Mechanically Robust, Self-Repairable, Shape Memory and Recyclable Ionomeric Elastomer Composites with Renewable Lignin via Interfacial Metal-Ligand Interactions

Chitosan/PVA composite film enhanced by ZnO/lignin with high-strength and antibacterial properties for food packaging

This study aims to develop a chitosan/polyvinyl alcohol (CS/PVA) composite film (QZCS/PVA) for food packaging, enhanced by the incorporation of quaternary ammonium lignin/ZnO nanoparticles (QAL/ZnO) to improve its antibacterial, antioxidant, and mechanical properties. The QAL/ZnO nanoparticles were synthesized using a co-precipitation method, resulting in a synergistic effect that enhances the uniformity and stability of the composite film. The double cross-linked CS/PVA composite film containing QAL/ZnO nanoparticles effectively mitigates the brittleness of pure chitosan films, achieving a tensile strength of 95.89 MPa. Crucially, the inclusion of QAL/ZnO imparts exceptional antioxidant and antibacterial properties to the QZCS/PVA composite film. Disk diffusion assays revealed markedly enhanced antibacterial efficacy against Staphylococcus aureus and Escherichia coli in comparison to analogous biopolymer films. The dense network structure of the composite film also provides excellent water resistance, which contributes to extending the shelf life of food products. In a 12-day grape preservation experiment, the composite film exhibited outstanding preservation performance. These results underscore the potential of the CS/PVA composite film containing lignin and chitosan for food packaging applications, offering significant advantages in improving food preservation.

A one-step and solvent-free strategy for high lignin-containing polyurethane elastomers with excellent mechanical and shape memory performance

Lignin, a renewable and biodegradable polymer, offers a promising alternative to petroleum-based polyols for polyurethane elastomer synthesis. However, its complex structure poses challenges, such as poor dispersibility and reactivity. This study introduces a novel one-step and solvent-free method for synthesizing lignin-containing polyurethane elastomers (SF-LPUes-ONE) with a high lignin substitution rate of at least 30 wt%. By directly incorporating a dispersion of ethanol-extracted lignin and long-chain polyols into the reaction with isocyanates, we successfully prepared SF-LPUes-ONE with remarkable mechanical properties. The tensile strength, elongation at break, and toughness of the resulting sample reached 42.3 MPa, 584.7 %, and 110.0 MJ/m3, respectively. In addition, the phenolic hydroxyl groups in lignin endowed SF-LPUes-ONE with excellent anti-aging resistance, ensuring sustained high performance under demanding conditions. Furthermore, the dynamic hydrogen bonding and chemical cross-linking dual-network endowed SF-LPUes-ONE with exceptional shape memory capabilities, achieving shape fixation and recovery rates exceeding 99 % after 3 cycles. This work demonstrates a green and efficient approach to high-performance lignin-based polyurethane elastomers, showcasing their potential for broad industrial applications.

Bio-Based Polyurethane Composites with Adjustable Fluorescence and Ultraviolet Shielding for Anti-Counterfeiting and Ultraviolet Protection

Polyurethane and its composites play an important role in innovative packing materials including anticounterfeiting and ultraviolet protection, however, they are mainly derived from petroleum resources that are not sustainable. In this study, a 100% biobased thermoplastic polyurethane (Bio-TPU) was synthesized using biobased poly(trimethylene ether) glycol, pentamethylene disocyanate, and 1,4-butanediol. Subsequently, biobased tannic acid (TA) was employed to prepare biobased composites. The structures and properties of Bio-TPU and its composites were systematically evaluated. The results showed that the Bio-TPU/TA composite films had excellent and controllable fluorescence and UV-shielding properties. The fluorescence colors of the Bio-TPU/TA composite films could be adjusted to blue, green, and yellow by varying the TA content and adding coupling agents. Moreover, the UV transmittance of the Bio-TPU/TA composites decreased from 79.25 to 5.43% below 400 nm with an increasing TA content, indicating an excellent ultraviolet-barrier performance. Consequently, biobased TPU/TA composite films can be utilized as innovative anticounterfeiting materials and UV-shielding protection films. This study is expected to facilitate sustainable development in the polyurethane industry and broaden the high-end applications of polyurethane such as fashion, electronics, food manufacturing, pharmaceuticals, and finance.

Mini-review on lignin-based self-healing polymer

Lignin, a biopolymer derived from plant biomass, is recognized as a highly promising substance for developing self-healing polymers owing to its dynamic linkages and functional groups. This paper provides a thorough review of lignin-based self-healing polymer, from the process of extracting lignin, chemical modification, synthesis techniques such as via reversible addition-fragmentation chain transfer (RAFT) polymerization, crosslinking with polymers like polyvinyl alcohol (PVA) and chitosan, and reactions with isocyanates to create lignin-based networks with reversible interactions. This work also summarizes the optimization of self-healing ability, such as including dynamic copolymers, encapsulating healing agents like dicyclopentadiene and polycaprolactone (PCL), and chain extenders with disulfide or Diels-Alder (DA) moieties. The material's characterization focuses on its capacity to recover via hydrogen bonding and dynamic re-associations, improved mechanical properties from lignin's rigid structure, and enhanced temperature resistance. Primary obstacles involve the optimization of lignin extraction, enhancement of polymer compatibility, and the establishment of efficient procedures for synthesis and characterization. Overall, lignin shows great potential as a renewable component of self-healing polymers, with plenty of opportunities for further development.

Lignin-based vitrimer containing dynamic borate ester bonds with intrinsic photoconversion and excellent photothermal remoldability

The development of photoresponsive shape memory materials based on the photothermal conversion properties of lignin and the low activation energy of the dynamic covalent borate bond is of great importance. In this paper, a kind of lignin-based vitrimer polymer (LBP) containing dynamic boronic ester bonds was prepared by a "sulfhydryl-epoxy" click reaction and etherification reaction. The results show that the rigid segment EP-EL (lignin-based epoxy resin) and BDB (2,2'-(1,4-phenylene)-bis-[4-mercapto-1,3,2-dioxaneborane]) with benzene ring structure can impart tensile strength (20.8 MPa) to the LBP, while the flexible segment PEG imparts good elongation at break (15 %). The dynamic binding and dissociation exchange mechanism of the boronic ester bonds enables LBP to exhibit thermal remodelling properties (up to 36.2 %) and water-assisted self-healing properties at room temperature (up to 49.0 %). In addition, LBP exhibits excellent thermal and light-responsive shape memory properties due to its own photothermal conversion performance (photothermal conversion efficiency up to 18.2 %) and the dynamic boronic ester bond thermal activation bond exchange mechanism. The insulating properties of LBP make it suitable for use in high temperature protection circuit devices and light-responsive circuit devices. This study provides new insights into the design and application of Vitrimer and photoresponsive shape memory polymers, and also offers a new avenue for high-value utilization of lignin.

Photothermal-responsive lignin-based polyurethane with mechanically robust, fast self-healing, solid-state plasticity and shape-memory performance

In light of the depletion of petrochemical resources and increase in environmental pollution, there has been a significant focus on utilizing natural biomass, specifically lignin, to develop sustainable and functional materials. This research presents the development of a lignin-based polyurethane (DLPU) with photothermal-responsiveness by incorporating lignin and oxime-carbamate bonds into polyurethane network. The abundant hydrogen bonds between lignin and the polyurethane matrix, along with its cross-linked structure, contribute to DLPU's excellent mechanical strength (30.2 MPa) and toughness (118.7 MJ·m-3). Moreover, the excellent photothermal conversion ability of DLPU (54.4 %) activates dynamic reversible behavior of oxime-carbamate bonds and hydrogen bonds, thereby endowing DLPU with exceptional self-healing performance. After 15 min of near-infrared irradiation, DLPU achieves self-healing efficiencies of 96.0 % for tensile strength and 96.3 % for elongation at break. Additionally, DLPU exhibits photocontrolled solid-state plasticity as well as an excellent phototriggered shape-memory effect (70 s), with shape fixity and recovery ratios reaching 98.8 % and 95.3 %, respectively. By exploiting the spatial controllability and photothermal-responsiveness of DLPU, we demonstrate multi-dimensional responsive materials with self-healing and shape-shifting properties. This work not only promotes the development of multi-functional polyurethanes but also provides a pathway for the high-value utilization of lignin.

Effect of lignin on the structure-property behavior of metal-coordinated and chemically crosslinked ethylene-propylene-diene-monomer composites

The efficient development and utilization of green biomass-based macromolecule engineering materials are essential for the sustainable development of human civilization. In this study, lignin-based ethylene-propylene-diene-monomer (EPDM) composites with excellent mechanical performance were fabricated using a simple method. The effects of water-insoluble enzymatically hydrolyzed lignin (EL) and alkali lignin (KL) on the mechanical performance of the composites were investigated separately. The results showed that the tensile strength of EPDM reinforced with KL and EL increased to 24.5 MPa and 22.1 MPa, respectively, surpassing that of the carbon black (CB)-reinforced EPDM. After 72 h of thermo-oxidative aging, the retention rates of the tensile strength and elongation at break in the lignin-reinforced EPDM were much better than those formed with pure CB, indicating that lignin significantly improved the thermo-oxidative aging resistance of the composites. In summary, the Zn2+ coordination bonds formed between the interface of EPDM and lignin in lignin/CB/EPDM ternary composites effectively improved the mechanical performance and aging resistance of the composites. This study has significant implications for enhancing the utilization of lignin and green functional polymer materials.

Polymerizable deep eutectic solvent treated lignocellulose: Green strategy for synergetic production of tough strain sensing elastomers and nanocellulose

Liquid free ion-conductive elastomers (ICEs) have demonstrated promising potential in various advanced application scenarios including sensor, artificial skin, and human-machine interface. However, ICEs that synchronously possess toughness, adhesiveness, stability, and anti-bacterial capability are still difficult to achieve yet highly demanded. Here, a one-pot green and sustainable strategy was proposed to fabricate multifunctional ICEs by extracting non-cellulose components (mainly lignin and hemicellulose) from lignocellulose with polymerizable deep eutectic solvents (PDES) and the subsequent in-situ photo-polymerization process. Ascribing to the uniform dispersion of non-cellulose components in PDES, the resultant ICEs demonstrated promising mechanical strength (a tensile strength of ~1200 kPa), high toughness (~9.1 MJ m-3), favorable adhesion (a lap-shear strength up to ~61.5 kPa toward metal), conducive stabilities, and anti-bacterial capabilities. With the help of such advantages, the ICEs exhibited sensitive (a gauge factor of ~23.5) and stable (~4000 cycles) performances in human motion and physiological signal detection even under sub-zero temperatures (e.g., -20 °C). Besides, the residue cellulose can be mechanically isolated into nanoscale fibers, which matched the idea of green chemistry.

Recent Advances of Lignin Functionalization for High-Performance and Advanced Functional Rubber Composites

The biomass lignin is the only large-volume renewable feedstock that is composed of aromatics but has been largely underutilized and is sought for valorization as a value-added material. Recent research has highlighted lignin as a promising alternative to traditional petrol-based reinforcements and functional additives for rubber composites. This review summarized the recent advances in the functionalization of lignin for a variety of rubber composites, as well as the compounding techniques for effectively dispersing lignin within the rubber matrix. Significant progress has been achieved in the development of high-performance and advanced functional rubber/lignin composites through carefully designing the structure of lignin-based additives and the optimization of interfacial morphologies. This Review discussed the effect of lignin on composite properties, including mechanical reinforcement, dynamic properties, antiaging performance, and oil resistance, and also the advanced stimuli-responsive performance in detail. A critical analysis for the future development of rubber/lignin composites is presented as concluding remarks.

Lignin, the Lignification Process, and Advanced, Lignin-Based Materials

At a time when environmental considerations are increasingly pushing for the application of circular economy concepts in materials science, lignin stands out as an under-used but promising and environmentally benign building block. This review focuses (A) on understanding what we mean with lignin, i.e., where it can be found and how it is produced in plants, devoting particular attention to the identity of lignols (including ferulates that are instrumental for integrating lignin with cell wall polysaccharides) and to the details of their coupling reactions and (B) on providing an overview how lignin can actually be employed as a component of materials in healthcare and energy applications, finally paying specific attention to the use of lignin in the development of organic shape-memory materials.