Polyamide applications

Miscellaneous Applications. Polyamides, prepared from polyamines and neodecanoic acid, are used as wash-cycle antistatic agents (qv)... 

Materials. High density polyethylene (HDPE) having different molecular weights, and specific gravity of 0.951 (Marlex 5202, HXM 50100, made by Phillips 66 Co), were used for extrusion applications. Polyamides used were a semicrystalline copolyamide of adipic acid, hexamethylene diamine and caprolactam, and a copolyamide containing isophthalic acid as well. An anhydride modified polyethylene (3-5) as an interlaminar adhesive/compatibilizer was also used. The combinations are generally included in "Selar" barrier materials supplied by E. I. du Pont de Nemours Co. 

Engine components. Parts fabricated from injection-molded fiber-reinforced polyamide-imides provide a lower-cost solution to previously machined metal pieces and maintain, due to low shrinkage, very tight tolerances which are required in these applications. Polyamide-imide compounds have replaced expensive titanium in air return grills for commercial aircraft engines (Fig. 12.13). The shroud on the interior of the aircraft engine, responsible for directing airflow, consists of an assembly of multiple polyamide-imide injection-molded pieces (Fig. 12.14). 

The above-mentioned properties of polyamides in combination with their extensive use in connection with synthetic absorbable sutures in surgery demonstrate the possibility of designing iimovative polyamide-based delivery systems. Various systems are proposed to deliver protein and peptide drugs after their entrapment in nanoparticles, nanoaggregates or complexes based on polyamide backbone [449]. They are suitable for either oral or parenteral administration [450]. Polyamides have also been explored for nucleic add transportation [451,452]. Other than these pharmaceutical applications, polyamides are reported to be utilized in tissue engineering for the development of transplants to treat defedive or malfunctioning tissues and cells [453]. 

Even if other t5 es of polyamides have also gained a certain importance on the world market for particular applications, polyamide 6 and polyamide 66 still represent over 90 % of the world s production of polyamides. 

Saverio Russo is a senior professor of industrial chemistry at Genoa University, Italy. He has been, and still is, project leader of several research programs supported by the European Union, Italian Ministry of University, and Chemical Companies. He has been working for more than 40 yeare in the field of macromolecular science and technology, mainly on advanced polymeric materials synthesis, characterization and applications. Polyamide 6 by the anionic routes has been one of the major topics of his research. He is author of more than 250 scientific publications, mostly in international journals, and six patents. Prof Russo has been member of the Scientific Committee of INSTM (Interuniversity Consortium of Materiab Science and Technology) and director of its S Hon on Functional and Structural Polymeric Materials. He was the co- itor of four volumes of Comprehensive Polymer Science, Peigamon, 1989 and two supplement volumes (1992 and 1996). He was the organizer and co-chairman of two lUPAC Symposia of Free Radical Polymerization Kinetics and Mechanism, in 1987 and 1996. 

Technical polymers (also called engineering plastics) exhibit mechanical characteristics that enable them to replace traditional materials (metals, ceramics, etc.) in many applications polyamides, polyacetals, and so on, are part of this family ... 

Comparable but equally specific considerations must be applied to other condensation polymer systems. The following example is an illustration of the application of these ideas to the molecular weight of polyamides. 

The combination of strong intermolecular forces and high chain stiffness accounts for the high melting points of polyamides through application of Eq.(4.5). 

This polymerization is carried out in the two stages indicated above precisely because of the insolubility and infusibility of the final product. The first-stage polyamide, structure [IX], is prepared in polar solvents and at relatively low temperatures, say, 70°C or less. The intermediate is then introduced to the intended application-for example, a coating or lamination-then the second-stage cyclization is carried out at temperatures in the range 150-300°C. Note the formation of five-membered rings in the formation of the polyimide, structure [X], and also that the proportion of acid to amine groups is 2 1 for reaction (5.II). 

Dyes, application and evaluation). Foi dyeing fibei blends such as viscose—polyamide, polyamide—Spandex, oi polyestei—cotton, only compatible FWAs may be used that do not inteifeie with one another oi have any detrimental effect on fastness properties. 

Military Application and Aerospace Wires. Depending on the specific appHcation, a variety of polymers can be considered PVC, polyamides, PTEE, etc (Eig. 3). Navy shipboard specifications require cables with dame retardancy, low smoke emission during fire, and containing no halogen. 

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). 

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 ... 

Among these dye classes, anthraquiaone dyes are ia an important position ia reactive dyes and vat dyes for cellulose fibers, disperse dyes for polyester, and acid dyes for polyamide. Application for high performance organic pigments for plastics and paints are also important areas. 

Polymerization of /3-lactams to yield linear polyamides could have industrial applications if the cost of the starting materials can be reduced sufficiently to make the process economically attractive (75S547 p. 58l). 

Polymer Membranes These are used in filtration applications for fine-particle separations such as microfiltration and ultrafiltration (clarification involving the removal of l- Im and smaller particles). The membranes are made from a variety of materials, the commonest being cellulose acetates and polyamides. Membrane filtration, discussed in Sec. 22, has been well covered by Porter (in Schweitzer, op. cit., sec. 2.1). 

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

Whilst by far the bulk of polyamide materials are used in the form of fibres, they have also become of some importance as speciality thermoplastics of particular use in engineering applications. The fibre-forming polyamides and their immediate chemical derivatives and copolymers are often referred to as nylons. There are also available polyamides of more complex composition which are not fibre-forming and are structurally quite different. These are not normally considered as nylons (see Section 18.10). 

Since large tonnage production is desirable in order to minimise the cost of a polyamide and since the consumption of nylons as plastics materials remains rather small, it is important that any new materials introduced should also have a large outlet as a fibre. There are a number of polyamides in addition to those already mentioned that could well be very useful plastics materials but which would be uneconomical for all but a few applications if they were dependent on a limited outlet in the sphere of plastics. Both nylon 7 and nylon 9 are such examples but their availability as plastics is likely to occur only if they become established fibre-forming polymers. This in turn will depend on the economics of the telomerisation process and the ability to find outlets for the telomers produced other than those required for making the polyamides. 

The transparent polyamides have increased significantly in importance in recent years. For transparent applications they are competitive with poly(methyl methacrylate), polycarbonates, polysulphones and MBS. In terms of toughness they are like polycarbonates, polysulphones and MBS and much better than the... 

The thermoplastic elastomer polyamides have found use in conveyor and drive belts, ski and soccer shoe soles, computer keyboard pads, silent gears in audio and video recorders and cameras, and thin film for medical applications. 

Applications of the elastomeric polyamides include keyboard pads, sports footwear, loudspeaker gaskets and, in the case of filled grades, watch straps. 

Polyamide PPOs are manufactured by General Electric (Noryl GTX), BASF having now withdrawn from marketing their product (Ultranyl). Usage of the blends has so far been mainly in the automobile field for such applications as valance panels, wheel trims, grilles, rear quarter panels, front bumpers and tailgates. 

Elevated temperatures are necessary for cure and the chemical resistance of the laminates is inferior to those from unmodified resins. Because of problems in handling, the polyamides have found only limited use with epoxy resins, mainly for coating and adhesive applications. 

Where plastics are to be used for electrical applications, then electrical properties as well as mechanical and other properties need to be considered. Whilst properties such as resistivity, power factor and dielectric constant are important, they may not be all-important. For example, although polyamides and many thermosetting plastics may show only moderate values for the above properties, they have frequently been used successfully in low-frequency applications. Perhaps more important for many purposes are the tracking and arcing resistance, which are frequently poor with aromatic polymers. 

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