相思樹熱處理材之吸脫濕性質探討

Abstract

本研究以相思木(Acacia confusa)心材木粉為材料，4組樣本分別為未處理樣本及經170°C、190°C、210°C熱處理1 hr之樣本，其中所得樣本之重量損失分別為1.91%、7.96%、16.92%。另以色差計測量，探討樣本熱處理後L*(明暗值)、a*(紅綠值)、b*(黃藍值)及∆E(色差值)數值之變化，顏色量測結果L*、a*、b*皆隨熱處理溫度增加而下降，而∆E隨熱處理溫度增加而增加，顯示樣本受熱處理 後，顏色變暗、偏綠、偏藍，以及色差度增加。 熱重分析(Thermogravimetric analysis, TGA)可知，未處理及170°C、190°C熱處理樣本分別在250°C及310°C產生兩階段熱裂解，未處理及170°C、190°C樣本重量保留率分別為24.84%、27.96%、28.18%。而210°C樣本僅在300°C有一階段熱裂解，重量保留率為72.03%。而700°C時之焦炭率(char content)分別為15.11%、12.30%、10.72%、44.63%。 利用動態水分吸附設備(Dynamic vapour sorption apparatus, DVS)測得樣本之吸脫濕動態曲線，得到未處理及170°C、190°C、210°C樣本之吸脫濕等溫曲線在95%RH時，EMC分別為19.57%、17.76%、14.82%、11.89%。並以HH (Hailwood- Horrobin)模型、GAB (Guggenheim-Anderson-de Boer)模型及PEK (parallel exponential kinetics)模型來擬合木材之吸脫濕等溫曲線，探討木材吸脫濕性質、等溫曲線趨勢與遲滯現象之變化，結果顯示3種模型都提供優良之擬合結果，其中，HH模型於未處理及170°C、190°C、210°C樣本所求得之單層水含水率，分別為3.5%、2.9%、2.4%、3.1%；GAB模型Vm值得到與HH模型1800/W參數相同之趨勢，顯示脫濕程序之單層水總容量值大於吸濕程序；PEK與HH模型之單/多層水曲線比較後，結果顯示快速與慢速曲線與單/多層水無明確相關性。 最後，利用示差掃描量熱儀(Differential scanning calorimetry, DSC)測得未處理及170°C、190°C、210°C樣本之FSP分別為25.0%、22.3%、19.1%、14.0%MC，與HH模型之p-FSP之結果相近。由DSC得4組樣本之積分濕潤熱，再經計算得未處理及170°C、190°C、210°C樣本之初始微分濕潤熱(QL)'0分別為298.35 cal/g、361.22 cal/g、336.75 cal/g、340.81 cal/g；而微分濕潤熱曲線分別為 (QL')_ctrl = 298.35 exp⁡(-9.86 m)、 (QL')_170°C = 361.22 exp⁡(-11.63 m)、 (QL')_190°C = 336.75 exp⁡(-12.30 m)、 (QL')_210°C = 340.81 exp(-16.65 m)。

In this study, Acacia confusa heartwood powder was used as the raw material. The four groups of samples were untreated samples and heat treated at 170°C, 190°C and 210°C for 1 hr. The weight loss of the samples at 170°C, 190°C and 210°C after heat treatment was 1.91%, 7.96% and 16.92%, respectively. The color meter is used to measure the change of L*, a*, b* and ∆E after heat treatment of the samples. L*, a*, and b* all decrease as the heat treatment temperature increases, and ∆E increases as the heat treatment temperature increases, indicating that after the sample is subjected to heat treatment, the color becomes dark, greenish, bluish, and the color difference increases. Thermogravimetric analysis (TGA) showed that the untreated and 170°C, 190°C samples produced pyrolysis at 250°C and 310°C, respectively. The weight retention rates of the untreated and 170°C, 190°C samples were 24.84%, 27.96% and 28.18%, respectively. The 210°C sample only had a stage thermal cracking at 300°C, and the weight retention rate was 72.03%. The char content at 700 °C of the untreated and 170°C, 190°C and 210°C samples were 15.11%, 12.30%, 10.72% and 44.63%, respectively. The absorption and desorption dynamic curves of the samples were measured using a dynamic vapour sorption apparatus (DVS). The equilibrium moisture content (EMC) of the untreated and 170°C, 190°C and 210°C samples at 95%RH were 19.57%, 17.76%, 14.82% and 11.89%, respectively. The HH (Hailwood-Horrobin) model, GAB (Guggenheim-Anderson-de Boer) model and PEK (parallel exponential kinetics) model are used to fit the sorption isotherm curves of the samples to figure out the effects of sorption properties, isothermal curve trend and hysteresis in samples. The results show that all three models provide excellent fitting results. The moisture content (MC) of single layer water of HH model in the untreated, 170°C, 190°C, and 210°C samples were 3.5%, 2.9%, 2.4% and 3.1%, respectively. The Vm value of GAB model has the same trend as the 1800/W parameter of HH model, indicating that the total volume of the single layer water of the desorption is greater than the adsorption. After comparing the single/multilayer water curves of PEK and HH models, the results show that there is no clear correlation between fast and slow curves and single/multilayer water. Finally, the fiber saturation points (FSP) of the untreated, 170°C, 190°C and 210°C samples were determined to be 25.0%, 22.3%, 19.1% and 14.0%MC, respectively, using differential scanning calorimetry (DSC), which are similar to the p-FSP of HH model. The integral heat of sorption of the four samples was obtained by DSC, and the initial differential heat of sorption (QL)'0 of the untreated, 170°C, 190°C and 210°C samples were calculated to be 298.35, 361.22, 336.75 and 340.81 cal/g, and the differential heat of sorption curves are (QL')_ctrl = 298.35 exp⁡(-9.86 m), (QL')_170°C = 361.22 exp⁡(-11.63 m), (QL')_190°C = 336.75 exp⁡(-12.30 m) and (QL')_210°C = 340.81 exp(-16.65 m), respectively.