Polymer fibre highly oriented

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... 

The strength of a fibre is not only a function of the test length, but also of the testing time and the temperature. It is shown that the introduction of a fracture criterion, which states that the total shear deformation in a creep experiment is bounded to a maximum value, explains the well-known Coleman relation as well as the relation between creep fracture stress and creep fracture strain. Moreover, it explains why highly oriented fibres have a longer lifetime than less oriented fibres of the same polymer, assuming that all other parameters stay the same. 

The effects of processing will be illustrated by considering injection moulding of a semicrystalline polymer. The molten plastic is injected into the mould under high pressure and temperature. The edges of the mould retard flow and cool more rapidly, leading to a boundary layer of high shear, which in semicrystalline polymers leads to orientation of the polymer chains and of short fibre reinforcements parallel to the direction of flow. At the centre the structure is less oriented. Where two separate flow streams meet, there is a... 

A special category is formed by oriented polymers, which have considerably higher stiffnesses. The most obvious example is the textile fibre the orientation, frozen-in in a crystalline structure, raises E by a factor of 3 to 5. Extremely high orientations, as met in liquid-crystal polymers (LCP s) result in even higher E-values, namely 60 to 120 GPa ... 

A completely different approach to polymer crystallisation in extended-chain conformation became possible with the coming of a new class of polymers the para-para type aromatic polymers. These polymers possess inherently rigid molecular chains in an extended conformation (Preston, 1975 Magat, 1980 Northolt, 1974, 1980, 1985 Dobb, 1985). Theoretically they should give rise to high orientation in fibre form without the necessity of subjecting the as spun filaments to the conventional drawing process. 

The first method is to manufacture a malleable polymer that can be easily converted into a conjugated polymer. This is done when the initial polymer is in the desired form and then, after conversion, is treated so that it becomes a conductor. The treatment used is most often thermal treatment. The precursor polymer used is often made to produce highly aligned polymer chain which are retained upon conversion. These are used for highly orientated thin films and fibres. Such films and fibres are highly anisotropic, with maximum conductivity along the stretch direction. 

The solubility of the electrically conductive form, the protonated EM salt, is poor in common solvents, and so, initially, EM base was used to form films from NMP solution before conversion to the salt with HC1. Attempts to increase solubility by incorporating pendent alkyl chains were counterproductive as such polymers had significantly lower electrical conductivity. Better solubility is obtained for salts produced with sulphonic acids. Thus the camphor sulphonic acid salt dissolves in m-cresol and the 2-acrylamido-2-methyl-l-propanesulphonic acid salt dissolves in dichloro-acetic acid. The use of these systems, and polymer synthesised below room temperature, has facilitated the spinning of fibres with oriented polymer chains and conductivity along the fibre as high as 2x 105f2-Im-1 (Pomfret et ai, 1998). 

It is not excluded that this mechanism is observed during the formation of fibres from X-500 The authors of this work pointed out that when the fibre was heated to 250-300 °C, its spontaneous elongation took place. Note that to attain higher orientation of a polymer in a fibre, it is necessary not only to transfer it to the liquid crystalline state but also to orient the liquid crystalline domains formed along the axis of the fibre. This orientation of the domain in which the macromolecules have been already mutually ordered requires not too high a draw ratio (the theoretical value must be <2). Indeed, experiments have shown that at the draw ratio of 1.53 to 1,70 the modulus (E) and the tensile strength (a) of the fibre at thermal treatment increase, which can be seen from the table compiled according to the results of this work. 

Brittle fracture in glassy polymers occurs by the prior formation of crazes which then fracture. In the craze, fibrils of highly oriented polymer are produced and it is the fracture of these fibrils that almost certainly produces the observed radicals. Even in this case, then, the signal derives ultimately from a fibre in which... 

Moreover, new and exceptional material properties arise from this unique combination of LC and polymeric features, implying various technological applications. For example, the ease with which LC main chain polymers can be oriented by shear fields has been employed in the formation of fibres with unusually high tensile strengths and moduli [1-3]. Similarly, LC side chain polymers in the assy state have been used as storage materials [32], Further applications in the display technology and in the field of non-linear optics are currently being developed [5,33]. 

The conclusion is that, for a rotating crystal, most sets of crystal planes give rise to four spots lying at particular points on the imaginary circle where the corresponding powder-pattern circle would have been. These points are symmetrically placed with respect to the plane that contains the incident X-ray beam and the rotation axis and to the plane that contains the incident X-ray beam and is normal to the rotation axis, as shown in fig. 4.9. A similar conclusion can be drawn for a stationary, highly oriented polymer fibre. Planes parallel to the rotation or fibre axis give rise to only two diffraction spots. 

An X-ray diffraction pattern was obtained from a very highly oriented fibre of a polymer using a cylindrical camera of radius 5.00 cm and X-rays of wavelength 0.154 nm, with the fibre coincident with the axis of the camera. First-order layer lines were observed at distances 3.80 cm above and below the equator. Determine the c-axis spacing. 

Natural polymers often owe their important properties to the fact that they are highly oriented, e.g. cellulose, in the form of wood and cotton, and silk fibre, which is a protein. 

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