Polymer fibers, properties

Polyethylene terephthalate modification hexsaazocyclanes by additives was carried out and fibers were formed. Additives introduction did not influence on the process of formation, and, consequently on the polymer fiber properties. 

The heated polymer solution emerges as filaments from the spinneret into a column of warm air. Instantaneous loss of solvent from the surface of the filament causes a soHd skin to form over the stiU-Hquid interior. As the filament is heated by the warm air, more solvent evaporates. More than 80% of the solvent can be removed during a brief residence time of less than 1 s in the hot air column. The air column or cabinet height is 2—8 m, depending on the extent of drying required and the extmsion speed. The air flow may be concurrent or countercurrent to the direction of fiber movement. The fiber properties are contingent on the solvent-removal rate, and precise air flow and temperature control are necessary. 

Terephthahc acid (TA) or dimethyl terephthalate [120-61 -6] (DMT) reacts with ethyleae glycol (2G) to form bis(2-hydroxyethyl) terephthalate [959-26-2] (BHET) which is coadeasatioa polymerized to PET with the elimination of 2G. Moltea polymer is extmded through a die (spinneret) forming filaments that are solidified by air cooling. Combinations of stress, strain, and thermal treatments are appHed to the filaments to orient and crystallize the molecular chains. These steps develop the fiber properties required for specific uses. The two general physical forms of PET fibers are continuous filament and cut staple. 

Itaconic acid is a specialty monomer that affords performance advantages to certain polymeric coatings (qv) (see Polyesters, unsaturated). Emulsion stabihty, flow properties of the formulated coating, and adhesion to substrates are improved by the acid. Acrylonitrile fibers with low levels of the acid comonomer exhibit improved dye receptivity which allows mote efficient dyeing to deeper shades (see Acrylonitrile polymers Fibers, acrylic) (10,11). Itaconic acid has also been incorporated in PAN precursors of carbon and graphite fibers (qv) and into ethylene ionomers (qv) (12). 

Fabric Composition. The method of fabric manufacture dictates many of the characteristics of the sheet, but intrinsic properties are firmly estabhshed by the base polymer selected. Properties such as fiber density, temperature resistance, chemical and light stabiUty, ease of coloration, surface energies, and others are a function of the base polymer. Thus, because nylon absorbs more moisture than polypropylene, spunbonded fabrics made from nylon are more water absorbent than fabrics of polypropylene. 

Effect of Fiber Properties. Acid dyes are attracted to the accessible amine ends of the nylon chains located in the amorphous regions of the fiber. Acid dye affinity of nylon can be adjusted by a dding excess diamine or diacid to the polymer salt or by changing the molecular weight in polymerization. A light acid-dyeable nylon-6,6 is spun with 15—20 amine ends, expressed in terms of gram equivalents per 10 g of polymer. A medium or... 

CL must be very carefully purified to exclude small concentrations of (1) ferric ions which would catalyze die thermal oxidative degradation of polycaprolactam and (2) aldehydes and ketones which would markedly increase oxidizability of CL. The impurities in CL may retard die rate of CL polymerization as well as having a harmful effect on die properties of die polymer fiber. In die vacuum depolymerization of nylon-6, a catalyst must be used because in die absence of a catalyst by-products such as cyclic olefins and nitrides may form, which affects the quality of die CL obtained.1... 

Microscopic techniques are extensively used to study the surface morphology of reinforcing fibers. The characterization of microstructure of polymer fibers provides an insight into stmcture-property relationship of the fiber. Microscopy techniques have been employed for the... 

Although they have an endless variety of properties, polymers can be divided into three general categories, based on their form and resistance to stretching. These are plastics, fibers, and elastomers. Plastics differ in form from fibers whereas plastics exist as blocks or sheets, fibers have been drawn into long threads. Unlike plastics or fibers, elastomers can be stretched without breaking. Polyethylene packaging films and polyvinylchloride (PVC) pipe are examples of plastics. Orion carpets are made from polymer fibers, and mbber bands are elastomers. Some polymers, such as Nylon, can be formed into both plastics and fibers. 

Except at rather low extents of reaction, W polymers are insolu- o ble and infusible no fiber properties mod- g ate strength g... 

We control fiber properties by changing the relative speeds of different stages of the process. Orientation is increased and fiber thickness decreased by increasing the final take-up speed relative to the rate at which the molten polymer strands leave the spinneret. To produce high modulus fibers we generally adopt conditions that maximize orientation. Fiber diameters... 

Combinatorial approach to unsymmetrically tiered macromolecules [214] is a brand new area of research which would allow dendrimerization of materials (e. g., glass, classical polymers, fibers) and thus enable fine tuning of macromole-cular properties. For example, treatment of an amine terminated dendrimer with a mixture of complementary, isocyanate-based monomers [215, 216] affords a heterogeneous surfaced dendrimer. Selective transformation of the surface nitrile moieties via metal-catalyzed reduction to obtain a new polyamine dendrimer allows further combinatorial-based elaboration as illustrated in Fig. 42. 

Figure 5.23 Variation in the concentration of carboxylic end groups and intrinsic viscosity during the postcondensation of PET powder produced from DMT (1) and TPA (2) prepolymers (7, 240 °C) [49]. From Gerking, L., Modifications of fiber properties by polymer and within spinning line, presentation (Paper 52b) given at the 32nd International Man-Made Fibre Congress, 22-24 September, 1993, Dornbirn, Austria, and reproduced with permission of EMS Inventa-Fischer, GmbH Co. KG...

It was previously mentioned was that a large number of minor copolymers of PET have been developed over the past 50 years, with the intent of modifying textile fiber properties and processability [2, 3], Of broader interest is that some of these textile modifications, such as PET copolymers with metal salts of 5-sulfoisophthalic acid (SIPA), have their own rich chemistries when the extent of polymer modification is increased beyond textile levels. An example of such a modification is that changing the counterions associated with SIPA can significantly effect the kinetics of polyester transesterification reactions (the... 

One key requirement in the commercial production of fibers is to control fiber diameters within narrow ranges of the target. Another is to control the internal structure of the fiber, particularly the orientation of the polymer molecules. It is this orientation along the fiber axis that controls the morphology, and hence the fiber properties, such as dye uptake, shrinkage and tensile strength. 

The chemistry of fibers is the same as chat for resins. The important difference is the mechanics. For polymers to be suitable for fibers, you must be able to draw them into a fibrous form, normally by extrusion. Second, the size and shape of the molecules that make up the fiber must be correct. To have acceptable fiber properties, the molecules must be long, so they can be oriented tO lie parallel to the axis of the fiber. Normally, thats done (or enhanced) by drawing or stretching the fiber to several times its original length. The essential differences then between resins and fibers are the shape and the orientation of the molecules. 

To prepare croscarmellose sodium, crude cellulose is steeped in sodium hydroxide solution [1] and treated with sodium monochloroacetate to form carboxymethylcellu-lose sodium. After completion of the reaction, the excess sodium monochloroacetate slowly hydrolyzes to glycolic acid. The glycolic acid converts a few of the sodium earboxymethyl groups to the free acid and catalyzes the cross-linkage to form croscarmellose sodium. The by-products sodium chloride and sodium glycolate can be removed by extraction with alcohol to achieve 99.5% purity. Croscarmellose sodium may be milled to break the polymer fibers into shorter lengths and hence improve flow properties. 

TMA measures the mechanical response of a polymer looking at (1) expansion properties including the coefficient of linear expansion, (2) tension properties such as measurement of shrinkage and expansion under tensile stress, i.e., elastic modulus, (3) volumetric expansion, i.e., specific volume, (4) single-fiber properties, and (5) compression properties such as measuring the softening or penetration under load. 

If one follows the solution viscosity in concentrated sulfuric acid with increasing polymer concentration, then one observes first a rise, afterwards, however, an abrupt decrease (about 5 to 15%, depending on the type of polymers and the experimental conditions). This transition is identical with the transformation of an optical isotropic to an optical anisotropic liquid crystalline solution with nematic behavior. Such solutions in the state of rest are weakly clouded and become opalescent when they are stirred they show birefringence, i.e., they depolarize linear polarized light. The two phases, formed at the critical concentration, can be separated by centrifugation to an isotropic and an anisotropic phase. A high amount of anisotropic phase is desirable for the fiber properties. This can be obtained by variation of the molecular weight, the solvent, the temperature, and the polymer concentration. 

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