奈米纖維素製備之優化:磷酸前處理

Abstract

奈米結晶纖維素為一種具有可再生性及生物可降解性的綠色永續材料，其可透過纖維素製備，傳統上經過硫酸水解製備奈米結晶纖維素相當耗時且產率低落，而本研究發現，透過磷酸水解能大幅提升奈米結晶纖維素之水解效率以及產率。本研究使用四種木質纖維素原料，透過磷酸預處理，降低纖維素之結晶區的密度，再以3, 5, 7.5, 10分鐘之硫酸水解，製備奈米結晶纖維素。研究結果顯示，經由磷酸預處理之樣品，可在10分鐘內獲得奈米結晶纖維素，粒徑分佈介於10到100 nm之間，並且擁有較集中的粒徑分佈，而未經磷酸前處理之樣品再經過3小時硫酸水解後，各樣品之平均粒徑仍大於100 nm。藉由添加陰電性電解質，能夠提升纖維素在預處理完後的分散性，降低纖維素自集成的現象發生，其界達電位由原本的-9±-0.8 mv下降至-20.9±-2.1 mv，相較於未添加電解質之BEK樣品，添加1 %陰性電解質之樣品能在更短的時間內達到奈米尺度。而比較磷酸前處理與未經過磷酸前處理之樣品間的差異，可發現經過磷酸前處理之奈米結晶纖維素的水解效率與尺寸均一性皆有上升，顯示磷酸處理有其發展與應用之潛力。

Cellulose nanocrystals (CNCs) is a renewable and biodegradable materials, traditional approach for preparing CNCs is through sulfuric acid hydrolysis, but it is time-consuming with low yield. In this study, we aim to produce high quality CNCs in efficient way. We prepare four kinds of cellulose feedstocks, including microcrystalline cellulose, bleached pulp, unbleached pulp and α -cellulose, each material was first decrystallized by phosphoric acid pretreatment, follow by sulfuric acid hydrolyzed to prepare cellulose Nanocrystals. The result shows that with phosphoric acid pretreatment, the nanoscale cellulose can be obtained within 7.5 min, particle size was between 10-100 nm with unimodal distribution, which is much efficient than the control group, and as hydrolysis time rising the smaller particle size can be observed. Adding anionic electrolyte increased dispersibility and reduce self-assembly by reducing zeta potential from -9±-0.8 to -20.9±-2.1 mv, which lead to better hydrolysis efficiency. All cellulose after sulfuric acid hydrolysis got massive weight loss due to degrading, cause by glycosidic bond breaking, two stage hydrolysis microcrystalline cellulose after 7.5 min sulfuric acid hydrolysis, molecular weight drop dramatically from 61.68 to 12.82. These result prove that more homogenous cellulose can be acquired by implementing phosphoric acid pretreatment.