Homopolymers
The first of a group of stereo-regular (isotactic) polymers. It's melting point is about 174℃. The extremely good flow properties of PP combine with its availability in a wide range of flow rates and other unique polymer characterizations to provide excellent processing features in a wide range of products. Extrusion is the largest market, with textile fibers and filaments the largest segment within the market. Film makes up the second largest segment of the extrusion market. Injection molding, the next largest market for homopolymers, includes containers and closures, automotive applications, housewares, toys, and many other consumer and industrial end-uses. Excellent moisture-barrier properties, combined with adequate clarity, make PP the choice for many blow molded containers. It's good flowability allow it to be used to incorporate a built it "living hinge" in containers.
Impact Copolymers
Polypropylene that has been made more impact resistant by the addition of impact modifiers, usually ethylene/propylene rubber. The chief commercial use for impact PP is injection molding of articles used in automotive applications, housewares, and appliances. The impact resistance, low density, colorability, and processibility of impact PP make it ideal. Medium-impact resin grades with high MFR have good flow properties, making it especially useful in injection molding large items such as automotive panels. High-impact resin grades with low MFR can be converted into film that offers good puncture resistance. Some applications are medical waste bags and fender and truck liners.
Random Copolymers
Polypropylene that has had the basic structure of the polymer chain modified by the incorporation of a different monomer molecule, most commonly ethylene. This makes the molecular chain less regular and more flexible. In comparison with homopolymers, it has better clarity, improved impact resistance, increased flexibility, and a decreased melting point. Random copolymer PP is mainly used in film, blow molding, and injection molding applications where high clarity is a requirement.
