Recent Advances in the Application of Functionalized Lignin in Value-Added Polymeric Materials

Abstract

The quest for converting lignin into high-value products has been continuously pursued in the past few decades. In its native form, lignin is a group of heterogeneous polymers comprised of phenylpropanoids. The major commercial lignin streams, including Kraft lignin, lignosulfonates, soda lignin and organosolv lignin, are produced from industrial processes including the paper and pulping industry and emerging lignocellulosic biorefineries. Although lignin has been viewed as a low-cost and renewable feedstock to replace petroleum-based materials, its utilization in polymeric materials has been suppressed due to the low reactivity and inherent physicochemical properties of lignin. Hence, various lignin modification strategies have been developed to overcome these problems. Herein, we review recent progress made in the utilization of functionalized lignins in commodity polymers including thermoset resins, blends/composites, grafted functionalized copolymers and carbon fiber precursors. In the synthesis of thermoset resins such as polyurethane, phenol-formaldehyde and epoxy, they are covalently incorporated into the polymer matrix, and the discussion is focused on chemical modifications improving the reactivity of technical lignins. In blends/composites, functionalization of technical lignins is based upon tuning the intermolecular forces between polymer components. In addition, grafted functional polymers have expanded the utilization of lignin-based copolymers to biomedical materials and value-added additives. Different modification approaches have also been applied to facilitate the application of lignin as carbon fiber precursors, heavy metal adsorbents and nanoparticles. These emerging fields will create new opportunities in cost-effectively integrating the lignin valorization into lignocellulosic biorefineries.

Polymer Adsorbents vs. Functionalized Oxides and Carbons: Particulate Morphology and Textural and SurfaceCharacteristics

“…Lignins, polymer/lignins and other related composites are of interest from a practical point of view [ 112 , 113 ]. However, the analysis of their texture is not a simple task.…”

Lignin and Lignin-Derived Compounds for Wood Applications—A Review

“…It is the main pulping method for non-wood species. The main difference between soda pulping lignin and Kraft lignin is the lower sulfur content [ 2 , 9 ].…”

“…To improve the reactivity and thus the feasibility of lignin, various pretreatment methods are used [ 2 , 37 ]. An important method for pretreatment of lignin is methylolation.…”

“…Lignin is the most abundant aromatic polymer in nature and the second most abundant biomass on earth [ 1 , 2 , 3 ]. In paper production and other processes, lignin is obtained as a side product [ 4 ].…”

Characterisation of mass distributions of solvent-fractionated lignins using analytical ultracentrifugation and size exclusion chromatography methods

“…Lignins are abundant natural biopolymers produced by plants that account for approximately 30% of planetary non-fossil organic carbon 1 , 2 . Due to their high carbon content and aromatic structural units, they are increasingly recognised as renewable resources for the production of biofuels, chemicals, aromatic compounds including antioxidants and biopolymers 3 – 14 . Lignins are amorphous, irregular three-dimensional, and highly branched phenolic macromolecular polymers.…”