Abstract
There is a need for safe and sustainable alternatives in the coating industry. Bio-based coatings are interesting in this perspective. Although various oils and waxes have been used as traditional wood coatings, they often lack sufficient durability. Lignin is an abundant natural polyphenol that can be used to cure epoxies, but its poor water solubility has impeded the use of unmodified lignin in coatings in the past. To address this issue, water-dispersible colloidal lignin particles (CLPs) and an epoxy compound, glycerol diglycidyl ether (GDE), were used to prepare multiprotective bio-based surface coatings. With the GDE/CLP ratios of 0.65 and 0.52 g/g, the cured CLP–GDE films became highly resistant to abrasion and heat. When applied as a coating on wooden substrates, the particulate morphology enabled effective protection against water, stains, and sunlight with very thin layers (less than half the weight of commercial coatings) while retaining the wood’s breathability excellently. Optimal hydrophobicity was reached with a coat weight of 6.9 g(CLP)/m2, resulting in water contact angle values of up to 120°. Due to their spherical shape and chemical structure, the CLPs acted as both a hardener and a particulate component in the coating, which removed the need for an underlying binding polymer matrix. Light interferometry measurements showed that while commercial polymeric film-forming coatings smoothened the substrate noticeably, the particulate morphology retained the substrate’s roughness in lightweight coatings, allowing for a high water contact angle. This work presents new strategies for lignin applications in durable particulate coatings and their advantages compared to both currently used synthetic and bio-based coatings.
Highlights
Coatings and paints are essential for protecting and repairing surfaces[1] and to enhance sustainability by prolonging the lifetime of products
The coatings were prepared using aqueous dispersions of colloidal lignin particles (CLPs) mixed with glycerol diglycidyl ether (GDE) in various ratios and concentrations
We observed that coat weights of 60 g(CLP)/ m2 on wooden samples resulted in Water contact angles (WCAs) of only 93° with a GDE/CLP ratio of 0.52 g/g
Summary
Coatings and paints are essential for protecting and repairing surfaces[1] and to enhance sustainability by prolonging the lifetime of products. One example of bio-based particulate coatings is the layer-bylayer approach to attach wax particles onto wood, textiles, or other cellulosic substrates using a cationic polymer or particle as binder.[30,36−38] Electrostatically bound coatings such as these can be used extremely sparingly while providing excellent hydrophobicity They are easy to apply but can be washed away by detergents.[36] The resistance against washing and abrasion can be increased by covalently binding particles to a polymer matrix or by embedding the particles in a polymer matrix bound to the substrate. The coating demonstrates good resistance to abrasion, solvent, water, and UV light while having outstanding breathability compared to the commercial oil, lacquer, and epoxy coatings that were examined and can be applied onto a wide range of rigid materials, as demonstrated by its application on wood and metal surfaces
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