title: Cellulose Nanofibrils from Nonderivatizing Urea-Based Deep Eutectic Solvent Pretreatments.
abstract: Deep eutectic solvents (DESs) are a fairly new class of green solvents applied in various fields. This study investigates urea-based DES systems as novel pretreatments for cellulose nanofibril production. In the experiments, deep eutectic systems having urea and ammonium thiocyanate or guanidine hydrochloride as a second component were formed at 100 °C and then applied to disintegrate wood-derived cellulose fibers. The DES-pretreated fibers were nanofibrillated into three different levels of mechanical treatments with a microfluidizer, and their properties were analyzed. Moreover, nanofibril films were fabricated by solvent casting method. Both DES systems were able to loosen and swell the cellulose fiber structure as indicated by the increase in the lateral dimension of the fibers. Nonpretreated birch cellulose fibers had difficulties in mechanical nanofibrillation as clogging of the chamber occurred often. However, cellulose nanofibrils with widths ranging from 13.0 to 19.3 nm were successfully fabricated from DES-pretreated fibers with both systems. Translucent nanofibril films generated from DES-pretreated cellulose nanofibrils had good thermal stability and mechanical properties, with tensile strengths of approximately 135-189 MPa and elastic modulus of 6.4-7.7 GPa. Consequently, both urea-based DESs showed a high potential as environmentally friendly solvents in the manufacture of cellulose nanofibrils.
authors.affiliation: Fibre and Particle Engineering Research Unit, University of Oulu , P. O. Box 4300, FI-90014 Oulu, Finland.
authors.forename: Panpan
authors.identifier: http://orcid.org/0000-0002-8740-2955
authors.initials: P
authors.lastname: Li
authors.affiliation: Fibre and Particle Engineering Research Unit, University of Oulu , P. O. Box 4300, FI-90014 Oulu, Finland.
authors.forename: Juho Antti
authors.identifier: http://orcid.org/0000-0002-7404-3340
authors.initials: JA
authors.lastname: Sirviö
authors.affiliation: Wood Materials Science, University of Eastern Finland , P. O. Box 111, FI-80101 Joensuu, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Haapala
authors.affiliation: Fibre and Particle Engineering Research Unit, University of Oulu , P. O. Box 4300, FI-90014 Oulu, Finland.
authors.forename: Henrikki
authors.identifier: http://orcid.org/0000-0002-7911-2632
authors.initials: H
authors.lastname: Liimatainen
keywords: cellulose nanofibrils; deep eutectic solvents; films; mechanical properties; pretreatments