Within a family of catalyst systems wherein TiCl3 was made by mixing TiCl4 and aluminum alkyl solutions, the primary particles of TiCl3 were usually thin, flat polygons with average diameters ranging from 300 to 1000 A. Even in unused catalyst these primary catalyst particles were bound together into large (∼30 μ) secondary particles. A small amount of polyolefin which formed from the aluminum alkyl reducing agent aided in cementing the particles. When propylene monomer was introduced to a slurry of secondary catalyst particles in a liquid hydrocarbon, polymer formed at the surfaces of the ultimate solid particles. The resulting polymer flakes, i.e., particles of as‐polymerized polypropylene, were several times larger than the secondary catalyst particles from which they grew but they retained the same shape. The primary catalyst particles, not visibly altered by the catalytic reaction which they propagated, were distributed uniformly throughout the flake polymer. Each polymer flake consisted of many thousands of cohering roundish flakelets about a 1/2 μ in diameter. How the flakelets are agglomerated and the extent to which they are coalesced accounts for the flakes' texture. The basic morular structure of the flakes, which was manifested further by their papillary surfaces, was not altered by purification procedures which removed catalyst from the nascent polymer. Although all the flakes had the same basic small‐scale structure there were significant coarse textural dissimilarities among them. Some catalysts gave rise to flakes with an open porous texture: other catalysts gave rise to flakes which were dense and compact. In the former, the flakelets were less tightly appressed, and fissures and slits were larger and more numerous than in the latter. The genetic basis for the differences in flake texture resides in the parent catalyst. Secondary catalyst particles whose constituent primary particles are held together in a dense mass produce dense flakes. Conversely, loose aggregates of primary particles produce flakes with loosely aggregated flakelets. Briefly, dissimilarities in catalyst structure carry over to the texture of the flake progeny. Such textural differences contribute importantly to properties of the flake polymer.
An investigation was undertaken to obtain information concerning the fine details of structure of wool fibers and especially of their constituent scale and cortical cells. Treatment of chemically modified wool with the enzyme, pepsin, was found to be an excellent method for releasing individual cells for such studies,It is shown by microdissection that the striated appearance of the cortical cells is due to the presence of many fibrils which can be separated with microneedles. Near the center of each cell is a nucleus which has a granular structure. Between crossed nicols, the fibrillar part of the cortical cells appears birefringent, whereas the nucleus does not.The scales show little internal organization such as exhibited by the cortical cells. When examined with crossed nicols they appear nonbirefringent. Unlike the cells of the cortex, the scales are not easily separated by treatment with enzymes, but remain attached to each other in a manner comparable to the arrangement of shingles on a roof.A comparison of root and shaft of the fiber reveals numerous differences in reaction to microchemical color tests, as well as differences in cellular structure. The root, for example, gives a positive test for sulfhydryl groups whereas the shaft gives a negative test. Similarly, the shaft appears birefringent whereas the root does not. These and other observations clearly indicate that as the cells of the root emerge into the shaft a number of physical and chemical changes take place simUltaneously.When wool is placed in chlorine water, swellings arise on the surface of the fibers (Allworden reaction). Evidence is presented in support of the view that these sacs arise solely from the scales and that their formation is associated with the reaction of the chlorine with disulfide groups of the cystine in the scales.
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.
Because natural cellulose is fundamentally fibrous, degradation—be it caused by chemical agents such as acids and alkalies, by physical agents such as grinding and ultrasonic vibration, or by biological agents such as molds and bacteria—proceeds in a manner which reflects this basic fibrillate structure. The dimensions of the threadlike fibrils into which cellulose breaks down vary, depending upon the severity of the treatment and perhaps also on innate differences among celluloses from various sources. Following degradative action, light microscopy reveals fibrils of the order of several tenths of a micron in diameter. At the higher magnifications obtainable with the electron microscope, still finer fibrils, a few hundred Ångströms wide, are detectable. Certain degradative treatments cause a further transverse splitting of these fibrils into rod-shaped structures. From x-ray and chemical investigations it is known that cellulose is made up of long-chain molecules whose arrangement with respect to one another gives rise to more or less ordered but poorly reactive crystalline regions and to disordered but easily reactive amorphous regions. Since microscopical studies show that many reactions proceed more easily in the regions between the fibrils than within the fibrils themselves, it appears that the crystalline cellulose is located principally in the fibrils, whereas the interfibrillar regions compose, in large measure, the amorphous fraction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.