Facile preparation of cellulose/lignosulfonate derivatives composite films with high UV-shielding and gas barrier properties

Herein, a serial of full cellulose and lignosulfonate derivatives (LS), including sodium lignosulfonate (LSS), calcium lignosulfonate (LSC), lignosulfonic acid (LSA), composite films were generated through dissolving cellulose in reversible carbon dioxide (CO₂) ionic liquids solvent system (TMG/EG/DMSO/CO₂ solvent system), followed by a facile solution-gelation transition and absorption strategy. The findings indicated that LS aggregated and embedded inside the cellulose matrix via H-bond interaction. The cellulose/LS derivatives composite films showed good mechanical properties which the tensile strength reaches the maximum value of 94.7 MPa in MCC3LSS film. While for the MCC1LSS film, the breaking strain increases to 11.6 %. The outstanding UV shielding effect and high transmittance in the visible region of composite films were also achieved and the shielding performance of the whole UV region (200-400 nm) tended to 100 % for MCC5LSS film. In addition, thiol-ene click reaction was selected as model reaction to verify the UV-shielding performance. It was also found that the oxygen and water vapor barrier performances of composite films were evidently associated with the intense H-bond interaction and tortuous path effect. The OP and WVP of MCC5LSS film were 0 and 6 × 10^-3 g·μm/m²·day·kPa, respectively. These outstanding properties make them with great potential for packaging field.

High value valorization of lignin as environmental benign antimicrobial

Lignin is a natural aromatic polymer of p-hydroxyphenylpropanoids with various biological activities. Noticeably, plants have made use of lignin as biocides to defend themselves from pathogen microbial invasions. Thus, the use of isolated lignin as environmentally benign antimicrobial is believed to be a promising high value approach for lignin valorization. On the other hand, as green and sustainable product of plant photosynthesis, lignin should be beneficial to reduce the carbon footprint of antimicrobial industry. There have been many reports that make use of lignin to prepare antimicrobials for different applications. However, lignin is highly heterogeneous polymers different in their monomers, linkages, molecular weight, and functional groups. The structure and property relationship, and the mechanism of action of lignin as antimicrobial remains ambiguous. To show light on these issues, we reviewed the publications on lignin chemistry, antimicrobial activity of lignin models and isolated lignin and associated mechanism of actions, approaches in synthesis of lignin with improved antimicrobial activity, and the applications of lignin as antimicrobial in different fields. Hopefully, this review will help and inspire researchers in the preparation of lignin antimicrobial for their applications.

Modification of Paper Surface by All-Lignin Coating Formulations

All-lignin coating formulations were prepared while combining water-soluble cationic kraft lignin (quaternized LignoBoost®, CL) and anionic lignosulphonate (LS). The electrostatic attraction between positively charged CL and negatively charged LS led to the formation of insoluble self-organized macromolecule aggregates that align to films. The structures of the formed layers were evaluated by atomic force microscopy (AFM), firstly on glass lamina using dip-coating deposition and then on handsheets and industrial uncoated paper using roll-to-roll coating in a layer-by-layer mode. Coated samples were also characterized by optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (SEM/EDS), and contact angle measurements. It was suggested that the structure of all-lignin aggregates is the result of the interaction of amphiphilic water-soluble lignin molecules leading to their specifically ordered mutual arrangement depending on the order and the mode of their application on the surface. The all-lignin coating of cellulosic fiber imparts lower air permeability and lower free surface energy to paper, mainly due to a decrease in surface polarity, thus promoting the paper's hydrophobic properties. Moderate loading of lignin coating formulations (5-6 g m-2) did not affect the mechanical strength of the paper.

Optimized preparation of spruce kraft lignin/ZnO composites and their performance analysis in polyurethane films

Spruce kraft lignin (SKL) has received considerable attention in recent years for its application in the field of polymer materials. However, its structural complexity and polydispersity pose significant challenges for commercial applications. In this study, molecular structure models of acetone soluble kraft lignin (ASKL) and acetone insoluble kraft lignin (AIKL) were proposed based on quantitative calculations of the connection mode of functional groups and structural units. The lignin was modified by quaternization and synthesized in situ as lignin/ZnO composites. Based on the detailed characterization of the micromorphology and structure of the composites, waterborne polyurethane (WPU) films were optimally prepared using 0.6 wt% of the composites. The results showed that the composite films prepared from ASKL have the best UV-blocking performance and mechanical properties. The highest UVA and UVB blocking rates were 98% and 100%, respectively, and the highest tensile strength and elongation at break were 31.2 MPa and 732%, respectively. The differences in the structure and functional groups of the different types of SKL were accurately identified. ASKL is advantageous for the development of UV-blocking films because of its low molecular weight and the presence of abundant phenolic hydroxyl groups, which facilitate the formation of hydrogen bonds, improve the compatibility, and ensure uniform dispersibility. The results of this study are of practical importance in the field of nano-functional materials for the high-value application of industrial lignin.

Lignin-Mediated Silver Nanoparticle Synthesis for Photocatalytic Degradation of Reactive Yellow 4G and In Vitro Assessment of Antioxidant, Antidiabetic, and Antibacterial Activities

This study explored the potential of abundantly available sodium lignosulfonate (LS) as a reducer and fabricating agent in preparing silver nanoparticles (LS–Ag NPs). The operational conditions were optimized to make the synthesis process simpler, rapid, and eco-friendly. The prepared LS–Ag NPs were analyzed via UV–Vis spectroscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy. Results demonstrated that LS–Ag NPs were of crystalline structure, capped with LS constituents, and spherical in shape with a size of approximately 20 nm. Under optimized conditions, LS–Ag NPs exhibited significant photocatalytic activity in Reactive Yellow 4G degradation. The effects of photocatalyst (LS–Ag NPs) dosage, dye concentration, and its reusability for dye degradation were studied to make the process practically applicable in textile wastewater treatment. Additionally, the synthesized LS–Ag NPs displayed significant free radical scavenging against 2-diphenyl-1-picrylhydrazyl (DPPH) with an IC₅₀ value of (50.2 ± 0.70 µg/mL) and also exhibited antidiabetic activity in terms of inhibition in the activity of carbohydrate-degrading marker enzyme α-glucosidase with an IC₅₀ value of (58.1 ± 0.65 µg/mL). LS–Ag NPs showed substantial antibacterial potential against pathogenic strains, namely E. coli and S. aureus. In conclusion, LS–Ag NPs can be a reliable and eco-friendly material for their possible application in the treatment of dye-containing wastewater and have a great perspective in the biomedical and pharmaceutical sectors.

Fabrication of litchi-like lignin/zinc oxide composites with enhanced antibacterial activity and their application in polyurethane films

Lignin has been demonstrated to be green and effective for the modification of ZnO-based materials. In this work, quaternized lignin/zinc oxide nanostructured hybrid composites (QLS/ZnO NCs) were synthesized with good dispersion and uniform particle size via a facile hydrothermal method. Sodium lignosulfonate (LS) was modified by quaternization to endow the positive charges, which effectively captured bacteria due to the electrostatic interactions. Interestingly, QLS/ZnO NCs show a litchi-like morphology consisting of nanorods with diameters of 5-10 nm, which further resulted in damage to the bacterial cell membrane. Owing to the surface charge and rough surface topology for bacterial capture, QLS/ZnO NCs exhibited greatly enhanced antibacterial activity compared with bare ZnO. After being treated with QLS/ZnO NCs for 90 min, the sterilization rates of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) reached 97.54% and 99.55%, respectively. Due to the reactive oxygen species (ROS) produced by ZnO under light irradiation, the antibacterial activity of QLS/ZnO NCs could be further enhanced. In addition, the minimal inhibition concentrations (MICs) of QLS/ZnO NCs towards E. coli and S. aureus were both 100 μg/mL, and the minimum bactericidal concentrations (MBCs) were 100 μg/mL and 200 μg/mL, respectively. Moreover, with the incorporation of QLS/ZnO NCs into polyurethane films, the composite films showed excellent antibacterial activity, strong tensile strength and enhanced ultraviolet light blocking performance.

Design and Preparation of Multiple Function-Integrated Lignin/Tannin/ZnONP Composite Coatings for Paper-Based Green Packaging

Lignin/tannin/ZnONP composite coatings were designed for paper-based green packaging. Multiple functions, such as high strength, moisture resistance, low air permeance, heat endurance, UV aging resistance, and antibacterial/mold properties, were successfully integrated into one biobased coating. Prepolymerization improved the physical properties of coatings at high lignin contents. The best ingredient ratio was: 40% lignin, 15% tannin, and 10% ZnONPs (based on tannin weight), and the as-prepared biocoating was labeled LTZn-10. After coated with LTZn-10, the tensile strength and bursting strength of the packaging were efficiently enhanced by more than 3 times and were dramatically increased by 51.6 and 5.6 times at the wet state, respectively, which reveals that the packaging has favorable moisture resistance and it can be used in high humidity environments. Scanning electron microscopy (SEM) proved that most of the pores on the paper were blocked by the coatings, which helped to decrease the air permeance by 10.3 times. Meanwhile, ZnONPs were evenly spread on the coatings, which endowed the packaging with excellent antibacterial/mold performance. No colony or mycelium was found in the test against Gram-negative/positive bacteria and eight common molds. Besides, antibacterial activity is only available while the bacteria come in contact with the coating and no active substances were released into the culture medium, which is a good property that can keep the cargo from contamination of antibacterial agents. In addition, the coated paper presented an improved T_g and thermal degradation temperature, indicating that the coated package has favorable thermostability and can maintain its outstanding physical properties in a wider temperature range. Lignin and tannin promoted the UV stability and service life of the coated paper, as a rare physical decrease was observed after UV aging for 72 h. The function-integrated biobased coating with favorable sustainability is a good candidate to be widely used in paper-based green packaging fields.

Improving air barrier, water vapor permeability properties of cellulose paper by layer-by-layer assembly of graphene oxide

A paper-based packaging material with improved air barrier and water vapor permeability (WVP) properties was synthesized based on layer-by-layer assembly consisted of poly(ethylenimine) (PEI)/graphene oxide (GO) on a filter paper substrate. The effect of the pH of GO suspension on the zeta potential and air permeability (AP) of the modified paper was investigated in detail. The results indicated that the pH of GO suspension resulted in significant difference in the AP of the modified paper. Compare with the pristine paper, the AP of the modified paper with (PEI/GO)₁₀ multilayer films synthesized at pH 2.5 decreased by 99.99 %, while the WVP increased by 15.82 %. The modified paper as packaging material could prolong the shelf-life of oyster mushroom, indicating the modified paper has huge potential application on the preservation of agricultural products.

One-step synthesis of strongly confined, defect-free and hydroxy-terminated ZnO quantum dots

This paper reports the production of strongly confined ligand-free, defect-free, hydroxy-terminated ZnO quantum dots with a mean diameter of 1.9 nm, by radio frequency atmospheric pressure microplasma. Systematic characterization is performed to understand the surface chemistry of ZnO quantum dots. Photoluminescence studies show strong confinement effect on emission with only ultraviolet (UV) emission without any defect-related visible emission. Emission is again tested after eighteen months and confirms the QDs long-term emission stability. The mechanism responsible for this UV emission is also discussed and originates from OH-related surface terminations.

Assessing metal-lignosulfonates as fertilizers using gel filtration chromatography and high-performance size exclusion chromatography

Lignosulfonates (LSs) are by-products from the paper industry used as biodegradable fertilizers. However, metal-LS ability to provide micronutrients to crops is related to the stability of the complex and the amount of metal complexed. This work evaluated these parameters using ultraviolet-visible (UV-Vis), Fourier-transform infrared (FTIR), and ¹³C-nuclear magnetic resonance (NMR), along with gel filtration chromatography (GFC) and high-performance size exclusion chromatography (HPSEC), for different spruce, eucalyptus, and pine LSs. GFC and HPSEC pointed out that the amount and type of complexed metal in the LS depends on the molecular weight, pH, and sulphite pulping processes. Both techniques indicated that the low molecular weight LS enriched with phenolic groups has the highest Fe(III) complexing capacity. Also, Fe(III)/LS showed the formation of high molecular weight compounds, whereas Zn(II)/LS and Mn(II)/LS complexes did not form aggregates. Metal-LS fractionation provided considerable information to identify LSs with potential fertilizer capacity and to assess the effectiveness of their complexes.

Construction of Antifouling Membrane Surfaces through Layer-by-Layer Self-Assembly of Lignosulfonate and Polyethyleneimine

Lignin is the second most abundant and low-cost natural polymer, but its high value-added utilization is still lack of effective and economic ways. In this paper, waste lignosulfonate (LS) was introduced to fabricate antifouling membrane surfaces via layer-by-layer self-assembly with polyethyleneimine (PEI). The LS/PEI multilayers were successfully deposited on the polysulfone (PSf) membrane, as demonstrated by ATR-FTIR, XPS, Zeta potential measurements, AFM, and SEM. Meanwhile, the effect of the number of bilayers was investigated in detail on the composition, morphologies, hydrophilicity, and antifouling performance of the membrane surface. As a result, with the bilayer numbers increase to 5, the PSf membrane shows smooth surface with small roughness, and its water contact angle reduces to 44.1°, indicating the improved hydrophilicity. Accordingly, the modified PSf membrane with 5 LS/PEI bilayers repels the adsorption of protein, resulting in good antifouling performance. This work provides a green, facile, and low-cost strategy to construct antifouling membrane surfaces.

Enhanced antibacterial profile of nanoparticle impregnated cellulose foam filter paper for drinking water filtration

Filtration is a promising water treatment method to purify drinking water. To develop highly efficient drinking water filter paper, water-resistant cellulose foam paper with a high wet strength property was fabricated using diverse metal oxide (e.g., copper oxide (CuO), zinc oxide (ZnO), and silver oxide (Ag₂O)) nanoparticles. These nanoparticles were synthesized using the hydrothermal reaction method. Their morphological structures were studied using a field emission scanning electron microscope (FESEM). The presence of coated nanoparticles on the cellulose foam filter was verified by energy dispersive X-ray spectroscopy (EDX) methods. The antibacterial performance of different types of modified cellulose foam filters was studied against E. coli, P. aeruginosa, B. subtilis, and B. cereus strains using the zone of inhibition test. The antibacterial profile of the cellulose foam filter impregnated with Ag₂O nanoparticles, when tested against different types of bacteria, exhibited higher antibacterial activity than the cellulose foam filter impregnated with ZnO and CuO nanoparticles.

Rhelogical and antibacterial performance of sodium alginate/zinc oxide composite coating for cellulosic paper

Coating of antibacterial layer on the surface of cellulosic paper has numerous potential applications. In the present work, sodium alginate (SA) served as a binder to disperse Zn²⁺ and the prepared zinc oxide (ZnO) particles were used as antibacterial agents. The rheology test revealed that there were cross-linking between Zn²⁺ and SA molecular chains in the aqueous solution, resulting in the viscosity of ZnO/SA composite coating increased in the low shear rate region and decreased in the high shear rate region as compared with pure SA. SEM and EDS mapping images showed that the ZnO particles were prepared successfully at 120 °C and dispersed homogeneously on the surface of cellulose fibers and the pores of cellulosic papers. The thermal stabilities of the coated papers decreased as compared to the original blank cellulosic paper, which was ascribed to the low thermal stability of SA and the catalytic effect of ZnO on SA. The tensile stress and Young's modulus of ZnO/SA composite coated paper increased up 39.5% and 30.7%, respectively, as compared with those of blank cellulosic paper. The antibacterial activity tests indicated that the ZnO/SA composite coating endowed the cellulosic paper with effectively growth inhibition of both Gram-negative bacteria E. coli and Gram-positive bacteria S. aureu.

Anti-microbial surfaces: An approach for deposition of ZnO nanoparticles on PVA-Gelatin composite film by screen printing technique

Initially micro-organisms get exposed to the surfaces, this demands development of anti-microbial surfaces to inhibit their proliferation. Therefore, herein, we attempt screen printing technique for development of PVA-GE/ZnO nanocomposite (PG/ZnO) films. The synthesis of PG/ZnO nanocomposite includes two steps as: (i) Coating of Zinc Oxide nanoparticles (ZnO NPs) by poly ethylene glycol in order to be compatible with organic counterparts. (ii) Deposition of coated nanoparticles on the PG film surface. The results suggest the enhancement in anti-microbial activity of PG/ZnO nanocomposite over pure ZnO NPs against both Gram positive Bacillus subtilis and Gram negative Escherichia coli from zone of inhibition. The uniformity in deposition is further confirmed by scanning electron microscopy (SEM) images. The phase identification of ZnO NPs and formation of PG/ZnO nanocomposite has been confirmed by X-ray diffraction (XRD) analysis and UV-vis spectroscopy (UV-vis). The Attenuated total reflection Spectroscopy (ATR) analysis indicates the ester bond between PVA and gelatin molecules. The thermal stability of nanocomposite is studied by thermogravimetric analysis (TGA) revealing increase in crystallinity due to ZnO NPs which could be utilized to inhibit the growth of micro-organisms. The tensile strength is found to be higher and percent elongation is double of PG/ZnO nanocomposite than PG composite film.