synopsisAn examination of powder x-ray diff ractograms of native and hydrolyzed cellulosic materials obtained from widely different sources revealed the presence of materials having a higher degree of molecular order than ramie hydrolyzate, the conventional crystalline standard for cellulose. With the use of these materials as new crystalline standards, a critical reappraisal has been made of the validity of the application of the two-phase (i.e., fringed-micelle) hypothesis to the fine structure of cotton and related cellulosic materials. It is concluded that the lattice structure of cotton and related celluloses of plant or bacterial origin is liquid-like or paracrystalline.
The form and crystal structure of the fibers attached to the diatom Thalassiosiraj?uviatilis were studied by the electron microscope and x-ray diffraction.These fibers, which were shown previously to be pure, highly crystalline 13-(1 -> 4) linked poly-N-acetyl-D-glucosamine (chitan), are strap-like in cross section, 1000-2000 A in width at their widest point close to the base, from which they taper uniformly to a very small tip at their outer extremity. Three connected filaments or microfibrils form the fiber at its widest point. The unit cell of chitan is monoclinic with the space group P2,. The parameters of the unit cell are a = 4.80, b = 10.32, c = 9.83 A, and 13 = 112 ". The density of the chitan fibers is 1.495 g/cm3. There is only one polymeric chain per unit cell with a two-fold screw axis and therefore the chains are parallel to each other. A three-dimensional structure is proposed for chitan which is reasonable from stereochemical considerations and which is in good agreement with all observed x-ray diffraction data.
SynopsisChemical etching of poldethylene terephthalate) filaments with aqueous methylamine has revealed a complex stress-cracking behavior, which varied with orientation and thermal crystallization conditions. The appearance of both longitudinal and transverse cracks, can be explained on the basis of the existence of two types of domains, where the stresses are preferentially concentrated. They are explained on the basis of Prevorsek's structural model. In heat-st fibers, there exists a skin to core differentiation in the internal stress distribution.The crack pattern also varied depending on whether the fibers were heat-set in the taut or slack conditions. This chemical etching technique can prove to be a very useful tool, for the study of the internal stress distribution induced in fibers by various fabrication processes or post mechanical deformations.
Crystallinity and crystallite size determinations have been carried out on a number of samples of swollen, hydrolyzed, and swollen and hydrolyzed cotton fibers, employing x-ray diffraction techniques and a Geiger counter recording spectrometer. A new hi variate analysis technique has been developed in order to determine the crystalline con tent of samples in which two crystalline phases are present, namely cellulose I and II. In the determination of crystallite dimensions the tilted fiber technique has been adopted for measuring crystallite lengths. A new method of resolving superposed line profiles for the measurement of crystallite width has also been developed. The results of these studies seem to suggest that there is a very close relationship between crystallinity and crystallite volume for all the types of chemical treatment studied, and that increasing crystallinity is a measure of increasing crystallite volume. On the other hand, no unique relationship between crystallinity and any one crystallite dimension has emerged for all the treatments studied. However, there are relationships which are specific to different kinds of chemical treatment of cotton.
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