The Improvement In The Wettability Of Wheat Straw Surface By Lipases

The effects of lipase treatment conditions such as pH, reaction time, lipase dosage, and temperature were investigated on the removal of lipophilic extractives and improvement in the outer surface wettability of wheat straw.The optimum conditions on which the lipase could remove the lipophilic extractives at its maximum was obtained: pH 7.64, temperature 50℃, reaction time 10 h, lipases dosage 7 kU/g wheat straw and the removal rate of lipophilic extractives could reach 61.64 %.The FT-IR spetra of outer surface wheat straw showed that the lipases could remove parts of lipophilic extractives and the substances containing Si. The SEM of wheat straw outer surface showed that the waxy layer on the wheat straw outer surface was partly removed off. The EDS of wheat straw outer surface further exhibited that Si element's percentage droped obviously after lipase treatment. The TG analysis demonstrated that the exposure of water-affinity groups in the treated wheat straw made the content of the bound water to be higher than the fresh wheat straw while the decomposition performance of the cellulose and hemicellulose didn't changed much. The lipase can selectively remove parts of the lipophilic extractives by GC-MS.The property of the treated wheat straw were as follows after treated by lipases at the condition of pH 7.64, temperature 50℃, reaction time 6 h, lipases dosage 7 kU/g wheat straw:the weight gain percentage by acetylation was 14.06% ,the surface bonding strength was 0.60 MPa and the inner bonding strength was 0.083 MPa.The addition of tween20 and SDS during the lipase treatment could be helpful in the removal of the lipophilic extractives and the adhesion performances. When adding 0.3 % tween20 or 0.25 % SDS to the reaction system, the removal percentage of the lipophilic extractives was increased by 15.59,21.30 %, respectively, and the weight gain percentage after acetylation was increased by 24.75,26.69 %, respectively, and the surface bonding strength was enhanced by 1.44, 1.56 times and the inner bonding strength was enhanced by 3.06, 3.19 times, respectively. But the addition of tween80 reduced its removal.The results reported above could fully prove that the outer surface wettability of wheat straw was improved duo to the removal of lipophilic extractives by the lipase.