作 者：
曹梦丹;张雪霞;任文庭;朱家伟;王汉坤;徐皓诚;余雁
单 位：
国家林业与草原局/北京市共建竹藤科学与技术重点实验室;国际竹藤中心;福建农林大学材料工程学院
关键词：
毛竹;细胞壁孔隙;气体吸附法;常规干燥;冷冻干燥;CO_2超临界干燥
摘 要：
干燥是竹材细胞壁孔隙坍塌的一个重要因素。为研究不同干燥方式对竹材细胞壁孔隙的影响规律,采用常规干燥、冷冻干燥和CO_2超临界干燥3种干燥方式对毛竹进行干燥处理,采用场发射扫描电镜对毛竹中尺寸较大的孔隙结构进行观察,以比重瓶法、N_2吸附法和CO_2吸附法对细胞壁孔隙率、中孔和微孔特征进行了表征。测试结果显示:毛竹的横切面上可见尺度大小不同的孔隙结构,包括原生和后生木质部大导管、韧皮部筛管、薄壁组织细胞腔、竹纤维细胞腔、细胞间隙等孔隙结构。常规干燥后毛竹细胞壁孔隙率(3.35%)明显低于冷冻干燥(4.89%)和CO_2超临界干燥(5.35%),表明冷冻干燥和CO_2超临界干燥能较好地保存毛竹细胞壁的孔隙结构。毛竹细胞壁中的孔隙为裂缝状,干燥处理方式不会改变其孔隙形状。干燥后毛竹细胞壁中孔区域的孔径主要为2～10 nm,微孔的孔径主要为0.4～0.6 nm。CO_2超临界干燥对毛竹细胞壁中孔的保留效果要显著优于冷冻干燥,但两者对微孔的影响不显著。从总体上看,CO_2超临界干燥对毛竹细胞壁孔隙结构的保护效果最好。
译 名：
Effect of drying methods on the cell wall pore structure of Phyllostachys edulis
作 者：
CAO M engdan;ZHANG Xuexia;REN Wenting;ZHU Jiawei;WANG Hankun;XU Haocheng;YU Yan;International Center for Bamboo and Rattan;NFGA and Beijing Co-built Key Laboratory of Bamboo and Rattan Science & Technology,National Forestry and Grassland Administration;College of Material Engineering,Fujian Agriculture and Forestry University;
关键词：
moso bamboo;;cell wall pore;;gas adsorption isotherms;;conventional drying;;freeze drying;;CO_2 supercritical drying
摘 要：
Bamboo is a natural polymer composite material with a complex hierarchical structure, and it is also a complex porous material with micrometer to nanometer scale. The pore structure of the cell wall not only affects the accessibility of chemical agents to the cell walls for the wood modification, but also has an important impact on the material's thermal insulation, ion transmission, mass transfer and other properties. Drying is an important factor affecting the collapse of bamboo cell wall pores. In order to study the effect of drying methods on cell wall pores of bamboo, moso bamboo(Phyllostachys edulis) samples were dried using three different drying methods, namely the conventional air drying, freeze drying and CO_2 supercritical drying. The pore structure of moso bamboo was observed by the field emission scanning electron microscope. The cell wall porosity, mesopores and micropores were characterized by the pycnometer, N_2 adsorption and CO_2 adsorption methods, respectively. The results showed that the pore structures of different sizes could be observed on the cross section of moso bamboo, including the primary and epigenetic xylem vessels, phloem sieve tubes, lumen of parenchyma cells, lumen of bamboo fiber intercellular space and other pore structures. The porosity of cell walls of the moso bamboo was 3.35% after the conventional drying, which was significantly lower than that of the freeze drying(4.89%) and the CO_2 supercritical drying(5.35%), indicating that the freeze drying and CO_2 supercritical drying could better preserve the pore structure of cell walls of moso bamboo, and the CO_2 supercritical drying had the best protection performance. The adsorption isotherms of all samples belonged to the mixed adsorption isotherms of Ⅱ and Ⅳ. The pores in the cell walls of moso bamboo were slit shape, and the drying method would not change the pore shape. The pore size of mesopores in dried bamboo cell walls was mainly 2-10 nm and the freeze-drying and CO_2 supercritical drying could better retain the pores in this range, and the CO_2 supercritical drying had the best performance. After drying, the pore size of cell wall micropores of moso bamboo was mainly in the range of 0.4-0.6 nm, which has been shown to exist mainly in lignin. The effect of the CO_2 supercritical drying on the retention of mesopores in cell walls of moso bamboo was significantly better than that of the freeze drying, while the difference was not significant for the micropores. In general, the CO_2 supercritical drying exhibited the best protection on the pore structure of cell walls of moso bamboo.
