自然界中，纖維素是植物細胞壁的主要成分，是世界上含量最多的生物質來源。由於纖維素在植物體中扮演支撐及保護的角色，其多半以晶型的狀態存在於大自然中，形成堅硬有韌性的結構。在工業界中，此晶型的特性使得酸觸媒難以進入纖維素結構內進行降解，因而大幅度地降低了觸媒降解纖維素的效力。因而自製非晶型纖維素被視為有效的解決方法。此研究中利用X光粉末繞射儀與膠體滲透層析儀來鑑定纖維素在水解反應後的固體產物。利用X光粉末繞射儀，我們發現非晶型纖維素在低酸下水解時有再結晶化的現象，其結晶強度隨著溫度反應溫度上升會又上升的趨勢。另一方面，從膠體滲透層析儀的鑑定結果，我們發現雖然纖維素分子量會因反應溫度上升而下降，但當溫度介170 oC到210oC時，分子量分布卻落於6,500Da左右，沒有明顯下降的趨勢。從以上的觀察，我們得到纖維素再結晶化的確是阻礙纖維素降解的原因之一。 此外，晶體纖維素有著四種同質異型(allomorphs)的型態，在X光粉末繞射圖譜的觀測下，我們發現，反應溫度可能是影響一型纖維素及二型纖維素生成的最大因素。此發現可帶領我們開啟下一階段關於纖維素同質異型的研究。 ;In this study, recrystallization of amorphous cellulose has been discovered in the homogeneous hydrolytic depolymerization with relatively high saccharide concentration (2.5 wt%) and low catalytic ratio for acidic hydrolysis (4.87 mol%) at various reaction temperatures. The cellulosic residues collected after aforementioned acid hydrolysis were characterized by powder X-ray diffraction (PXRD) as well as gel-permeation chromatography (GPC). The PXRD study revealed the trend of structural transformation for amorphous cellulose to recrystallized cellulose escalated during hydrolysis, while elevating reaction temperature from 130oC to 210oC. In addition, GPC study suggested that weight average molecular mass (Mw) centering around 6,500 Da exhibited similar distribution after hydrolytic depolymerization while elevating reaction temperature from 170oC-210oC. These observations above indicated that recrystallization of amorphous cellulose indeed took place to impede the depolymerization during acid hydrolysis. In addition, judging from the correlation between the average molecular weight and the crystallinity index of recrystallized amorphous polysaccharides, we have found that shorter cellulosic polymer exhibited higher degree of recrystallization during hydrolytic depolymerization which might lead to understand better to design efficient catalysts for hydrolytic depolymerization of polysaccharides in the future. On the other hand, the dynamic study of the hydrolysis of amorphous cellulose shows that both cellulose I and cellulose II have their own preferable forming condition, from which we found that controlling the reaction temperature might play a key role to produce a single allomorph of cellulose. This might lead us to study further about the kinetics and thermodynamics behind the formation of the allomorphs of cellulose.
