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.
Cellulose and tannin are both abundant and biodegradable natural polymers. This 19 study proposes a strategy to construct biohybrid films combining the characteristics of cationic 20 cellulose nanofibrils (CCNFs) and tannin extract for film applications. Multi-functional 21 biohybrid films with anti-oxidative and UV-adsorbing characteristics were successfully 22 fabricated from CCNF and tannin mixtures with different mass ratios. The results indicated that 23 pure CCNF could be endowed with multi-functionality by a small amount of introduced 24 flavonoid-rich tannin extract. By adding 5% (w/w) of extract, CCNF-tannin film achieved good 25 anti-oxidant and UV-shielding ability, and simultaneously obtained ca. 15% improved thermal 26 stability and tensile strength of up to 160 ± 9 MPa. In addition, tannin extract was able to 27 enhance the optical clarity of CCNF film with tailorable appearances. The biohybrid films 28 essentially consisted of renewable materials, and they can potentially be exploited in sustainable 29 applications such as biocomposites and packaging materials. 30 31 32 33 34 35 36
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