A review of lignin as a precursor for macromonomers: Challenges and opportunities in utilizing agri-food waste

Lignocellulosic biomass, rich in cellulose, hemicellulose, and lignin, represents a promising renewable resource. However, lignin, a complex polyphenolic material, remains underutilized despite its surplus production. This review focuses on the conversion of lignin into macromonomers for polymer production. While lignin's potential in polymer science is gaining recognition, studies focusing specifically on lignin-based macromonomers remain limited. This review addresses this gap by discussing the synthesis of lignin macromonomers and their role in polymer synthesis. It also highlights the potential and challenges of sourcing lignin from agri-food waste, with the goal of inspiring advancements and fostering innovation in the development of more sustainable and circular polymer systems.

In Situ Lignin Adhesion for High-Performance Bamboo Composites

Bamboo composite is an attractive candidate for structural materials in applications such as construction, the automotive industry, and logistics. However, its development has been hindered due to the use of harmful petroleum-derived synthetic adhesives or low-bonding biobased adhesives. Herein, we report a novel bioadhesion strategy based on in situ lignin bonding that can process natural bamboo into a scalable and high-performance composite. In this process, lignin bonds the cellulose fibrils into a strong network via a superstrong adhesive interface formed by hydrogen bonding and nanoscale entanglement. The resulting in situ glued-bamboo (glubam) composite exhibits a record-high shear strength of ∼4.4 MPa and a tensile strength of ∼300 MPa. This in situ lignin adhesion strategy is facile, highly scalable, and cost-effective, suggesting a promising route for fabricating strong and sustainable structural bamboo composites that sequester carbon and reduce our dependence on petrochemical-based adhesives.

Lignocellulosic biomass pretreatment by deep eutectic solvents on lignin extraction and saccharification enhancement: A review

Biomass recalcitrance hinders efficient utilization of lignocellulosic biomass, making pretreatment process a crucial step for successful biorefinery process. Pretreatment processes have been developed for processing biomass, while technical obstacles including intensive energy requirement, high operational cost, equipment corrosions resulted from currently applied techniques promote the development of new pretreatment process for biomass. The deep eutectic solvent (DES) has been recognized as a promising solvent for biomass pretreatment, although the DES application toward biomass is still in its nascent stage. This review summarized the current researches using DES for biomass pretreatment, focusing particularly on lignin extraction and saccharification enhancement of lignocellulosic biomass. The mechanisms for biomass fractionation using DES as agents are introduced. Prospect and challenge were outlined.

Synthesis of High-Water-Resistance Lignin-Phenol Resin Adhesive with Furfural as a Crosslinking Agent

In this study, furfural was used as a crosslinking agent to enhance the water resistance of lignin-phenol-formaldehyde (LPF) resin. The effect of the furfural content on the physicochemical properties of the adhesives was explored, and the possible synthesis mechanism of the furfural-modified lignin-phenol-formaldehyde (LPFF) resin adhesives was investigated. Compared with the LPF adhesive, the LPFF adhesive with 15% furfural content and 50% lignin substituent exhibited outstanding properties in all considered aspects; it had a high wet shear strength (1.30 MPa), moderate solid content (54.51%), and low viscosity (128 mPa∙s), which were 38.0% higher, 3.6% higher, and 37.5% lower than those of the LPF adhesive. Analyses via nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy confirmed that the furfural content improved water resistance of the lignin-based adhesive; this improvement was due to the formation of new chemical bonds between furfural and lignin to construct a dense crosslinked network structure. In addition, the decrease in viscosity and the increase in solid content enabled the adhesive to better penetrate into the wood porous structure, showing stronger adhesion. Therefore, the LPFF adhesive has superior water resistance, high strength, and good thermal stability; thus, it has a great potential for industrial applications.

Bio-Based Alternatives to Phenol and Formaldehyde for the Production of Resins

Phenol-formaldehyde (PF) resin continues to dominate the resin industry more than 100 years after its first synthesis. Its versatile properties such as thermal stability, chemical resistance, fire resistance, and dimensional stability make it a suitable material for a wide range of applications. PF resins have been used in the wood industry as adhesives, in paints and coatings, and in the aerospace, construction, and building industries as composites and foams. Currently, petroleum is the key source of raw materials used in manufacturing PF resin. However, increasing environmental pollution and fossil fuel depletion have driven industries to seek sustainable alternatives to petroleum based raw materials. Over the past decade, researchers have replaced phenol and formaldehyde with sustainable materials such as lignin, tannin, cardanol, hydroxymethylfurfural, and glyoxal to produce bio-based PF resin. Several synthesis modifications are currently under investigation towards improving the properties of bio-based phenolic resin. This review discusses recent developments in the synthesis of PF resins, particularly those created from sustainable raw material substitutes, and modifications applied to the synthetic route in order to improve the mechanical properties.

Phenol-Furfural Resin/Montmorillonite Based High-Pressure Green Composite from Renewable Feedstock (Saccharum munja) with Improved Thermo-Mechanical Properties

This research endeavour aimed to explore the potential of a native, nonedible and low market value plant feedstock, i.e., Saccharum munja for green synthesis of woodware materials and improve its features by incorporating an economical blending material. A significant amount of furfural, i.e., 58%, was extracted from Saccharum munja through the modified acid digestion method. Extracted furfural was reacted with phenol to prepare phenol-furfural resin, an alternative to phenol-formaldehyde resin but with no harmful effects for humans. The synthesized resin was also blended with montmorillonite clay after modification via Dimethyl Sulfoxide (DMSO) treatment for improved thermo-mechanical properties. These resins and composites were characterized by XRD, SEM, and FTIR spectroscopy. Resultant resins and composites were further employed as a binding agent to make high-pressure composite from leftover plant residue by hot-press method. The resultant product was subjected to TGA analysis and furnished high value of degradation temperature (T_deg), i.e., 607 °C. Prepared high-pressure composite samples were mechanically tested through compression tests by Tinius Olsen Testing Machine and hardness tests by Rockwell Hardness Tester. Its tensile strength value was 58.3 MPa while hardness value was found to be 64 RHB which was greater than mild copper with hardness value 48.9 RHB. Thus, green high-pressure composite material was successfully developed by employing Saccharum munja and montmorillonite clay while no toxic resin was used, nor was any residue left over.

Cellulose enzymatic saccharification and preparation of 5-hydroxymethylfurfural based on bamboo hydrolysis residue separation in ionic liquids

Ionic liquid/ethanol was used in bamboo hydrolysis residue (BHR) to separate lignin and cellulose.