コウゾおよびミツマタのじん皮繊維壁の構造

Abstract

和紙の諸特性はその原料であるじん皮繊維の性質や構造が関与しているものと考えられるが, その構造についての知見は乏しい。そこでコウゾおよびミツマタのじん皮繊維壁について光学顕微鏡, 走査型ならびに透過型電子顕微鏡を用いて観察し次の結果を得た。(1) コウゾとミツマタのじん皮繊維壁はともに外層と内層からなり, 木化度は低い。(2) 外層はさらに4層に分かれ, 外側から, ミクロフィブリル配向がランダムな層, 概して軸方向の層, 横巻きの層, 横巻きから徐々に30 - 45°までかわる層が見られた。(3) 内層は厚く, 数層のラメラからなり, ミクロフィブリルは全層にわたって軸方向に対して小さい角度でらせんを描いて配向しており, 木化度の低い点とあわせて広葉樹あて材のゼラチン層に似た構造をもつことを確認した。

Japanese paper is made from bast fibers of Kozo (Broussonetia Kazionoki SIEB.) and Mitsumata (Edgeworthia papyrifera SIEB. et ZUCC.) and so on. In this study the cell wall structure of bast fibers of the two species, which had not been fully understood, was investigated using optical microscope, scanning electron microscope and transmission electron microscope. The results obtained are as follows: 1. No noticiable difference in cell wall structure was found between Kozo and Mitsumata. The cell wall was found to consist of a thin outer layer (O layer) and a thick inner layer (C layer) which is detached from the former, as noted in several papers (Figs. 1, 2 and 3). 2. The O layer includes four sub-layers; O1, O2, O3, and O4. The O1, whose fibrils run in random orientation, is easily torn away, allowing a view of the randomly but more steeply arranged microfibrils of O2 (Fig. 5). Hence the O1 and O2 are thought to be the primary wall. The underlying O3 has its fibrils oriented perpendicularly to the fiber axis. The O4 has many lamellae which go through a gradual transition from the orientation of the O3 to a fibril angle of about 30°-45° against the fiber axis (Figs. 4 and 7). 3. The C layer is like the gelatinous layer of tension wood fibers, as noted by LIESE, showing well oriented microfibrils nearly parallel to the fiber axis (Figs. 4 and 8). The microfibrils in the C layer have a uniformity of orientation from the exterior to the lumen surface, though several concentric lamellae are observed (Fig. 3). The compression failure is shown in Fig. 12.