Authors: Timo Pääkkönen Katarina DimicMisic Hannes Orelma Raili Pönni Tapani Vuorinen Thad Maloney
Publish Date: 2015/12/08
Volume: 23, Issue: 1, Pages: 277-293
Abstract
alkaliwashed nanofibrillated cellulose NFC samples obtained from hardwood kraft pulp with different amounts of retained xylan were prepared to study the influence of xylan on the waterretention properties of NFC suspensions In this study NFC was produced using an oxoammoniumcatalyzed oxidation reaction that converts the cellulosic substrate to a more highly oxidized material via the action of the nitroxide radical species 2266tetramethylpiperidine1oxyl Reduction of the xylan content in NFC was achieved by cold alkali extraction of kraft pulp The pulps were then oxidized to a set charge under constant chemical conditions and the reaction time was determined The xylan content of the feed pulp was found to have a large negative influence on the oxidation rate of the pulp as the oxidation time shortened when xylan was removed from 220 min for 252 xylan content to 28 min for 73 xylan content Following fibrillation by homogenization the swelling of the NFC was determined by a twopoint solute exclusion method The distribution of hemicellulose over the fibril surface was observed by atomic force microscopy Xylan was found to be distributed unevenly over the surface and its presence increased the water immobilized within flocs of NFC ie socalled network swelling The swelling of the NFC had a large impact on its rheology and dewatering Comparison of the morphological and swelling properties of the suspensions with their rheological and dynamic dewatering behavior showed that reducing the xylan content in NFC results in a weaker gel structure of the nanocellulose suspension The results indicate that most of the water is held by the swollen structure by means of xylan particles trapped within the hemicellulose layer covering the fibril surface Samples with high xylan content had high shear modulus and viscosity and were difficult to dewaterThe Academy of Finland is thanked for supporting this research The authors thank Mr Antton Lahnalammi for performing TEMPOmediated oxidation of birch pulp samples and Ms Anu Anttila for performing fluidization of TEMPOoxidized pulp solutions Ms Ritva Kivelä is acknowledged for technical assistance with AFM imaging We also thank Ms Mirja Reinikainen Ms Tuyen Nguyen and Ms Leena Nolvi for excellent laboratory work
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