A novel green method for the amination of condensed tannins to produce bio-based coagulants

The main drawback of most tannin-based coagulants is their reliance on formaldehyde as a crosslinking agent, which introduces toxicity and limits their sustainability. To overcome this issue, a novel green synthesis route was developed using condensed tannin from Acacia mearnsii , ethanolamine, and cinnamaldehyde under mild conditions, without the use of toxic reagents, yielding the coagulant named TEC. TEC achieved a charge density of 3.37 ± 0.05 meq g −1 , confirming successful cationization, and showed an increased molecular weight (from 1390 Da to 2610 Da), indicating the incorporation of new functional groups into the tannin. Proton nuclear magnetic resonance and carbon-13 nuclear magnetic resonance confirmed the incorporation of amine signals from ethanolamine and new aromatic signals from cinnamaldehyde into the tannin structure. Fourier-transform infrared spectroscopy confirmed successful amination while preserving the characteristic features of the tannin after modification. TEC was evaluated for the coagulation of high-turbidity wood-based industry water samples, specifically pulp mill water (2700 NTU) and debarking water (1600 NTU), where more than 99 % and 97 % of the turbidity, respectively, were removed. TEC selectively reduced organic extractives, with the highest efficiencies achieved for steryl esters and triglycerides (≥98 %). TEC neutralized the negatively charged particles in water mainly via charge neutralization mechanisms. These results demonstrate that TEC offers a sustainable alternative to water treatment, providing an ideal combination of charge density and molecular weight that enhances coagulation and flocculation without introducing toxic substances, thereby overcoming the key limitations of current tannin-based coagulants. • Replacement of formaldehyde in the amination of tannin-based coagulants with cinnamaldehyde. • The coagulant (TEC) achieved a charge density of 3.37 ± 0.05 meq g −1 . • TEC molecular weight increased from 1390 Da to 2610 Da. • Analytical techniques confirmed the tannin structure and the modifications after synthesis. • TEC was effective in the treatment of wood-based industry water samples.