Lignin Biopolymers in the Age of Controlled Polymerization

Abstract

Polymers made from natural biomass are gaining interest due to the rising environmental concerns and depletion of petrochemical resources. Lignin isolated from lignocellulosic biomass is the second most abundant natural polymer next to cellulose. The paper pulp process produces industrial lignin as a byproduct that is mostly used for energy and has less significant utility in materials applications. High abundance, rich chemical functionalities, CO2 neutrality, reinforcing properties, antioxidant and UV blocking abilities, as well as environmental friendliness, make lignin an interesting substrate for materials and chemical development. However, poor processability, low reactivity, and intrinsic structural heterogeneity limit lignins′ polymeric applications in high-performance advanced materials. With the advent of controlled polymerization methods such as ATRP, RAFT, and ADMET, there has been a great interest in academia and industry to make value-added polymeric materials from lignin. This review focuses on recent investigations that utilize controlled polymerization methods to generate novel lignin-based polymeric materials. Polymers developed from lignin-based monomers, various polymer grafting technologies, copolymer properties, and their applications are discussed.

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

“…Lignin-based copolymers are usually synthesized via controlled polymerization including atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT) and ring-opening polymerization (ROP). The “graft from” method, in which the lignin macromolecules serve as a core unit and new polymer chains grow on the initiating sites, is considered as a cost-effective way to produce lignin-based copolymers at industrial scale [ 43 ]. The grafted polymers containing new functional groups expand the utilization of lignin further in biomedical nanofibers, thermoplastics and additives such as dispersants, flocculants and surfactants ( Table 1 ) [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ].…”

Vegetable Additives in Food Packaging Polymeric Materials

“…Industrially, lignin is isolated from cellulosic fibers by chemical treatment, which breaks down lignin-carbohydrate complexes. During this process, partial depolymerization of the complex lignin macromolecules occurs along with re-polymerization (condensation) which may alter the native lignin structure [37]. The paper pulping process (lignin extraction from lignocellulosic biomass) which produces industrial lignin as a byproduct [37] may include chemical methods [38], such as -Kraft process which uses a mixture of Na 2 S and NaOH (White Liquor) at high temperature (150-180 • C), -sulfite process which employs sulfite or bisulfite to digest biomass, -organosolv pretreatment of lignocellulose which involves a biomass extraction in a mixture of solvent (ethanol being the most common) and water under high pressure [39], -single pot soda cooking pre-treatment for extracting lignin and isolate cellulose nanofibrils simultaneously [13].…”

“…Lignin draws attention as a valuable environmentally friendly and biodegradable raw natural resource. Lignin is the second most abundant organic substance in the world, estimated to represent 30% of the total biomass produced in the biosphere and is mostly produced by the paper pulping industry [37].…”

Using Sulfobutylated and Sulfomethylated Lignin as Dispersant for Kaolin Suspension

“…Lignin is a suitable candidate for the production of non-toxic, renewable, and sustainable dispersants as it is available in large quantities [ 17 , 18 ]. However, lignin is not suitable for direct use as a dispersant due to its limited solubility in water [ 19 ].…”