期刊
POLYMER DEGRADATION AND STABILITY
卷 93, 期 2, 页码 406-412出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.polymdegradstab.2007.11.020
关键词
degradation reactions; wood constituents; wood welding; thermal degradation; NMR; FT-IR
The essential chemical modifications involving the polymeric constituents of wood in friction welding occur in the first 5-6 s slowing down or even stopping afterwards. FT-IR and CP-MAS C-13 NMR of the welded area of wood have shown dehydration and an apparent increase in the crystallinity of cellulose. A certain level of hemicelluloses degradation occurs, accompanied by the generation of some furfural. Cellulose degradation is instead very slight. Both analytical techniques show an increase in the proportion of lignin in the welding interphase. A proportion of methoxy groups of lignin is de-etherified to phenolic hydroxy groups. Self-condensation of lignin occurs by internal rearrangement with the formation of Ar-Ar and Ar-CH2-Ar bridges. This progresses throughout the whole process of welding. The formation of C-O-C bridges, although stopping after 6 s welding, at the start of wood carbonisation, also appears to contribute to the increase in cross-linking of the lignin network. (c) 2007 Elsevier Ltd. All rights reserved.
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