Preparation of nanofibers from pulp fibers

TEMPO-mediated oxidation is a powerful technique for preparation of highly crystalline, individualized cellulose nanofibers.This regioselective oxidation can be achieved with sodium hypochlorite and catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and sodium bromide under aqueous conditions at pH 10 and room temperature.In this master thesis, the TEMPO-mediated oxidation for preparation of nanofibers from hardwood kraft pulp fibers has been examined, with the purpose to find the optimum process conditions.An obvious disadvantage of this oxidation procedure is the use of TEMPO and sodium bromide, which both are associated with environmental issues.Therefore, an important factor was to examine the possibility to reduce the addition levels of these two chemicals.Several methods were used to characterize the oxidized pulp fibers.Total fiber charge, water retention value and intrinsic viscosity were considered most important.The results showed that pH is, undoubtedly, the most important parameter, concerning both the oxidation procedure and the properties of the nanofibers.Moreover, it was shown that it is possible to prepare nanofibers of high quality with low charges of TEMPO and sodium bromide.To set the properties of the nanofibers in relation to dry and wet strength applications, the fibers were evaluated as a binder in paper sheets.The strength properties of the paper sheets can be significantly increased with addition of nanofibers and at a given addition level, the highly charged nanofiber product had the best performance.