根类中药材孔隙结构及其分形特征

Porous Structure of Root-Like Chinese Herbs and its Fractal Characteristic

认识和表征中药材的孔隙结构,对优化其中有效成分的提取过程有指导作用。今利用SEM、压汞法等考察了根类中药材甘草、黄芪、丹参的饮片及粉末在不同溶剂环境下的孔隙结构。研究结果表明,三种药材的粉末均主要由致密组织和薄壁组织组成,与未处理的情况相比,水溶胀会使薄壁组织含量增加,孔容和比表面积增大,乙醇溶胀不会带来明显的显微结构变化,孔容和比表面积有所减小。对压汞法实验数据的拟合证实三种药材均具有典型的热力学分形特征,分形维数在2.30～2.90之间。对于同一种药材,在水中的分形维数比未处理和在乙醇中的大。中药材分形维数是孔隙结构的综合反映,分形维数越大,孔径的分布范围越宽、小孔越多,越有利于传质。测定分形维数为表征中药材的整体孔隙结构提供了一种手段。

The understanding of the porous structure of Chinese Herbs is helpful for the optimization of their effective components extracting process. Using licorice, astragalus root and red sage root as examples, the porous structures of the root-like Chinese Herbs slices, powders and their swellings with different solvents were determined by SEM and mercury intrusion method. The powders of these three herbs consist of compact and loosen parts with obvious visual difference. Comparing with untreated herbs, water swelling increases the content of loosens part, thus resulting in the increase of pore volume and specific surface area; ethanol swelling has little effect on the microstructure change, but it decreases the pore volume and specific area a little. The fitting of experimental data from mercury intrusion method indicates that all these three herbs have typical thermodynamic fractal characters with fractal dimensions ranging from 2.30 to 2.90; the water swelling herb has higher fractal dimension than untreated herb and ethanol swelling herb. The fractal dimension reflects the overall pore structure of the Chinese Herbs; higher fractal dimension implies more small pores and wider pore size distribution, which is prefer for the mass transfer within herb. Fractal dimension determination provides a measure for characterizing the overall pore structure of the Chinese Herbs.