Properties of organic acid–precipitated lignins from industrial black liquor for packaging

Two primary industries that generate black liquor (BL), specifically paper mills and bioethanol production, may act as potential sources of lignin. The paper mill’s BL is obtained from Acacia mangium through the Kraft process, while the bioethanol is produced from oil palm empty fruit bunches through the steam-explosion-alkali process. The distinction between lignin derived from paper mills and that from bioethanol leads to variations in their properties. Lignin is primarily used in low-value products, despite its significant antioxidant and antibacterial properties, UV protection, and potential as a sustainable material for food packaging. This study investigated the effects of BL, extraction, and isolation techniques on lignin production. Lignins were isolated using acid precipitation with hydrochloric acid, citric acid, and acetic acid. Their physicochemical properties were assessed through comprehensive characterization, including thermal behavior, chemical composition, molecular weight, antioxidant activity, and antimicrobial activity. The results indicated that Kraft-HCl exhibited the highest purity (99.70%) and yield (31.24%) compared to all other isolated lignins. Kraft-HCl displayed the highest antioxidant and antibacterial activity against Salmonella typhi, Staphylococcus aureus, and Bacillus subtilis. The results demonstrated that Kraft-HCl possesses excellent properties; however, Kraft-CA exhibited significant potency due to its high antioxidant and antimicrobial properties, also its environmental friendliness.