Kraft lignin as a partial replacement for a traditional surfactant in thymol-based biocidal suspensions: physical and chemical features

Abstract

Thymol is a renewable substance and has a high antimicrobial efficiency, which indicates that it could be used to produce sustainable biocides. In this study, we used kraft lignin as a partial replacement for a traditional surfactant in order to solubilize thymol in water. In this sense, this article reports an unprecedented method for using a kraft lignin solution to stabilize a thymol-based biocide with high fungicidal activity. The results showed that the lignin was crucial for stabilizing the suspensions. When the lignin was not added to the surfactant, there was a water-oil phase separation and the thymol crystallized after its rest for 30 days. Results obtained by in vitro experiments indicated that one of the studied lignin:thymol suspension (volume ratio of 1:0.1) presented an excellent fungal resistance. Furthermore, even the sample with the smallest thymol concentration (c.a. 0.5%) was able to inhibit the mycelial growth of the bracket fungus (Ganoderma applanatum), which is a promising feature for a biocidal application. HIGHLIGHTS This research addresses multidisciplinary concepts for obtaining sustainable products; Lignin is a good renewable stabilizer for thymol suspensions in water; Thymol and lignin, at three different mass ratios, were successfully applied for obtaining stable suspensions; Lignin-thymol suspensions seem to be promising biocides.