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標題: 乙醯化竹纖維之熱分解動力學及其對聚丙烯結晶行為之影響
Thermal decomposition kinetic of acetylated bamboo fiber and its effect on the crystallization behavior of polypropylene
作者: 朱羽珊
Yu-Shan Jhu
關鍵字: 桂竹;乙醯化改質;聚丙烯;熱分解動力學;結晶動力學;Phyllostachys makinoi;Acetylation;Polypropylene;Thermal decomposition kinetics;Crystallization kinetics
本研究利用不同配比之醋酸酐/二甲基甲醯胺混合溶液對桂竹(Phyllostachys makinoi)纖維進行乙醯化改質,藉以取得重量增加率(Weight percent gain,WPG)為2、6、9、13以及19%之乙醯化竹纖維。同時,利用熱重分析儀、示差掃描熱分析儀以及偏光顯微鏡,探討未改質及不同乙醯化改質程度竹纖維之熱分解活化能及其對聚丙烯(Polypropylene,PP)結晶行為之影響。熱重分析之試驗結果顯示,竹纖維之起始降解溫度及最大降解溫度皆隨乙醯化改質程度提高而往高溫處偏移。此外,以Friedman、Flynn-Wall-Ozawa(F-W-O)、Starink以及modified Coats-Redfern(modified C-R)四種等轉化率法評估不同乙醯化程度竹纖維之熱分解動力學得知,未改質、WPG 2、WPG 6、WPG 9、WPG 13以及WPG 19竹纖維於轉化率10-70%之平均活化能分別為167−212、163−216、167−226、155−217、158−205以及158−226 kJ/mol。再者,由Avrami分析法所得之反應級數可以得知,未改質竹纖維之熱分解反應級數(0.47)均較不同改質程度之乙醯化竹纖維為低。
而在PP結晶行為方面,以非等溫結晶動力學(Non-isothermal crystallization kinetics)分析乙醯化竹纖維對PP結晶行為之影響。試驗結果顯示,於PP中添加未改質及不同改質程度之乙醯化竹纖維時,各組試材之Avrami指數(n)並無顯著差異,其值介於2.54−3.09,顯示PP之晶體生長主要為異相成核之三維成長。而由Friedman法之結晶活化能分析結果可以得知,添加未改質竹纖維之PP具有最大之結晶活化能,其值為-130 kJ/mol,而添加WPG 19乙醯化竹纖維之PP結晶活化能則最小,其值為-158 kJ/mol。另一方面,以偏光顯微鏡於等溫結晶溫度(130oC)下,觀察PP於未改質及不同乙醯化改質程度竹纖維表面之結晶型態時發現,除了WPG 19之乙醯化竹纖維表面無穿晶(Transcrystallization,TCL)結構外,未改質及其他低改質程度(WPG 2−9)之乙醯化竹纖維表面均具有穿晶結構。

In this study, Phyllostachys makinoi fibers were acetylated by different content of acetic anhydride/dimethyl formamide, and thus received acetylated bamboo fibers with various weight percent gains (WPGs) of 2, 6, 9, 13, and 19%. The effects of unmodified and acetylated bamboo fibers on thermal decomposition were evaluated by thermogravimetric analysis (TGA). The crystallization behavior of polypropylene (PP) with unmodified and acetylated bamboo fibers were investigated by differential scanning calorimeter (DSC) and polarizing optical microscope (POM). Accrording to thermogravimetric analysis, the results of thermal decomposition revealed that the shifting of both the onset and max decomposition temperature moved toward higher temperature with the increasing acetylated weight percent gain. Besides, four iso-conversional methods, including Friedman, Flynn-Wall-Ozawa (F-W-O), Starink, and modified Coats-Redfern (modified C-R) were used to determine the thermal decomposition kinetics. The results showed that the activation energies of thermal decomposition between 10% and 70% conversion rates were 167−212, 163−216, 167−226, 155−217, 158−205, and 158−226 kJ/mol for unmodified bamboo fiber and acetylated bamboo fibers with WPG 2, 6, 9, 13, and 19, respectively. The reaction order of unmodified bamboo fiber analyzed by Avrami method (0.47) was lower than that of acetylated bamboo fibers.
With regard to the crystallization behavior of polypropylene, the non-isothermal crystallization kinetics were applied to investigate the effects of unmodified and acetylated bamboo fibers on the crystallization behavior of polypropylene. The results showed that the Avrami index (n) were 2.54−3.09 with no significant differences, which implied a heterogeneous nucleation with three-dimensional growth of polypropylene crystals. According to Friedman method, PP with unmodified bamboo fiber showed the highest crystallization activation energy (ΔE) (-130 kJ/mol) while PP with WPG 19 showed the lowest ΔE (-158 kJ/mol). On the other hand, the results obtained from POM under isothermal temperature (130oC) of PP with unmodified and acetylated bamboo fibers showed that the surfaces of unmodified and most of acetylated bamboo fibers were to form transcrystallization, except WPG 19.
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