Fibre highly oriented

Japanese researchers20 have attained a high degree of uncoiling of molecules and a high orientation of the latters in fibres by extension below the glass transition temperature... 

Peroxidic groups in oxidized polyolefins have frequently been employed as sources of free radicals to allow grafting of vinyl monomers to polyolefins (2f[). Some of the products from the gas reactions also have interesting potential as reactive sites. For example, chloroformate groups are well known to react with alcohols, and amines 2J[). Thus chloroformate groups could be useful for example in coupling highly oriented polyolefin fibres to resins such as epoxy based systems. 

Figures 26 and 27 present the modulus and strength as a function of the orientation parameter sin2 for the PpPTA, PBO and PIPD-HT fibres, assuming a fibre with a single orientation angle. As the precise value of g for the PBO fibre is not known, we have taken the same value as for PpPTA. This enables us to demonstrate the effect of the chain modulus on the modulus and the strength of the fibres, in particular at medium values of the orientation parameter and for highly oriented fibres. For example, at an orientation parameter value of sin2 =0.028 the modulus and strength for a PpPTA fibre are =84 and crb=3.9 GPa, for PBO =104 and ab=5.2 GPa, and for PIPD-HT =241 and crb=8.6 GPa.

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. 

Interest in the role of the matrix in mineralization was reawakened by the demonstration, that the crystals in bone were highly oriented with respect to the collagen fibres. This in turn has led to studies on the chemical nature of the matrix related to its ability to calcify184). 

Cellulose fibres are probably packed parallel to one another lengthwise along the axis to form bundles, so called micelles, which are highly oriented along the fibre axis, thus giving cellulose its characteristic mechanical properties. 

Fig. 4. Raman spectra of a highly oriented polyethylene fibre. The meaning of the three experiments, shown here is evident from Ref. 10. Full line and broken line indicate electric vector of the laser beam perpendicular and parallel to the fibre axis, respectively. "Sp" spurious emission from the laser...

It is probable that suitable thermal treatment of the tensioned fibres promotes molecular chain displacements, thus permitting the formation of regular bonding between adjacent chains leading to highly oriented regions of crystalline order. 

Generally it is found that PPT fibres are highly oriented and that those variants with the lowest values of orientation angle exhibit the highest tensile modulus. Indeed the average crystallite orientations derived from azimuthal peak widths at half maximum intensities of the 200 reflections in Kevlar 49 and Kevlar 29 are found to be nine and eleven degrees respectively. 

A particularly interesting property of Durham polyacetylene is that it can be stretched to draw ratios of up to 20 during the transformation, to yield a polyacetylene sample with high levels of orientation. This effect was reported by Bott et al. 378) for thin films in the electron microscope and then by Leising et al. 379), who drew single fibres of polyacetylene to a highly oriented /rani-state with a density of 1.06 g cm-3. 

Fig. 10 Sherby-Dorn plots of creep rate versus strain showing the different creep phases a U PVC pipes for constant hoop stresses of 37 to 42 MPa at a temperature of 20 °C (60 K below Tg) (using data of Castiglione et al. [42]) b Highly oriented UHMWPE fibres at room temperature (using data of Berger et al. [43])...

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). 

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