Preparation and characterization of zwitterion-substituted lignin/Nafion composite membranes.

In this study, a novel zwitterion-substituted lignin (ZL) containing amino and sulfonic acid groups was synthesized, and ZL/Nafion composite membranes were fabricated as proton exchange membranes. Kraft lignin was modified using an aminosilane and 1,3-propanesultone via a continuous grafting reaction to provide zwitterionic moieties. Chemical structural analyses confirmed the successful introduction of the zwitterion moiety into lignin. In particular, the surface charge of ZL is positive in an acidic medium and negative in a basic medium, suggesting that ZL is a zwitterionic material. ZL was incorporated into a Nafion membrane to enhance its ion exchange capacity, thermal stability, and hydrophilicity. The proton conductivity of ZL/Nafion 0.5 %, 151.0 mS/cm, was 55.3 % higher than that of unmodified ML (methanol-soluble lignin)/Nafion 0.5 % (97.2 mS/cm), indicating that the zwitterion moiety of ZL enhances the proton transport ability. In addition, oxidative stability evaluation confirmed that ZL/Nafion 2 % was chemically more durable than pure Nafion. This confirmed that using lignin as a membrane additive yielded positive results in terms of chemical durability and oxidation stability in Nafion. Therefore, ZL is expected to be utilized as a multifunctional additive and exhibits the potential for fuel cell applications.

Multi-physics coupling reinforced polyvinyl alcohol/cellulose nanofibrils based multifunctional hydrogel sensor for human motion monitoring.

Ionic conductive hydrogels have been widely used for sensor, energy storage and human-machine interface. To address the problems of the traditional ionic conductive hydrogels fabricated with the soaking method, such as the lack of frost resistance, poor mechanical properties, time-consuming and chemical-wasting, herein, a multi-physics crosslinking reinforced strong, anti-freezing and ionic conductive hydrogel sensor is fabricated utilizing the tannin acid-Fe2(SO4)3 through the simple one-pot freezing-thawing process at low electrolyte concentration. The results show that the P10C0.4T8-Fe2(SO4)3 (PVA10%CNF0.4%TA8%-Fe2(SO4)3) displayed better mechanical property and ionic conductivity due to hydrogen bonding and coordination interaction. The tensile stress reaches up to 0.980 MPa (570 % strain). Moreover, the hydrogel presents excellent ionic conductivity (0.220 S⋅m-1 at room temperature), anti-freezing performance (0.183 S⋅m-1 at -18 °C), large gauge factor (1.75), excellent sensing stability, repeatability, durability and reliability. This work paves a way for preparing mechanical strong and anti-freezing hydrogel based on multi-physics crosslinking with one-pot freezing-thawing process.

Yielding and thixotropic cellulose microgel-based network in high-content surfactant for stably suspending of functional beads.

Functional particles, such as microcapsules of perfumes, enzymes, or anti-mite agents, are desired to stably suspend in the high-content surfactant solution, providing additional functionalities for household products. Due to the disassociation of high-content surfactant, most linear or branched polymers would fail to modify the rheological properties of the high-content surfactant solution, especially for the suspending ability. In this research, the 2,2,6,6-tetramethylpiperidine-1-oxyl oxidized bacterial cellulose microgel (T-microgel) and hydroxypropyl methylcellulose (HPMC) were employed as "island" and "chain," respectively, which could self-assemble together to fabricate a yield and thixotropic continuous network in a high-content surfactant solution. The suspending ability of microgel in high-content surfactant is better than cellulose nanofiber and carboxymethylcellulose. This is the first time to report a cellulose microgel-based rheological modifier. T-microgel/HPMC synthetic system mixed with high content surfactant presented a typical Carreau-Yasuka fluid. Meanwhile, the effects of the HPMC and surfactant on the rheological properties of the combined system were investigated, and an optimal ratio for the 'island'/'chain' synthetic system was found to modify its yield and thixotropy behavior successfully. The potential application of this combined system was explored and found to work with all kinds of surfactants at high concentrations, which is more advantageous than most commercial suspending agents.

Preparation of amine-functionalized lignins for the selective adsorption of Methylene blue and Congo red.

Research on low-cost bio-adsorbents for the removal of harmful substances from effluents has recently attracted significant attention. In this study, three types of amino-silane-modified lignins (ASLs) with primary, secondary, and tertiary amine groups were prepared, and their adsorption behavior toward cationic and anionic dyes was investigated. Chemical structural analyses indicated that the three amino-silane reagents resulted in different molecular self-assembly structures on the lignin surface. The ASLs exhibited enhanced thermal stabilities and increased surface areas with different surface charges in different pH ranges. Owing to the high density of primary, secondary, and tertiary amine groups, the ASLs exhibited excellent adsorption capacities for cationic and anionic dyes. Additionally, they selectively adsorb anionic and cationic dyes according to the pH conditions. The ASL with primary amine had the highest adsorption capacity for Methylene blue and Congo red, reaching 187.27 and 293.26 mg·g-1, respectively, followed by ASLs with the secondary amine and tertiary amine. All adsorption processes followed the Langmuir and Temkin isotherms and had pseudo-second-order kinetics. The hypothesized adsorption mechanism mainly involves electrostatic interaction, NH-π interaction, hydrogen bonding interaction and π-π interaction.

One-step silanization and amination of lignin and its adsorption of Congo red and Cu(II) ions in aqueous solution.

In this work, silanized and aminated lignin (SAL) was synthesized in one step and its adsorption of Congo red and Cu(II) ions in aqueous solution was explored. Lignin was subjected to amine-silanization with (3-aminopropyl) triethoxysilane (APTES). Structural characterization substantiated successful amine-silanzation of lignin and formation of multi-layer APTES intermolecular crosslinked structure. The prepared SAL (nitrogen content = 6.1%) exhibited enhanced molecular weight, thermal stability, and water- and organic solvent-resistance properties. Additionally, the present of the porous structure of particle surface and an increase in the specific surface area and zeta potential promoted the accessibility of contaminants to the effective adsorption sites of SAL. Adsorption experiments showed that both Congo red and Cu(II) ion could be completely removed at original pH value, and their adsorption involved electrostatic attraction and complexation, respectively. The adsorption isotherms and kinetics were well described by the Langmuir and pseudo-second-order equations, respectively. The results showed that SAL is a promising adsorbent for the treatment of effluents.

Fractionation of enzymatic hydrolysis lignin by sequential extraction for enhancing antioxidant performance.

The heterogeneity of lignin chemical structure and molecular weight results in the lignin inhomogeneous properties which also covers the antioxidant performance. In order to evaluate the effects of lignin heterogeneity on its antioxidant activity, four lignin fractions from enzymatic hydrolysis lignin were classified by sequential organic solvent extraction and further evaluated by DPPH (1,1-Diphenyl-2-Picrylhydrazyl) free radical scavenging capacity and reducing power analysis. The characterization including FTIR, 1H NMR and GPC showed that the fractionation process could effectively separate lignin fractions with distinctly different molecular weight and weaken the heterogeneity of unfractionated lignin. The antioxidant performance comparison of lignin fractions indicated that the dichloromethane fraction (F1) with lowest molecular weight (4585g/mol) and highest total phenolics content (246.13mg GAE/g) exhibited the highest antioxidant activity whose value was close to commercial antioxidant BHT (butylated hydroxytoluene). Moreover, the relationship between the antioxidant activity and the structure of lignin was further discussed to elucidate the mechanism of antioxidant activity improvement of lignin fractionation. Consequently, this study suggested that the sequential extraction was an effective way to obtain relatively homogeneous enzymatic hydrolysis lignin fractions which showed the potential for the value-added antioxidant application.