Semicrystalline polymers polyamides, properties

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). 

A. Xenoponlos, B. Wunderlich, Thermodynamic properties of liquid and semicrystalline linear aliphatic polyamides, J. Polym. Sci. Part B Polym. Phys., 28, 2271-2290 (1990). 

The presence of crystalline regions tends to rednce the level of light transmission, and pnre semicrystalline polymers in moderate thickness are generally translucent. They include the polyolehns, polyamides, and thermoplastic polyesters. However, several crystallizing polymers can be made into highly transparent, relatively thick prodncts. They are polymethylpentene and polyethyleneterepthalate. Films of many crystallizing polymers, particnlarly oriented hhns, can also be transparent See also optical properties. 

Gapex should be processed similar to other semicrystalline polymers. The best results are obtained when molding tools are cut for polyamides. The preferred melt temperature for best physical properties is 299°C. 

Properties of semicrystalline thermoplastics are normally enhanced via reinforcing filler. However, the type and amount of such fillers would complicate any comparison. Hence, properties of various unfilled semicrystalline resins are compared shown in Tables 1.1-1.3. For comparison two commodity semicrystalline polymers, high density polyethylene (HDPE) and polypropylene (PP), are included in Table 1.1. Table 1.1 summarizes properties of HDPE, PP, POM, and polyesters. Table 1.2 contains properties of polyamides and SPS. Table 1.3 lists properties of the highly aromatic, semicrystalline polymers. Clearly, semicrystalline ETPs exhibit very broad performance enhancements over commodity semicrys-talhne polymers. 

There are many fibers of S3mthetic origin, most of them spun or extrusion-drawn semicrystalline polymers (e.g., polyolefins, polyamides, polyesters), which are not used as fillers for polymers. The main reason is that, for a material to play a potential reinforcement role as a filler for polymer, large differences in certain key properties must exist between the filler and the polymer matrix. It follows that only three types (or classes) of fibrous products can be considered as valid short synthetic fibers candidates for polymer reinforcement glass fibers, carbon fibers and aramid fibers. 

The highly intractable chemical stmcture vMch. inq)arts the outstanding mechanical properties also makes the PATs very difficult to process (4, 5). In the ftilly imidized form PAI is not processable hence a poly(amic acid) (PAA) precursor is the usual form in which they are supplied and bricated. The precursors themselves have very hi viscosities in the melt state and hence the flow characteristics tend to be very poor. Semicrystalline and amorphous polyamides (6) and aromatic sulfone polymers such as poly(phenylene sulfide), poly(ether sulfone) and polysulfone (7) have been blended with the precursor to PAI, to obtain better flow characteristics. 

Polyamide 6/10 (Nylon 6/10, PA 6/10) A semicrystalline PA with low moisture absorption compared to other nylons. Thus, it retains its properties better when wet. Similar to most forms of nylon, PA 6/10 is smooth to the touch and can be manufactured to range in luster from dull to shiny. Nylon 6/10 can be extruded into thin filament fibers to make fabric fibers and brush bristles, or casted into a predetermined shape, similar to other hardened plastic parts. The filament can be dyed by infusing the plastic polymer with a coloring agent and the substance does not lose its color easily. 

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