Polypropylene resins semicrystalline

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. 

Polypropylene is a white, semicrystalline polymer. The resins are generally solid and used according to their melt index, which in the case of polypropylene is more commonly called the melt flow rate (MFR). Polymers with MFRs ranging from less than 1 to more than 35 are commercially produced. Most fibers are produced from resins having MFR between 3 and 35. 

Different plastics have different amount of shrink upon cooling, higher for semicrystalline resins (eg, polypropylene can shrink 0.030 in./in.) and lower for amorphous plastics (eg, polystyrene can shrink 0.006 in./in.). Further, shrinkage, especially for semicrystalline materials, varies due to thickness, cooling rate, and often color. Whatever stays hotter for a longer time will shrink more. Therefore, changes in nominal wall thickness cause differential cooling, which causes... 

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. 

---