Liquid crystalline polymers high modulus fibers

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. 

The liquid crystalline polymer industry now covers diverse products, from high modulus rope to high strength composite, from the tennis racket to the radial tire cord, from the cover layer of the optical fiber to the microwave oven, from the bullet-proof vest to thermal insulated clothing, and from the electro-optic display to non-linear optical material, etc. 

In conclusion then, we have synthesized a series of extended-chain, aromatic polyazomethlnes under on-degradatlve conditions. Fusible, tractable polymers were obtained by use of unsymmetrlcally placed substituents, copolymerization, and/or limited proportions of flexible chain units. Many of the polymers yield liquid crystalline melts which were spun Into oriented, high tenacity, high modulus fibers. The fibers were further strengthened by heat treatment. The ease of preparation of the aromatic polyazomethlnes and the outstanding tenacity and modulus range of the fibers make these products excellent candidates for use as reinforcing fibers In resins and rubber. 

Thermotropic liquid crystal polymers (LCI ) are of considerable current interest, because of their theoretical and technological aspects [1-3]. Evidently, a new class of polymers has been developed, combining anisotropic physical properties of the liquid crystalline state with diaracteristic polymer features. This unique combination promises new and interesting material properties with potential ai lications, for example in the field of high modulus fibers [4], storage technology, or non-linear optics [5]. 

Although as-spun fiber of Me-HQ/Cl-PEC showed high modulus of 72 GPa,the modulus of the injection molded test pieces of Me-HQ/Cl-PEC was only 26 GPa.Ph-HQ/Cl-PEC and tBu-HQ/Cl-PEC showed no liquid crystallinity,but the moduli of the injection molded test were 7.5 and 15.1 GPa,respectively,which were 2-5 times higher than that of isotropic polymers.tBu-HQ/Cl-PEC showed many fibrils on the cross section of the flexural fractured test pieces as shown in Fig. 6(2).We assumed that tBu-HQ/Cl-PEC was a quasi liquid crystalline polymer which could orient at the high shear rate.Although W.B.Black reported a lyotropic quasi liquid crystalline polymer which could orient at the high shear rate,tBu-HQ/Cl-PEC is the first example of the thermotropic quasi liquid crystalline polymer(6). 

The primary motivation for industrial participation in the development of liquid crystalline polymers was the search for high performance tensile properties, i.e., fiber tensile strength and modulus. As it later turned out, the wholly aromatic, thermotropic polyesters were found to offer a great many more useful properties than just their now well-known tensile capabilities. 

High modulus fibers and films are produced from extended chain crystals in both conventional polymers, notably PE, and liquid crystalline polymers. Carter and Schenk [18], Jaffe and Jones [19], and Zachariades and Porter [20] have reviewed the topic of high modulus organic... 

Liquid crystalline polymers have been discussed in many texts and review papers [65, 400-413] during the last decade, in which the synthesis, processing, morphology, orientation and structure-property relations are described. The major applications of these materials have been as high modulus fibers and films, with unique properties due to the formation of ordered lyotropic solutions or thermotropic melts which transform easily into highly oriented, extended chain structures in the solid state. 

Fig. 5.119. The model suggests there are structures on the scale from 500 nm to < 50 nm, specific to the liquid crystalline polymers. The key element is the microfibril, the same micro-structural unit basic to melt spun and drawn flexible polymers. The orientation of the microfibrils is along the fiber or elongational axis and this results in extremely high tensile modulus values for these materials. However, on a local scale it is clear that the microfibrils meander along the path of the director and are not literally rigid rods.

Another type of liquid crystalline polymers are those having rod-shaped side chains. TTius, the backbone may be a random coil, but the side chains are organized into one- or two-dimensional liquid crystals. The stiff backbone types make very high modulus fibers and high temperature plastics. The side chain types are useful for their action in magnetic and electrical fields. (Note the behavior of battery-driven liquid crystalline watches, for example. The liquid crystalline material is held between crossed Nicols the orientation of the molecules is controlled by an electric field.) In the following, the terms mesophase and liquid crystal phase are used interchangably. 

High modulus fibers and films are produced from extended chain crystals in both conventional polymers, notably PE, and liquid crystalline polymers. Carter and Schenk [18], Jaffe and Jones [19] and Zachariades and Porter [20] have reviewed the topic of high modulus organic fibers, fully describing their preparation, structure and properties. High modulus fibers are found in such critical applications as fiber reinforced composites for aerospace and military applications and industrial fibers such as belts and tire cords. Extended chain crystals can also form when polymers are crystallized very slowly near the melting temperature but they are weak and brittle. 

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