Investigating the influence of the composition of the modified lignin-epoxy coating on hydrophobicity, using Box–Behnken design optimization model

Conventionally bisphenol A epichlorohydrin (BPA-EC) is used as epoxy resin and cycloaliphatic amine is used as a curing agent for industrial corrosion mitigation. However, due to their noticeable toxicity, alternative curing agents and decreasing the conventional compounds in the coating  is a demanding task. Aminopropyltriethoxysilane can be an alternative curing agent and lignin can partially replace BPA-EC , as the preliminary adhesion study of the developed coating suggested. However, other characteristics of the coating need to be examined to evaluate the coating holistically. Hydrophobicity is such a characteristic, which plays a leading role in enhancing the anti-corrosivity of the coating, especially for coating, implemented on submerged metallic bodies. The current study attempted to find the justification of  BPA-EC in terms of hydrophobicity. The response surface methodology has been followed using the Box–Behnken design model to investigate the respective and cumulative effect of each element. Initially, the model has a P value of 0.0198, with some of the terms not significant. Thus, a modified model has been introduced keeping only the terms, close to the significant p-value of 0.05. Finally, a P-value of 0.0001 has been achieved. Experimental verification of the response values exhibited an average error of 9.84%. The result showed a non-linear association between the respective constituents. Statistics showed that BPA-EC positively impacts hydrophobicity. Thus, to maintain the hydrophobicity rather than 100% replacement by lignin, a minimum level of bisphenol epichlorohydrin is obligatory; ensuring the legitimacy of the constituents in the coating.