(144e) Rapid Lauroylation of Wheat Straw Hemicellulosesunder Microwave Heating

Lauroylation of wheat straw hemicelluloses in the N,N-dimethylformamide/lithium chloride system under microwave irradiation was studied. The parameters optimized included lauroyl chloride concentration as the molar ratio of xylose unit in hemicelluloses/lauroyl chloride (1:1-1:4), 4-dimethylaminopyridine concentration (2-10%), reaction time (1-8 min), molar ratio of xylose unit in hemicelluloses/triethylamine (1:2), and reaction temperature (78°C). The reaction efficiency was measured by the yield and degree of substitution (DS). Under an optimum reaction condition (molar ratio of xylose unit in hemicelluloses/lauroyl chloride 1:3, molar ratio of xylose unit in hemicelluloses/triethylamine 1:2, 5% 4-dimethylaminopyridine, 78°C, 5 min), a degree of substitution of 1.63 was obtained. The changes in the structure of hemicelluloses were verified by FT-IR, and 1H and 13C NMR spectroscopy. The result showed that the lauroylation occurred preferentially at the C-3 position of xylose unit in hemicelluloses. The behaviour of the lauroylated hemicelluloses was monitored by means of thermogravimetric (TG) and differential thermogravimetric (DTG) analysis. It was found that the product with low DS had a lower thermal stability than the native hemicelluloses, whereas the lauroylated polymers with high DS showed a higher thermal stability than the un-modified hemicelluloses. Keywords: Hemicelluloses; microwave; lauroylation; 13C NMR, thermal stability