Investigation of the anticorrosion performance of lignin coatings after crosslinking with triethyl phosphate and their adhesion to a polyurethane topcoat
This study investigates the anticorrosion properties of sustainable organic coatings,
which were prepared by dissolution of two different types of technical lignins - organosolv lignin
(OL) and kraft lignin (KL) - in an organic solvent and applied onto iron-phosphated steel by airassisted spray coating. Influence of triethyl phosphate (TEP) as a crosslinking agent for lignin
and its effect on the anticorrosion properties of coatings during 24 h of immersion in 3.5% NaCl
were investigated. Results obtained from electrochemical impedance spectroscopy (EIS) of
coated steels suggest that the initial protection performance (1 h immersion) of non-crosslinked
OL is higher than that of KL. Nevertheless, KL coatings that contained TEP and were heat-treated
at elevated temperature (180 °C) demonstrated the best overall anticorrosion performance. In
contrast, a similar trend was not observed for OL coatings, which indicates that the structural
properties of lignin may be a crucial factor in applicability of TEP as a crosslinking agent. In
addition, a layer of polyurethane was applied on all the different types of lignin coatings prepared
and their adhesion characteristics were studied by crosscut adhesion measurements (ISO 2409).
These adhesion results revealed that neither KL-TEP nor OL-TEP coatings demonstrate proper
adhesive characteristics with a polyurethane (PU) topcoat and consequently these coatings are
not suitable for utilization as a primer coating for the PU topcoat studied