Synthesis and Characterization of Thermally Stable Lignosulfonamides

Proton Exchange Membranes from Sulfonated Lignin Nanocomposites for Redox Flow Battery Applications

Redox flow batteries (RFBs) are increasingly being considered for a wide range of energy storage applications, and such devices rely on proton exchange membranes (PEMs) to function. PEMs are high-cost, petroleum-derived polymers that often possess limited durability, variable electrochemical performance, and are linked to discharge of perfluorinated compounds. Alternative PEMs that utilize biobased materials, including lignin and sulfonated lignin (SL), low-cost byproducts of the wood pulping process, have struggled to balance electrochemical performance with dimensional stability. Herein, SL nanoparticles are demonstrated for use as a nature-derived, ion-conducting PEM material. SL nanoparticles (NanoSLs) can be synthesized for increased surface area, uniformity, and miscibility compared with macrosized lignin, improving proton conductivity. After addition of polyvinyl alcohol (PVOH) as a structural backbone, membranes with the highest NanoSL concentration demonstrated an ion exchange capacity of 1.26 meq g-1, above that of the commercial PEM Nafion 112 (0.98 meq g-1), along with a conductivity of 80.4 mS cm-1 in situ, above that of many biocomposite PEMs, and a coulombic efficiency (CE), energy efficiency (EE) and voltage efficiency (VE) of 91%, 68% and 78%, respectively at 20 mA cm-2. These nanocomposite PEMs demonstrate the potential for valorization of forest biomass waste streams for high value clean energy applications.

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.

Chemical and Physical Modification of Lignin for Green Polymeric Composite Materials

Lignin, a valuable polymer of natural origin, displays numerous desired intrinsic properties; however, modification processes leading to the value-added products suitable for composite materials' applications are in demand. Chemical modification routes involve mostly reactions with hydroxyl groups present in the structure of lignin, but other paths, such as copolymerization or grafting, are also utilized. On the other hand, physical techniques, such as irradiation, freeze-drying, and sorption, to enhance the surface properties of lignin and the resulting composite materials, are developed. Various kinds of chemically or physically modified lignin are discussed in this review and their effects on the properties of polymeric (bio)materials are presented. Lignin-induced enhancements in green polymer composites, such as better dimensional stability, improved hydrophobicity, and improved mechanical properties, along with biocompatibility and non-cytotoxicity, have been presented. This review addresses the challenges connected with the efficient modification of lignin, which depends on polymer origin and the modification conditions. Finally, future outlooks on modified lignins as useful materials on their own and as prospective biofillers for environmentally friendly polymeric materials are presented.