Structural Analysis of Lignin by Pyrolysis-Gas Chromatography (VII). Conditions for Acid Hydrolysis of Wood Pulps and Characteristics of Acid-Insoluble Residues.
Year: 1997
Type: article
Abstract: Acid-insoluble lignin can be hardly analyzed by spectroscopy because of the insoluble character in all organic solvents, and hence its chemical characteristics are not sufficiently clarified. To know the lignin content and the carbohydrate composition in pulps and woods, standard methods : JIS, Japan TAPPI, and TAPPI methods have been used, but different conditions for acid hydrolysis are chosen in these methods. It is required that conditions for acid hydrolysis are modified to shorten the time for determining the lignin content and the carbohydrate composition in many samples. To characterize the acid-insoluble residues prepared under various acid-hydrolysis conditions, pyrolysis-gaschromatography (Py-GC) is expected to be effective. In this paper, chemical characteristics of acid-insoluble lignins were discussed using Py-GC in order to find an improved method for determining the lignin content and the carbohydrate composition.The treatment period of the primary acid hydrolysis with 72% sulfuric acid should be at least 2.5 hours for analyzing lignin and carbohydrate composition in pulps and wood meals. If it is less than 1 hour, acid hydrolysis of cellulose is not sufficient, and in this case, it is in dictated by the pyrogram of the acid-insoluble residue that there are some peaks originating from holocellulose. This pyrogram also shows that the guaiacol peak is higher than the 4-methylguaiacol peak and is quite different from that of the acid insoluble lignin given by the Klason lignin method (the JIS method). Therefore, the J. TAPPI and TAPPI methods for determining the carbohydrate composition should be modified in their periods, which should be at least 2.5 hours. The modified method for carbohydrate composition, the Klason lignin method (the JIS method), and the modified Klason lignin method by Yoshihara give similar results on lignin contents and on pyrograms of the lignin residues in the case of akamatsu (Pinus densiflora) wood meals. In the case of akamatsu pulps, the yield of acid insoluble residue by the modified method for carbohydrate composition is slightly lower than the lignin content by the Klason lignin method (the JIS method), but the two methods show similar pyrograms of the lignin residues. It is concluded by the Py-GC results that the modified method for carbohydrate composition can be used for determining the lignin content in many wood and pulp samples.
Source: JAPAN TAPPI JOURNAL
Authors: Hiroshi Ohi, Yan Ju, Ken-ichi Kuroda
Institution: University of Tsukuba
Language: English
Topic: Lignin and Wood Chemistry
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2335150359