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How does delignification influence the furfurylation of wood?

Yang, Tiantian, Cao, Jinzhen, Ma, Erni
Industrial crops and products 2019 v.135 pp. 91-98
Fourier transform infrared spectroscopy, Populus canadensis, adsorption, cell wall components, cell walls, confocal laser scanning microscopy, delignification, dimensional stability, equilibrium moisture content, furfural, furfuryl alcohol, intercellular spaces, lignin, lignin content, moieties, nitrogen, nuclear magnetic resonance spectroscopy, polymerization, scanning electron microscopes, scanning electron microscopy, surface area, wood
To investigate the influence of delignification on wood furfurylation, poplar wood (Populus euramericana Cv.) was partly delignified prior to the impregnation of furfuryl alcohol (FA) at concentration of 25%. The observation by using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM) showed that many intercellular spaces appeared in middle lamella and cell corners in the wood with 8.86% lignin loss (LL), after further furfurylation, these spaces were filled with polymerized furfural resin, which contributed to the more uniform distribution of modifier and larger bulking of cell wall in furfurylated wood with low lignin (LF) than furfurylated control (CF). The size distribution of mesopores increased after delignification but decreased after furfurylation, and the specific surface area was reduced over 20% for LF with about 50% total pore volume decrease compared with the control from the analysis of nitrogen adsorption. Lignin loss and chemical polymerization of furfural resin were confirmed but without chemical reaction between FA and cell wall components by both results of Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Delignification resulted in increased equilibrium moisture content (EMC) and dimensional instability, after further furfurylation, the EMC and dimensional changes of LF decreased and were lower than those of control by 16.3% on average, suggesting the availability of furfurylation in reducing moisture sorption and improving dimensional stability of low lignin content wood. The number of accessible hydroxyl groups in wood calculated by using Hailwood-Horrobin theory exhibited in the following order: LL > control > LF > CF. The results can potentially help with understanding the action of delignification in wood furfurylation, as well as providing information on the possibility of make sustainable use of wood products with degraded lignin by furfurylation.