Studies On The Pre-treatment By Compression For Wood Drying And Impregnation

Impregnation with chemicals is a very important way to improve the wood mechanical properties of plantation wood,while the amount of chemicals imprgnated into wood is very limited under the regular impgregnation methods,therefore,the wood properties improvement with regular methods is very limited.The pre-treatment by compression is studied in this paper under the hypothesis that it can greatly improve the imgregnation of wood and can reduce the MC of wood in a great extent and in a very short time.For this purpose,poplar(Populus tremula)and Chinese fir(Cunninghamia lanceolata),two of most popular plantations in China,were studied on the effects of compression directions,compression speed,compresion ratio on MC change,impregation,wood dimension and mechanical properties.Further more,the drying defects of wood by compression treatement were also studied.The main conclusions are summarized as follows:1.The compression directions,compression speed had a significant effect on the MC decrease and dimmension recovery,while had no signifcant effect on the mechanical properties of wood.The tangential compression redumced more water than 45°compression.3mm/min and 5mm/min compression speed is recommended for poplar and Chiense fir respectively.2.The compression ratio had a signicant effect on MC decrease and dimmension recovery,while had no significant effect on the mechnaical proeprties of wood.The MC decreased with the increase of compression ratio,while the MC decreased rapidly after the compression ratio of 20%,therefore,no less than 40% of compression ratio is recommended for industry is recommended.Higher compression ratio was always led to a lower dimension recovery,although the size decrease is acceptable.The compress stress increased obviously when the compressed ratio reached about 44% and 48% for the poplar and Chinese fir respcetivly.3.There existed no differenc in impregnation of wood after compression in radial direction and 45° direction.3mm/min and 5mm/min are the recommended compession speed for poplarand Chinese fir respectively because at these speed the impregnation is good and the wood can keep a good shape.4.The wood recovery ratio of wood under radial compression is better than 45°cmpression.The impregnation increased evenly with the increase of compression ratio,while there showed a obvious increase when the compression ratio reached at about 40%.5.Wood with pre-treatment by compression occurred a few split or check defects during drying compared with the controled wood.Although the compressed wood occurred deformation or twist,it is still a good pre-treatment for wood drying since it can reduced MC in a very short time.The effects of pre-treatment by compression on the drying defects should be further studied on other hard-to-dry wood species.6.The pre-treatment by compression could reduced MC instantly for greenwood and could improve the impregation in a great extent,and therefore is a feasible pre-treatment for wood drying and impregnation.