Solubility study of lignin in industrial organic solvents and investigation of electrochemical properties of spray-coated solutions
Arman Dastpak, Tainise V. Lourenҫon, Mikhail Balakshin, Syed Farhan Hashmi, Mari Lundström, Benjamin P. Wilson
Abstract
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 pilot-scale 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.