The structure of polypropylene determines its great versatility and allows it to have multiple applications. The final application is mainly conditioned by the type of polypropylene (homopolymer, random copolymer and heterophasic copolymer), its fluidity index and its isotacticity.
Polypropylene homopolymer is formed when propylene is the only monomer present. Its high crystalline phase content and glass transition temperature of 0 °C mean that its applications are primarily focused on extrusion processes—both with and without post-stretching—where stiffness is valued more highly than impact resistance.
Azare copolymers are characterized by the presence of comonomer units randomly inserted into the structure, with the aim of disrupting the crystalline structure. Their major advantage is their transparency and the reduction in the melting temperature (Tm), which are desirable characteristics in film manufacturing. The decrease in Tm directly translates into a reduction in processing cycles, since the film seals at a lower temperature and in less time. The transparency achieved by disrupting the crystalline structure allows for the use of polypropylene in both extrusion—primarily film—and injection-molded products with aesthetic requirements.
A heterophasic or block copolymer consists of a homopolymer matrix or continuous phase and a second phase (between 5 and 20% by weight), dispersed within the first, and is produced using cascade reactors. The second phase, which is elastomeric in nature, grows within the first, resulting in a heterophasic composition that offers an excellent balance of impact strength and stiffness. These grades are primarily intended for the injection molding of technical parts: automotive components, household goods, furniture, containers, etc.