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.

Deep eutectic solvents (DESs) are potential green systems that can be used as reagents, extraction agents and reaction media. DESs are often biodegradable, easy to prepare and have low toxicity. In this work, a recyclable DES formed from aminoguanidine hydrochloride and glycerol (AhG) was used as a reaction medium and reagent (aminoguanidine hydrochloride) for the production of cationic nanocelluloses. Under mild conditions (i.e., a reaction time of 10 min at 70 °C), dialdehyde celluloses (DACs) with two different aldehyde contents (2.18 and 3.79 mmol g) were cationized by AhG DES to form cationic dialdehyde celluloses (CDACs). Both CDACs achieved a similar high charge density of approximately 1.1 mmol g. At 80 °C (for 10 min), a very high cationic charge density of 2.48 mmol g was obtained. The recyclability of AhG DES was demonstrated by reusing it five times without decreasing the reaction efficiency. In particular, due to the low consumption of amoniguanidine hydrochloride, high recycling efficiency could be achieved without the use of any additional chemicals. The cationized celluloses, CDACs, were further mechanically disintegrated to obtain cationic nanocelluloses. According to the initial aldehyde content of DACs, the morphology of the nanocellulose could be tailored to produce highly cationic cellulose nanofibrils (CNFs) or cellulose nanocrystals (CNCs). Transmission electron microscopy confirmed that individual CNFs and CNCs with an average width of 4.6 ± 1.1 nm and 5.7 ± 1.3 nm, respectively, were obtained. Thus, the results presented here indicate that the AhG DES is a promising green and recyclable way of producing cationized CNFs and CNCs.

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

Highlights Mechano-chemical pretreatment was developed to produce anionic wood nanofiber. Deep eutectic solvent worked both as reactive agent and medium for the reaction. The reaction consistency of wood biomass was greatly improved (up to 60 wt%). Anionic wood nanofibers obtained high sulfate group contents (up to 3.1 mmol g -1 ). Multi-functional films can be fabricated from anionic wood nanofibers.ASNFs was obtained with high sulfate group contents (up to 3.1 mmol g -1 ). Besides, the ASNFs possessed a well-individualized structure with a homogeneous size distribution (3-5 nm in width). More importantly, films fabricated from ASNFs achieved strong flame resistance and good mechanical strength. Due to the presence of lignin, ASNF films were able to block over 90% of UV light (at a wavelength of 200-400 nm). The investigated functionalities of ASNFs led the lignocellulosic biomass residuals to be converted to high value-added bioproducts.Therefore, the reactive DES treatment combined with milling and heating process offers a practical and sustainable route for multi-functional biomaterial production, which can be potentially utilized, even at an industrial scale.