A proposed microwave-aided method for the determination of wood klason lignin

• Main Author: 蔡永松
• Other Authors: 郭蘭生
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/68494633030879688885

碩士 === 國立中興大學 === 森林學系 === 87 === The classical method for the quantitative determination of wood lignin is based on Klason's technique involving hydrolysis with 72 % H2SO4 for 2-4 hours at 15-20 0C and then followed by condensing the dissolved lignin with 3 % H2SO4 at boiling temperature for 4 hours. In this procedure lignin is left as an insoluble residue and is recovered by filtration and gravimetrically determined. While this method works satisfactorily for most woods, it requires modification to save the long testing time i.e., 8-10 hours for one test. Based on the similar klason-lignin contents, the use of microwave method , the decomposition of carbohydrates from Calocedrus formosana, Acacia confusa, Leucaena leucocephala and Taiwania cryptomerioides Hay with 3 % H2SO4 can be accomplished in 10-20 minutes when compared with conventional methods using a flame or hot plate for 4 hours. By comparing the scanning electron micrographs and the densities of the klason lignin powders, there were more splittings outside the cell wall and lower density for the microwave treated samples due to its high energy than that of the conventional treated ones. In addition, the difference in infrared spectra and gas chromatographs of the two methods is due to the different mechanism by which energy is transferred to the molecules of the 3 % H2SO4 solution. The color difference for the two Klason lignin samples, i.e., dark black for microwave treated one and brown for conventional one might be due to the microwave energy is directly transferred to all of the samples of the solution simultaneously without heating the vessel. Thus, boiling temperature is reached throughout the entire solution very quickly. However, no discernible differences in C, H, O, S contents between the two samples by elemental analysis can be found . Of course, we are not intended to replace the current Klason lignin determination method as specified in Tappi T222 om-98 with the microwave-aided method, our proposal will focus on the larger economic gains which result from significant savings in time.