Network swelling of TEMPO-oxidized nanocellulose

This study examines the swelling of TEMPO-oxidized nanofibrillated cellulose (NFCTEMPO, shortly NFC) on both the particle and interparticle levels. The sum of the intraparticle and interparticle swelling is referred to as the network swelling. A centrifugal method, based on a modification of the water retention value test, was used to measure the network swelling of NFC, a pigment, and some pulp fibers. It was found that the network swelling of NFC is highly dependent on its concentration within a fiber matrix. The particle swelling of NFC and pulp fibers was analyzed by differential scanning calorimetry (DSC) and solute exclusion. The counterion for the NFC varied among the Na+, H+, and Ca2+ forms. The counterion has a very large effect on the particle and network swelling of NFC, with Ca2+ giving the lowest swelling and Na+ the highest swelling. An industrially feasible method for changing the counterion of NFC from the nominal Na+ to the Ca2+ form, and thus improving dewatering properties, is given.