Crystalline Fibrils Research Articles

Electron Diffraction Study of Cellulose

Cellulose is the most abundant polymer occurring in nature. It constitutes the cell wall of most, if not all, green plants. In the form of wood, wood pulp and cotton, cellulose represents a very valuable agricultural commodity and is, therefore, the subject of much intensive research.Chemical modifications of cotton are brought about predominately by the reaction of various reagents upon the surface of the crystalline elementary fibrils which make up the sub-fiber structure. For this reason, electron diffraction studies were undertaken to evaluate this microstructure and its various modifications. Electron-diffraction techniques offered several advantages over x-ray methods. Electrons have intensity; therefore, much smaller samples can be used.

A model for the degradation of cotton cellulose

AbstractCertain correlations have been established experimentally on degraded cotton cellulose between degree of polymerization (DP) on the one hand and the polymolecularity (quotient of weight‐average DP and number‐average DP), tenacity, and rate of degradation, on the other hand. It was found that these correlations may be accounted for by the assumption of weak and reactive spots in the cellulose macromolecules at regular intervals of about 500 base units. The same characteristic length of 500 base units follows also from recent concepts of cotton fiber structure.According to our model all ends of the composing macromolecules in a newly matured yet undegraded cotton fiber cause areas of disorder in the crystalline elementary fibrils at intervals of 500 base units. These disorders bring about stresses that activate the chemical bonds in the rigid cellulose chains.This model is in agreement with current ideas and is supported by various other experimental results published in the literature.

Accessibility of cellulose: a critical review

The controversy as to whether the accessibility of cellulose is a measure of crystal surfaces or of amorphous regions in the cellulose is reviewed. Recent claims that cellulose is composed of completely crystalline elementary fibrils of dimensions 40 × 50 Å and that all chemical reactions of cellulose occur on the surface of the fibrils, do not explain many observations which indicate the presence of amorphous structures. Based on X-ray diffraction, chemical hydrolysis, moisture absorption, theoretical calculations of elastic constant, kinetic studies of alkaline degradation, and the lateral-order distribution curve of cellulose, evidence exists favouring the conventional micellar theory. The assumption of a gradual transition between the amorphous and crystalline regions in cellulose offers an explanation of the discrepancies among the accessibility values recorded by different methods.

Evidence for Two Types of Accessible Surfaces in Fibrous Cotton

Diethylaminoethyl (DEAE)-cellulose, prepared at low DS and without change in crystallinity from that of the original cottons, was subjected to hydrolysis with 2.5 N HCI for various lengths of time ranging from 20 min to 5 hr. The yield of DEAE-hydrocellulose (insoluble fraction) ranged from 90.5% at 20 min to 79.2% at 5 hr. Throughout the hydrolysis, the percent nitrogen in the solubilized fraction was triple that in the insoluble fraction. Gas-liquid chroma tographic analysis to determine the distribution of substituents in the solubilized and insoluble fractions showed that the ratio of substituents in the 2-0- and 6-0-positions was higher in the insoluble fraction than in the solubilized frac tion. The 3-0-/6-0-ratio was higher in the solubilized fraction than in the insoluble fraction. The significance of these results as supporting evidence for two types of accessible surfaces of crystalline elementary fibrils in fibrous cotton cellu lose is discussed.

Disposition of D‐glucopyranosyl units on the surfaces of crystalline elementary fibrils of cotton cellulose

AbstractThe results from two different chemical approaches to study the disposition of D‐glucopyranosyl segments of the cellulose chains on the surfaces of microstructural units accessible to chemical reagents in cotton cellulose are compared, correlated, and rationalized. These studies provide the basis for a suggested disposition of D‐glucopyranosyl units in the crystalline surfaces of elementary fibrils, for a proposed arrangement of hydrogen bonds on these surfaces, and for estimates of the size of the elementary fibrils.

The Influence of Carbonylcyanide-m-chlorophenylhydrazone and 3-(3,4-Dichlorophenyl)-1,1-dimethylurea on the Fusion of Primary Thylakoids and the Formation of Crystalline Fibrils in Bean Leaves Partially Greened in Far Red Light

The Influence of Carbonylcyanide-<i>m</i>-chlorophenylhydrazone and 3-(3,4-Dichlorophenyl)-1,1-dimethylurea on the Fusion of Primary Thylakoids and the Formation of Crystalline Fibrils in Bean Leaves Partially Greened in Far Red Light

On polymeric materials containing fibrils with a phase transition. I. General discussion of mechanics applied particularly to wool fibers

Abstract Wool and other a-keratin fibers are known to consist mainly of aligned crystalline fibrils embedded in a less ordered matrix. The fibrils contain a large proportion of protein chains folded in the a-helical configuration. Under an external stress the fibril is capable of transforming to a second thermodynamic phase in which the protein chains are nearly fully extended into the pleated-sheet crystalline structure of β-keratin. This transformation involves local extensions in the fibril of the order of 100%. A constant stress, known as the equilibrium stress, is necessary to maintain the thermodynamic equilibrium between the two phases in the one fibril and this stress is independent of the relative quantities of each phase present. However, the concept is developed that a stress greater than the equilibrium stress is required to nucleate the extended β form from the folded a-form. In the composite fibril-matrix system undergoing extension, the matrix surrounding portions of the fibril which have t...

The fine structure of fibers and crystalline polymers. III. Interpretation of the mechanical properties of fibers

AbstractThe mechanics of extension of plant fibers is considered in terms of a spiral arrangement of crystalline fibrils embedded in a noncrystalline matrix. Deformation may take place either by stretching of the fibrils or by extension such as that of a spiral spring. In the latter, the major resistance comes from the reduction in volume. The extension mechanism predominates for low spiral angles; the spring mechanism, for high spiral angles. There is reasonable agreement between the theoretical expressions and experimental results. The application of similar ideas to other types of fiber structure is considered.

The effect of pressure and temperature on the specific volume of polyethylene

AbstractA spherulitic crystallization process can be divided into three successive stages: the formation of spherulite centers, the growth by means of crystalline fibrils with many branches extending into the melt, and finally crystallization of the intervening regions between these already crystallized fibrils. The three stages were identified with parts of a typical dilatometric isotherm for crystallization from the melt. The last stage of the isotherms was analyzed as crystal growth accompanied by the predetermined nucleation of one‐dimensional character. Isothermal annealing was also studied dilatometrically and was found to be similar in mechanism to the last stage of crystallization from the melt. The influence of the thermal history, including the conditions of crystallization, on the degree of crystallinity were summarized as a kinetic factor, and was distinguished from the thermodynamic consequence of branches on the equilibrium degree of crystallinity. Specific volumes of the crystal (estimated) and the melt were determined at various temperatures and pressures. The relationship between the entropy of fusion and pressure was determined from the volume of fusion by utilizing Clausius‐Clapeyron's equation. The entropy of fusion at atmospheric pressure thus obtained was found in agreement with values obtained elsewhere by other methods. The compressibility of the melt and the true volume of fusion decreased substantially under high pressure, while the entropy of fusion was essentially unchanged. This was ascribed to the change of the melt property from the familiar free‐volume type of behavior to a more solidlike one without an increase in structural order.

ポリプロピレン繊維の粘弾性吸収と微細構造

Structure of fibers of isotactic polypropylene (PP) was investigated by the effects of isotacticity of raw materials and extraction with several solvents upon temperature characteristics of dynamic modulus, E', and dynamic loss, E".E' and E" of PP fibers were measured at 100c/s using the direct reading dynamic viscoelastometer. The specimens were prepared by drawing the quenched film to the seven times of the original length at 95°C. Two remarkable absorptions were observed for all specimens: the αa absorption located at about 20°C ascribed to the amorphous region and the αc absorption located at about 100°C ascribed to the crystalline region. The intensities and temperatures of these absorption maxima are shown in Table 2.In the extreme case, where the amorphous region (A) and the crystalline region (C) have the respective characteristic relaxation mechanisms and are combined in parallel with respect to transmission of applied stress, there consists the fundamental relation that two absorptions appear at temperatures characteristic of the regions of A and C and their intensities are proportional to the volume fraction of each corresponding phase. On the contrary, only one absorption appears in the A-C series model. The relations of Fig. 1 are qualitatively interpreted by the A-C parallel model. In this case, it is essential for appearance of the αc absorption that the fibrils formed with continuous crystalline phase, scarcely interrupted by the amorphous region in the course of stress-transmission, exists in the structure of fiber, while some defects of crystal lattice may be contained within the fibrils. On the other hand, the amorphous region causing the αa absorption will exist in the interfibrillar space and also perhaps between crystallites as seen in the fringed micell model heretofore accepted.Fig. 4 shows temperature characteristics of E'and E" for specimens separately extracted with ether, acetone or n-hexane on the seven times drawn PP fibers (the sample D in Table 1). According to Fig. 4, the intensity of the αa absorption decreases and the value of E' increases systematically with proceeding of extraction. From these results, it is clear that selective extraction of the amorphous region took place. The invariance of locations of the αa absorptions with extraction shows the fact that the state of aggregation of unextractable amorphous chains, e.g. due to anchoring a part of the chains in the crystal lattice of fibril, are in the same state as in that of the extractable amorphous chains consisting chiefly of atactic structure.The E' vs. temperature curves scattered in Fig. 4 meet together in Fig. 5 at temperatures above that of the αa absorption, when E' and E" of the extracted specimens are calculated with the use of the same cross sectional area as that of the original specimen. This fact could be easily understood, if the region causing the αa absorption combines in parallel with fibrils causing the αc absorption with regard to stress-transmission, as illustrated in Fig. 6 schematically. It is difficult to consider that the regions capable of the micro-Brownian movement and causing the αa absorption are contained within the continuous crystalline phase of fibrils. From these, the separate existence of the continuous crystalline phase, or fibril, are reasonably understood, although some defects may exist within it.In the structure of fibers, there will also be contained such a region as expressed by the fringed micell model as an intermediate structure besides the above mentioned continuous crystalline fibrils and the isolated amorphous phase.