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Lignin-based epoxy resins approach viability for metal coatings
Researchers have developed fully lignin-based epoxy resin systems for metal coating applications that deliver reliable adhesion, impact resistance and durability – positioning depolymerised lignin as a scalable, bio-based alternative to bisphenol-derived resins.
Bisphenol-based epoxy resins remain widely used in the coatings industry, but growing regulatory pressure – particularly regarding endocrine-disrupting effects in food-contact applications – is driving the search for safer alternatives. Lignin, a renewable and abundantly available bio-aromatic polymer, has attracted considerable industrial interest as a potential substitute. However, variability in lignin quality and sourcing has so far limited its broader adoption in high-performance coating formulations.
A research team has now systematically addressed this challenge by developing a series of epoxy resin formulations based on glycidylated depolymerised lignin (GDL) with varying characteristics. The bio-based content was progressively increased by replacing fossil-based epoxy components with bio-based alternatives, enabling the team to study the impact of the bio-based transition on coating properties.
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Structure–property relationships guide formulation design
The resulting crosslinked networks were thoroughly characterised, with thermomechanical performance analysis used to investigate structure–property relationships. The study demonstrates that lignin variability – often considered a drawback – can be treated as a design factor when formulations are appropriately tailored. By controlling both the lignin source and the formulation architecture, consistent coating quality was achieved across different GDL grades.
Coating performance on metal substrates was evaluated using standardised industrial test methods, including assessments of appearance, adhesion, peel resistance and impact resistance. The fully lignin-based epoxy systems delivered reliable results across these criteria, confirming their suitability for metal coating applications.
Consistency and formulation design are key to success
The findings demonstrate that lignin can play a meaningful role in the transition towards bio-based coatings, provided that both the consistency of the lignin feedstock and the formulation strategy are carefully managed. The work represents a significant step towards scalable, high-performance bio-based coating materials that could reduce the industry’s dependence on bisphenol-derived resins while meeting increasingly stringent regulatory requirements.
Source: Celada, I. et al., Impact of the biobased transition on the properties of depolymerized lignin-derived epoxy resin for metal coating applications. Progress in Organic Coatings 109931 (2025).
