Nylon semicrystalline

Polyamides, often also lefeiied to as nylons, are liigli polymers which contain the amide repeat linkage in the polymer backbone. They are generally characterized as tough, translucent, semicrystalline polymers that ate moderately low cost and easily manipulated commercially by melt processing. 

Nylon-6 [25038-54-4] was first made in 1899 by heating 6-aminohexanoic acid (143), but its commercially feasible synthesis from caprolactam was discovered by Paul Schlack at 1. G. Farbenindustrie in 1938. Like nylon-6,6, it is a tough, white translucent, semicrystalline sofld, but melts at a lower temperature (T = 230° C. The physical properties and primary producers of nylon-6 are Hsted in Tables 9 and 10, respectively. 

Because of the capacity to tailor select polymer properties by varying the ratio of two or more components, copolymers have found significant commercial appHcation in several product areas. In fiber-spinning, ie, with copolymers such as nylon-6 in nylon-6,6 or the reverse, where the second component is present in low (<10%) concentration, as well as in other comonomers with nylon-6,6 or nylon-6, the copolymers are often used to control the effect of sphemUtes by decreasing their number and probably their size and the rate of crystallization (190). At higher ratios, the semicrystalline polyamides become optically clear, amorphous polymers which find appHcations in packaging and barrier resins markets (191). 

In addition to the semicrystalline nylons, which comprise the vast majority of commercial resins, nylon is also available in an amorphous form that gives rise to transparency and improved toughness at the expense of high temperature properties and chemical stress crack resistance. Table 2 shows the properties of some different polyamide types. 

PBT is produced by the transesterification of dimethyl terephthalate with 1,4-butanediol by means of a catalyzed melt polycondensation (19). PBT is also semicrystalline and is an extremely tough resin. Several commercial resins use a blend of PBT with another resin, such as PET, polycarbonate, or nylon. Typically, composites of PBT contain 20—30 vol % fiber glass. 

Fibers are thin threads produced by extruding a molten polymer through small holes in a die, or spinneret. The fibers are then cooled and drawn out, which orients the crystallite regions along the axis of the fiber and adds considerable tensile strength (Figure 31.3). Nylon, Dacron, and polyethylene all have the semicrystalline structure necessary for drawing into oriented fibers. 

Nylon fibers are semicrystalline, that is, they consist of crystallites separated by amorphous regions. Hydrogen bonding is an important secondary valence interaction in nylon-6 and nylon-6,6. Individual chains in the microcrystalline regions of nylons are held together by hydrogen bonds. Nylons are resistant to aqueous alkali but deteriorate more readily on exposure to mineral acids. 

Nylons are semicrystalline polymers whose properties are controlled primarily by their amide concentration, molecular orientation, crystallization conditions, and the level of absorbed water. As discussed earlier, the level of crystallinity and hence product stiffness, is maximized by high concentrations of amide groups, high orientation, slow cooling, and the absence of absorbed water. 

Nylons, 19 739, 764. See also Nylon blow molding of, 19 790-791 electrical properties of, 19 777-778 manufacture of, 19 783-787 mechanical properties of, 19 779-781 polycondensation to form, 20 390 processing of, 19 787-791 properties of, 19 773-774t semicrystalline, 19 775 time-dependent properties of, 19 781 Nylon stabilization, 14 370 Nylon staple, 19 747... 

Other semicrystalline polymers, such as nylon prepared in Experiment 9. 

The model PBZT/ABPBI molecular composite system is limited since the rod and the matrix do not possess glass transition temperatures for subsequent post form consolidation. In an effort to improve the processability for molecular composites, thermoplastics were used as the host matrix. Processing from acidic solvents requires the thermoplastic host to be soluble and stable in meth-anesulfonic add. Thermoplastic matrices were investigated including both amorphous and semicrystalline nylons [71,72], polyphenylquinoxaline (PPQ) [73] and polyetheretherketone (PEEK) [74], Table 5 shows the mechanical properties obtained for various processed PBZT thermoplastic molecular composite systems. As an example, the PBZT/Nylon systems showed 50-300% improvement over uniaxially aligned chopped fiber composite of comparable compositions. However, the thermally-induced phase separation during consol-... 

Nylon-6,6 [32131 -17-2] is a tough, translucent white, semicrystalline, high melting (Tm = 265 ° C) material. The common physical properties are shown in Table 9, and principal producers worldwide in Table 10, for nylon-6,6 and other commercial polyamides. 

By definition, thermoplastics have limitations at elevated temperatures. It is in this particular property that fibrous glass can lead to remarkable improvements. However, a sharp division exists for reinforced thermoplastics. The various reinforced thermoplastics can be put in two groups relative to DTUL. These consist of amorphous and crystalline or semicrystalline polymers. The amorphous polymers such as styrene-acrylonitrile, polystyrene, polycarbonate, poly (vinyl chloride), and acrylo-nitrile-butadiene-styrene are generally limited to modest DTUL improvements, usually on the order of 20°F with 20% glass. However, crystalline polymers such as the nylons, linear polyethylene, polypropyl-... 

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