木材表面緻密化之研究

Study on Densification of Wood Surface Layer

密度木材及疏伐木之利用價值，以台灣杉（Taiwania cryptomerioides）、杉木（Cunninghamia lanceolata）小徑木為試材，分別經浸水－熱壓、浸水－冷凍－熱壓及浸水－蒸煮－熱壓之處理後，形成表面密度較中間層密度為高之材料，然後分別檢測材料的密度剖面、吸水率、吸水厚度膨脹率、靜曲強度、硬度與壓縮強度等性質。未處理之試材平均含水率約為12 ± 2%，經各條件處理後之試材含水率均約為2 ± 1%。處理過之試材置於室溫下，其尺寸極為安定，回彈約0.5 ~ 0.7%。浸水－熱壓與浸水－冷凍－熱壓處理者其吸水厚度膨脹率隨吸水率增加而增加，而浸水－蒸煮－熱壓處理者則無。三種處理方法均能提升木材表面密度，達表面緻密化之效果，其中以浸水－冷凍－熱壓處理者效果最明顯，其表面密度平均可達2g /cm3以上，遠高於中間層的密度（0.43g/cm3）。處理後試材之表面粗糙度較對照組試材鉋光者低，即經處理之試材表面較光滑。浸水－熱壓及浸水－冷凍－熱壓兩種處理提高靜曲強度30~130%、硬度8~86%及壓縮強度25~70%，具有明顯之改善效應，而浸水－蒸煮－熱壓處理者僅對壓縮強度具有改善效應，但浸水－蒸煮－熱壓處理對表面緻密化的台灣杉之靜曲強度產生負效應，約降低30%。 To improve the quality and performance of low-density wood and thinning logs, Taiwania (Taiwania cryptomerioides) and China fir (Cunninghamia lanceolata) were treated by soaking, soaking-freezing and soaking-cooking in water respectively , and then hot-pressed (200°C). The density of surface layer is higher than that of middle layer after treatments. The physical properties (such as density profiles, water absorption and thickness swelling) and mechanical properties (such as static bending strength, hardness, compressive strength parallel to grain) of the treated materials were tested. The average moisture content of untreated materials approximates to 12±2%, and that of treated materials approximates to 2±1% only. The spring-back of treated materials (0.5~0.7%) is not obvious. The thickness swelling of treated materials that were soaked in water and frozen increased with water absorption increased, but cooking treatment were not. The densification of surface layer would be increased by soaked, frozen and cooked in water respectively. The density of surface layer by frozen treated (2g/cm3) is higher than that of middle layer (0.43g/cm3). The surface roughness of treated materials was lower than untreated ones. It showed more smooth on the surface of treated materials. The dimension stability of treated materials was stable under room temperature. The static bending strength, hardness and compressive strength parallel to grain would be obviously enhanced by soaked in water and frozen treated, but treated with cooked ones were not except for compressive strength. The MOE of cooking treated Taiwania decrease about 30%, but the others show positive effects in 30~130% enhanced obviously.

To improve the quality and performance of low-density wood and thinning logs, Taiwania (Taiwania cryptomerioides) and China fir (Cunninghamia lanceolata) were treated by soaking, soaking-freezing and soaking-cooking in water respectively , and then hot-pressed (200°C). The density of surface layer is higher than that of middle layer after treatments. The physical properties (such as density profiles, water absorption and thickness swelling) and mechanical properties (such as static bending strength, hardness, compressive strength parallel to grain) of the treated materials were tested. The average moisture content of untreated materials approximates to 12±2%, and that of treated materials approximates to 2±1% only. The spring-back of treated materials (0.5~0.7%) is not obvious. The thickness swelling of treated materials that were soaked in water and frozen increased with water absorption increased, but cooking treatment were not. The densification of surface layer would be increased by soaked, frozen and cooked in water respectively. The density of surface layer by frozen treated (2g/cm3) is higher than that of middle layer (0.43g/cm3). The surface roughness of treated materials was lower than untreated ones. It showed more smooth on the surface of treated materials. The dimension stability of treated materials was stable under room temperature. The static bending strength, hardness and compressive strength parallel to grain would be obviously enhanced by soaked in water and frozen treated, but treated with cooked ones were not except for compressive strength. The MOE of cooking treated Taiwania decrease about 30%, but the others show positive effects in 30~130% enhanced obviously.