Mechanical properties and dimensional stability of heat-treated Chinese fir

In this study, we selected Chinese fir (Cunninghamia lanceolata) as the test material to investigate the effect of nine high-temperature heat treatment technologies. The mechanical properties and dimensional stability of the Chinese fir before and after heat treatment were determined to evaluate the effects of temperature and processing time on wood properties. The results show that the bending modulus of rupture (MOR) and the bending modulus of elasticity (MOE) of heat-treated Chinese fir decrease with increases in temperature and time, but the effect of temperature is more important. The MOR of heat treated Chinese fir increased much greater than the MOE. The compressive strength parallel to the grain showed no significant change over time, but decreased with temperature. The radial, tangential and volume swelling rates of the specimens were lower than those of untreated wood from oven-dry to air-dry (relative humidity 65%, temperature 20℃) and from oven-dry to the stage of dimensional stability in water absorption. The tangential swelling rate was greater than the radial swelling rate. On the whole, the three indices decreased with increases in temperature and time. Anti-shrink efficiency (ASE) of treated wood was negative and its absolute values increased with increases in temperature and time. The enhanced range of dimensional stability increased gradually, which was more affected by temperature and declined significantly at 210℃.