熱處理技術應用於國產柳杉造林木性質之研究

Abstract

本研究係將國產中小徑木柳杉（Cryptomeria japonica），於空氣環境下進行熱處理，探討最終處理溫度（170、190、210°C）、持溫時間（1、2 及 4 h）等變因，尋求最佳熱處理條件。試驗項目包括質量損失、密度、平衡含水率、色差值、粗糙度、接觸角、尺寸安定性、機械性質、化學分析、傅立葉紅外線光譜、加速耐候試驗、戶外耐候試驗，以及熱處理前後柳杉實大材作為結構用材之工程性能。 經試驗結果發現，柳杉之密度、含水率與吸濕性皆隨熱處理溫度與時間增加而減少，而質量損失率則隨熱處理溫度與時間增加而上升。另外，柳杉材色會隨熱處理溫度時間增加變深，而熱處理柳杉表面之疏水性則有提升。而熱處理後化學組成之改變，多醣類之特定吸收峰強度隨熱處理溫度提升有減弱之趨勢，木質素則反之；而全纖維素、半纖維素及α-纖維素含量減少，木質素相對比例則增加。 190°C-2 h熱處理之柳杉，其抗彎彈性模數（MOE）會較未處理柳杉有些微上升；而柳杉經熱處理後抗彎強度（MOR）與剪斷強度則會隨著熱處理溫度與時間之增加而下降；170oC熱處理柳杉之壓縮強度則會有明顯上升。根據MOE變化決定，190°C-2 h應為本試驗對中小徑木熱處理改質之最佳條件。 耐候性質方面，隨加速耐候時間增加，熱處理與未處理柳杉MOE與MOR保留率皆有下降之趨勢，且熱處理後柳杉色差值隨著耐候時間之增加會較未處理者低。而戶外耐候試驗後，未處理與190°C-2 h熱處理柳杉，密度及機械性質會隨著耐候天數增加而下降。 評估未處理與熱處理柳杉實大材用以結構用途之可行性，透過機械分等，未處理與190°C-2 h熱處理之柳杉，隨著MOE等級增加，密度、DMOE、MOE與MOR皆有上升趨勢，且熱處理後柳杉之MOE等級會集中在E70與E90。而透過未處理與熱處理柳杉分等材抗彎性質之特徵值與容許應力值分析，未來可將未處理與熱處理柳杉實大材，作為結構用材使用。

This study investigated using heat treatments to treat wood sampled from small-and medium-diameter C. japonica in the medium of air. The heat treatment parameters (e.g., temperature and treatment duration) were examined to optimize the heat-treatment process. This study conducted a set of tests to examine the heat-treatment-induced changes in wood characteristics, such as mass, moisture content, density, color, roughness, dimensional stability, contact angle on the surface, and mechanical and chemical properties. In addition, accelerated weathering tests, outdoor weathering tests, and Fourier transform infrared spectroscopy analyses were performed. Furthermore, the feasibility of the structural use of untreated and heat-treated C. japonica wood was evaluated. The results revealed that when heat treatment temperature and duration increased, the wood density, equilibrium moisture content, and hygroscopic decreased, but the mass loss increased. Moreover, when heat treatment temperature increased, the wood color darkened and hydrophobicity increased. After the heat treatments, the changes in the holocellulose, hemicellulose, and α-cellulose contents have shown a decreasing tendency. A favorable relationship between the absorptive peak of polysaccharides and chemical composition was observed. After the wood was treated at 190°C for 2 h, the MOE increased. Moreover, the increase of heat treatment temperature and duration led to decreased MOR and shear strength but increased compression strength. The increase of the MOE indicated that the treatment temperature of 190°C and duration of 2 h can be used to achieve an optimal heat treatment efficacy. In the accelerated weathering tests, when the accelerated weathering duration increased, the retention of the MOE and MOR of the untreated and heat-treated wood decreased. But the CIE Delta E of the heat-treated wood after accelerated weathering was lower than the untreated wood. The results of outdoor weathering tests indicated that the density and mechanical strength of untreated and treated (190°C and 2 h) wood decreased due to the increase of weathering time. According to the E-rating conducted, the density, dynamic MOE, MOE, and MOR increased associated with better grades. After C. japonica lumber was heat treated, the MOE values of the treated lumber clustered around grade E70 and E90. According to the parametric tolerance limit and allowable stress of the heat-treated lumber, the E-rated untreated and treated (190°C and 2 h) lumber could be used for structural applications.