Raw Lignin Modification and Waste Recovery for Tissue Adhesive Formulations
Emek Yukseka*, Aysegul Okumus Ermisa, H. Cuneyt Unlub, F. Elif Genceli Gunera**
aIstanbul Technical University, Chemical Engineering Department, bIstanbul Technical University, Chemistry Department,
Ayazaga 34469 Maslak, Sariyer Istanbul, Turkey
The low adhesion properties of raw lignin necessitate its purification and modification for use in tissue adhesive formulations. In this study, glyoxal was employed to modify lignin, which was first dissolved in a NaOH solution at pH 12. The optimum glyoxal concentration was determined by evaluating the quality of lignin modified with different glyoxal amounts. Following the reaction, which was conducted at a constant temperature, the pH was reduced to approximately 1.5 using HCl to induce lignin precipitation. The precipitated modified lignin was separated via centrifugation after overnight storage at 4°C. The liquid from centrifuge was considered as waste, and its composition was identified as NaCl, glyoxal, HCl, and water.
The objective of this study was to maximize the lignin modification process while minimizing glyoxal and HCl consumption and to explore the potential for waste recovery or reuse. To minimize the consumption of fresh HCl, the waste solution was reutilized for pH reduction instead of adding fresh acid solution. The properties of the modified lignin precipitated through this recycling approach were analyzed.
After three recycling cycles, an increase in solution volume was observed. To maintain balance, water was removed from the system, and the recycling process continued.
Based on analysis and calculations of accumulated NaCl, the recycling process was found to be feasible for up to 24 cycles. Throughout the study, lignin quality was assessed, and a comprehensive mass balance was established. According to the mass balance, the total process loss remained below 10%.