Effect of Oxidation on Heat Fixation of Compressed Wood of China Fir

In order to study the effect of oxidation on fixation of compression set, water-saturated specimens of China fir (Cunninghamia lanceolata) are compressed in the radial direction in a hot press with the average compression rate of about 50%. After the compressed specimens and some control specimens (for measuring the weight loss (WL) and the anti-swelling efficiency (ASE) during heat treatment) are oven-dried in an oven at about 105℃, they are heat-treated in a common oven in the presence of air (heat treatment in air) or in a vacuum oven with much reduced pressure of air (heat treatment in vacuum). The two kinds of heat treatment involve five temperatures of 140, 160, 180, 200, 220℃ and various time. This investigation shows: (1) Oxidation reaction accelerates the efficiency of heat treatment dramatically. For example, RS (recovery of compression set) is zero after being heat treated in air for about 2.5 hours at 220℃, while about 30 hours is required for the compression set being completely fixed at 220℃in vacuum. (2) It seems that oxidation is not indispensable to the fixation of set, the change of weight or the improvement of dimension stability. Oxidation reaction almost has no influence on the rela-tionship between RS and WL, or the relationship between ASE and WL. But it has some influence on the relationship between RS and ASE. (3) The isolines of RS in a T-T plane (w ith the time as X-axis and the temperature as Y-axis), the relationship between Δt (the difference of the required time between heat treatment in air and heat treatment in vacuum) and temperature at a given RS, and the coefficient η (ηis the increased efficiency due to oxidation, ranges from 0.80 to 0.93) show the great influence of oxidation on the efficiency of fixation of compression set.