Modification of nanofibrillated cellulose in aqueous media

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Karoliina Junka Name of the doctoral dissertation Modification of nanofibrillated cellulose in aqueous media Publisher School of Chemical Technology Unit Department of Forest Products Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 30/2014 Field of research Forest Products Chemistry Manuscript submitted 1 November 2013 Date of the defence 4 April 2014 Permission to publish granted (date) 11 February 2014 Language English Monograph Article dissertation (summary + original articles) Abstract In this work, the modification of nanofibrillated cellulose (NFC) was conducted both indirectly via polysaccharide adsorption and directly by chemical modification in aqueous media. Developing modification methods for NFC in aqueous media is of importance because NFC has a tendency for surface passivation and aggregation in any other solvent than water. All the NFC modifications described herein were carried out using anionic carboxyl groups as anchor groups.In this work, the modification of nanofibrillated cellulose (NFC) was conducted both indirectly via polysaccharide adsorption and directly by chemical modification in aqueous media. Developing modification methods for NFC in aqueous media is of importance because NFC has a tendency for surface passivation and aggregation in any other solvent than water. All the NFC modifications described herein were carried out using anionic carboxyl groups as anchor groups. The adsorption and interactions between NFC and different water-soluble, linear polysaccharides were studied in a molecular level using cellulose model surfaces and surface sensitive techniques such as quartz crystal microbalance with dissipation monitoring (QCMD), surface plasmon resonance (SPR), atomic force microscopy (AFM) and colloidal probe microscopy (CPM). The results pointed out that cellulose-like, linear polysaccharides can be irreversibly adsorbed on NFC surface which in turn allowed the use of polysaccharides as premodifiers of the NFC substrate. Indirect NFC modification via polysaccharide adsorption was demonstrated by using modified carboxymethyl cellulose (CMC). In detail, CMC was first functionalized (azide or alkyne) and then adsorbed on NFC surface. Subsequently clickchemistry reaction (Cu(I)-catalyzed azide-alkyne cycloaddition), was utilized for the covalent immobilization of different counterparts on NFC substrate. In addition, the use of CMCadducts as lubricants in NFC system was explored by grafting CMC with polyethylene glycol and adsorbing the corresponding CMC-derivative (CMC-g-PEG ) on NFC. Direct modification of NFC was carried out by using carboxymethylation as a pre-treatment. Next, carboxymethylated NFC (CM-NFC) substrates were subjected for carbodiimide-assisted conjugation chemistry (EDC/NHS) which allowed covalent attachment of luminescent carbon dots on CM-NFC model films and nanopaper. Furthermore, titrimetric methods for determining the surface and total charge of NFC in aqueous media were developed. The developed generic, mild and rather effortless modification methods of NFC in aqueous media are expected to open new venues for the larger scale applications of NFC .