Synthesis of Renewable Thermoset Polymers through Successive Lignin Modification Using Lignin-Derived Phenols

Abstract

An approach to lignin−based epoxy networks from both organosolv lignin and lignin derived phenol (dihydroeugenol) are developed using multiple chemical modifications including demethylation, phenolation and phenol−formaldehyde reaction. Structures of lignin incorporated novolac polyphenols (LINPs) and epoxy networks (LINENs) were characterized using proton nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. Compared to a common synthesis route in which lignin was epoxidized prior to blend with comonomers (LBEN), LINEN derivatives exhibited improved crosslink density (ρ), α−relaxation temperature (T α ) and storage modulus in glassy region (E g ') as obtained from dynamic mechanical analysis (DMA), and increased thermal stability measured by thermogravimetric analysis (TGA). This study widens the routes of lignin modification.Renewable epoxy networks derived from both lignin and lignin derivatives are economically and ecologically attractive.However, steric hindrance and poor dispersion of modified lignin impair covalent crosslinking. 12,20 Another chemical modification is to make covalent links prior to epoxidation and curing. For example, LDPs can be grafted onto lignin through phenolation, substituting lignin aliphatic hydroxyl by ortho/para−bound LDPs. The grafted LDPs do not only improve lignin's compatibility, they also introduce additional sites (ortho and para), which can be used in building up cross−linked networks.In this study, organosolv lignin and LDPs are deployed through chemical modifications as illustrated in Figure 1. First, lignin's aromatic methoxy groups are deprotected, 21 followed by addition of deprotected dihydroeugenol (DHEO), which can be obtained from catalytic depolymerization of lignin (CDL). 22 As depicted in Figure 1, deprotected lignin (DL) is reacted with excess amount of DHEO under acid catalysis to yield phenolated lignin (PL). Formaldehyde solution is subsequently added to make a deprotected lignin incorporated novolac polyphenol (DLINP). The latter is reacted with epichlorohydrin to yield epoxy monomer that can be cured with diethylenetriamine (DETA) to make deprotected lignin incorporated novolac epoxy network (DLINEN). A comparison between the proposed synthesis routes with direct epoxidation of lignin (or deprotected lignin, DL) followed by blending with epoxidized DHEO novolac oligomer (DLBEN) is presented in Figure 2.

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

“…They also prepared epoxy resin, employing both lignin-derived phenols (LDPs) and lignin itself. 397 This procedure involved demethylation of lignin followed by the addition of 4-propylguaiacol ( M7G ) and formaldehyde solution to make a deprotected lignin incorporated novolac polyphenol (DLINP). Consequently, the DLINP was reacted with epichlorohydrin and cured with diethylenetriamine (DLINEN).…”

Development of sustainable bio-adhesives for engineered wood panels – A Review

“…Biorenery-based technical lignin has also been used in preparing lignin-phenol-formaldehyde synthesis for wood based panel applications. [81][82][83] Zhao and Abu-Omar 84 have performed lignin modications through deprotection, phenolation and phenol-formaldehyde reactions and have successively improved the uniformity and mechanical and thermal properties of bio-based thermosets.…”

Epoxidized soybean oil cured with tannic acid for fully bio-based epoxy resin

“…Many chemical modications of lignin and TA have been described for these purposes. [37][38][39] As a type of biobased polyphenol, TA has abundant reactive terminal phenolic hydroxyl groups with a hyperbranched aromatic/alicyclic polyester core, which can make up for the exible chain defects of ESO and form highly crosslinked networks. The chemical formula for commercial TA is oen given as C 76 H 52 O 46 , which corresponds with decagalloyl glucose, 40 as shown in Scheme 1.…”