Polymer fibre structure

Figure 8.9. Diagram of the structure of a drawn polymer fibre. The Young s modulus of the crystallised portions is between 50 and 300 GPa, while that of the interspersed amorphous tangles will be only 0.1-5 GPa. Since the strains are additive, the overall modulus is a weighted average of...

We will confine ourselves to those applications concerned with chemical analysis, although the Raman microprobe also enables the stress and strain imposed in a sample to be examined. Externally applied stress-induced changes in intramolecular distances of the lattice structures are reflected in changes in the Raman spectrum, so that the technique may be used, for example, to study the local stresses and strains in polymer fibre and ceramic fibre composite materials. 

The simplest case of fibre structure is the step-index one, characterized by a constant circular refractive index profile in the core and polymer cladding of lower refractive index (Figure 3). The refractive indexes of the core and cladding depend on the materials used. The cores of these structures can be prepared from melts as well as from preforms without radial and azimutal variations of the refractive index. To obtain suitable mechanical... 

As will be shown in this report, polymer fibres gain additional strength by an increase of the molecular weight and by a more contracted orientation distribution, i.e. a higher modulus. For the wet-spun fibres, a strength increase can be achieved by improvement of the coagulation process, which makes for a more uniform structure and chain orientation in the cross section of the fibre, and by a reduction of the amount of impurities. 

Immediately upon fracture the fibre drops from a high-energy state equal to the stored elastic energy to its lowest energy, viz. the unloaded state. Hence, initiation of fracture in the domains in the tail of the orientation distribution p(0) does release most effectively the stored energy of a loaded polymer fibre. So, if there are no impurities and structural irregularities, fracture of the fibre is... 

In view of the development of the continuous chain model for the tensile deformation of polymer fibres, we consider the assumptions on which the Coleman model is based as too simple. For example, we have shown that the resolved shear stress governs the tensile deformation of the fibre, and that the initial orientation distribution of the chains is the most important structural characteristic determining the tensile extension below the glass transition temperature. These elements have to be incorporated in a new model. 

The presented derivations of the load rate and the lifetime relationships applying the shear failure criterion are based on a single orientation angle for the characterisation of the orientation distribution. Therefore these relations give only an approximation of the lifetime of polymer fibres. Yet, they demonstrate quite accurately the effect of the intrinsic structural parameters on the time and the temperature dependence of the fibre strength. 

FIG. 13.95 The single-phase structural model for a polymer fibre. From Northolt and Baltussen (2002). Courtesy John Wiley Sons, Inc. 

There is overwhelming evidence that the aramide fibres possess a radially oriented system of crystalline supramolecular structure (see Fig. 19.1). The background of the properties, the filament structure, has been studied by Northolt et al. (1974-2005), Baltussen et al. (1996-2001), Picken et al. (2001), Sikkema et al. (2001, 2003), Dobb (1977-1985) and others. The aramid fibres (and the "rigid" extended chain fibres in general) are exceptional insofar as they were - with the rubbers - the first polymer fibres whose experimental stress-strain curve can very well be described by a consistent theory. 

Source The Japanese Ministry of International Trade Industry, cellulosic fibres is expected to decline marginally at the rate of 0.3%. The interplay between fibre structure, morphology and chemical composition is an essential part of all pre-treatment processes and thus, it is necessary to know the differences in the structures of different polymers and their effects on the properties of the fibres. There are many good books on this subject and hence only general fibre chemistry and manufacturing processes are presented in reference form and then proceeded to discuss how preparatory processes are chosen for use as fibre processing. 

The more fundamental aspects of fiber constitution and behavior are dealt with in Astbury s Fundamentals of Fibre Structure 27) and Textile Fibres under the X-Rays 28), Hermans Contributions to the Physics of Cellulose Fibres 39), and Physics and Chemistry of Cellulose Fibres (40 Marsh s Textile Science (40 Preston s Fibre Science 59) and the High Polymers series of monographs, three of which are concerned with natural fibers—Volume IV, Natural and Synthetic High Polymers, by Kurt H. Meyer 53), Volume V, Cellulose and Cellulose Derivatives, edited by Emil Ott 56), and Volume VI, Mechanical Behavior of High Polymers, by Turner Alfrey, Jr. 21 ... 

High degree of crystallinity causes high fibre density, resistance to the action of chemical reagents and physico-chemical properties of polymer. Fibrillar structure of the fibre is seen in microphotoes of modified fibres, moreover introduction of hexaazocyclanes into PETP facilitates increase of regularity and density of polymer structure. All this proves that introduction of hexaazocyclanes additives increases PETP ability to crystallization. 

M. Granstrom and O. Inganas, Electrically conductive polymer fibres with mesoscopic diameters 1. Studies of structure and electrical properties. Polymer, 36, 2867-2872... 

Smart textile and polymer fibres for structural health monitoring... 

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