Semicrystalline polyamide resins

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). 

The primary rationale for developing the ASA/polyamide blends is to combine the high UV resistance of ASA resins with high heat and solvent resistance properties of the common semicrystalline polyamides such as PA6. The compatibUization of the ASA/PA6 blends uses the same technical approach as for the ABS/PA6 blends, viz., the use of a maleic anhydride-modified (copol5mierized) SAN copolymer as a polyamide-reactive compatibilizer as discussed before under the ABS/PA blends... 

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. 

Most polymers fall in the class of translucent resins. These include acetal, polyamide, polybutylene terephthalate (PBT), polyethylene, and polypropylene as examples. There are very few neat polymers that are truly opaque (this depends on thickness as well). Liquid crystal polymer (LCP) is an example of a typically opaque polymer. It is theorized that these semicrystalline and crystalline resins will scatter some portion of incident light due to spherulitic crystal structure and the amorphous-crystalline region interfaces themselves. 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

Linear, aromatic polyamides (PARA) are either liquid crystalline, semicrystalline, or amorphous. Mainly the latter resins are used in blends with PP, viz. PARA with PP-MA [Iwanami et al.,... 

Linear, aromatic polyamides (PARA) are either liquid crystalline, semicrystalline, or amorphous. Mainly the latter resins are used in blends with PP, viz., PARA with PP-MA (Iwanami et al. 1990), PARA with PE-MA, or PP and hydrazine (Yoshihara 1990). Blends of copolyphthalamide (PPA) with PP were compatibihzed using either PP-MA (Paschke et al. 1993, 1994) or PP grafted with acrylic acid (Brooks et al. 1993, 1994). 

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. 

---