Characterization of pyrolytic lignin as phenol substitute in phenolic resins

摘要

Lignin, a polyphenolic component, is one of potential renewable raw materials to substitute phenols produced from petroleum. Industrial applications of lignin as a chemical feedstock have, however, been seriously limited for its low reactivity caused by several factors including complicated structural characteristics, excessively large molecular size, scattered molecular weight distribution. For the purpose of practical use of lignin, therefore, it is important to reduce structural complexity and to increase chemical reactivity. Fast pyrolysis technique was attempted to obtain suitable lignin as a substitute for phenol in manufacturing process of phenol formaldehydk(PF) resins. Kraft lignin(KL) and milled wood lignin(MWL) were also separated as comparative materials from same kind of wood, Pinus radiata D. Don, which pyrolytic lignin(PL) is produced from. The quality of treated lignin could be determined by the guidelines based on physico-chemical characteristics such as molecular weight, structural configuration, and the number of hydroxyl groups. Lower molecular weight lignin is considered more soluble in common organic solvents, and its structure may be more easily transformed. Molecular weight should, therefore, be one of useful criteria. Methoxyl group is also noticeable, because this functional group is combined with the phenol ring that is a part of unit lignin molecule, deactivating the aromatic ring of lignin. On the other hand, phenolic hydroxyl group has an advantage of resin formation. The average molecular weights of lignin samples were determined using gel permeation chromatography (GPC). OH groups were analyzed with gas chromatography (GC). ~(13)C-NMR spectra were also applied to understand the structural features of lignins obtained by different methods. According to results of experiments, PL tends to have lower average molecular weigt, less methoxyl groups than KL.