Abstract: This paper discussed the change of molecular weight,content of acid soluble lignin,content of phenolic-OH,-COOH and -OCH₃,surface activity of the oxidative degradation products obtained from wheat straw alkaline lignin under different oxidization conditions.It indicated that when alkaline dosage is high,for example,60% and 30%,the molecular weight polydispersities of oxidized lignin are low.The content of component with molecular weight higher than 10 000 decreases after the addition of H₂O₂.However,when alkaline dosage is low,for example,10% and 5% the polydispersities are high.It indicated that alkalinity has a great influence on lignin oxidation when O₂/H₂O₂ is used as oxidizing agents.As to acid soluble lignin content,the same rule plays,oxidative degradation of lignin results in increase of phenolic hydroxyl,and decrease of carboxyl and methoxyl contents.The surface tensions of oxidized lignin solution decrease very much at high alkaline dosage(60%,30%),and decreases further after addition of H₂O₂.Under condition of alkaline dosage 60%,H₂O₂ dosage 10%,the surface tension of 4% oxidized lignin solution decerases from the original 46.8 mN/m to 38.8 mN/m.

Key words: lignin, surface activity, phenolic hydroxyl, carboxyl, methoxyl