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Nanocellulose is already being used in products and its market footprint is only expected to grow. Product safety concerns regarding nanocellulose usage in consumer goods require nanocellulose grades that are labeled with a detectable marker to facilitate localization, particularly in terms of leaching from products. Thus, new nanocellulose labeling approaches need to be explored, with the following criteria: (1) easy and reproducible chemistry, (2) labeling does not significantly alter the properties of the nanocellulose, and (3) the degree labeling is sufficient to allow facile detection. One such promising avenue for the labeling and identification of nanocellulose is by the covalent attachment of a fluorescent probe.
In this thesis project, CNFs will be labeled with the fluorescent molecule (5-(4,6) dichlorotriazinyl) aminofluorescein, DTAF. DTAF labeling of cellulose substrates occurs spontaneously at alkaline pH, where the deprotonated cellulose hydroxyls attack the triazinyl moiety with chlorine as a leaving group.1 The efficiency of DTAF labeling depends on the crystallinity and surface charge of the cellulose substrate, as well as the ionic strength of the reaction medium. In this work, pulps with different surface charges will be fluorescently labeled. The pulps will then be defibrillated to different extents in a microfluidizer (i.e. varying pass number). A related study that directly labeled the smaller sized and more crystalline cellulose nanocrystals (CNCs) found that dye labeling efficiency increased at higher ionic strengths and suggested that the highly crystalline material is less available to chemical modification.2 By employing pulp as a substrate, dye labeling efficiency is expected to improve since both crystalline and amorphous cellulose is present in this case. Alternatively, and if necessary, ready-made CNFs of varying charge and degree of fibrillation can be dyed.
The labeled materials will be characterized by solid state NMR (%crystallinity), fluorescence and UV-Vis spectroscopy (labeling efficiency), atomic force microscopy (structure), and high-resolution fluorescence microscopy (dye distribution & structure). Other complimentary routine tools including dialysis, ultrafiltration, dry content measurement, dynamic light scattering, and zeta-potential may be utilized to characterize materials before and after dye-labeling.
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Final application date: 15/1, 2019.
If you have any questions about the master thesis project, please contact Recruiting Manager Tiffany Abitbol, tel. 070 377 6036
Union representatives: Anna Jensen (Unionen), 08-676 72 23 and Elisabeth Sjöholm (Sveriges Ingenjörer), 08-676 74 44.
Master thesis, RISE, Bioeconomy, cellulose nanofibrils (CNFs), Exjobb, Uppsats, Stockholm