Aromatic nylon

Cellulose-acetate-propionate resin Aromatic nylons... 

Aromatic nylons, [—NH—C5H4—CO—] (also called aramids), have specialty uses because of their improved clarity. 

Nylon 6/9, molding and extrusion Nylon 6/12 Nylon 11, molding and extrusion Nylon 12, molding and extrusion Aromatic nylon (aramid), molded and unfilled ... 

Other nylons are made by varying the molecular length of the diamines and the dibasic acids Nylon-fi. in u.ses sebacic acid (10 carbon atoms), nylon-11 uses an acid from castor oil, and nylon-12 uses butadiene. These variations decrease moisture absorption. Other variations use amines with a ring structure, e.g., the aromatic nylons to give polymers with softening points above 577 F,... 

Melamine formaldehyde Melamine phenolic Nitrile resins Phenolics Polyamides Nylon 6 Nylon 6/6 Nylon 6/9 Nylon 6/12 Nylon 11 Nylon 12 Aromatic nylons Poly(amide-imide)... 

About 98% of the fibers employed in composites are glass (Sections 12.5 and 12.6), carbon (graphite, carbon fibers, etc. Section 12.16), and aromatic nylons (often referred to as aramids Section 4.8). New composites are emerging that employ carbon nanotubes and the fibers (Section 12.17). Asbestos (Section 12.13), a major fiber choice years ago, holds less than l%i of the market today because of medical concerns linked to it. 

Two general varieties of aromatic nylons are often employed. A less stiff variety is employed when some flexibility is important, whereas a stiffer variety is used for applications where greater strength is required. While good adhesion with the resin is often desired, poor adhesion is sometimes an advantage such as in the construction of body armor where delamination is a useful mode for absorbing an impact. 

Fiber-reinforced composites contain strong fibers embedded in a continuous phase. They form the basis of many of the advanced and space-age products. They are important because they offer strength without weight and good resistance to weathering. Typical fibers are fiberous glass, carbon-based, aromatic nylons, and polyolefins. Typical resins are polyimides, polyesters, epoxys, PF, and many synthetic polymers. Applications include biomedical, boating, aerospace and outer space, sports, automotive, and industry. 

Nylon-4,6 was developed by DSM Engineering Plastics in 1990 and sold under the trade name Stanyl giving a nylon that has a higher heat and chemical resistance for the automotive industry and in electrical applications. It has a of 295°C and can be made more crystalline than nylon-6,6. A number of other nylons, such as the aromatic nylons and aramids, are strong and can operate at high temperatures, and they have good flame-resistant properties. 

Polymers form the basis for fire-resistant textiles. For instance, many of the firefighters and race car drivers wear clothing made from aromatic nylons because these materials resist melting, dripping, supporting combustion in air, or burning. 

Ethylene-propylene monomer (EPM) elastomers Aromatic nylons (aramids) (Nomex DuPont)... 

This crystalline aromatic nylon, combines the high strength and stiffness of nylon with the thermal stability of polyphenylene sulfide. Molding characteristics are similar to nylon 6/6, with similar or better chemical resistance, but its 24 h water absorption is only 0.2 versus 0.7% for nylon 6/6. A key behavior is high heat resistance. 

Besides the aliphatic and aliphatic/aromatic nylons, aromatic polyamides have excellent capability to form fibers. Among aromatic polyamides the most common are Kevlar or poly(imino-1,4-phenyleneiminocarbonyl-1,4-phenylenecarbonyl) or poly(phenylene terephthalimide), and Nomex or poly(phenylene isophthalimide). These compounds are included in a group of polyamides known as aramids. The structures of Kevlar and Nomex are shown below ... 

Kuhn model, Equation (1.1). Data for several polymers in addition to polyethylene are given, including a rigid-rod aromatic nylon polymer, poly(p-phenylene terephthalamide) (Kevlar ), as well as the aliphatic nylon polymer poly(hexamethylene adipamide) (nylon-6,6). 

With the exception of both the EVOH grades, the remaining four barrier resins were orientable in the solid state. Generally, amorphous resins SELAR PA 3426 and polyacrylic-imide XHTA-50A were easier to orient than the semicrystalline resins, VDC copolymer and aromatic nylon MXD-6. In the case of both EVAL EP-E105 and SOARNOL D resins, all attempts to orient from the solid state were unsuccessful. 

The effect of orientation on permeability is dependent on the morphological nature of the barrier resin. Semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6... 

With the growing demand for coextruded products, barrier plastics have shown significant growth in the last several years. Historically, the high barrier resins market has been dominated by three leading materials — vinylidene chloride (VDC) copolymers, ethylene vinyl alcohol (EVOH) copolymers, and nitrile resins. Since 1985, however, there has been a lot of interest worldwide in the development of moderate to intermediate barrier resins, as apparent from the introduction of a number of such resins, notably, aromatic nylon MXD-6 from Mitsubishi Gas Chemical Company, amorphous nylons SELAR PA by Du Pont and NovamidX21 by Mitsubishi Chemical Industries, polyacrylic-imide copolymer EXL (introduced earlier as XHTA) by Rohm and Haas and copolyester B010 by Mitsui/Owens-Illinois. 

Materials The competitive oxygen barrier resins investigated include Dow Chemical Company s vinylidene chloride/vinyl chloride (VDC) copolymer (experimental grade XU 32009.02), Mitsubishi Gas Chemical Company s aromatic nylon MXD-6, Du Pont s amorphous nylon SELAR PA 3426, Rohm Haas s polyacrylic-imide XHTA-50A and two EVOH resins — Kuraray s EVAL EP-E105 (44 mole% ethylene content) and Nippon Gohsei s SOARNOL D (29 mole% ethylene content). ... 

Orientation of aromatic nylon MXD-6 was rendered somewhat difficult by the occurrence of rapid cold crystallization above 100°C. The cold crystallization phenomenon as seen in figure 1 is similar to the well known cold crystallization behavior observed in other crystallizable polyamides and PET. To compensate for this, very short heat-up times had to be employed for successful orientation. 

Figure 1. DSC scans of aromatic nylon MXD-6 films illustrating cold crystallization behavior.

Semicrystalline polymers, VDC copolymer and aromatic nylon MXD-6 (Table II) showed little if any reduction in permeability at these moderate orientation levels. In fact, recent unpublished work has shown that aromatic nylon MXD-6 exhibits an initial increase in permeability up to 3X orientation followed by a significant reduction in permeability at higher orientation levels. The VDC copolymer also showed higher permeability with moderate biaxial orientation — 1.5 times the permeability of the unoriented film. This is believed to be due to orientation of the polymer after crystallinity is fully developed. If the orientation of VDC copolymers is induced prior to full development of crystallinity in the material, one would not expect to see an increased oxygen permeability. In commercial practice, therefore, forming of VDC copolymer structures is normally done on rapidly quenched polymer to orient it while still in the amorphous state at temperatures near or above the Tm of VDC copolymer. 

The effect of orientation on oxygen permeability of the medium and high barrier resins is seen to be dependent upon the morphological nature of the barrier resin prior to orientation. A plot of the oxygen transmission rates as a function of the overall draw ratio (figure 3) illustrates this clearly. While the semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6, show little change in the permeability with moderate amounts of orientation in the solid state, orientation of the amorphous polymers SELAR PA 3426 and XHTA-50A causes reduction in the permeability by 5-30% in both resins, depending upon the overall level of orientation. 

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