Microscopic structure of the cotton fiber

Abstract

During the examination of cotton fibers that had received various chemical treatments, a number of observations pertaining to the structural details of the fiber were made. Those phenomena which appeared to be new were investigated in detail. In addition, experiments described by earlier investigators were repeated in order to have a better composite picture of the structure of the fiber.The cell wall of a cotton fiber consists of a primary and a secondary wall. The latter, which comprises the bulk of the fiber, consists of innumerable spirally oriented cellulose fibrils enclosed by a winding which also makes a spiral, but in the opposite direction from the former. Both the winding and the fibrils reverse their direction at frequent intervals along the axis of the fiber, their points of reversal being coincident. The secondary wall is enclosed by a thin primary wall. The latter is made up of fine crisscrossing strands of cellulose embedded in a membrane consisting principally of wax and pectic substance. The lumen also contains wax and pectic materials, plus various amounts of degenerated protoplasm.When cotton fibers are swollen under certain conditions, a lamellate structure is discernible in the secondary wall. The number of these lamellae increases with the age of the fiber.On treatment of cotton fibers with cuprammonium hydroxide reagent, the cellulose dissolves, leaving residues which vary in amount and in structure, depending upon the extent of purification of the fibers. The residue from raw and from dewaxed fibers consists of fragments of the primary wall, and of a lesser amount of material from the lumen. The behavior of the fibers in the r eagent depends in part on their maturity. Immature fibers containing only small amounts of cellulose swell relatively little in the reagent, and the undissolved wax and pectic materials maintain the original tubular shape of the primary wall. When older fibers are given the same treatment, they swell abruptly, thereby causing the primary wall to break in many places, giving rise to "balloons."Irregular swelling along the fiber axis, which results in the formation of balloons, appears to be dependent in part on the orientation of the fibrils, and in part on the constricting influences of the winding and of the primary wall.

Microscopic structure of flax and related bast fibers

“…After several minutes the field was black, which indicated that the birefringent material had disappeared. Under the conditions of this experiment, balloon-like swellings which commonly arise when cotton fibers are similarly treated [15], were not observed.…”

“…The presence of concentric lamellas in the cell wall of the cotton fiber has been clearly established [15,17,18]. That the ,vall of the flax cell has a similar configuration is suggested by the work of Tammes [2], Nodder [3], Searle [5], Anderson [7], Aldaba [19], and others.…”

“…When handled and dissected with microneedles this residue appeared gelatinous and rubbery, and was less readily torn apart than similar residues from cotton. Whereas in cotton the pectic substances are usually restricted to the primary wall and to the lumen [15], in flax cells this material, which appears to be of a pectic nature and which stains with ruthenium red, is present in the secondary wall also. It is distributed in narrow lamellas, which are especially prominent around the lumen ( fig.…”

“…At the tip of the stem, where the cell walls were thin, there were fewer lamellas than in the walls of mature fibers from the base. Because of the similarity in the lamellar structure of the flax and cotton fibers, it seems probable that the deposition of lamellas in flax may be related to environmental factors, as has been shown for cotton [15,17,18]. However, because of the complex structure of the flax stem, the time at which the fibers originate in the stem is unknown and their development cannot be followed.…”

“…These observations, which are in agreement with those of Herzog [6], indicate an opposite orientation of the cellulose in the two groups of fibers. In cotton, contrasting colors indicative of differences in orientation occur within a single fiber and upon swelling it is seen that in a single fiber the direction of fibrillate orientation is frequently reversed [15]. It is interesting to note, accordingly, that when the moisture test was applied to single cotton fibers · they twisted either clockwise or counterclockwise during drying, and sometimes different parts of the same fiber twisted in opposite directions.…”