Fibrous Polymers Research Articles

Studies on fibronectins in the skin. VIII. Influence of corticosteroids on cell cultures from normal human skin

Fibronectins are important glucoproteins of mesenchymal tissue. Fibronectins are also found in the human skin, and tissue cultures demonstrate the production of soluble dimers and insoluble fibrous polymers from dermal fibroblasts. Under the influence of different glucocorticoids, inhibited production of these fibronectins from cultured human skin cells is demonstrated.

Theoretical Evaluation of the Extent of the Mesophase in Particulate and Fibrous Composites

The concept of the mesophase and its extension in fibrous and particulate composite polymers has been investigated experimentally in the past. A theoretical method for the evaluation of the thickness of the mesophase is introduced in this paper. The method was based on the unfolding models, which describe the variation of the variable elastic- modulus, E,(r), of the mesophase material with respect to its thickness. By applying to E 1(r) the restriction based on the principle of continuity, that its variation curve must be tangent to the value of the constant elastic-modulus of the polymeric matrix, the thickness of the mesophase may be analytically determined. This is accomplished, of course, by the use of the appropriate models describing the properties of the com posite. A review of the properties of the existing unfolding models indicated the possibility of a modification of these models. This modified unfolding model, with the already existing two-term model, yields a band, as lower and upper bounds respectively, in which lie all existing experimental values for the thickness of the mesophase for fibrous composites. Numerical results derived from this theoretical treatment are in satisfactory agree ment with experimental values for fibrous composites, while for particulate composites there is a divergence between the theoretical and experimental values. The reasons of this fact are known and are explained in the appropriate section of this paper.

The Present Aspects and Future Trends of Fibrous Polymers in Biomedical Technology

The Present Aspects and Future Trends of Fibrous Polymers in Biomedical Technology

Synthesis of aromatic polyimines by the condensation of aromatic dialdehyde and diamine

Film-forming aromatic polyimines were prepared by low temperature solution polymerization of aromatic dialdehyde and aromatic diamine usingm-cresol. The polymerization proceeded rapidly to give high molecular weight polyimine solutions. Fibrous polymers were precipitated by pouring the solutions into anhydrous methanol. Lemon yellow-to-orange films were cast in situ from the reaction solutions. The polymers showed typical C=N stretching absorption near 1620 cm−1 in infrared spectra and had high glass transitions of over 200 ‡C but showed low crystallinity.

Cross-linking study on skeletal muscle actin: properties of suberimidate-treated actin.

Cross-linking experiments were performed on muscle skeletal actin, using imidoesters of various chain lengths. Chemical analyses on all products except one (derived from succinimidate) show evidence of the presence of intramolecular cross-links in the molecule. The detailed properties of suberimidate-treated actin (SA) are as follows: SA contains nearly 1 mol of intramolecular cross-link per mol of actin and less than 15% of intermolecularly cross-linked products. Even at a low salt concentration, SA is polymeric, exchanges slowly its bound nucleotide with free nucleotides in solution, and shows an F-actin-type CD spectrum. Electron micrographs of SA reveal that SA exists actually as fibrous polymers in solutions of low ionic strength, although the fibers seem to be less rigid than those at high salt concentration. The F-form of SA at a high salt concentration is indistinguishable from intact F-actin. SA can bind heavy meromyosin and activate the ATPase of heavy meromyosin as observed for intact F-actin. Tropomyosin binds SA only at a high salt concentration. These results show that SA possesses the properties of F-actin even in media of low salt concentration, which are favorable for depolymerization of F-actin. Thus, we may infer that the conformation of SA is frozen in the F-state of actin by the introduction of intramolecular cross-links in the protein.

X-ray diffraction analysis of fibrous polymers

X-ray diffraction analysis of fibrous polymers

Interface in composite materials

mechanical properties of the combined materials, the surface of the fibre, the nature of the fibre-resin bonding as well as the mode of stress transfer at the interface. These two last points are related to the surface properties of the fibres. The various types of bonding that may occur between fibrous materials (carbon, glass and organic fibres) and organic polymers, including the relevant theories, are briefly reviewed. In order to optimize the fibre-resin interactions, it is often essential that the interface should be chemically modified. The various possible treatments may be classified under three headings: chemical surface modification of the fibre, sizing and polymer fixation (grafting). The major factors that influence the interactions between high-performance fibres and organic resins will be established and discussed, as illustrated in a few selected examples.

An in-vitro study of the effect of buffer on the degradation of poly(glycolic acid) sutures.

The tensile strengths of poly(glycolic acid) (PGA) sutures immersed in buffered and unbuffered aqueous media were compared. The media used were an unbuffered physiological saline solution (pH = 5.0) and a phosphate-buffered physiological saline solution (pH = 7.4). PGA samples were immersed for various periods in each medium, and kept at 37 +/- 1 degree C in a constant temperature oven. The tensile strengths of the specimens were tested immediately after removal from the medium. Stress-strain curves of the specimens were expressed in terms of the stress unit "tenacity," commonly used in the study of fibrous polymers; it is an appropriate unit for materials of fibrous nature. These stress-strain curves were investigated as functions of buffering and duration of immersion. Degradation reduced the tensile strength of PGA more in the buffered saline solution than in the unbuffered. This higher rate of degradation in the buffered solution might be due to the presence of Na2HPO4, which removed the degradation products, shifted the reaction toward increased hydrolosis, and accelerated the loss of tensile strength in the PGA. A continuous decrease in the pH of the unbuffered solution supports this explanation. Tied-chain segments of macromolecules, a theory widely used in the study of mechanical strength of fibrous polymer may be the key to a comprehensive description of the degradation phenomenon of PGA.

X-ray diffraction study of fibrous polymers. I. Degree of paracrystallinity—a new parameter for characterizing fibrous polymers

It has been recognized that paracrystallinity dominates a considerable portion of the fibrous polymers. In the general case, the folding of long chains in fibrous polymers result in several domains, some being crystalline, some amorphous, while the remainder are paracrystalline. Based on this model a new parameter-degree of paracrystallinity-has been proposed. This paper reports a method of determining this parameter. Native cellulose fibres of ramie, hemp and jute have been studied. It is found that degree of paracrystallinity in hemp and degree of crystallinity in ramie are greater than in the other fibres. Crystallinity index has been found to be less than that generally reported in the literature. This has been attributed to the intensity peaks previously considered in calculating the degree of crystallinity having components of paracrystallinity which have been evaluated and separated.

Crystallinity, Crystallite Size and Lattice Perfection in Fibrous Polymers

The X-ray diffraction patterns from fibrous polymers are generally characterized by a small number of relatively broad overlapping peaks often overlaid with a diffuse halo. Single fibres give the same pattern as a parallel bundle of fibres, so that the pattern is equivalent to the rotation pattern of a single crystal. Despite the inherent difficulty of insufficient well-defined reflections, all commercially useful fibres have been indexed, starting with cellulose, through nylon 66 and polyester, to the more recent fibres, such as Nomex and Kevlar. Only the structural complexities of the natural fibres of keratin (wool and hair) remain to be fully determined.Many sophisticated computations have been carried out to refine unit-cell constants; unfortunately, much of this work is of doubtful value to those interested in fibre characterisation. Fibres are semicrystalline materials and their molecules are insufficiently well ordered for precision calculations of atomic positions. Indeed, there can be significant error involved in evaluating unit-cell constants from overlapping peaks, unless precise profile resolution is carried out.

Microvoids in aramid-type fibrous polymers

The presence of microvoids in aramid fibres has been suspected for some time. This communication reports their detection together with an investigation of their distribution and size in Kevlar 29 and 49 by electron microscopy and X-ray diffraction techniques. The voids appear to be located mainly around the periphery of the fibres and their dimensions measured from direct microscope examinations are compared with those obtained from a Guinier-type analysis of the low-angle X-ray diffraction data.

Fracture of fibrous polymers

AbstractThe fibrous material obtained by drawing or extrusion exhibits a more than linear increase in the axial elastic modulus with draw ratio, a much slower increase in tensile strength and a decrease in strain to break. The reason for such a behavior is found in the existence of structural defects of fibrous material, which is composed of very long and narrow microfibrillar elements. At their ends the axial connection by taut‐tie molecules is almost completely interrupted. Hence the transfer of tensile stress through such a defect is only possible by lateral shift of the load to adjacent microfibrils. The incompleteness of this transfer, the excess straining of the material in the defect area, and the relatively easy axial displacement of the ends of microfibrils favor the local formation of microcracks which grow and coalesce with close‐by microcracks until a critical size crack is formed and the strained sample fails. The process is favored by a high elastic modulus of microfibrils which is practically identical with that of the drawn or extruded sample. Hence the fibrous polymer fails at lower strain the higher its axial elastic modulus, i.e., the higher the draw ratio.

Crazing of fibrous polymers

AbstractHighly oriented filaments of nylon 6 and polypropylene (PP) are shown to craze when deformed slowly at room temperature. A marked yield point occurs at 20‐40 percent elongation. After this point extensive voiding occurs until at fracture the overall density is reduced by ∽25 percent for PP and ∽15 percent for nylon 6. SAXS analysis indicates that for PP the voids are elongated in the fiber axis while for nylon 6 voiding occurs both parallel and perpendicular to the fiber axis. Optical and electron microscopy show typical craze structures. The use of etching demonstrates that crazing occurs across the whole filament cross section. This yielding behavior is shown to be associated with the use of a low temperature of drawing during fiber production and becomes less important when a higher temperature of drawing or a separate annealing step are used. The crazing mechanism is thought to involve progressive separation of interfibril boundaries with the production of elongated voids.

An automated procedure for the correction of background due to inelastic scattering in electron diffraction patterns

The use of electron diffraction in structural studies of fibrous polymers is complicated by the presence of an intense background associated with inelastic scattering. A method of digital processing is described which effectively removes the undesirable features of this background. The method is also applicable in low-angle X-ray diffraction studies.

Factors affecting the photo‐induced graft copolymerization of methyl methacrylate onto fibrous polymer

AbstractThe effects of sample swelling, photosensitizer, and solvent on the photo‐induced graft copolymerization of methyl methacrylate onto fibrous polymers such as Vinylon, nylon 6, and polyester were examined. Each separate factor, sample swelling, or solvent, or their combination, increased activity of polymerization. Only some sensitizer were effective. Studying the ESR spectra of photo‐irradiated polymers also showed that either the sample swelling, the photosensitizer, or the organic solvent is very effective for the formation of polymer radicals under irradiation.

Lattice resolution in an electron-beam sensitive polymer

RECENT developments in our understanding and application of high-resolution defocusing phase contrast electron microscopy have contributed significantly to structural studies of carbon fibres from a range of precusor materials1–4. For example, we are now able to follow the natural pattern of carbonisation in the standard commercial process for poly-acrylonitrile (PAN)-based carbon fibres, and to detect variations in structure which give rise to abnormal physical properties5,6. One major factor which has influenced the success of the work on carbon fibres is the stability of the stacked carbon ribbons to irradiation by an electron beam, and the relative ease with which the {002} lattice fringes can be recorded. In fibrous organic polymers we have observed massive degradation of structural order as revealed by the rapid deterioration of the electron-diffraction pattern7,8; this has precluded the recording of lattice-fringe images and so prevented the breakthrough in understanding which would undoubtedly follow as a result of direct observation of fibre structure at the molecular level.

Analysis of polymeric X-ray diffraction profiles. II. The significance of the fourth moment–range function of the diffraction profile in the analysis of first order reflexions

An expression has been developed for the fourth moment–range function of an X-ray diffraction profile in terms of the effects of finite crystal size and type II lattice distortions. A methodology has also been developed for its determination, which would be valuable in the analysis of the first order peaks from fibrous polymers. A computer program written in Fortran II for an IBM 1620 Computer, is described for this purpose.

Fibrous polymers

Abstract This review is written for readers who are not familiar with fibrous polymers, and it is hoped that it will make an interesting introduction to the subject, which the younger readers will be able to follow completely. It is mainly concerned with the molecular structure and physical properties of fibres and includes a number of examples of the relations between them. By far the largest amount of fibrous material consists of carbon, hydrogen, oxygen and nitrogen atoms arranged in the form of long chain molecules and the first part of this article, on molecular structure, deals with the commonest arrangements encountered, with the cohesive forces which hold the chain molecules together and the sequences of the molecular building units, and concludes with brief mention of the physical methods of investigating these structures. Since the mechanical properties of these materials are of major importance, special emphasis is given to them and in particular to the application of mechanical vibrations which allows the elastic and viscous responses to be separated. Brief mention is made of their rheological, thermal and electrical properties and also of the improvement in properties brought about by copolymerization and grafting. The article concludes with brief reference to some interesting uses and future developments.

Optical Activity of Oriented Helices

Optical activity in anisotropic solutions of helical polymers in which the orientational distribution of the polymers is given arbitrarily is studied theoretically. The Moffitt-Yang plot for the optical rotatory dispersion (ORD) in anisotropic solutions and the corresponding one for the circular dichroism (CD) in anisotropic solutions are discussed. The electronic states of helical polymers are assumed to be described in terms of the degenerate coupled oscillator theory of Moffitt, Fitts and Kirkwood. For fibrous helical polymers it is shown that information about the directions of induced dipole moment vectors relative to the helical axis can be obtained from the measurements of ORD or CD in anisotropic solutions. It is also shown that for globular polymers containing helical parts in them informations about the directional distribution of the helical parts can be obtained.

Application of histochemical techniques in electron microscopy as applied to high polymers

AbstractStaining reactions are necessary to reveal the fine structure of fibrous polymers in electron microscopical investigations. Reactions of heavy metal salts with organic compounds yield different results depending on pretreatment of the fibers, the nature of the heavy metal employed, and the conditions of treatment. In the case of keratin fibers, the structure as revealed by the electron microscope depends mainly on the conditions of treatment. For example, wool, after carboxymethylation, shows a complete reversion in contrast compared with untreated material. It is thus possible to reveal the sulfur‐rich fraction of keratin with a staining reactive which normally reveals the low‐sulfur fraction. The quantitative analysis is, in both cases, in good agreement with the electron‐microscopical results. Further examples of staining reactions are discussed, especially the reactions of keratin and cellulose fibers with silver salts.