Abstract: Lignosulfonates were prepared by sulfonation of lignin product purchased from the market that was obtained from plant stalk with mild technological process;followed by neutralization with sodium hydroxide.Different sulfonation methods were used separately such as Na₂SO₃ method,Na₂SO₃-CuSO₄ method,Na₂SO₃-FeCl₃ method,Na₂SO₃-formaldehyde method,Na₂SO₃-formaldehyde-FeCl₃ method,sulfuric acid method and fuming sulfuric acid method.Both surface tension at air/water and interfacial tension at n-heptane/water of the aqueous solutions of lignosulfonate products were measured by drop volume method.Acid-base titration method,infrared spectra and thermal gravity analysis were used to characterize the starting material and the sulfonated products prepared.The results showed that the surface activity of lignosulfonates obtained is relatively high,especially for the products prepared by Na₂SO₃ method,Na₂SO₃-FeCl₃ method and sulfuric acid method whose surface tension can be as low as 34-38 mN/m (25 ℃).This work showed that surface activity of the lignosulfonate products may greatly depend on the uniformity as well as content of the acidic groups in the starting lignin material.

Key words: lignosulfonate, lignin, sulfonation, surface activity