Grafting strategies for hydroxy groups of lignin for producing materials

Abstract

Lignin is one of the most abundant biopolymers on Earth and is considered as the primary resource of aromatic compounds. Recently, lignin has attracted attention from scientists and industrialists due to its inherent potential arising from its unique structure, which leads to its possible use in many applications.Many efforts have been made to ameliorate the reactivity and compatibility of lignin in different areas. Although methods have been proposed for endowing lignin with different properties, there continues to be a considerable demand for discovering new and effective ways of unraveling the beneficial uses of this aromatic polymer. Considering the structure of lignin, different grafting modifications can occur on the aliphatic and/or aromatic groups of lignin. To date, there has been a lack of fundamental understanding of the modification pathways of lignin for generating lignin-based products. In this review paper, we discuss comprehensively the chemical reactions that were introduced in the literature for preparing lignin with different features via modifying its phenolic and aliphatic hydroxy groups for altered uses. This review paper critically and comprehensively elaborates on the recent progress in lignin reactions as well as the challenges, advantages and disadvantages associated with the reaction procedures and the product development processes. Furthermore, the research gap in reaction strategies and product development are described throughout this study.

Multifunctional Lignin-Based Composite Materials for Emerging Applications

“…In past decades, billions of tons of non-biodegradable plastics have been produced, which is a significant source of pollution. As an abundant natural polymer, lignin could be integrated into plastics to fabricate high-value biodegradable materials with economic competitiveness (Sen et al, 2015;Kazzaz et al, 2019). Therefore, the preparation of composite materials by mixing lignin with various plastics had attracted attention.…”

Biobased Resins Using Lignin and Glyoxal

“…For methylolation, the reaction conditions are comparable (alkaline medium and temperature range of 25−90°C) to glyoxalation; however, shorter reaction times are typically applied due to the higher reactivity of formaldehyde compared to glyoxal. 110 From Table 1, it can be concluded that most of the studies applied a glyoxal solution to lignin (G/L), mass ratio between 0.1 and 1 (glyoxal is typically supplied as a 40 wt % solution). However, it is difficult to compare all glyoxal:lignin ratios applied in the different studies.…”

Sulfomethylation of radiata pine kraft lignin and its use as a molybdenite depressant in selective chalcopyrite-molybdenite separation by flotation

“…Signals at δ 3.9 to 3.6 are assigned to -OCH3 hydrogens and ~ δ 3.3 to -CH2 hydrogens from hydroxymethyl groups (Jiao et al 2018). During sulfomethylation, formaldehyde introduces a hydroxymethyl group into the lignin at the C5 position of the aromatic ring, which is the main reaction location in the sulfonation reaction with sodium sulfite (Yu et al 2013;Kazzaz et al 2019). Thus, the increase in the signal intensity in this region is due to the introduction of hydroxymethyl groups in the OSKL.…”

“…The sulfomethylation reaction of lignin involves the addition of a methylene sulfonate group (-CH2SO3) into the aromatic ring, i.e., the C5 position of G-type lignin. Briefly, the precursors formaldehyde (CH2O) and sodium sulfite (Na2SO3) under determined reaction parameters combine to form sodium hydroxymethyl sulfonate, the reactive species responsible for introducing the sulfonic group into lignin (Meister 2002;Konduri and Fatehi 2015;Huang et al 2018;Kazzaz et al 2019). However, due to the complex and highly branched polyphenolic structure of lignin along with the sulfomethylation reaction conditions, different degrees of sulfonation and structural changes of lignin can be promoted, which could affect the depression performance of the lignin-derived product.…”