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1. Recent developments towards performance-enhancing lignin-based polymers

   https://doi.org/10.1039/d1py00694k  

   Bass, Garrett F.; Epps, Thomas H. (July 2021, Polymer Chemistry)

   null (Ed.)

   Fossil fuels are a cheap and abundant feedstock for polymeric materials that have enabled innumerable quality-of-life improvements. Yet, their declining supply and non-renewable nature have driven the pursuit of bio-based alternatives. Lignin represents the largest natural source of aromatic carbon on the planet, and thus, lignin-derived products have emerged as critical elements in the next generation of polymers. The relative abundance, large concentration of functional handles, and thermal stability of lignin make it an attractive target for bio-based polymers. However, the valorization of lignin to high-performance and cost-competitive materials remains a challenge. In this review, developments in the translation of lignin into value-added macromolecular components are discussed. Strategies to incorporate bulk lignin in polymer blends and composites are introduced with a focus on applications. Furthermore, recent advances in the preparation of higher-value thermoplastics, thermosets, and vitrimers from deconstructed lignin products are highlighted from a synthetic perspective. Finally, key hurdles and future opportunities in lignin valorization are explored. 

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2. Thermal and Mechanical Properties of Lignin Derivative–Sulfur Composites

   https://doi.org/10.1002/pol.20240566  

   Kapuge_Dona, Nawoda L; Sauceda‐Oloño, Perla Y; Smith, Rhett C (February 2025, Journal of Polymer Science)

   ABSTRACT Lignin, comprising 20%–35% of lignocellulosic biomass, is the second most abundant biopolymer after cellulose. As the bioethanol industry expands, the accumulation of lignin by‐products necessitates innovative valorization strategies. This study explores the synthesis and characterization of lignin‐derived composites. Specifically, the reaction of 20 wt. % lignin‐derived guaiacol or syringol with 80 wt. % elemental sulfur gives composites GS₈₀and SS₈₀, respectively. The chemical structures of composites were elucidated using GC–MS,¹H NMR, and UV–Vis spectroscopy, revealing the formation of both SC_aryland SC_alkylbonds. Thermal and morphological analysis (via TGA, DSC, PXRD, and SEM‐EDS) indicated SS₈₀has higher crystallinity and thermal stability than GS₈₀, attributed to a higher degree of crosslinking and a greater content of dark sulfur. Mechanical testing showed SS₈₀exhibits superior compressional and flexural strengths, and enhanced Young's modulus and Shore hardness, compared to GS₈₀. Notably, the mechanical strength parameters for SS₈₀are comparable to those of C62 class bricks used in construction applications. These findings suggest that lignin‐derived composites, particularly those incorporating syringol, can provide viable alternatives to traditional materials in various applications, contributing to both waste valorization and sustainable materials science. 

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3. Tailoring Polymer Properties Through Lignin Addition: A Recent Perspective on Lignin-Derived Polymer Modifications

   https://doi.org/10.3390/molecules30112455  

   Kapuge_Dona, Nawoda L; Smith, Rhett C (June 2025, Molecules)

   Lignin, an abundant and renewable biopolymer, has gained significant attention as a sustainable modifier and building block in polymeric materials. Recent advancements highlight its potential to tailor mechanical, thermal, and barrier properties of polymers while offering a greener alternative to petroleum-based additives. This review provides an updated perspective on the incorporation of lignin into various polymer matrices, focusing on lignin modification techniques, structure–property relationships, and emerging applications. Special emphasis is given to recent innovations in lignin functionalization and its role in developing high-performance, biodegradable, and recyclable materials such as polyurethanes, epoxy resins, phenol-formaldehyde resins, lignin-modified composites, and lignin-based films, coatings, elastomers, and adhesives. These lignin-based materials are gaining attention for potential applications in construction, automated industries, packaging, textiles, wastewater treatment, footwear, supporting goods, automobiles, printing rollers, sealants, and binders. 

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4. Valorisation of waste to yield recyclable composites of elemental sulfur and lignin

   https://doi.org/10.1039/C9TA03222C  

   Karunarathna, Menisha S.; Lauer, Moira K.; Thiounn, Timmy; Smith, Rhett C.; Tennyson, Andrew G. (January 2019, Journal of Materials Chemistry A)

   Lignin is the second-most abundant biopolymer in nature and remains a severely underutilized waste product of agriculture and paper production. Sulfur is the most underutilized byproduct of petroleum and natural gas processing industries. On their own, both sulfur and lignin exhibit very poor mechanical properties. In the current work, a strategy for preparing more durable composites of sulfur and lignin, LSx , is described. Composites LSx were prepared by reaction of allyl lignin with elemental sulfur, whereby some of the sulfur forms polysulfide crosslinks with lignin to yield a three-dimensional network. Even relatively small quantities (<5 wt%) of the polysulfide-crosslinked lignin network provides up to a 3.4-fold increase in mechanical reinforcement over sulfur alone, as measured by the storage moduli and flexural strength determined from dynamic mechanical analysis (temperature dependence and stress–strain analysis). Notably, LSx composites could be repeatedly remelted and recast after pulverization without loss of mechanical strength. These initial studies suggest potential practical applications of lignin and sulfur waste streams in the ongoing quest towards more sustainable, recyclable structural materials. 

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5. One-pot synthesis of enzyme@metal–organic material (MOM) biocomposites for enzyme biocatalysis

   https://doi.org/DOI https://doi.org/10.1039/D1GC00775K  

   Pan, Y.; Li, H.; Lenertz, M.; Han, Y.; Ugrinov, A.; Kilin, D.; Chen, B.; Yang, Z. (March 2021, Green chemistry)

   null (Ed.)

   Metal–organic frameworks/materials (MOFs/MOMs) are advanced enzyme immobilization platforms that improve biocatalysis, materials science, and protein biophysics. A unique way to immobilize enzymes is co-crystallization/co-precipitation, which removes the limitation on enzyme/substrate size. Thus far, most enzyme@MOF composites rely on the use of non-sustainable chemicals and, in certain cases, heavy metals, which not only creates concerns regarding environmental conservation but also limits their applications in nutrition and biomedicine. Here, we show that a dimeric compound derived from lignin, 5,5′-dehydrodivanillate (DDVA), co-precipitates with enzymes and low-toxicity metals, Ca2+ and Zn2+, and forms stable enzyme@Ca/Zn–MOM composites. We demonstrated this strategy on four enzymes with different isoelectric points (IEPs), molecular weights, and substrate sizes. Furthermore, we found that all enzymes displayed slightly different but reasonable catalytic efficiencies upon immobilization in the Ca–DDVA and Zn–DDVA MOMs, as well as reasonable reusability in both composites. We then probed the structural basis of such differences using a representative enzyme and found enhanced restriction of enzymes in Zn–DDVA than in Ca–DDVA, which might have caused the activity difference. To the best of our knowledge, this is the first aqueous-phase, one-pot synthesis of a lignin-derived “green” enzyme@MOF/MOM platform that can host enzymes without any limitations on enzyme IEP, molecular weight, and substrate size. The different morphologies and crystallinities of the composites formed by Ca–DDVA and Zn–DDVA MOMs broaden their applications depending on the problem of interest. Our approach of enzyme immobilization not only improves the sustainability/reusability of almost all enzymes but also reduces/eliminates the use of non-sustainable resources. This synthesis method has a negligible environmental impact while the products are non-toxic to living things and the environment. The biocompatibility also makes it possible to carry out enzyme delivery/release for nutritional or biomedical applications via our “green” biocomposites. 

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