Solubility study of lignin in industrial organic solvents and investigation of electrochemical properties of spray-coated solutions

In the present study, six organic solvents that are commonly used in the paint industry (1-butanol, 1-methoxy-2-propanol, 2-propanol, butyl acetate, propylene glycol monomethyl ether acetate, and diethylene glycol monobutyl
ether) were tested for their ability to dissolve two distinct lignins: an industrial kraft lignin (KL) and a pilotscale organosolv lignin (OL). Among the solvents investigated, 1-methoxy-2 propanol (Dowanol™ PM, DPM) and diethylene glycol monobutyl ether (Butyl Carbitol™, BC) demonstrated high degrees of solubility (> 98 wt. % at 25 °C) that were comparable to the commonly used lignin solvent, dimethyl sulfoxide (DMSO). Lignin coatings were prepared by spray-coating the new lignin-solvent solutions on iron-phosphated steel, prior to investigation
of their subsequent morphological and electrochemical performance characteristics. It was found that KL/DPM coatings demonstrate suitable short-term (1 h, 5% NaCl) anticorrosive characteristics with an increased charge transfer resistance (Rct) compared to the bare steel (1.5×10⁵ Ω. cm² cf. 1.9×10³ Ω. cm²). However, a prolonged (24 h) immersion resulted in a decrease in Rct values (1.1×10⁴ Ω. cm²), which may indicate that the lignin coating alone is unable to provide long-term protection under these aggressive conditions.