Exploring the Utilities of Rice Straw Black Liquor: (Part X) Antioxidant/Antimicrobial New Sizing Additive for Brown Recycled Papers Properties Improvement

Black liquor (BL), a byproduct of the alkaline solar pulping of rice straw, was subjected to various extraction methods to obtain phenolic-rich extracts. These extracts were evaluated for their antimicrobial and antioxidant properties, revealing moderate activity in both areas. To enhance the value of BL, lignin/silica and fatty acids were removed through precipitation as calcium salts. The resulting liquor molasses (LM) primarily composed of hemicelluloses and their natural phenolic ester derivatives was further extracted. The obtained extractives were utilized to modify recycled brown papers. The LM extractive demonstrated significant improvements in sheet sizability, microbial resistance, and overall mechanical and physical properties of the recycled paper. These findings suggest that LM extractive can serve as a sustainable, green additive for enhancing the quality and performance of recycled brown paper products.