Effect of lignin on the morphology and rheological properties of nanofibrillated cellulose produced from γ-valerolactone/water fractionation process
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The influence of lignin content on nanocellulosic fibril morphology, charge, colloidal stability and immobilization has been systematically investigated employing a series of nanofibrillated cellulose (NFC) with varying residual lignin content and compared to those of NFC made from fully bleached pulp. The lignin-containing pulps were obtained from the fractionation of Eucalyptus globulus wood chips in gamma-valerolactone (GVL)/water under the same conditions, they differ by the intensity of washing for lignin removal. The reference pulp originated from another cook of eucalyptus wood chips, and was fully bleached with a short Elemental-Chlorine-Free (ECF) sequence. All the pulps have a comparable hemicellulose-to-cellulose ratio and CED viscosity. NFC suspensions of 1 wt% concentration were mechanically produced from fluidization. The results indicated that the fibrils morphology, thickness and corresponding flocculation within NFC suspensions was highly influenced by the presence of lignin unevenly distributed on the fibril surface and within the suspension as particles. The presence of lignin in NFC suspension had a large impact on the rheology and dewatering of the NFC. Samples with high lignin content had distinguishable viscoelastic properties due to the greater flocculation of thicker fibrils and lower gel-like characteristics, with better dewatering properties.
KeywordsNanocellulose Lignin Dissolving pulp Rheology Gamma-valerolactone
Funding from Aalto University, School of Chemical Technology and Finnish Bioeconomy Cluster Oy (FIBIC) via the Advanced Cellulose to Novel Products (ACel) research program is gratefully acknowledged. This work made use of Aalto University Bioeconomy Facilities. The authors would like to thank Ms. Ritva Kivelä for her support with the NFC suspensions production, Dr. Kaarlo Nieminen for his support with the mathematical solutions, Ms. Rita Hataka for her support with the chromatographic analyses, Dr. Juan José Valle-Delgado for his advices on AFM image analysis, Dr. Krista Vajanto for her support on SEM images acquisition, Dr. Michael Hummel, Dr. Marc Borrega and Prof. Eero Kontturi for their advices on the manuscript.
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