Polyamide characteristics

Some of the polyphthalamide (PPA)/high-perfor-mance polyamide characteristics are as follows ... 

In the area of moleculady designed hot-melt adhesives, the most widely used resins are the polyamides (qv), formed upon reaction of a diamine and a dimer acid. Dimer acids (qv) are obtained from the Diels-Alder reaction of unsaturated fatty acids. Linoleic acid is an example. Judicious selection of diamine and diacid leads to a wide range of adhesive properties. Typical shear characteristics are in the range of thousands of kilopascals and are dependent upon temperature. Although hot-melt adhesives normally become quite brittle below the glass-transition temperature, these materials can often attain physical properties that approach those of a stmctural adhesive. These properties severely degrade as the material becomes Hquid above the melt temperature. 

A number of thermally stable polymers have been synthesized, but in general the types of stmctures that impart thermal resistance also result in poor processing characteristics. Attempts to overcome this problem have largely been concentrated on the incorporation of flexible groups into the backbone or the attachment of stable pendent groups. Among the class of polymers claimed to be thermally stable only a few have achieved technological importance, some of which are polyamides, polyimides, polyquin oxalines, polyquinolines, and polybenzimidazoles. Of these, polyimides have been the most widely explored. 

The polyamides are soluble in high strength sulfuric acid or in mixtures of hexamethylphosphoramide, /V, /V- dim ethyl acetam i de and LiCl. In the latter, compHcated relationships exist between solvent composition and the temperature at which the Hquid crystal phase forms. The polyamide solutions show an abmpt decrease in viscosity which is characteristic of mesophase formation when a critical volume fraction of polymer ( ) is exceeded. The viscosity may decrease, however, in the Hquid crystal phase if the molecular ordering allows the rod-shaped entities to gHde past one another more easily despite the higher concentration. The Hquid crystal phase is optically anisotropic and the texture is nematic. The nematic texture can be transformed to a chiral nematic texture by adding chiral species as a dopant or incorporating a chiral unit in the main chain as a copolymer (30). 

Because of the rotation of the N—N bond, X-500 is considerably more flexible than the polyamides discussed above. A higher polymer volume fraction is required for an anisotropic phase to appear. In solution, the X-500 polymer is not anisotropic at rest but becomes so when sheared. The characteristic viscosity anomaly which occurs at the onset of Hquid crystal formation appears only at higher shear rates for X-500. The critical volume fraction ( ) shifts to lower polymer concentrations under conditions of greater shear (32). The mechanical orientation that is necessary for Hquid crystal formation must occur during the spinning process which enhances the alignment of the macromolecules. 

To accommodate the various uses in 100% form and in blends, the tenacities and elongations of the nylon staple offerings range from 0.3 to 0.6 N /tex (3—7 g/den) and from 50 to 100% elongation. Most other fiber properties of nylon staple differ tittle from those of the continuous filament property characteristics of nylon-6 and nylon-6,6 are similar (see Polyamides, general). 

An all aromatic polyetherimide is made by Du Pont from reaction of pyromelUtic dianhydride and 4,4 -oxydianiline and is sold as Kapton. It possesses excellent thermal stabiUty, mechanical characteristics, and electrical properties, as indicated in Table 3. The high heat-deflection temperature of the resin limits its processibiUty. Kapton is available as general-purpose film and used in appHcations such as washers and gaskets. Often the resin is not used directly rather, the more tractable polyamide acid intermediate is appHed in solution to a surface and then is thermally imidi2ed as the solvent evaporates. 

Aramid Fibers. Aromatic polyamide fibers exhibiting a range of mechanical properties are available from several manufacturers, perhaps the best known being Du Pont s proprietary fiber Kevlar. These fibers possess many unique properties, such as high specific tensile strength and modulus (see Fig. 4). Aramid fibers have good chemical resistance to water, hydrocarbons, and solvents. They also show excellent flame retardant characteristics (see High PERFORMANCE fibers Polyamdes). 

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

Acid—mordant dyes have characteristics similar to those of acid dyes which have a relatively low molecular weight, anionic substituents, and an affinity to polyamide fibers and mordant dyes. In general, brilliant shades caimot be obtained by acid—mordant dyes because they are used as their chromium mordant by treatment with dichromate in the course of the dyeing procedure. However, because of their excellent fastness for light and wet treatment, they are predominandy used to dye wool in heavy shades (navy blue, brown, and black). In terms of chemical constitution, most of the acid—mordant dyes are azo dyes some are triphenyhnethane dyes and very few anthraquinone dyes are used in this area. Cl Mordant Black 13 [1324-21 -6] (183) (Cl 63615) is one of the few examples of currentiy produced anthraquinone acid—mordant dyes. It is prepared by condensation of purpurin with aniline in the presence of boric acid, followed by sulfonation and finally by conversion to the sodium salt (146,147). 

The polyimides have the characteristic functional group below and are thus closely related to the polyamides. However, the branched nature of the... 

Polyamides (nylon). There are several different types of nylon (e.g. nylon 6, nylon 66, nylon 11) but as a family their characteristics of strength, stiffness and toughness have earned them a reputation as engineering plastics. Table 1.3 compares the relative merits of light metal alloys and nylon. 

The behavior of the physico-mechanical characteristics of polymeric composites is easily traceable in the table given in [144] which presents the results of experiments with polyamide matrices filled with resite particles of different shape. The filler concentrations were adjusted so that the integral contact surface area in the filler-matrix system remained the same. 

Second, in the case of polyoxazoline hybrid, the characteristic property of high compatibility of organic polymer with polar organic commodity polymers such as poly(vinyl chloride) or polyamide can be used as a type of compatibilizer. That is, it makes possible to incorporate the third organic polymer in the polyoxazoline-silica gel hybrid. 

Honeywell has also been active in developing a combined active-passive oxygen barrier system for polyamide-6 materials [201]. Passive barrier characteristics are provided by nanoclay particles incorporated via melt processing techniques, while active contribution comes from an oxygen-scavenging ingredient (undisclosed). Oxygen transmission results reveal substantial... 

The ability of nanoclay incorporation to reduce solvent transmission through polymers such as polyamides has been demonstrated. Data provided by de Bievre and Nakamura [203] of UBE Industries reveal significant reductions in fuel transmission through poIyamide-6/66 polymers by incorporation of a nanoclay hller. As a result, considerable interest is now being shown in these materials as both fuel tank and fuel line components for cars. Of further interest, the reduced fuel transmission characteristics are accompanied by significant material cost reductions. 

PESA can be blended with various thermoplastics to alter or enhance their basic characteristics. Depending on the nature of thermoplastic, whether it is compatible with the polyamide block or with the soft ether or ester segments, the product is hard, nontacky or sticky, soft, and flexible. A small amount of PESA can be blended to engineering thermoplastics, e.g., polyethylene terepthalate (PET), polybutylene terepthalate (PBT), polypropylene oxide (PPO), polyphenylene sulfide (PPS), or poly-ether amide (PEI) for impact modification of the thermoplastic, whereas small amount of thermoplastic, e.g., nylon or PBT, can increase the hardness and flex modulus of PESA or PEE A [247]. 

Principles and Characteristics The prospects of Raman analysis for structural information depend upon many factors, including sample scattering strength, concentration, stability, fluorescence and background scattering/fluorescence from the TLC substrate. Conventional dispersive Raman spectroscopy has been considered as a tool for in situ analysis of TLC spots, since most adsorbents give weak Raman spectra and minimal interference with the spectra of the adsorbed species. Usually both silica and cellulose plates yield good-quality conventional Raman spectra, as opposed to polyamide plates. Detection limits for TLC fractions... 

Laser microprobe MS (LMMS) can be used for direct analysis of normal-phase HPTLC plates [802,837]. Kubis et al. [802] used polyamide TLC plates polyamide does not interfere with compound identification by the mass spectrum, owing to its low-mass fragment-ions (m/z < 150). LMMS is essentially a surface analysis technique, in which the sample is ablated using a Nd-YAG laser. The UV irradiation desorbs and ionises a microvolume of the sample the positive and negative ions can be analysed by using a ToF mass spectrometer. The main characteristics of TLC-LMMS are indicated in Table 7.84 [838],... 

The main characteristics of the application of NMR to polymer/additive dissolutions are given in Table 9.6. NMR solvent-additive interactions should be avoided. This may be problematic for some systems, such as polyamides, where the polymer solvent (e.g. formic... 

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