FIBERS AND ORIENTED FILMS

Glycol phthalate resin n. A type of thermoplastic polyester used mainly for fibers and oriented films. 

In addition to depressing melting point, DEG units adversely affect the crystallinity of the polymer, reduce the strength of both fibers and oriented films, and increase the susceptibility of the polymer to chemical attack and aqueous hydrolysis. 

Polypropylene film is found in a variety of applications. Films are thin plastic sheets with thicknesses less than 250 pm. Applications for these films include candy mappers, plastic label material, electrical capacitors (which requires very pure polymer), and fiber glass insulation backing. There are two general categories of polypropylene films unoriented and oriented. Films are manufactured through either a cast or a blown film extrusion process. Oriented films exhibit improved strength relative to unoriented films. This means that they can be... 

As a result of this the manufacturers of polymers have found it necessary to exercise leadership in pioneering the methods by which their polymers are formed—sometimes to the extent that the manufacturer has himself often sold the polymer in the fabricated form. Hercules, for example, pioneered in the manufacture and sale of polypropylene resin. We soon realized, however, that the conversion of this resin to fiber and to film and to foam, would have to be done by us because of the complex technologies and large investments involved. Consequently, the resin manufacturer now finds himself selling polypropylene fiber, biaxially-oriented film, and foam—successfully too if I may be allowed to add. 

With optically anisotropic samples (crystals and oriented films and fibers), dichroism measurements indicate the direction of the transition dipole moment. Since the... 

A TEM image and electron diffraction pattern (inset) of P(3HB) single nanofiber spun from lwt.% HFIP solution are shown in Figure 15(c). Many arc-shaped reflections were observed in the diffraction pattern. Similar diffraction patterns have been observed for the drawn fibers and stretched films of P(3HB) in which molecular chains are highly oriented. Particularly, the appearance of (002) diffraction on the meridian su ests that the crystallographic c-axis of a-form P(3HB) crystal, that is, the molecular chain axis, lies parallel to the fiber direction. 

Most polysaccharides are macroscopically amorphous, but molecules of the linear polysaccharides of natural and artificial fibers, and stretched films are generally oriented parallel to one another, and appear partially or almost completely crystalline on X-ray crystallc raphic examination. Some unstretched linear molecules, amylose (in its complexes) for example, also exhibit partial crystallinity. In a number of cases the size of the unit cell of the crystal lattice has been evaluated. Comparison of the crystallographic data with scale models of short lengths of the polysaccharide chain has been used to reveal the manner in which inter- or intra-molecular hydrogen bonding hold the chains in the rigid framework of a crystal lattice. 

Applications. The polyamides have important appHcations. The very high degree of polymer orientation that is achieved when Hquid crystalline solutions are extmded imparts exceptionally high strengths and moduli to polyamide fibers and films. Du Pont markets such polymers, eg, Kevlar, and Monsanto has a similar product, eg, X-500, which consists of polyamide and hydra2ide-type polymers (31) (see High performance fibers Polyamides, fibers). 

Polypropylene is used in battery cases and in the replacement of metal parts in automobiles. It is also widely used in consumer products, eg, kitchen wares, trays, toys, and packaging materials. Its future appHcations are expected to include an increased portion of the fibers and filaments markets, especially for continued growth in carpet backing and carpet face yams. Film, both oriented and unoriented, is also expected to be a significant growth market for polypropylene. 

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

Both stress-induced crystallization and orientational crystallization can be used for the preparation of polymer materials with mechanical property values (e.g. tenacities and elastic moduli) much higher than those for polymer films and fibers obtained by conventional processing. We believe that the advantage of orientational crystallization over more complex methods consists in the possibility of obtaining samples of elastic moduli and tenacities in a one-step continuous process. 

P. Poulin, B. Vigolo, and P. Launois, Films and fibers of oriented single wall nanotubes. Carbon 40, 1741-1749 (2002). 

Polymers have been valued since antiquity for their solid state properties. By this is meant their ability to undergo chain entanglement or co-linear orientation and microcrystalll-zatlon in the solid state. This underlies their use as structural materials, films, fibers, and elastomers. Such properties still constitute the driving force for most pol)nner-orlented research, especially with respect to the synthesis of heat-stable, radiation-stable, or highly flexible materials. 

A network of oriented microfibrils is formed during coagulation in the spinning process of PBT fibers and films. The microfibrils have a typical diameter on the order of 100 A, and have irregularly shaped cross sections. This network is the basis for the structure and the properties of the final material. 

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