Oriented polymers ultra-high modulus

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Zachariades, A. E., Mead, W. T., Porter, R. S. Recent developments in ultramolecular orientation of polyethylene by soldid-state extrusion, in Ultra-High Modulus Polymers (eds.) Ciferri, A., Ward, I. M., p. 77, London, Applied Science 1979... 

Because of the possible use of ultra-high modulus LPE for engineering applications, extensive studies of the creep and recovery behaviour have been undertaken °. The creep response is much reduced by increased orientation, but there are also major effects of polymer molecular weight and copolymerisation. It is very instructive to plot the creep... 

The first commercially important liquid-crystalline polymer was Kevlar. Kwolek wrote in 1965 about anisotropic solutions of wholly aromatic polyamides in alkylamide and alkylurea solvents. This development led to Kevlar, i.e. ultra-oriented fibres of poly(p-phenylene terephthalamide) (Fig. 6.17). The solution of the polymer in concentrated sulphuric acid is nematic (the term nematic will be explained in section 6.5.3) and fibres of high modulus and high strength can be spun from the solution. 

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