High performance PVA/lignin nanocomposite films with excellent water vapor barrier and UV-shielding properties

Sprayable oxidized polyvinyl alcohol with improved degradability and sufficient mechanical property for fruit preservation

Besides their limited preservation capacity and low biosafety, traditional fruit preservation procedures exacerbate "white pollution" because they utilize excessive plastic. Herein, an environmentally friendly one-pot method was developed to obtain degradable polyvinyl alcohol (PVA), where the hydroxyl radicals generated through the reaction between hydrogen peroxide (H2O2) and iron ions functioned to oxidize PVA. The oxidized PVA (OPVA-1.0) with abundant ketone groups, reduced crystallinity, and short molecular chains was completely degraded into H2O and CO2 after being buried in the soil for ∼60 days. An improvement in its degradation rate did not weaken the mechanical properties of OPVA-1.0 compared to other modified PVA films because the adverse effect of decreased crystallinity on its mechanical performance was offset by its ion coordination. Alternatively, the tensile strength or toughness of OPVA-1.0 was enhanced due to its internal multi-level interactions including molecular chain entanglement, hydrogen bonding, and metal coordination bonds. More interestingly, OPVA-1.0 was water-welded into various products in a recyclable way owing to its reversible physical bonds, where it was sprayed, dipped, or brushed conformally onto different perishable fruits to delay their ripening by 5-14 days. Based on the cellular biocompatibility and biosafety evaluations in mice, OPVA-1.0 obtained by the facile oxidation strategy was demonstrated to alleviate "white pollution" and delay the ripening of fruits effectively.

Strategies for the incorporation of organosolv lignin in hydroxypropyl methylcellulose-based films: A comparative study

Organosolv lignin extracted from vine pruning residues was added to hydroxypropyl methylcellulose (HPMC)-based films using three strategies: i) lignin incorporated into the film (lignin-based film), ii) lignin nanoparticles (LNPs) incorporated into the film (LNPs-based film), and iii) lignin coated on HPMC films' surface (lignin-coated film). The films obtained were evaluated in terms of morphology, water barrier and mechanical properties, and antioxidant capacity. Results showed that LNPs incorporation did not affect the films´ water vapour permeability (WVP). Nonetheless, the lignin-based and lignin-coated films improved the water barrier properties of HPMC-based films, achieving a 31.5 and 36 % reduction of WVP, respectively. The morphological evaluation, performed by scanning electron microscopy, revealed films' morphology changes with the lignin incorporation, which was more evident in the lignin-based films. Fourier transform infrared spectroscopy (FTIR) showed minor changes in the film's structure using the different lignin incorporation methods. The mechanical properties were improved, including a significant increase in the tensile strength in the lignin-based and lignin-coated films. All films showed high radical scavenging activity (RSA) after 24 h, with a gradual increase in the lignin-coated films over time. The lignin-coated films showed to be the most promising incorporation strategy to improve the HPMC-based film's properties.

A demethylated lignin improved PVA-based supramolecular plastic with tough, degradable, and water-resistant performances

Poly (vinyl alcohol) (PVA), as an excellent degradable plastic feedstock, is limited by its diminishing stability in wet environment, low strength, thermal instability and nonopaque properties. In response to these concerns, a PVA/demethylated lignin-based supramolecular plastic (DPVA-HA-Fe-5) was designed and produced from PVA, demethylated lignin (DL), humic acid (HA) and Fe3+ ions via a simple casting method. As compared with pure PVA plastic, the tensile strength of DPVA-HA-Fe-5 were increased by 411 % to 410.61 MPa, and the breaking strain was increased by 149 % to 239.47 %. Notably, the hydrophobicity of DPVA-HA-Fe-5 was also significantly improved. Although in highly humid environment (stored in RH = 100 % for 10 days) or in alkaline organic solvent (stored in pyridine for 3 h), DPVA-HA-Fe-5 also showed excellent mechanical strengths of 302.9 and 222.99 MPa, respectively, which are equivalent or even superior to the most of commercial petroleum-based plastics. Moreover, the prepared plastics showed an outstanding UV resistance and shading performance, and about 98.3 % protection against ultraviolet radiation B rays and 90.7 % protection against visible light were obtained. In short, the introduction of lignin to improve the performance of PVA-based plastic is a feasible method, and it could facilitate the development of high-value utilization of lignin.

Lignin-Based Composite Film and Its Application for Agricultural Mulching

Agricultural mulching is an important input for modern agricultural production and plays an important role in guaranteeing food security worldwide. At present, polyethylene (PE) mulching is still commonly used in agricultural production in most countries around the world, which is non-biodegradable, and years of mulching have caused serious agricultural white pollution. Lignin is one of the three major components of plant cell walls, and it is also the main renewable natural aromatic compounds in nature. Lignin-based composite film materials are green, biodegradable, and show good prospects for development in the field of agricultural mulch. This paper introduces the types, structure, and application status of lignin, summarizes the preparation of lignin-based composite film materials and its latest research progress, focuses on the types, preparation methods, and application examples of lignin-based agricultural mulching, and looks forward to the future development prospects of lignin-based agricultural mulching.

UV-blocking, antibacterial, corrosion resistance, antioxidant, and fruit packaging ability of lignin-rich alkaline black liquor composite film

The novel multifunctional active packaging composite film with antimicrobial, antioxidant, water-vapor and UV-barrier, and corrosion resistance properties was successfully prepared from waste biomass. In this study, waste poplar sawdust was pretreated using green liquor to extract black liquor (BL). BL was then mixed with polyvinyl alcohol (PVA) solution for synthesizing silver nanoparticles (AgNPs). PVA-BL-AgNPs film was fabricated by solution casting method, and the microstructure characterization and macroscopic performance testing of the composite film were conducted. The results revealed that PVA-BL-AgNPs film exhibited inhibitory effects against Staphylococcus aureus (inhibition zone: 33.6 mm), Pseudomonas aeruginosa (inhibition zone: 31.6 mm), and Escherichia coli (inhibition zone: 32.0 mm). It could eliminate over 99 % of 2,2-diazodi (3-ethyl-benzothiazol-6-sulfonic acid) (ABTS) free radicals and provided 100 % UV-blocking, reducing light-induced food damage. It exhibited the improvement of water-vapor barrier properties and corrosion resistance. In vitro cytotoxicity assays demonstrated that no significant impact occurred on cell proliferation, confirming the safety of the film. Packaging experiments showed that PVA-BL-AgNPs film effectively inhibited milk spoilage and prolonged the shelf-life of bread and bananas. Therefore, PVA-BL-AgNPs film might extend the shelf-life of food and offer significant opportunities in addressing the issues of low safety and environmental pollution associated with traditional packaging films.

Overcoming Challenges of Lignin Nanoparticles: Expanding Opportunities for Scalable and Multifunctional Nanomaterials

ConspectusThe increasing demand for polymeric materials derived from petroleum resources, along with rising concerns about climate change and global plastic pollution, has driven the development of biobased polymeric materials. Lignin, which is the second most abundant biomacromolecule after cellulose, represents a promising renewable raw material source for the preparation of advanced materials. The lucrative properties of lignin include its high carbon content (>60 atom %), high thermal stability, biodegradability, antioxidant activity, absorbance of ultraviolet radiation, and slower biodegradability compared to other wood components. Moreover, the advent of lignin nanoparticles (LNPs) over the last ten years has circumvented many well-known shortcomings of technical lignins, such as heterogeneity and poor compatibility with polymers, thereby unlocking the great potential of lignin for the development of advanced functional materials.LNPs stand out owing to their well-defined spherical shape and excellent colloidal stability, which is due to the electrostatic repulsion forces of carboxylic acid and phenolic hydroxyl groups enriched on their surface. These forces prevent their aggregation in aqueous dispersions (pH 3-9) and provide a high surface area to mass ratio that has been exploited to adsorb positively charged compounds such as enzymes or polymers. Consequently, it is not surprising that LNPs have become a prominent player in applied research in areas such as biocatalysis and polymeric composites, among others. However, like all ventures of life, LNPs also face certain challenges that limit their potential end-uses. Solvent instability remains the most challenging aspect due to the tendency of these particles to dissolve or aggregate in organic solvents and basic or acidic pH, thus limiting the window for their chemical functionalization and applications. In addition, the need for organic solvent during their preparation, the poor miscibility with hydrophobic polymeric matrices, and the nascent phase regarding their use in smart materials have been identified as important challenges that need to be addressed.In this Account, we recapitulate our efforts over the past years to overcome the main limitations mentioned above. We begin with a brief introduction to the fundamentals of LNPs and a detailed discussion of their associated challenges. We then highlight our work on: (i) Preparation of lignin-based nanocomposites with improved properties through a controlled dispersion of LNPs within a hydrophobic polymeric matrix, (ii) Stabilization of LNPs via covalent (intraparticle cross-linking) and noncovalent (hydration barrier) approaches, (iii) The development of an organic-solvent-free method for the production of LNPs, and (iv) The development of LNPs toward smart materials with high lignin content. Finally, we also offer our perspectives on this rapidly growing field.

Fabrication of PVA-Silica Sol Wood Composites via Delignification and Freezing Pretreatment

The efficient exploitation of planted fast-growing wood is crucial for enhancing wood resource utilization. In this study, the fast-growing poplar wood was modified by in situ impregnation through vacuum impregnation with polyvinyl alcohol and nano-silica sol as impregnation modifiers, combined with delignification-freezing pretreatment. The samples were characterized by FTIR, XRD, SEM, and the universal mechanical testing machine. The results showed that the wrinkle deformation and cracking of the wood blocks were greatly alleviated after the delignification-freezing pretreatment and the polyvinyl alcohol and nano-silica sol were successfully integrated into the wood. The resulting polyvinyl alcohol-silica sol poplar composites exhibited about 216%, 80% and 43% higher compressive strength with respect to delignified wood, natural wood and impregnated natural wood, respectively, thereby demonstrating superior mechanical properties and potential opportunities for value-added and efficient utilization of low-quality wood.

Self-Formation of Lignin Particles Through Melt-Extrusion for Active Biodegradable Food Packaging

This study presents a method for the self-formation of lignin particles within a polylactic acid (PLA) matrix during melt-extrusion, eliminating the need for separation and drying steps typically associated with submicro-size lignin particles. This method effectively mitigates the problem of agglomeration often associated with the drying step. Softwood kraft lignin, guaiacyl lignin (GL-lignin), was dissolved in low-molecular-weight poly(ethylene glycol) (PEG) and was introduced into a twin-screw extruder using a liquid feeder. Lignin particles within a particle size range of 200-500 nm were observed in the extrudate of the PLA/PEG/GL-lignin composites. PLA/PEG/GL-lignin composite films were produced through blown film extrusion. These composite films demonstrated superior ultraviolet (UV)-barrier and antioxidant properties compared to neat PLA films, with optical and mechanical characteristics comparable to those of neat PLA. Moreover, migration values of the composite films in various food simulants were below regulatory limits, suggesting their potential for food packaging applications. This self-formation process offers a promising approach for utilizing lignin for PLA applications.

Effect of post-heat treatment on the UV transmittance, hydrophobicity, and tensile properties of PVA/Uncaria gambir extract blend films

The physical and mechanical properties of biopolymers can be improved by heating technologies. In this research, we improved the properties of Polyvinyl alcohol (PVA)/Uncaria gambir extract (UGE) blend films by post-heating method. After post-heating, the blend film exhibited higher resistance to UV light and improved contact angle performance, while water vapor permeability and moisture absorption decreased. The tensile strength and toughness of the PVA/UGE blend film with a post-heating duration of 40 min were 68.8 MPa and 57.7 MPa, respectively, an increase of 131 % and 127 %, compared to films without post-heating. This facile and cost-effective fabrication method, with environmentally friendly properties, can be applied to biodegradable PVA/UGE blend films to achieve desired properties for optical devices or food packaging materials.

High performance polyvinyl alcohol/lignin fibers with excellent mechanical and water resistance properties

To address the shortcoming of Polyvinyl alcohol (PVA) fibers for food or medical packaging materials including low mechanical strength and poor water resistance, lignin (LN) was used as raw material, acetone/H2O as solvent to self-assemble into lignin nanoparticles (LNP) by adverse solvent precipitation approach, and then PVA/LNP composite fibers with different LNP contents were fabricated successfully by wet and dry spinning. Herein, vast hydrophilic hydroxyl groups in PVA decreased owing to the hydrogen bond between LN and PVA, Especially, with only 0.5 wt% loading of LNP into the PVA/LNP fibers, the diameter was 94.4 dtex, tensile strength was 10.1 cN/dtex (1279.8 MPa), initial modulus was 94.7 cN/dtex (12.0 GPa), the crystallinity was 56.7 %, the orientation was 97.1 %, and water contact angle was 103.1°. Compared with pure PVA fibers, the tensile strength of PVA/LNP-0.5 fibers was increased by 44.2 % and the contact angle was increased 37°. This work provides novel insights into obtaining lignin-reinforced PVA composite fibers with strong mechanical properties and excellent water resistance properties, indicating the potential of the PVA/LNP fibers for food or medical packaging application.

Melt-processable polyvinyl alcohol/lignin composites with improved strength via synergistic plasticization of lignin

The characteristics of multi-hydroxyl structure and strong hydrogen bonding in polyvinyl alcohol (PVA) make its melting point close to its decomposition temperature, causing melt-processing difficulty. In this work, following the plasticization of small-molecule primary plasticizer acetamide, lignin was demonstrated as a green secondary plasticizer in realizing the melt processing and simultaneous reinforcement of PVA. During the plasticization process, lignin was able to combine with the hydroxyl groups of PVA, so as to destroy the hydrogen bonds and regularity of the PVA chains. The synergistic plasticization effect of lignin dramatically reduced the melting point of PVA from 185 °C to 151 °C. The thermal processing window of PVA composites was expanded from 50 °C to roughly 80 °C after introducing lignin. In contrast to acetamide, the addition of lignin significantly increased the tensile strength and Young's modulus of the composites to 71 MPa and 1.34 GPa, respectively. Meanwhile, lignin helped to hinder the migration of acetamide via hydrogen bonds. With the addition of lignin, the composites also displayed enhanced hydrophobicity and excellent UV shielding performance. The strategy of synergistic plasticization of lignin provides a feasible basis for the practical application of lignin in melt-processable PVA materials with good comprehensive properties.

Lignin-derived carbon quantum dot/PVA films for totally blocking UV and high-energy blue light

Excessive exposure to UV and high-energy blue light (HEBL) can cause fatal eye and skin injuries. As a result, it is crucial to protect our bodies from UV and HEBL radiation. To achieve complete blocking of UV and HEBL, we developed a lignin-derived carbon quantum dot (L-CQD)/polyvinyl alcohol (PVA) film. L-CQD was synthesized from lignin, a waste woody biomass, and then blended with a PVA matrix to create a flexible L-CQD/PVA film. Thanks to simultaneous UV and HEBL absorption characteristics and bright color of L-CQD, the PVA film with 0.375 wt% L-CQD demonstrated outstanding blocking efficiency: 100 % in UV-C, UV-B, and UV-A, and at least 99.9 % in HEBL. It also exhibited a 44 % increase in lightness and a 12 % enhancement in transparency compared to lignin/PVA film. The film's ability to block UV and HEBL was further demonstrated by reducing >40 % UV-induced ROS formation in both cancerous and normal cell lines (Hs 294T, HeLa, CCD-986sk, and L929), as well as by blocking blue laser diode (LD) and LED. Since the L-CQD/PVA film is simple to produce, environmentally friendly, flexible, and thermally stable, it is suitable for use as a protective coating against sunlight and harmful emissions from IT devices.

Scalable Fabrication of Structurally Stable Polymer Film with Excellent UV-Shielding, Fluorescent, and Antibacterial Capabilities

This research presents a new approach to facilely fabricating a multifunctional film using polyvinyl alcohol (PVA) as the base material. The film is modified chemically to incorporate various desirable properties such as high transparency, UV-shielding, antibacterial activity, and fluorescence. The fabrication process of this film is straightforward and efficient. The modified film showed exceptional UV-blocking capability, effectively blocking 100% of UV radiation. It also exhibits strong antibacterial properties. Additionally, the film emitted bright blue fluorescence, which can be useful in various optical and sensing applications. Despite the chemical modification, the film retained the excellent properties of PVA, including high transparency (90%) at 550 nm and good mechanical strength. Furthermore, it demonstrated remarkable stability even under harsh conditions such as exposure to long-term UV radiation, extreme temperatures (-40 or 120 °C), or immersion in different solvents. Overall, this work showcases a promising strategy to develop versatile, structurally stable, transparent, and flexible polymer films with multiple functionalities. These films have potential applications in various fields that require protection, such as packaging materials, biomedical devices, and optical components.

Preparation and Application of Degradable Lignin/Poly (Vinyl Alcohol) Polymers as Urea Slow-Release Coating Materials

The massive amount of water-soluble urea used leads to nutrient loss and environmental pollution in both water and soil. The aim of this study was to develop a novel lignin-based slow-release envelope material that has essential nitrogen and sulfur elements for plants. After the amination reaction with a hydrolysate of yak hair keratin, the coating formulation was obtained by adding different loadings (2, 5, 8, 14 wt%) of aminated lignin (AL) to 5% polyvinyl alcohol (PVA) solution. These formulations were cast into films and characterized for their structure, thermal stability, and mechanical and physicochemical properties. The results showed that the PVA-AL (8%) formulation had good physical and chemical properties in terms of water absorption and mechanical properties, and it showed good degradation in soil with 51% weight loss after 45 days. It is suitable for use as a coating material for fertilizers. Through high-pressure spraying technology, enveloped urea particles with a PVA-AL (8%) solution were obtained, which showed good morphology and slow-release performance. Compared with urea, the highest urea release was only 96.4% after 30 days, conforming to Higuchi model, Ritger-Peppas model, and second-order dynamic model. The continuous nitrogen supply of PVA-AL coated urea to Brassica napus was verified by potting experiments. Therefore, the lignin-based composite can be used as a coating material to produce a new slow-release nitrogen fertilizer for sustainable crop production.

Lignin-xylan nanospheres prepared by green and quick method from lignocellulose and used as additive in PVA films

Lignin, as an amorphous three-dimensional aromatic polymer, was able to self-assemble into lignin nanoparticles (LNPs) to realize valorization of lignin. Here, lignin-xylan extractives were extracted from grape seed (GS) and poplar by acidic THF at room temperature, and effectively produced lignin-xylan nanospheres via spin evaporation. The morphology and chemical properties of nanospheres were determined by its natural origins, consequently influencing its application. For the lignin-xylan extractive from grape seed, the lignin was composed of guaiacyl (G) and p-hydroxylphenyl (H) units and the hollowed nanospheres (GS-LNPs) with 362.72 nm diameter was produced. The extractive from poplar was composed of G-syringyl (S) typed lignin (80.30 %) and xylan (12.33 %), that can assemble into LNPs with smaller size (229.87 nm), better PDI (0.1), and light color. The hybrid particles showed the qualities of lignin and xylan, that properties led to the LNPs@PVA composite films with UV-blocking capability, strong mechanical strength and hydrophobicity, and transparency ability of visible light. P-LNPs showed better performance as the film additives, due to its lower particles size and high content of unconjugated -OH from xylan. Xylan was significant in the composite films, and lowering the xylan content resulted in the decrease of the composite film's mechanical properties and hydrophobicity.

Starch biocomposites preparation by incorporating organosolv lignins from potato crop residues

Plastic wastes accumulated due to food packaging pose environmental threats. This study proposes biopolymeric films containing lignins extracted from potato crop residues (PCR) through organosolv treatment as a green alternative to non-degradable food packaging. The isolation process yielded 43.9 wt% lignins with a recovery rate of 73.5 wt% achieved under optimum conditions at 180 °C with 50 % v/v ethanol. The extracted lignins were then incorporated into a starch matrix to create biocomposite films. ATR-FTIR analysis confirmed interactions between the starch matrix and extracted lignins, and XRD analysis showed the amorphous structure of lignins, reducing film crystallinity. The addition of 1 wt% of extracted lignins resulted in a 87 % reduction in oxygen permeability, a 25 % increase in the thermal stability of the film, and a 78 % enhancement in antioxidant. Furthermore, introducing 3 wt% lignins led to the lowest water vapor transmission rate, measuring 9.3 × 10-7 kg/s·m2. Morphological studies of the films demonstrated a homogeneous and continuous structure on both the surface and cross-sectional areas when the lignins content was below 7 wt%. These findings highlight the potential of using organosolv lignins derived from potato crop residues as a promising additive for developing eco-friendly films designed for sustainable food packaging.

Sustainable lignin nanoparticles from coconut fiber waste for enhancing multifunctional properties of macroalgae biofilms

Multifunctional and sustainable packaging biofilms felicitous to changeable conditions are in large demand as substitutes to petroleum-derived synthetic films. Macroalgae with noticeable film-formation, abundant, low-cost, and edible properties is a promising bioresource for sustainable and eco-friendly packaging materials. However, the poor hydrophobicity and mechanical properties of sustainable macroalgae biofilms seriously impede their practical applications. Herein, lignin nanoparticles (LNPs) produced by a sustainable approach from black liquor of coconut fiber waste were incorporated in the macroalgae matrix to improve the water tolerance and mechanical characteristics of the biofilms. The effect of different LNPs loadings on the performance of biofilms, such as physical, morphological, surface roughness, structural, water resistance, mechanical, and thermal behaviors, were systematically evaluated and found to be considerably improved. Biofilm with 6 % LNPs presented the optimum enhancement in most ultimate performances. The optimized biofilm exhibited great hydrophobic features with a water contact angle of over 100° and high enhancement in the tensile strength of >60 %. This study proposes a facile and sustainable approach for designing and developing LNPs-macroalgae biofilms with excellent and multifunctional properties for sustainable high-performance packaging materials.

Bioinspired multiscale cellulose/lignin-silver composite films with robust mechanical, antioxidant and antibacterial properties for ultraviolet shielding

Constructing a high-performance ultraviolet shielding film is an effective way for addressing the growing problem of ultraviolet radiation. However, it is still a great challenge to achieve a combination of multifunctional, excellent mechanical properties and low cost. Here, inspired by the multiscale structure of biomaterials and features of lignin, a multifunctional composite film (CNF/CMF/Lig-Ag) is constructed via a facile vacuum-filtration method by introducing micron-sized cellulose fibers (CMF) and lignin-silver nanoparticles (Lig-Ag NPs) into the cellulose nanofibers (CNF) film network. In this composite film, the microfibers interweave with nanofibers to form a multiscale three-dimensional network, which ensures satisfactory mechanical properties of the composite film. Meanwhile, the Lig-Ag NPs are employed as a multifunctional filler to enhance the composite film's antioxidant, antibacterial and ultraviolet shielding abilities. As a result, the prepared CNF/CMF/Lig-Ag composite film demonstrates excellent mechanical properties (with tensile strength of 133.8 MPa and fracture strain of 7.4 %), good biocompatibility, high thermal stability, potent antioxidant and antibacterial properties. More importantly, such composite film achieves a high ultraviolet shielding rate of 98.2 % for ultraviolet radiation A (UVA) and 99.4 % for ultraviolet radiation B (UVB), respectively. Therefore, the prepared CNF/CMF/Lig-Ag composite film shows great potential in application of ultraviolet protection.

Lignin/PVA hydrogel with enhanced structural stability for cationic dye removal

In this study, a lignin-based hydrogel for wastewater treatment was prepared by incorporating kraft lignin (KL) into a poly (vinyl alcohol) (PVA) matrix. The underwater structural stability of the KL-PVA hydrogel was guaranteed through physicochemical crosslinking, involving freeze-thaw process and chemical crosslinking reaction. The KL-PVA hydrogel displayed superior compressive characteristics compared to the original PVA hydrogel. This improvement was attributed to the chemical crosslinking and the reinforcing effect of the incorporated KL microparticles. The incorporation of anionic KL microparticles into the PVA three-dimensional network structure enhanced the cationic methylene blue (MB) and crystal violet (CV) adsorption efficiency of the prepared KL-PVA hydrogel. The MB adsorption results were well explained by pseudo-2nd order kinetics model and Langmuir isotherm model. Electrostatic forces, hydrogen bonding and π-π stacking interactions were the main adsorption mechanisms between cationic dyes and KL surfaces, indicating the potential of KL-PVA hydrogel as an effective adsorption material. Moreover, regulating the molecular weight of PVA not only prevented lignin leakage from the KL-PVA hydrogel but also elevated the KL content within the hydrogel, consequently improving its dye removal performance. For KL-PVA hydrogel with high molecular weight PVA, the MB and CV adsorption capacities were 193.8 mg/g and 190.0 mg/g, respectively.

Lignin beyond the status quo: recent and emerging composite applications

The demand for biodegradable materials across various industries has recently surged due to environmental concerns and the need for the adoption of renewable materials. In this context, lignin has emerged as a promising alternative, garnering significant attention as a biogenic resource that endows functional properties. This is primarily ascribed to its remarkable origin and structure that explains lignin's capacity to bind other molecules, reinforce composites, act as an antioxidant, and endow antimicrobial effects. This review summarizes recent advances in lignin-based composites, with particular emphasis on innovative methods for modifying lignin into micro and nanostructures and evaluating their functional contribution. Indeed, lignin-based composites can be tailored to have superior physicomechanical characteristics, biodegradability, and surface properties, thereby making them suitable for applications beyond the typical, for instance, in ecofriendly adhesives and advanced barrier technologies. Herein, we provide a comprehensive overview of the latest progress in the field of lignin utilization in emerging composite materials.

Sonochemical synthesis of lignin nanoparticles and their applications in poly (vinyl) alcohol composites

Lignin is a common and abundant byproduct of the pulp and paper industry and is generally burned to produce steam. Opportunities exist to acquire greater value from lignin by leveraging the properties of this highly conjugated biomacromolecule for applications in UV absorption and polymer reinforcement. These applications can be commercialized by producing value-added lignin nanoparticles (LNPs) using a scalable sonochemical process. In the present research, monodisperse LNPs have been synthesized by subjecting aqueous dispersions of alkali lignin to acoustic irradiation. The resulting particle size distribution and colloidal stability, as determined by dynamic light scattering, transmission electron microscopy and zeta potential analysis, of LNPs can be adjusted by varying the solution pH and ultrasonication energy. As-synthesized LNPs with a mean diameter of 204 nm were incorporated into poly (vinyl) alcohol (PVA) to prepare thin and flexible nanocomposite films using a simple solvent casting method. The addition of 2.5 wt% LNP increased the material's Sun Protection Factor up to 26 compared to 0 for neat PVA, while maintaining light transmission above 75 % in the visible spectra. In addition, the tensile strength and elastic modulus of the PVA nanocomposites improved by 47 % and 36 %, respectively. The presence of LNP also enhanced the thermal stability of the materials. Significantly, the proposed sonochemical process may be generally applicable to the synthesis of a range of naturally-derived LNPs for a variety of value-added applications.

Experimental investigations on PVA/chitosan and PVA/chitin films for active food packaging using Oxytenanthera abyssinica lignin nanoparticles and its UV-shielding, antimicrobial, and antiradical effects

This study investigated the effect of adding lignin nanoparticles (LNPs) derived from Oxytenanthera abyssinica via alkali-acid nanoprecipitation method to polyvinyl alcohol/chitosan (PVA/CI) and polyvinyl alcohol/chitin (PVA/CH) films for the active food packaging applications. Adding LNPs at concentrations of 1 % and 3 % improved the films' thermal stability and mechanical properties. The lowest water solubility and moisture content were observed in PVA/CI/LNPs films. LNPs exhibited effective 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities, with the highest values observed in PVA/CH/LNPS and PVA/CI/LNPS films with values of 87.47 and 88.74 % respectively. The addition of LNPs also improved the UV-blocking abilities of the films. PVA/CH/LNP3 and PVA/CI/LNP3 have the smallest percentage transmission values of 3.34 % and 0.86 % in the UV range. The overall migration of dietary stimulants was lower in PVA/CI/LNPS and PVA/CH/LNPS films compared to PVA film. Antibacterial tests demonstrated the inhibitory capacity of the synthesized biofilms against both gram-positive and negative bacterial species, with the highest inhibitory value of 26 mm. The study suggests that PVA/CH/LNPS and PVA/CI/LNPS films have potential applications as active food packaging materials and can be explored in other potential applications such as drug delivery, tissue engineering, wound healing, and slow-release urea fertilizer development.

Lignin Nanoparticles Produced from Wheat Straw Black Liquor Using γ-Valerolactone

The valorization of the black liquor produced during the chemical pulping of wheat straw is the key to the sustainable use of this abundant agricultural waste. However, the silica problem has hampered the recovery process. Herein, nanoprecipitation technology was used to produce lignin nanoparticles (LNPs) from wheat straw black liquor using γ-valerolactone (GVL) as a solvent and water as an anti-solvent. The results showed that a uniform, well-dispersed, and stable LNP was produced. The particle size and Zeta potential of 161 nm and -24 mV of the LNP suspension were obtained at a GVL concentration of 87%. The chemical structure and bonding of the lignin were adequately preserved after nanoprecipitation based on two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) spectroscopy, Fourier transform infrared (FTIR) analysis, and thermal stability was improved based on thermogravimetric analysis. In addition, the abundant phenolic hydroxyl groups of LNP quantified by 31P-NMR analysis are beneficial for chemical cross-linking and modification. This work not only achieved the valorization of wheat straw black liquor but also opened up a new avenue for advanced nanomaterials.

Lignin Modification for Enhanced Performance of Polymer Composites

The biopolymer lignin, which is heterogeneous and abundant, is usually present in plant cell walls and gives them rigidity and strength. As a byproduct of the wood, paper, and pulp manufacturing industry, lignin ranks as the second most prevalent biopolymer worldwide, following cellulose. This review paper explores the extraction, modification, and prospective applications of lignin in various industries, including the enhancement of thermosetting and thermoplastic polymers, biomedical applications such as vanillin production, fuel development, carbon fiber composites, and the creation of nanomaterials for food packaging and drug delivery. The structural characteristics of lignin remain undefined due to its origin, separation, and fragmentation processes. This comprehensive overview encompasses state-of-the-art techniques, potential applications, diverse extraction methods, chemical modifications, carbon fiber utilization, and the extraction of vanillin. Moreover, the review focuses on the utilization of lignin-modified polymer blends across multiple manufacturing sectors, providing insights into the advantages and limitations of this innovative approach for the development of environmentally friendly materials.

Ultraviolet blocking ability, antioxidant and antibacterial properties of newly prepared polyvinyl alcohol-nanocellulose‑silver nanoparticles-ChunJian peel extract composite film

In this work, nanocellulose (CNC) from waste water chestnut (WCT) shell was firstly used for preparing nanocomposite films, by using ChunJian peel extract (CJPE) as a green reducing agent to synthesize silver nanoparticles (AgNPs), and then loading them into polyvinyl alcohol-nanocellulose (PVA-CNC) matrix, a multifunctional nanocomposite material that could be used in food packaging was developed. The prepared films were tested for mechanical strength, barrier properties, thermal properties, antibacterial, antioxidant and biocompatibility through various characterizations. The PVA-CNC-AgNPs-CJPE film had good thermostability, mechanical strength, barrier properties, and biocompatibility. Compared with pure PVA film and PVA-CNC film, PVA-CNC-AgNPs-CJPE could shield over 95 % of the UVB (320-275 nm) spectrum and UVC (275-200 nm) spectrum and most of the UVA (400-320 nm). By disk diffusion analysis, the inhibition zones of PVA-CNC-AgNPs-CJPE film against E. coli, P. aeruginosa, S. aureus and E. faecalis were 22.3 mm, 25.0 mm, 22.0 mm and 19.3 mm, respectively. The milk antibacterial simulation test confirmed that PVA-CNC-AgNPs-CJPE film could effectively limit bacterial reproduction and prolong the shelf life of milk. PVA-CNC-AgNPs-CJPE film had excellent UV barrier properties, good antioxidant properties and high-efficiency antibacterial activity, which is expected to be widely used in sustainable nanocomposite food packaging.

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.

Physicochemical properties of lignin nanoparticles from softwood and their potential application in sustainable pre-harvest bagging as transparent UV-shielding films

Technical lignin can be mainly obtained as a waste by-product from pulp industry, and it exhibits unique properties including ultraviolet adsorption, biodegradable, antibacterial, and antioxidant which can be utilized for bioplastic applications. However, common limitations of technical lignin for plastic applications are compatibility mainly due to poor interfacial adhesion, relatively large particle size and impurity. In this study lignin nanoparticles from softwood (S-LNPs) were successfully produced through a continuous-green-scalable antisolvent precipitation and the suitability of S-LNPs for fabrication of bio-composite polybutylene succinate (PBS) films using conventional blown film extrusion was examined. The attained S-LNPs showed lower ash content, higher phenolic content and higher lignin content compared to pristine softwood kraft lignin (S-lignin). Rheological property including shear viscosity and melt-flow index was determined. The obtained PBS/S-LNP composite films showed improved tensile modulus, higher water vapor transmission rate and excellent UV-shielding ability compared to neat PBS and PBS/S-lignin films. Accelerated weathering testing was conducted to replicate outdoor conditions. Degradation indices including carbonyl, vinyl and hydroxyl of the weathered PBS/lignin composites were evaluated for photo-oxidative stability. The S-LNPs as multifunctional bio-additives in biodegradable composite film exhibited superior performances of transparency, UV-absorption and stiffness with high photo-oxidative stability suitable for outdoor applications.

Enabling the complete valorization of hybrid Pennisetum: Directly using alkaline black liquor for preparing UV-shielding biodegradable films

The conversion of lignocellulosic biomass into various high-value chemicals has been a rapid expanding research topic in industry and agriculture. Among them, alkaline removal and utilization of lignin are important for the accelerated degradation of biomass. Modern biorefinery has been focusing the vision on the advancement of economical, green, and environmentally friendly processes. Therefore, it is indispensable to develop cost-effective and simple biomass conversion technologies to obtain high-value products. In this study, the black liquor (BL) obtained from the alkaline pretreatment of biomass was added to polyvinyl alcohol (PVA) solution and used to prepare degradable ultraviolet (UV) shielding films, achieving direct and efficient utilization of the aqueous phase from alkaline pretreatment. This method avoids the extraction step of lignin fraction from black liquor, which can be directly utilized as the raw materials of films preparation. In addition, the direct use of alkaline BL results in films with similar UV-shielding properties, higher physical strength, and similar thermal stability compared with films made by commercial alkaline lignin. Therefore, this strategy is proposed for alkaline-pretreated biorefineries as a simple way to convert waste BL into valuable products and partially recover unconsumed sodium hydroxide to achieve as much integration of biomass and near zero-waste biorefineries as possible.

Enhanced Functional Properties of Bioplastic Films Using Lignin Nanoparticles from Oil Palm-Processing Residue

The development of bioplastic materials that are biobased and/or degradable is commonly presented as an alleviating alternative, offering sustainable and eco-friendly properties over conventional petroleum-derived plastics. However, the hydrophobicity, water barrier, and antimicrobial properties of bioplastics have hindered their utilization in packaging applications. In this study, lignin nanoparticles (LNPs) with a purification process were used in different loadings as enhancements in a Kappaphycus alvarezii matrix to reduce the hydrophilic nature and improve antibacterial properties of the matrix and compared with unpurified LNPs. The influence of the incorporation of LNPs on functional properties of bioplastic films, such as morphology, surface roughness, structure, hydrophobicity, water barrier, antimicrobial, and biodegradability, was studied and found to be remarkably enhanced. Bioplastic film containing 5% purified LNPs showed the optimum enhancement in almost all of the ultimate performances. The enhancement is related to strong interfacial interaction between the LNPs and matrix, resulting in high compatibility of films. Bioplastic films could have additional advantages and provide breakthroughs in packaging materials for a wide range of applications.

Agri-Biodegradable Mulch Films Derived from Lignin in Empty Fruit Bunches

Mulch films increase soil temperature, maintain soil moisture, improve water and fertilizer absorption, and reduce weed growth. This work studied a mulching film made using polyvinyl alcohol (PVA) and lignin extracted from empty fruit bunches (EFBs). The mulch films were investigated for opaqueness, biodegradation, water-solubility, absorption, and mechanical properties. Life cycle assessment (LCA) and cost estimate analysis were conducted. The composite mulch film-PVA solution was blended with 6% EFB lignin in dimethyl sulfoxide (DMSO) solution using five different amounts (0, 20, 40, 60, or 80 wt% lignin). The results showed that increasing the amount of lignin increased the film’s water solubility, moisture content, and biodegradability. At the same time, water absorption tended to decrease. Consequently, the light transmittance of the film was reduced, which had a positive effect on preventing soil weed growth. Tests of the mechanical properties showed that 60% lignin in the PVA film had the highest tensile strength (16.293 MPa). According to the LCA studies and cost estimation, the lignin-mixed PVA film had the lowest impact and was cheaper than the commercial mulching film. The results suggested that it is possible to blend polyvinyl alcohol polymer with lignin to improve biodegradability up to 25.47% by soil burial and 32% by water solubility.

Fabrication of Densified Rice Husk by Sequential Hot-Compressed Water Treatment, Blending with Poly(vinyl alcohol), and Hot Pressing

Processing agricultural wastes into densified materials to partially substitute wooden product production is significant for reducing the consumption of forest resources. This work proposes the fabrication of high-strength rice husk (RH)-based composite materials with poly(vinyl alcohol) (PVA) via densification by hot pressing. RH was pretreated in hot-compressed water (HCW) prior to pulverization and blending with PVA or PVA/glycerol (GL). The incorporation of PVA greatly improved the strength, toughness, and waterproofness of the composite plate, which was discussed with the help of a variety of composite characterizations. The tensile strength, flexural strength, and toughness of a composite of HCW-treated RH, PVA, and GL with a mass ratio of 80:20:2 were 42, 81 MPa, and 5.9 MJ/m³, respectively. The HCW treatment and blending with PVA and GL improved those properties of the hot-pressed original RH plate by factors of 2.5, 2.3, and 6.7, respectively, and reduced the water uptake and swelling ratio in water by 57 and 53%, respectively, despite the hydrophilic nature of PVA and GL. Altogether, this work outlines a valuable and sustainable approach to the efficient utilization of agricultural wastes.

Nanolignin filled conductive hydrogel with improved mechanical, anti-freezing, UV-shielding and transparent properties for strain sensing application

Herein, we innovatively synthesized an ionic conductive PVA/LNP hydrogel with integrated excellent mechanical, anti-freezing, moisturizing, transparent and UV-shielding performances via incorporating nanolignin (also called lignin nanoparticle, LNP) and aluminum chloride (AlCl₃) into polyvinyl alcohol (PVA) matrix containing ethylene glycol/water (EG/H₂O) binary solvent. The rigid porous network structure was well constructed by the hydrogen bond interactions among the evenly distributed LNP and PVA chains, thus providing abundant ion transport channels, which attributed to the outstanding ionic conductivity (up to 1.35 × 10^-2 S/m, at -24 °C) with improved mechanical strength and flexibility. The tensile strength and elongation at break of PVA/LNP hydrogel were greatly increased from 574.6 kPa and 363.7% to 1241.4 kPa and 589% at the addition of 0.35% LNP, respectively. In addition, the UV-resistance ability was 95% at 365 nm, while the transparency was 74% at 550 nm. The binary solvent of EG and H₂O ensured long-term moisturizing capability (10 days) of the hydrogel at 35 °C and 60 RH%, as well as possessing superior anti-freezing performance over the temperature range of -62.6 to 24 °C. As a result, the fabricated PVA/LNP hydrogel was successfully used as strain sensor for detecting diverse human motions and electrophysiological signals.

High-efficient lignin-based polymerizable macromolecular photoinitiator with UV-blocking property for visible light polymerization

Developing high-efficient visible light macromolecular photoinitiator (macro PI) with excellent initiation performance, low migration, high biosafety and multi-function is beneficial to broaden the application of photopolymer. Lignin contains chromophores which could generate free radicals under light irradiation. In this study, a lignin-based polymerizable macro PI (DAL-11ene-amine) was designed and synthesized through covalent grafting 10-undecenoyl chloride (11ene) and hydrogen donor 4-(dimethylaminobenzoic acid) ethyl ester (EDAB) into dealkaline lignin (DAL) skeleton. The structure of DAL-11ene-amine was characterized by UV-vis, FTIR, ¹H NMR, GPC, and ³¹P NMR spectra. Under the irradiation of a 405 nm LED, DAL-11ene-amine can directly produce active species and initiate the polymerization of acrylate monomers or thiol-ene click reaction. The photoinitiation efficiency of DAL-11ene-amine is higher than that of DAL-11ene or the two-component combination of DAL-11ene and EDAB. Using DAL-11ene-amine as PI, the prepared polymer films exhibit excellent UV-blocking property. With only 0.5 wt% addition of DAL-11ene-amine, nearly 100% of UVB + UVC and the most of UVA can be blocked by the films. Moreover, DAL-11ene-amine exhibits higher migration stability and biosafety because it can be covalently linked into polymer cross-linking networks. The results indicate that DAL-11ene-amine has great application potentials in preparing environmentally friendly UV-blocking films and biosafety coatings.

Polyvinyl alcohol inclusion can optimize the sol-gel, mechanical and hydrophobic features of agar/konjac glucomannan system

The practical features (e.g., sol-gel, mechanical and hydrophobic) of biopolymer systems are crucial for their materials applications. This work reveals how polyvinyl alcohol (PVA) inclusion affects the practical features of agar/konjac glucomannan (KGM) system. From rheological analysis, incorporating PVA (especially 6%) enhanced the chain entanglements of resulted ternary solution (A₇₀K₂₄P₆) with stabilized sol-gel transition point. Such effect not only increased the zero-shear viscosity (ca. 1.5 times that of agar/KGM counterpart) and structural recovery degree of A₇₀K₂₄P₆ solution, but also caused reduced crystallites and simultaneously increased tensile strength, elongation at break and hydrophobicity for A₇₀K₂₄P₆ film from solution dehydration. This ternary film exhibited a tensile strength of ca. 105 MPa, an elongation at break of ca. 20%, and a water contact angle of ca. 97.6°. Additionally, incorporating PVA almost unaffected the morphology of film fracture surface. These results are valuable for the design of agar/KGM systems with improved practical features.

Lignin Nanoparticles and Alginate Gel Beads: Preparation, Characterization and Removal of Methylene Blue

A novel and effective green system consisting of deep eutectic solvent (DES) was proposed to prepare lignin nanoparticles (LNPs) without any lignin modification. The LNPs are obtained through the dialysis of the kraft lignin-DES solution. The particle size distribution, Zeta potential and morphology of the LNPs are characterized by using dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average diameter of LNPs is in the range 123.6 to 140.7 nm, and the LNPs show good stability and dispersibility in water. The composite beads composed of LNPs and sodium alginate (SA) are highly efficient (97.1%) at removing methylene blue (MB) from the aqueous solution compared to 82.9% and 77.4% by the SA/bulk kraft lignin composite and pure SA, respectively. Overall, the LNPs-SA bio-nanocomposite with high adsorption capacity (258.5 mg/g) could be useful in improving water quality and other related applications.

Dynamic Nanoconfinement Enabled Highly Stretchable and Supratough Polymeric Materials with Desirable Healability and Biocompatibility

Lightweight polymeric materials are highly attractive platforms for many potential industrial applications in aerospace, soft robots, and biological engineering fields. For these real-world applications, it is vital for them to exhibit a desirable combination of great toughness, large ductility, and high strength together with desired healability and biocompatibility. However, existing material design strategies usually fail to achieve such a performance portfolio owing to their different and even mutually exclusive governing mechanisms. To overcome these hurdles, herein, for the first time a dynamic hydrogen-bonded nanoconfinement concept is proposed, and the design of highly stretchable and supratough biocompatible poly(vinyl alcohol) (PVA) with well-dispersed dynamic nanoconfinement phases induced by hydrogen-bond (H-bond) crosslinking is demonstrated. Because of H-bond crosslinking and dynamic nanoconfinement, the as-prepared PVA nanocomposite film exhibits a world-record toughness of 425 ± 31 MJ m-3 in combination with a tensile strength of 98 MPa and a large break strain of 550%, representing the best of its kind and even outperforming most natural and artificial materials. In addition, the final polymer exhibits a good self-healing ability and biocompatibility. This work affords new opportunities for creating mechanically robust, healable, and biocompatible polymeric materials, which hold great promise for applications, such as soft robots and artificial ligaments.

Highly-toughened PVA/nanocellulose hydrogels with anti-oxidative and antibacterial properties triggered by lignin-Ag nanoparticles

In this study, Ag nanoparticles were firstly reduced on the surface of lignin nanoparticles (LNP_Ag) by direct reaction of silver nitrate without the use of a catalyst. Thermogravimetric analysis, Zeta potential and transmission electron microscopy measurements were performed to give evidence of the effectiveness of the reaction. After that, glutaraldehyde crosslinked PVA hydrogels, were produced by addition of unmodified LNP and Ag loaded LNP (LNP_Ag) in presence of cellulose nanocrystals (CNC). Thermal, mechanical, rheological, microstructural and biological anti-oxidative and anti-bacterial properties of the resulted hydrogels were investigated. It was proved that all the three nanofillers were homogeneously dispersed in PVA, and the pore diameter of the hydrogels was in the range of 0.5-2.0 μm. Nevertheless, the hydrogels showed high toughness, long-term and repeatable adhesiveness to a variety of substrates. In particular, composite hydrogels containing LNP_Ag nanoparticles showed excellent radical scavenging and antibacterial activities. Consequently, the effects of PVA-2CNC-2LNP_Ag on wound healing in mice model of full-thickness skin resection were evaluated by hematoxylin and eosin staining, taking as a reference the PVA-2CNC-2LNP system. The results showed that the wound healing time of PVA-2CNC-2LNP_Ag group was faster than that of neat PVA and PVA-2CNC, highlighting the role of LNP_Ag in enhancing the contact-active anti-oxidative and antibacterial activities mechanism in composite hydrogels. We expected that PVA hydrogels incorporating LNP_Ag could be used as green and efficient biomedical wound dressing materials.

Starch-Mucilage Composite Films: An Inclusive on Physicochemical and Biological Perspective

In recent years, scientists have focused on research to replace petroleum-based components plastics, in an eco-friendly and cost-effective manner, with plant-derived biopolymers offering suitable mechanical properties. Moreover, due to high environmental pollution, global warming, and the foreseen shortage of oil supplies, the quest for the formulation of biobased, non-toxic, biocompatible, and biodegradable polymer films is still emerging. Several biopolymers from varied natural resources such as starch, cellulose, gums, agar, milk, cereal, and legume proteins have been used as eco-friendly packaging materials for the substitute of non-biodegradable petroleum-based plastic-based packaging materials. Among all biopolymers, starch is an edible carbohydrate complex, composed of a linear polymer, amylose, and amylopectin. They have usually been considered as a favorite choice of material for food packaging applications due to their excellent forming ability, low cost, and environmental compatibility. Although the film prepared from bio-polymer materials improves the shelf life of commodities by protecting them against interior and exterior factors, suitable barrier properties are impossible to attain with single polymeric packaging material. Therefore, the properties of edible films can be modified based on the hydrophobic-hydrophilic qualities of biomolecules. Certain chemical modifications of starch have been performed; however, the chemical residues may impart toxicity in the food commodity. Therefore, in such cases, several plant-derived polymeric combinations could be used as an effective binary blend of the polymer to improve the mechanical and barrier properties of packaging film. Recently, scientists have shown their great interest in underutilized plant-derived mucilage to synthesize biodegradable packaging material with desirable properties. Mucilage has a great potential to produce a stable polymeric network that confines starch granules that delay the release of amylose, improving the mechanical property of films. Therefore, the proposed review article is emphasized on the utilization of a blend of source and plant-derived mucilage for the synthesis of biodegradable packaging film. Herein, the synthesis process, characterization, mechanical properties, functional properties, and application of starch and mucilage-based film are discussed in detail.