Preparation and Characterization of Bisphenol A-Based Thermosetting Epoxies Based on Modified Lignin

Abstract

Lignin is a highly abundant renewable natural resource with a unique structure, abundant reserves, and low cost. However, largescale utilization based on lignin still remains challenging due to its heterogeneity and inhomogeneity. Herein, we report the fabrication of tunable and mechanically tough lignin-based thermosetting epoxy resins with outstanding thermal stability by optimizing epoxidation conditions and the crosslinker. The obtained lignin-based bisphenol A composites show a tensile strength of 11.5 MPa, Young's modulus of 5.0 MPa, and heat resistance index temperature (T s ) up to 160.0 °C by tailoring the dosage of epichlorohydrin. It was found that the introduction of oxirane moieties on the lignin backbone limitedly improved the interfacial compatibility of the composite. Moreover, the enhanced mechanical and thermal properties were ascribed to the incorporation of modified lignin segments into the epoxy networks and the corresponding alternation of crosslink structures. Overall, this work provides a viable pathway to produce cost-efficient biobased materials with controlled mechanical properties for adhesives and engineering plastics.

From waste to resource: advancements in sustainable lignin modification

“…For instance, multiple literature reports demonstrated that bisphenol A (BPA) can be partially substituted by lignin to improve material properties. [76][77][78] A substitution of up to 30 wt% of bisphenol-A diglycidyl ether (BPADGE) with lignin-based epoxides is possible without negative effects on the properties of the resulting material. Instead, incorporation of lignin units into epoxy resins turned out to be beneficial for material properties, such as glass transition temperature and Young's modulus.…”

“…The incorporation of 10 wt% of epoxidized lignin (based on BPADGE mass) significantly improved the stiffness of the resulting material and its tensile strength (from 6.2 MPa without lignin to 10.9 MPa with lignin). 78…”

“…81,82 Depending on the report, E-factors for reactions of lignin with epichlorohydrin vary between 4 and 16, if epichlorohydrin is used as reagent and solvent (Table 3). [76][77][78]83,84 In 2017, BPA based epoxy resins with varying content of epoxidized lignin and isophorone diamine as hardener were reported (E complex : 6.35, Scheme 6). 76 In the used epoxy formulation, BPADGE was substituted gradually by glycidylated organosolv lignin to investigate the properties of the resulting material depending on the lignin content.…”

“…a No final weight of isolated product was reported, therefore final weight of the product was calculated based on theoretical yield (for more information see ESI †).Scheme 6 Synthesis of epoxy resins from glycidylated lignin, bisphenol-A diglycidyl ether (BADGE) and diamine hardener ( prepared by the authors, adapted from ref [76][77][78]…”

Waterborne Lignin-Based Epoxy Resin: A Green and Effective Chemical Cross-Linker to Form Soy Protein-Based Wood Adhesive with High Performance

“…Lignin, the main source of natural polyphenol, has been considered as one of the most potential candidates to substitute fossil-based materials in the formulation of epoxy resins. − Particularly, the low-molecular-weight oligomers derived from depolymerization or solvent fractionation of lignin demonstrated higher reactivity and better solvent solubility and could be used effectively in the preparation of lignin-based epoxy resins (LEPs) with excellent thermal and mechanical properties. − Nevertheless, the practical application of LEPs as chemical cross-linkers in SP adhesive modification remains a challenge. Because the LEPs always present high viscosity and can be dispersed only with organic solvents, this makes them difficult to disperse uniformly in the water-based SP matrix, thereby reducing their reinforcement efficiencies.…”