| Small clear samples at different moisture content(MC)conditions and practical size samples of Poplar(Populus euramevicana cv.‘I-214')and Chinese fir(Cunninghamia lanceolata)plantation were prepared to study the effects of MC and practical size on the pre-treatment by compression for the acceleration of wood drying and the improvement of impregnation.The main results are as follows:1.Compression for Poplar with a MC ranged from 210% to 38.9% at a compression ratio of 60% showed,MC after compression remained constantly at about 75% when the MC before compression were above 86%,otherwise it decreased gradually;Compression for Chinese fir with a MC ranged from 175% to 43% at a compression ratio of 40% showed,MC after compression decreased from 105% to 37% with the decrease of the MC before compression.Pre-treatment by compression took only a few minutes for a sample,while it took much longer time for the same ?MC when it was air-drying.For Poplar and Chinese fir,at the same air-drying conditions(with the same MC)the drying speed was 1.04~1.88 and 1.08~1.36 times of the control group respectively.The recovery rate was above 89% and 94% for Poplar and Chinese fir respectively,while the mechanical properties showed no significant change.2.For Poplar specimens with MC ranged from 210% to 38.9% and Chinese fir specimens from 175% to 43%,the impregnation increased rapidly immediately after release of compression,and increased gradually afterwards.For both Poplar and Chinese fir(the compression rate was 60% and 40% and compression speed was 3 mm/min and 5 mm/min,respectively),when the MC before compression was higher than 86% and 116% respectively,the total impregnation decreased with the decrease of MC before compression(Poplar from 0.45 g/cm~3 to 0.30 g/cm~3,while Chinese fir from 0.30 g/cm~3 to 0.07 g/cm~3);When the MC before compression was lower than 86% and 116% respectively,the total impregnation increased with the decrease of MC(Poplar from 0.30 g/cm~3 to 0.38 g/cm~3,while Chinese fir from 0.07 g/cm~3 to 0.16 g/cm~3).The penetration percentage along longitudinal direction and the percentage of impregnation area showed similar trend with the total impregnation.3.The moisture content of Poplar lumber with the dimension of 60×100×2000 mm~3 and 80×90×2000 mm~3 were quickly reduced from 175% to 104.62% and 109.02% respectively.The first compression was the most efficient,and the moisture content reduced 47.56% and 57.22% in 1.5 min respectively;While it took more than 48 h for air drying to reduce the same moisture content,suggesting the drying speed was quite higher than traditional air drying.Energy consumption of pre-treated(compression + kiln)and controlled(kiln)specimen with the same period of air drying showed that of former accounted only 73~85% of that of later,suggesting that the energy consumption could be reduced by means of pre-treatment by compression.Mechanical properties were well retained compared with the uncompressed ones.These results suggested that the pre-treatment by compression has a big potential in wood drying industry.4.Small diameter round wood of Chinese fir(with the top diameter 104 mm and butt diameter 122 mm)were compressed with newly developed multilevel compression machine.The results showed the penetration percentage along radial direction of pre-compressed Chinese fir round wood was 8.21% higher,the percentage of impregnation area was 24.49% higher,the intensity of the color was 39.23% higher than that of controlled specimen,respectively,suggesting that the pre-treatment by compression has a big potential in wood impregnation industry. |
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