离子液体-球磨法制备柠檬籽纤维素纳米纤丝及其结构表征

为推进柠檬加工副产物的高值化利用和开发纳米纤维素高效制备方法，本研究以柠檬籽为原料，采用不同质量分数（0～50%）的离子液体1-丁基-3-甲基咪唑氯化物（1-butyl-3-methylimidazolium chloride，BMIM]Cl）为湿磨介质，通过机械球磨法制备柠檬籽纤维素纳米纤丝（lemon seed cellulose nanofibrils，LSCNF），并以原子力显微镜、傅里叶变换红外光谱（Fourier transform infrared spectrometer，FTIR）、X射线衍射（X-ray diffraction，XRD）和热重分析对LSCNF的形貌和结构进行表征。结果表明，随着BMIM]Cl质量分数的增加，获得的LSCNF粒径逐渐缩短，直径逐渐增长；当BMIM]Cl质量分数为50%时，LSCNF的粒径最短，但直径相对较大（40～60 nm）。XRD和FTIR分析结果显示所有样品均为纤维素Iβ晶型，且添加BMIM]Cl使LSCNF的结晶区域不易被破坏。热重分析结果显示离子液体-球磨法制备的LSCNF在500 ℃时残余质量分数和柠檬籽纤维素相近，但都高于仅用球磨方式制备的LSCNF。流变学分析结果表明LSCNF悬浮液均表现为非牛顿流体，且剪切速率一定时，粒径更长的LSCNF黏度更高。综上，将离子液体和球磨结合的绿色方法能从柠檬籽中高效制备LSCNF，且能根据离子液体的质量分数对LSCNF的形态和结构进行调控。

Preparation and Structure Characterization of Lemon Seed Cellulose Nanofibrils Using Ionic Liquid-Assisted Ball Milling

In order to promote the high-value utilization of lemon processing by-products, an high-efficiency method for the preparation of lemon seed cellulose nanofibrils (LSCNF) was developed by mechanical ball milling with different concentrations (0–50%) of the ionic liquid 1-butyl-3-methylimidazole chloride (BMIM]Cl) as a wet milling medium in this study. The morphology and structure of LSCNF were characterized by atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetry (TG). The results showed that the length of LSCNF was reduced, while the diameter was increased with the increase of BMIM]Cl concentration. The LSCNF prepared with 50% BMIM]Cl showed the smallest length but a large diameter (40–60 nm). The XRD and FTIR results showed that all obtained LSCNFs formed cellulose Iβ crystals, and the addition of BMIM]Cl had a certain protective effect on the crystallinity of LSCNF. The TG results showed that the residual amount of LSCNF after ionic liquid-assisted ball milling was similar to lemon seed cellulose (LSC) at 500 ℃, and both of them were higher than that of LSCNF prepared by ball milling. The rheological results showed that LSCNF suspensions showed a non-Newtonian behavior, and the relative viscosity of LSCNF with longer length was higher at a constant shear rate. In summary, ionic liquid-assisted ball milling is a green and efficient method to prepare lemon seed cellulose nanofibrils with controllable morphology and structure depending on the concentration of ionic liquids.