crystal Microbalance with Dissipation (QCM-D) and Colloidal Probe Microscopy (CPM). The type of cationic polysaccharide was found to significantly affect the multilayer build-up and surface interactions. Cationic cellulose derivative quaternized hydroxyethyl cellulose ethoxylate (HECE) formed highly water-swollen layers with carboxymethyl cellulose (CMC), and the build-up was markedly influenced by both the ionic strength and pH. The ionic strength did not significantly influence the multilayer build-up of chitosan-CMC system, and adsorbed chitosan layers decreased the viscoelasticity of the system. Based on the results, it was also confirmed that electrostatic interaction is not the only driving force in case of the build-up of polysaccharide multilayers on nanofibrillated cellulose.

Effect of xylan structure on reactivity in graft copolymerization and subsequent binding to cellulose.

The grafting reactivities with glycidyl methacrylate (GMA) of five xylans from hardwood and cereal sources were compared. The structural property that best predicted the reactivities of xylans with GMA was the fraction of 4-O-methylglucuronic acid (MeGlcA) substitution. A comparatively high level of arabinose substitution was also positively correlated to reactivity with GMA. The impact of MeGlcA and arabinose branching groups is likely attributed to the solubilizing effect of these substituents. Consistent with this prediction, low water solubility and high lignin content were found to hinder reactivity. Even though oligomeric substrates have the advantage of water solubility, modified xylo-oligosaccharides were difficult to purify. Accordingly, delignified and high-molecular weight xylans that are soluble or dispersible in water are best suited for this type of backbone derivatization. Adsorption studies with a quartz crystal microbalance with dissipation indicated that grafting lowered the total adsorption of arabinoxylan but did not significantly affect the fraction of xylans adsorbed irreversibly on cellulose.