Alternative chemo-enzymatic treatment for homogeneous and heterogeneous acetylation of wood fibers

A new chemo-enzymatic treatment is proposed to produce cellulosic fibers suitable for heterogeneous- or homogeneous-phase acetylation. The procedure included enzymatic (laccase–violuric acid) lignin removal from the precursor fibers (unbleached sulfite pulp) followed by hydrogen peroxide treatment. An optional intermediate stage included partial hydrolysis (endoglucanase) to increase fiber reactivity. The obtained ‘‘biobleached’’ fibers were acetylated in the heterogeneous phase with acetic anhydride in nonpolar solvents, yielding various acetyl group contents, depending on the severity of the reaction. The degree of acetylation was highly sensitive to the treatment conditions, mainly the acetic anhydride activity in the system. The results were compared to those obtained after acetylation of commercial, dissolving-grade fibers, used as reference. The effect of the inherent nature of the fibers tested were elucidated as far as hemicellulose content, fiber length, fine content and crystallinity. Acetyl group content of up to 24% were determined after heterogeneous reaction with the chemoenzymatic fibers. The substitution of hydroxyl groups by acetyl moieties resulted in a lower hydrophilicity, as assessed by measurement of the water contact angle. Homogeneous acetylation of the chemo-enzymatic and reference fibers resulted in relatively similar acetyl group content (up to 36 and 33%, respectively). These samples were soluble in acetone and produced transparent films (via solvent casting), with enhanced dry strength and lower hydrophilicity. Overall, it is concluded that the proposed chemo-enzymatic treatment is a feasible alternative for the production of fibers that are suitable for efficient acetylationPostprint (author's final draft

Cellulose acetate films from chemo-enzymatic dissolving pulps

The purpose of this work is to obtain dissolving cellulose fibers that are suitable for the manufacturing of cellulose derivatives. Therefore, the combination of enzymatic and chemical treatments during the bleaching stage (lignin removal) and purification stage (hemicellulose removal) is proposed. The obtained dissolving cellulose was submitted to acetylation reactions, and then acetate films were prepared as an example of end product. Assessing the quality of acetate films, it was concluded that dissolving cellulose fibers had good properties and fulfilled the quality requirements. These satisfactory results were compared with acetate films obtained under same acetylation conditions, but the dissolving cellulose fibers used as a raw material came from a conventional and industrial process.This publication is part of the PID2020-114070RB-I00 (CELLECOPROD) project, funded by MCIN/AEI/10.13039/501100011033. O.J.R. acknowledges funding support by the Academy of Finland through its Center of Excellence Program (2014–2019) “Molecular Engineering of Biosynthetic Hybrid Materials Research”.Peer ReviewedPostprint (published version

Observation of micropores in hard-carbon using Xe-129 NMR porosimetry

The existence of micropores and the change of surface structure in pitch-based hard-carbon in xenon atmosphere were demonstrated using Xe-129 NMR. For high-pressure (4.0 MPa) Xe-129 NMR measurements, the hard-carbon samples in Xe gas showed three peaks at 27, 34 and 210 ppm. The last was attributed to the xenon in micropores (<1 nm) in hard-carbon particles. The NMR spectrum of a sample evacuated at 773 K and exposed to 0.1 MPa Xe gas at 773 K for 24 h showed two peaks at 29 and 128 ppm, which were attributed, respectively, to the xenon atoms adsorbed in the large pores (probably mesopores) and micropores of hard-carbon. With increasing annealing time in Xe gas at 773 K, both peaks shifted and merged into one peak at 50 ppm. The diffusion of adsorbed xenon atoms is very slow, probably because the transfer of molecules or atoms among micropores in hard-carbon does not occur readily. Many micropores are isolated from the outer surface. For that reason, xenon atoms are thought to be adsorbed only by micropores near the surface, which are easily accessible from the surrounding space.</p

Heterogeneous Acetylation of Plant Fibers into Micro- and Nanocelluloses for the Synthesis of Highly Stretchable, Tough, and Water-Resistant Co-continuous Filaments via Wet-Spinning

| openaire: EC/H2020/788489/EU//BioELCellHeterogeneous acetylation of wood fibers is proposed for weakening their interfibrillar hydrogen bonding, which facilitates their processing into micro- and nanocelluloses that can be further used to synthesize filaments via wet-spinning. The structural (SEM, WAXD), molecular (SEC), and chemical (FTIR, titration) properties of the system are used to propose the associated reaction mechanism. Unlike the homogeneous acetylation, this method does not alter the main morphological features of cellulose fibrils. Thus, we show for the first time, the exploitation of synergies of compositions simultaneously comprising dissolved cellulose esters and suspended cellulose micro- and nanofibrils. Such colloidal suspension forms a co-continuous assembly with a matrix that interacts strongly with the micro- and nanofibrils in the dispersed phase. This facilitates uninterrupted and defect-free wet-spinning. Upon contact with an antisolvent (water), filaments are easily formed and display a set of properties that set them apart from those reported so far for nanocelluloses: a remarkable stretchability (30% strain) and ultrahigh toughness (33 MJ/m3), both surpassing the values of all reported nanocellulose-based filaments. All the while, they also exhibit competitive stiffness and strength (6 GPa and 143 MPa, respectively). Most remarkably, they retain 90% of these properties after long-term immersion in water, solving the main challenge of the lack of wet strength that is otherwise observed for filaments synthesized from nanocelluloses.Peer reviewe

Mesoporous carbon soft-templated from lignin nanofiber networks

Flexible electrodes with supercapacitance were developed from highly mesoporous carbon fibers synthesized from lignin. Polyvinyl alcohol (PVA) facilitated the electrospinning of aqueous solutions of lignin and was used as a sacrificial polymer. Most importantly, PVA produced phase-separated domains for extreme surface area (>2000 m2 g-1) and mesoporous volume (0.7 cm3 g-1). An optimized sequential thermal treatment that initially included stabilization at 250 °C, allowed the formation of flexible, freestanding carbon networks upon PVA evolution to the gas phase and carbonization of the as-spun lignin-based fibers. Their main morphological and chemical characteristics were assessed by field emission scanning microscopy, transmission electron tomography reconstructions and Raman spectroscopy. The carbon fiber networks were used directly as electrodes with electrochemical double layer capacitance as determined by cyclic voltammetry and galvanostatic charge/discharge methods. Excellent electrochemical performancewas demonstrated from the measured high rate capability and long-term cycling stability. The determined specific capacitance (∼205 F g-1 in 0.5 M Na2SO4 electrolyte) is one of the highest recorded for electrodes obtained from biopolymer precursors. Moreover, the electrical conductivity of the carbon fiber network (386 S m-1) was significantly higher, by two-orders of magnitude, than that obtained from the precursor (non-fibrous, powder) sample (2.47 S m-1). The remarkable performance of the synthesized electrodes is ascribed to the robust network morphology and mesoporosity obtained by soft-templating from the phase-separated sacrificial polymer. This is a demonstration of lignin valorization for novel application in advanced materials.Peer reviewe

Surface energy properties of lignin particles studied by inverse gas chromatography and interfacial adhesion in polyester composites with electromagnetic transparency

| openaire: EC/H2020/788489/EU//BioELCell Funding Information: The authors acknowledge funding support by JSPS KAKENHI Grant Number JP 1 9 K 2 3 6 8 8 and 2 1 K 0 5 1 5 6 (MA). OJR also acknowledges supported by the Canada Excellence Research Chair initiative, the European Research Council under the European Union’s Horizon 2020 research and innovation program (ERC Advanced Grant No. 788489, “BioElCell”), and the Canada Foundation for Innovation (CFI). The authors are thankful to Ms. Kiyoko Kawashima for operating the EDX in the Collaborative Research Center, Meisei University and we are gratefully acknowledged Prof. Tetsuo Kondo, Kyusyu University for continuous discussions. We also thank Mr. Yutaka Igarashi CEO, Kazu-technica Co.ltd., Drs. Tatsuya Sakurai and Masashi Koyama, Meisei Univeristy for discussions. Publisher Copyright: © 2022, The Author(s), under exclusive licence to Springer Nature B.V.We introduce a simple spray drying method for the scaleup production of spherical organic (lignin) particles with sizes between 0.85 and 1.57 µm. We assess the surface energy of the lignin particles by inverse gas chromatography to reveal their role in composites synthesized with unsaturated polyester. Such nanocomposites are shown to be transparent to electromagnetic irradiation (millimeter wave bands). The permittivity and tanδ of the composite material reached values 3.01 and 0.01 at 28 GHz with 10% lignin content. Vinyl groups were introduced on the surface of the particles to achieve enhanced interfacial adhesion, and resulted in a reduced relative permittivity (2.75). Together with wave interactions, the mechanical and thermal properties of the composites are put in perspective, opening new opportunities in the development of bio-based devices for 5G high-speed communication.Peer reviewe

Shear and extensional rheology of aqueous suspensions of cellulose nanofibrils for biopolymer-assisted filament spinning

| openaire: EC/H2020/788489/EU//BioELCellThe shear and extensional rheology of aqueous suspensions of cellulose nanofibrils (CNF) were investigated under dynamic and steady flow fields. The results were compared to those for two biopolymer solutions, cellulose acetate, CA, and guar gum, GG. Wet-spinning experiments were conducted for each system and the outcome related to the respective rheological profile. The spinnability of the system correlated with strong Newtonian and viscous responses under shear as well as long breakup time in capillary breakup experiments. CA solution was the most spinnable, also displaying the strongest Newtonian liquid behavior and the longest capillary breakup time. In contrast, the most shear-thinning and elastic CNF suspension showed instant capillary breakup and was considerably less spinnable. This is due to the limited entanglement between the rigid cellulose fibrils. In order to enable continuous wet-spinning of CNF without filament breakup, GG and CA were used as carrier components in coaxial spinning. The shear and extensional rheology of the system is discussed considering both as supporting polymers.Peer reviewe