黃酸樹膠與共混物的結構和流變性質之研究

本論文主要研究的是黃酸樹膠與共混物的結構和流變性質。在偏光顯回鏡下可觀察到三個不同的相區，分別是：不溶解相，液晶相以及透明相。因酸水解和酯化，H3PO3 和 H3PO4 會嚴重降低液晶相的特性，特別是在高酸濃度和低水量的區域。當混合物有足夠的退火時間，因黃酸樹膠有大量的氫鍵，液晶會轉變成透明相。黃酸樹膠/水/H3PO3系統的結構穩定性比黃酸樹膠/水/H3PO4系統要好，這是因為兩種酸的氧化態不一樣。從兩種系統的流變測試可以看出黃酸樹膠溶液在液晶相裡有假塑性的性質，冪律指數大概是0.08。這個現象與酸的種類及黃酸樹膠的含量無關。黃酸樹膠和阿拉伯膠的協同作用會因不同的溶解程序導致不同的結構。分散性的液晶相可以從 AX-W 溶液中(黃酸樹膠和阿拉伯膠同時融於水)得到，而鏈狀性的液晶相是從 A-XW 溶液 (黃酸樹膠先溶於水，在溶阿拉伯膠)中所得到。另一方面A-XW系統的液晶相比AX-W系統的液晶相更穩定。當微量的黃酸樹膠加入羥丙甲纖維素水溶液中，將顯著擴大液晶區域成為透明相。在HPC/H2O/H3PO4系統中，液晶相的邊緣迅速抵到XG/H2O/H3PO4系統液晶的臨界濃度。在黃酸樹膠/羥丙甲纖維的混合比例只有10/90，黃酸樹膠與羥丙甲纖維素的互相作用很弱且不穩定。實際上，白濁相分離相（CS）的階段，其中在相對透射光強度與溫度的下降被確定為高於80％，縮小和消失時的更高於70/30對XG/HPC混合比例。因白濁相分離相縮小導致HPC/H2O/H3PO4 之系統從低臨界溶液溫度系統(LCST)轉變成高臨界溶解溫度系統(UCST)。

關鍵字

黃原膠；阿拉伯膠；羥丙基纖維素；液晶；叔胺體系；相變；過渡區；熱鬆弛；退火時間

並列摘要

This thesis is to study conformational and rheological manner of xanthan gum (XG) polysaccharide and its aqueous blends. Under polarized optical microscope (POM), three distinct phases - the completely separated immiscible (S) phase, the isotropic miscible (I) phase and the liquid crystalline (LC) miscible phase - were identified. A serious decrease in LC behavior strongly occurred by the presence of H3PO3 as well as H3PO4, especially in acid-rich but water-poor site by the acid hydrolysis and the esterification. However, the completely thermal transition from LC to I phase were found with enough long annealing time owing to a large amount of hydrogen bonds on XG macromolecules. Notably, the structural stability in XG/H2O/H3PO3 tertiary system was higher than that in XG/H2O/H3PO4 tertiary system by the difference in oxidation state between two acids. The rheological studies on these systems also showed that all the XG solutions in LC domain were shear thinning fluids with a specific power-law index of roughly 0.08, being independent on the type and the concentration of acid, XG content as well. The synergy between XG and acacia gum (AG) in aqueous solution considerably depended upon the dissolving methods that the dispersed and strand-like LC structures were obtained from AX-W solutions (i.e. AG and XG are simultaneously dissolved in H2O) and A-XW solutions (i.e. AG is mixed with the prepared XG/H2O system), respectively. On the other hand, the LC phase in A-XW system was much more stable than that in AX-W system. The addition a tiny XG amount to hydroxypropyl cellulose (HPC) aqueous solution significantly enhanced the anisotropic phase toward isotropic region. The LC boundary of HPC/H2O/H3PO4 tertiary system rapidly reached to the critical mesophase concentration C* of XG/H2O/H3PO4 system at XG/HPC blending ratio of only about 10/90. However, the interactions among XG and HPC molecules were quite weak and unstable. Actually, the cloudy suspension (CS) phase, in which the drop in the relatively transmitted light intensity with temperature was determined to be higher 80%, shrunk and disappeared at the XG/HPC blending ratios of higher 70/30. The conversion from the LCST behavior of HPC/H2O/H3PO4 system into the UCST behavior of XG/H2O/H3PO4 system gradually took place, resulting from such shrinkage of CS phase.

並列關鍵字

xanthan gum ； acacia gum ； hydroxypropyl cellulose ； liquid crystals ； tertiary system ； phase transition ； transitional region ； thermal relaxation ； annealing time

參考文獻

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黃酸樹膠與共混物的結構和流變性質之研究

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