含木質素之竹纖維素奈米微晶製程及性質探討

Abstract

使用酸水解生產的棒狀纖維素奈米微晶（Cellulose nanocrystals, CNCs）表面具有大量羥基，為高親水性材料，導致 CNCs 與疏水性聚合物基質間的相互作用及相容性較差，同時也使乾燥CNCs粉末難以均勻分布於基質中。然而，前人研究指出，在木質素存在的情況下，CNCs對基質將會有更好的分散性和相容性；對基質而言，含木質素之CNCs亦將有更高的結晶速率和結晶度。因此，本研究將在不同前處理條件下，探究以孟宗竹（Phyllostachys pubescens Mazel ex H. de Lehaie）為原料製造含木質素竹纖維素奈米微晶（Lignin-contained bamboo cellulose nanocrystals, L-BCNCs）之製程，並將進一步探討各組最終產物物理形態及化學性質，以確立可製造L-BCNCs的最佳製程。研究結果顯示，經不同前處理條件調控者，會因木質素留存量不同而呈現不同深淺黃褐色之顏色變化，顯示L-BCNCs中保留了相當程度的原有木質素。再進一步以FTIR圖譜確認，當中可發現自製L-BCNCs中皆有芳香環相關訊號，表示所製之L-BCNCs確實含有木質素存在。有鑑於木質素具有較高熱降解溫度，故以TGA觀察，可發現所製L-BCNCs之熱降解溫度皆高於竹纖維素奈米微晶（Bamboo cellulose nanocrystals, BCNCs）之熱降解溫度，顯示當中有木質素留存。其中，又以受熱處理及鹼處理後的L-BCNCs之熱降解溫度較高，反映較佳的熱穩定性。又熱穩定性益與結晶度有所關聯，以XRD進行測定，可發現BCNCs的結晶指數略低於市售CNCs，但仍屬於高結晶產物。因受木質素留存之影響，以亞氯酸鈉（Sodium chlorite, NaClO2）處理之L-BCNCs結晶度最低，而經熱處理之L-BCNCs組別皆高於市售CNCs，與熱性質的結論具有相似性。最後，由TEM圖則可觀察到竹CNCs產物同樣為細長棒狀纖維，長度範圍約為200-400 nm，寬度約為20 nm，與市售CNCs商品相似，顯示酸水解處理條件為可行之條件。綜上述可知，經熱處理及鹼處理之L-BCNCs具有更多的發展潛能，其奈米尺度與結晶剛性預期將可有效提升複合材料之機械性質，拓展其應用範疇。

Cellulose nanocrystals (CNCs) produced by acid hydrolysis have a large number of hydroxyl groups on their surfaces and are highly hydrophilic, which results in poor interaction and compatibility between CNCs and hydrophobic polymer matrices, as well as difficulties in the uniform distribution of dried CNCs powders in the matrix. However, previous studies have shown that in the presence of lignin, CNCs will have better dispersion and compatibility with the substrate, and CNCs with lignin will also have higher crystallisation rate and crystallinity for the substrate. Therefore, in this study, we will investigate the process of producing lignin-contained bamboo cellulose nanocrystals (L-BCNCs) from Phyllostachys pubescens under different pretreatment conditions, and further investigate the physical morphology and crystallisation of each group. The physical morphology and chemical properties of the final products will be further investigated to determine the optimal process for the production of L-BCNCs. The results of the study showed that the different pretreatment conditions resulted in different shades of yellow-brown colour variations depending on the amount of wood quality retained, indicating that a considerable amount of the original wood quality was retained in the L-BCNCs. Further confirmation by FTIR spectroscopy showed that all the homemade L-BCNCs had aromatic ring correlation signals, which indicated that the manufactured L-BCNCs did contain lignin. In view of the higher thermal degradation temperature of lignin, the thermal degradation temperature of the L-BCNCs was higher than that of the bamboo cellulose nanocrystals (BCNCs), indicating that lignin was present in the L-BCNCs. Among them, the thermal degradation temperature of heat-treated and alkaline-treated L-BCNCs was higher, reflecting better thermal stability. The thermal stability is also related to the crystallinity. The XRD measurement shows that the crystallinity index of BCNCs is slightly lower than that of commercially available CNCs, but it is still a high crystalline product. L-BCNCs treated with sodium chlorite (NaClO2) had the lowest crystallinity due to the effect of lignin retention, and the group of thermally treated L-BCNCs were all higher than that of the commercially available CNCs, which is similar to the conclusion of thermal properties. Finally, the TEM images showed that the products of bamboo CNCs were also long and thin rod-shaped fibres with a length range of about 200-400 nm and a width of about 20 nm, which were similar to those of commercially available CNCs, indicating that the acid hydrolysis treatment condition was a feasible condition. From the above, it can be seen that thermally treated and alkali treated L-BCNCs have more development potential, and their nanoscale and crystalline rigidity are expected to effectively improve the mechanical properties of the composite materials and expand their application scope.