Research On Superheated Steam Drying And Heat Treatment Of UF-impregnated Chinese Fir

With regard to the deficiencies of Chinese fir in softness,low density and strength,difficulty in high-value utilization,in this study,superheated steam drying and high-temperature heat treatment of UF modified fast-growing Chinese fir sawn specimens were conducted in this research.Drying characteristics and high temperature heat treatment properties were investigated,and an optimized drying and heat treatment process was obtained.The results of this study can provide reference for the efficient industrialized drying procedures and high temperature heat treatment of Chinese fir materials,and can also promote the high value-added utilization of fast-growing Chinese fir.The main conclusions of this study are as follows:(1)A conventional drying schedule for UF resin modified Chinese fir was obtained.The drying and treatment of UF resin modified Chinese fir were studied by 100? test method.The occurrence and development of initial cracking,internal fracture and cross-section deformation of the modified material were studied,and the drying defect grade and preliminary drying schedule were determined.An optimized conventional drying schedule was obtained by a small scale trial test.(2)The superheated steam drying characteristics of UF resin modified Chinese fir was investigated.Compared with conventional drying,superheated steam drying has obvious speed advantage.With the drying medium temperature increasing,the drying rate increased significantly,when the superheated steam temperature increased from 120? to 150?,the drying rate increased by 75%.The effect of steam drying on the color of UF-impregnated Chinese fir was not significant.When the medium temperature increased from 120? to 150?,the brightness of specimens(L*)decreased by 2.28%,the red-green index(a*)decreased by 5.74%,and the yellow-blue index(b*)decreased by 4.01%,The average color difference index(?E)decreased by 2.55%.(3)The properties of high temperature heat treatment for UF resin modified Chinese fir was also revealed.The effect of high temperature heat treatment on wood color,dimensional stability and mechanical strength was significant.When the heat treatment temperature increased from 160? to 220?,the brightness(L*)of the specimen decreased by 11.08%-67.17%and the red-green index(a*)decreased by 1.80%-17.30%.With the increase in treatment temperature and time,the equilibrium moisture content(EMC)of wood decreased,and the dimensional stability of wood increased.Compared with the control,EMC of the high temperature heat treated specimens decreased by 3.25%-37.84%,the volume expansive rate,the radial swelling rate and the tangential welling rate decreased by 9.20%-49.70%?2.56%-43.85%?5.56%-44.45%,respectively.With the increase in treatment temperature and time,the modulus of elasticity(MOE)and strength of the impregnated Chinese fir,the compressive strength overall and partial stress strength were decreased,the MOE modulus decreased by 1.0-11.4%,and the flexural strength decreased%8.2-65.1%,the compressive strength decreased by 2.7%-17.3%,and the ultimate stress and the radial compression ratio decreased by 3.0-60.9%,11.2-59.6%,respectively.Radial compressive force limit stress decreased by 0.43-36.5%,0.87-56.5%,respectively.The heat treatment had no obvious effect on the wood range of crystallinity,but the effect of high temperature heat treatment on the crystallinity of Chinese fir wood was obvious.The high temperature heat treatment has little effect on the total heat release(THR)in the combustion process of wood.The quality loss of the wood during the combustion process is synchronized with the heat release.The second smoke peak of the impregnated and heat treated material is compared with the amount of smoke The CO concentration increased during the high temperature heat treatment,and the effect of CO2 concentration on the combustion process of wood was not obvious.