Ductile, High-Lignin-Content Thermoset Films and Coatings

Abstract

In the context of transitioning toward a more sustainable use of natural resources, the application of lignin to substitute commonly utilized petroleum-based plastics can play a key role. Although lignin is highly available at low cost and presents interesting properties, such as antioxidant and UV barrier activities, its application is limited by its low reactivity, which is a consequence of harsh conditions normally used to extract lignin from biomass. In this work, the use of glyoxylic acid lignin (GA lignin), rich in carboxylic acid groups and hence highly reactive toward epoxy cross-linkers, is presented. GA lignin, which is directly extracted from biomass via a one-step aldehyde-assisted fractionation process, allowed the preparation of thermoset films and coatings via a simple reaction with sustainable poly(ethylene glycol) diglycidyl ether and glycerol diglycidyl ether cross-linkers. This allows one to prepare freestanding films containing up to 70 wt % lignin with tunable mechanical properties and covalently surface-attached coatings containing up to 90 wt % lignin with high solvent resistance. Both films and coatings display antioxidant properties and combine excellent UV barrier activity with high visible transparency, which is attractive for applications in sustainable food packaging.

Exploring Thermoset Fracture with a Quantum Chemically Accurate Model of Bond Scission

“…Another hypothesis is related to larger-scale structures such as air pockets or pores. Air pockets or pores could potentially expedite the fracture toward the elastic regime and exhibit a distinct temperature dependence through microstructural reorganization. − One piece of supporting evidence is that in experiments of thermoset films where length-scales are limited to micrometers, the elongation can exceed 100% before failure, in better alignment with the behaviors in the simulations. These factors also contribute to the ultimate strength at fracture of the material in the present simulations being greater than those in experiments.…”

From waste to resource: advancements in sustainable lignin modification

“…120 All epoxy films possessed excellent UV barrier properties while maintaining good visible light transparency and are therefore promising materials for food packaging applications. 120 The reported procedures for AAF with glyoxylic acid and epoxy resin synthesis are considered unsafe due to the use of possibly carcinogenic 1,4-dioxane as solvent. 64 In other procedures, more sustainable 2-methyltetrahydrofuran was used as solvent for AAF with isobutyraldehyde and propionaldehyde.…”

“…35 In another study, GA-lignin was used for the synthesis of epoxy resins that contained up to 70 wt% of lignin, by curing with polyethylene glycol diglycidyl ether (PEGDGE, Scheme 11). 120 All epoxy films possessed excellent UV barrier properties while maintaining good visible light transparency and are therefore promising materials for food packaging applications. 120 The reported procedures for AAF with glyoxylic acid and epoxy resin synthesis are considered unsafe due to the use of possibly carcinogenic 1,4-dioxane as solvent.…”

Hardener-Dependent Properties of Twice Renewable Epoxy Resins Combining Tailored Lignin Fractions and Recycled BPA

“…The remaining phenol groups within lignin serve as effective scavengers of radicals, preventing oxidation reactions, and work as chromophores capable of absorbing UV light, promoting protection barrier capabilities. While the aliphatic alcohols assist the material-substrate adhesion by forming H-bonds or strong polar attractions to oxide or hydroxyl surfaces. , …”

“…While the aliphatic alcohols assist the material- substrate adhesion by forming H-bonds or strong polar attractions to oxide or hydroxyl surfaces. 30,31 Herein, we have designed and characterized a family of 20 renewable epoxy resins by systematically modulating the structural parameters of the formulations, such as the hardener chemical structures, the epoxide/hardener (E/H) ratios, and the content of extracted Kraft lignin (EKL). In order to maximize the renewability of the epoxy resins, r-BPA (obtained by solvolysis of PC) was combined with EKL.…”