Potential Lignin-Derived Alternatives to Bisphenol A in Diamine-Hardened Epoxy Resins

Abstract

This work details the synthesis and characterization of potentially lignin-derived bisguaiacols as alternatives to petroleum-derived bisphenol A (BPA) in diamine-cured epoxy resins. The variations in the number of methoxy groups of lignin facilitate the systematic chemical and thermomechanical manipulation of bisguaiacol-based thermosets to achieve desirable properties. Herein, ten bisguaiacols (including structural isomers), differing in the number of methoxy groups and regioisomer content, were synthesized from substituted bioderivable hydroxybenzyl alcohols and phenols by acidcatalyzed electrophilic aromatic substitution approaches and then functionalized with oxirane groups. These bisguaiacol diglycidyl ethers were subsequently cured with a model diamine. All cured bioderivable resins had glass transition temperatures (T g 's) above 100 °C, 5 wt % loss temperatures above 300 °C, and room-temperature glassy storage moduli above 2.0 GPa, values that were comparable to bisphenol A diglycidyl ether (BADGE/DGEBA) cured resins. Furthermore, final cured resin T g 's (111−151 °C) and high-temperature rubbery moduli (15−46 MPa) were easily tuned by manipulating the relative number of methoxy moieties and the regioisomer content, demonstrating the versatility and robustness of these bioinspired materials.

Choosing the Right Lignin to Fully Replace Bisphenol A in Epoxy Resin Formulation

“…Therefore, hardwood lignins have a more linear structure and lower molecular weight compared to softwood lignin [46] . Moreover, during the pulping process, some intermolecular linkages (like β‐ O ‐4) in lignin are broken, affecting lignin properties [22] . For example, on average, kraft lignins had lower molecular weights ( M w =7100 Da) than organosolv lignins ( M w =10000 Da) [43] .…”

“…In contrast, lignin from herbaceous plants includes both G and S units and a high amount of H units [21] . Owing to the presence of phenolic hydroxy groups in lignin's structure, lignin is widely recognized as an alternative raw material to substitute BPA in epoxy resin formulation [22] …”

“…Although many studies have focused on utilizing lignin in epoxy resin, [23,27,33,34] they mostly used modified lignin (fractionated or lignin monomers) [23,27,29] . For instance, several studies used small compounds obtained from lignin, including syringaresinol, [35] isosorbide diferulate, [36,37] bisguaiacol, [22] diphenolic acid, [38] and ferulic acid [39–41] to synthesize epoxy resins. They reported that the cured epoxy thermosets made with lignin‐derived monomers/dimers had comparable properties to DGEBA thermosets, and properties of the epoxy systems can be tunable by using various curing agents.…”

Integrating anaerobic digestion and slow pyrolysis improves the product portfolio of a cocoa waste biorefinery

“…6). Therefore, extraction of these methyoxy(alkyl)phenols might be opportune, as these are considered renewable building blocks for chemistry and plastic industry [62][63][64][65][66] . Recently, an extraction scheme has been proposed, able to separate these methoxyphenols with an increased selectivity, by carefully controlling the pH of the extracted solution 54 .…”

Preparation of Renewable Epoxy-Amine Resins With Tunable Thermo-Mechanical Properties, Wettability and Degradation Abilities From Lignocellulose- and Plant Oils-Derived Components

“…Indeed, the aromatic moieties present in these bio-based chemicals confer rigidity to the resulting polymers (Wang et al, 2017; Feghali et al, 2018). For example, there have been many reports on epoxy resins from eugenol (Wan et al, 2016), vanillin (Fache et al, 2015a,b; Hernandez et al, 2016; Mauck et al, 2017; Nicastro et al, 2018; Savonnet et al, 2018; Zhao et al, 2018), ferulic and sinapic acids (Maiorana et al, 2016; Janvier et al, 2017; Ménard et al, 2017), guaiacols (Maiorana et al, 2015), and creosol (Meylemans et al, 2011) with promising performances capable of competing with current DGEBA-based materials. However, few researchers have considered the potential toxicity of these BPA substitutes, especially endocrine disruption, which remains a crucial health issue for both plastic sector workers and consumers (Jiang et al, 2018).…”