| To justify the conflicting options on the dominance of either "crosslinking" or "cleavage" in compressed wood fixation, a planum of medium recovery of compression set of Chinese fir wood was constructed with temperature (T) and time (f) as coordinates. This provides theories and technical parameters making selection of optimal heating pathway of compressed wood permanent fixation possible, and might eventually leading to the development of new technology on softwood compression. The equivalency of different pathways targeting same recovery level had also been evaluated based on this T-t planum. Furthermore, the dynamic viscoelastic behavior of fixed wood with equivalent recovery set (10%) from different pathways had also been investigated. Subsequently, the mechanics of different specimens was compared. Both X-ray diffraction and infrared absorption of compressed wood powder samples, which were fixed either by heating at different temperatures resulting 10% recovery, or incubated at 180 C for certain times with subsequent recovery levels had been measured. The changes of relative crystallinity, chemical components and internal structure of compressed Chinese fir wood under different heating pathways were discussed based on this spectrometric data. Here, Tobolsky's approximation method of discrete relaxation of stress in macromolecular viscoelasticity was first introduced to interpret the fixation mechanism of compressed wood. The distribution time of molecular bond breakage and crosslinking in the fixation process was deduced thereafter. The mechanistic change between different fixation pathways was proposed. We designed a strength-sensor meter to measure the stress relaxation in wood. The compressed Chinese fir wood continuous and/or discrete relaxation curves of stress were retrieved under different temperatures with this machine. Their apparent activation energies were subsequently calculated to uncover both the timedistribution of cleavage and crosslinking and the physical and chemical relaxation of stress. Finally, the stress relaxation curves of oven-dry wood had been monitored under different temperatures. The internal change at different stages of the fixation process was deduced as well. The ubiquitous existence of this relaxation process was confirmed, even in untreated wood.The major achievements of this research are following:(1) In heat fixation of compressed wood, low recovery levels (RS is less thanlO%) on T-t plane can be obtained by numerous different pathways composed of different time and temperatures, which have a high equivalence of fixation effect. The Breakage and crosslinking of molecular bond happened in wood during fixation. Crosslinking seems to contribute more on the recovery equivalence. But on the equivalent pathways of higher recovery, the influence of temperature can not be overlooked. The actual routes must be somewhat modified to obtain an expected result.(2) The wood physical properties decreased solely by compression had not been observed. This was clearly revealed by Young's modulus measurements. On the other hand, the wood layer close to the tangential surface of specimen was damaged more seriously.(3) Relative crystallinity increased at early stage of heating fixation, and then decreased more and more later on. Hemicelluloses and lignin decomposition was induced by the fixation process, Furthermore, cellulose crystal structures changed accordingly.(4) Lignin was degraded actively under 180 C. Adsorbed water evaporation after heating had also been found, but cellulose didn't change obviously. In the fixation pathways of 10% recovery level, hemicelluloses and lignin decomposed actively, accompanied by the losing of physical adsorbed water. However, the dominant reactions in different pathways were different accordingly. The fixation effect and rate are correlated to temperature range, temperature dynamic, and the speed of the temperature change.(5) The continuous relaxation of stress in compressed Chinese fir wood fixed under different tempera...
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