A multifunctional biogenic films and coatings from synergistic aqueous dispersion of wood-derived suberin and cellulose nanofibers.

Here, biogenic and multifunctional active food coatings and packaging with UV shielding and antimicrobial properties were structured from the aqueous dispersion of an industrial byproduct, suberin, which was stabilized with amphiphilic cellulose nanofibers (CNF). The dual-functioning CNF, synthesized in a deep eutectic solvent, functioned as an efficient suberin dispersant and reinforcing agent in the packaging design. The nanofibrillar percolation network of CNF provided a steric hindrance against the coalescence of the suberin particles. The low CNF dosage of 0.5 wt% resulted in dispersion with optimal viscosity (208.70 Pa.s), enhanced stability (instability index of <0.001), and reduced particle size (9.37 ± 2.43 µm). The dispersion of suberin and CNF was further converted into self-standing films with superior UV-blocking capability, good thermal stability, improved hydrophobicity (increase in water contact angle from 61° ± 0.15 to 83° ± 5.11), and antimicrobial properties against gram-negative bacteria. Finally, the synergistic bicomponent dispersions were demonstrated as fruit coatings for bananas and packaging for strawberries to promote their self-life. The coatings and packaging considerably mitigated fruit deterioration and improved their freshness by preventing moisture loss and microbial attack. This sustainable approach is expected to pave the way toward advanced, biogenic, and active food packaging based on widely available bioresources.

Pickering Emulsions and Hydrophobized Films of Amphiphilic Cellulose Nanofibers Synthesized in Deep Eutectic Solvent.

Herein, a dual-functioning deep eutectic solvent system based on triethylmethylammonium chloride and imidazole was harnessed as a swelling agent and a reaction medium for the esterification of cellulose with n-octyl succinic anhydride (OSA). The modified or amphiphilic cellulose nanofibers (ACNFs), synthesized using three different OSA-to-anhydroglucose unit molar ratios (0.5:1, ACNF-1; 1:1, ACNF-2; and 1.5:1, ACNF-3), were further converted into nanofibers with degree of substitution (DS) values of 0.24-0.66. The ACNFs possessed a lateral dimension of 4.24-9.22 nm and displayed surface activity due to the balance of hydrophobic and hydrophilic characteristics. The ACNFs made stable aqueous dispersions; however, the instability index of ACNF-3 (0.51) was higher than those of ACNF-1 (0.29) and ACNF-2 (0.33), which was attributed to the high DS-induced hydrophobicity, causing the instability in water. The amphiphilic nature of ACNFs promoted their performance as stabilizers in oil-in-water Pickering emulsions with average droplet sizes of 4.85 µm (ACNF-1) and 5.48 µm (ACNF-2). Self-standing films of ACNFs showed high contact angles for all the tested DS variants (97.48-114.12°), while their tensile strength was inversely related to DS values (ACNF-1: 115 MPa and ACNF-3: 49.5 MPa). Aqueous dispersions of ACNFs were also tested for coating fruits to increase their shelf life. Coatings improved their shelf life by decreasing oxygen contact and moisture loss.

Highly effective fractionation chemistry to overcome the recalcitrance of softwood lignocellulose.

The efficient fractionation and thus production of individual biomass components are pivotal processes in the biorefinery concept. However, the recalcitrant nature of lignocellulose biomass, especially in the case of softwood, is one of the main obstacles to the wider application of biomass-based chemicals and materials. In this study, the use of aqueous acidic systems in the presence of thiourea was studied for the fractionation of softwood in mild conditions. Despite relatively low temperature (100 °C) and treatment times (30-90 min), notable high lignin removal efficiency (approximately 90 %) was obtained. Chemical characterization and the isolation of minor fraction of cationic, water-soluble lignin indicated that the fractionation proceed via nucleophilic addition of thiourea to lignin, resulting in dissolution of lignin in acidic water in relatively mild conditions. Besides high fractionation efficiency, both fiber and lignin fractions were obtained with bright color, significantly elevating their usability in material applications.

High Oxygen Barrier Polyester from 3,3'-Bifuran-5,5'-dicarboxylic Acid.

An exceptional oxygen barrier polyester prepared from a new biomass-derived monomer, 3,3'-bifuran-5,5'-dicarboxylic acid, is reported. When exposed to air, the furan-based polyester cross-links and gains O2 permeability 2 orders of magnitude lower than initially, resulting in performance comparable to the best polymers in this class, such as ethylene-vinyl alcohol copolymers. The cross-links hinder the crystallization of amorphous samples, also rendering them insoluble. The process was observable via UV-vis measurements, which showed a gradual increase of absorbance between wavelengths of 320 and 520 nm in free-standing films. The structural trigger bringing about these changes appears subtle: the polyester containing 5,5'-disubstituted 3,3'-bifuran moieties cross-linked, whereas the polyester with 5,5'-disubstituted 2,2'-bifuran moieties was inert. The 3,3'-bifuran-based polyester is effectively a semicrystalline thermoplastic, which is slowly converted into a cross-linked material with intriguing material properties once sufficiently exposed to ambient air.

Insights into the role of molar ratio and added water in the properties of choline chloride and urea-based eutectic mixtures and their cellulose swelling capacity.

Eutectic mixtures and deep eutectic solvents (DESs) are promising green media for the pre-treatment of lignocellulose materials. They can be harnessed for the swelling of cellulose and further facilitate cellulose hydrolysis, derivatization, and production of cellulose-based (nano) materials. Several studies indicated that water can take part in the formation of the nanostructure of DES; however, it is still unclear how additional water influences many important properties and functioning of DES, especially when the molar ratio of compounds differs from the eutectic point composition. Here, viscosity, pH, conductivity, solvatochromic and solvatomagnetic solvent parameters, and fiber swelling capacity of choline chloride and urea mixtures demonstrating different molar ratios were investigated in the presence and absence of added water. The participation of water in the formation of molecular clusters with choline chloride and urea was indicated by viscosity, pH, and conductivity measurements. Hydrogen bond acceptor values of aqueous mixtures increased as a function of water content, and the results obtained using both methods were in line, indicating their suitability for the determination of hydrogen bond acidity of aqueous choline chloride-urea mixtures. However, hydrogen bond basicity determined by solvatochromic and magnetic methods exhibited almost opposite trends. The close investigation of the chemical shift of solvatomagnetic probes indicated that the chemical environment of the choline chloride-urea (1 : 2) mixture remained constant until the water content of 30 wt% was in line with previous molecular simulations. When cellulose fibers were treated with mixtures under mixing, the non-ideality of the choline chloride-urea mixture and the absence of water were found to be advantageous; however, aqueous mixtures efficiently increased the diameters of cellulose fibers in the absence of mixing, and water-containing mixtures appeared to be appealing systems for cellulose pretreatments.

Renewable Furfural-Based Polyesters Bearing Sulfur-Bridged Difuran Moieties with High Oxygen Barrier Properties.

With the goal of achieving high barrier with bio-based materials, for example, for packaging applications, a series of novel furfural-based polyesters bearing sulfide-bridged difuran dicarboxylic acid units with high oxygen barrier properties were synthesized and characterized. For the novel poly(alkylene sulfanediyldifuranoate)s, a 11.2-1.9× higher barrier improvement factor compared to amorphous poly(ethylene terephthalate) was observed which places the novel polyesters in the top class among previously reported 2,5-furandicarboxylic acid (FDCA) and 2,2'-bifuran-based polyesters. Titanium-catalyzed polycondensation reactions between the novel synthesized monomer, dimethyl 5,5'-sulfanediyldi(furan-2-carboxylate), and four different diols, ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, afforded difuran polyesters with high intrinsic viscosities (0.76-0.90 dL/g). These polyesters had good thermal stability, decomposing at 342-363 and 328-570 °C under nitrogen and air, respectively, which allowed processing them into free-standing films via melt-pressing. In tensile testing of the film specimens, tensile moduli in the range of 0.4-2.6 GPa were recorded, with higher values observed for the polyesters with shorter diol units. Interestingly, besides the low oxygen permeability, the renewable sulfide-bridged furan monomer also endowed the polyesters with slight UV shielding effect, with cutoff wavelengths of ca. 350 nm, in contrast to FDCA-based polyesters, which lack significant UV light absorption at over 300 nm.

Fast and Filtration-Free Method to Prepare Lactic Acid-Modified Cellulose Nanopaper.

Dewatering in the preparation of cellulose nanopapers can take up to a few hours, which is a notable bottleneck in the commercialization of nanopapers. As a solution, we report a filtration-free method that is capable of preparing lactic acid-modified cellulose nanopapers within a few minutes. The bleached cellulose nanofibers (CNFs), obtained using a Masuko grinder, were functionalized by sonication-assisted lactic acid modification and centrifuged at 14 000 rpm to achieve a doughlike, concentrated mass. The concentrated CNFs were rolled into a wet sheet and dried in a vacuum drier to obtain nanopapers. The nanopaper preparation time was 10 min, which is significantly faster than the earlier time period reported in the literature (up to a few hours of preparation time). The mechanical properties of nanopaper were comparable to the previous values reported for nanopapers. In addition, the method was successfully used to prepare highly conductive functional nanopapers containing carboxylated multiwalled carbon nanotubes.

A Fast Dissolution Pretreatment to Produce Strong Regenerated Cellulose Nanofibers via Mechanical Disintegration.

This study investigates a fast dissolution and regeneration pretreatment to produce regenerated cellulose nanofibers (RCNFs) via mechanical disintegration. Two cellulose pulps, namely, birch and dissolving pulps, with degree of polymerizations of 1800 and 3600, respectively, were rapidly dissolved in dimethyl sulfoxide (DMSO) by using tetraethylammonium hydroxide (TEAOH) as aqueous electrolyte at room temperature. When TEAOH (35 wt % in water) was added to the pulp-DMSO dispersion (pulp:DMSO and TEAOH:DMSO weight ratios of 1:90 and 1:9, respectively), 95% of the dissolving pulp and 85% of the birch pulp fibers dissolved almost immediately. Addition of water caused the regeneration of cellulose without any chemical modification and only a minor decrease of DP, whereas the crystallinity structure of cellulose transformed from cellulose I to cellulose II. The regenerated cellulose could then be mechanically disintegrated into nanosized fibers with only a few passes through a microfluidizer, and RCNF showed fibrous structure. The specific tensile strength of the film produced from both RCNFs exceeded 100 kN·m/kg, and overall mechanical properties of RCNF produced from birch pulp were in line with reference CNF produced by using extensive mechanical disintegration. Although the thermal stability of RCNFs was slightly lower compared to their corresponding original cellulose pulp, the onset temperature of degradation of RCNFs was over 270 °C.

Aqueous Modification of Chitosan with Itaconic Acid to Produce Strong Oxygen Barrier Film.

In this study, the chemical modification of chitosan using itaconic acid as a natural-based unsaturated dicarboxylic acid was investigated. In an aqueous environment, the amine group of chitosan reacts with itaconic acid to produce a chitosan derivative with pyrrolidone-4-carboxylic acid group. On the basis of the elemental analysis, 15% of the amine groups of chitosan reacted, thus creating modified chitosan with amine and carboxylic acid functionalities. Due to the presence of amine and carboxylic acid groups, the surface charge properties of the chitosan were notably altered after itaconic acid modification. In an aqueous solution, the modified chitosan exhibited zwitterionic properties, being cationic at low pH and turning anionic when the pH was increased over 6.5, whereas the original chitosan remained cationic until pH 9. Furthermore, it was demostrated that the modified chitosan was suitable for the preparation of a self-standing film with similarly high transparency but notably higher mechanical strength and oxygen barrier properties compared to a film made from the original chitosan. In addition, the thermal stability of the modified chitosan film was higher than that of the original chitosan film, and the modified chitosan exhibited flame-retardant properties.

Review: Periodate oxidation of wood polysaccharides-Modulation of hierarchies.

Periodate oxidation of polysaccharides has transitioned from structural analysis into a modification method for engineered materials. This review summarizes the research on this topic. Fibers, fibrils, crystals, and molecules originating from forests that have been subjected to periodate oxidation can be crosslinked with other entities via the generated aldehyde functionality, that can also be oxidized or reduced to carboxyl or alcohol functionality or used as a starting point for further modification. Periodate-oxidized materials can be subjected to thermal transitions that differ from the native cellulose. Oxidation of polysaccharides originating from forests often features oxidation of structures rather than liberated molecules. This leads to changes in macro, micro, and supramolecular assemblies and consequently to alterations in physical properties. This review focuses on these aspects of the modulation of structural hierarchies due to periodate oxidation.