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 the only monomer present is propylene. Its high proportion of crystalline phase and its glass transition temperature of 0 oC mean that its applications are mostly directed to extrusion processes with and without post-drawing, where stiffness is more important than impact resistance.
Random copolymers are characterized by the presence of randomly inserted comonomer units, aiming at breaking the crystalline structure. The great advantage they present is transparency and lower melting temperature Tm, desirable characteristics in film manufacturing. The decrease in Tm translates directly into a decrease in processing cycles since the film seals at lower temperature and in less time. The transparency achieved by interrupting the crystalline structure allows the use of polypropylene, both in extrusion -mainly film- and in injection products with aesthetic requirements.
The heterophase or block copolymer is formed by a matrix or continuous homopolymer phase and a second phase (between 5 and 20% by weight), dispersed in the first one, and is obtained by means of cascade reactors. The second phase, of an elastomeric nature, grows within the first, resulting in a heterophasic composition that has an excellent impact-stiffness balance. Fundamentally, these grades are oriented towards injection molding of technical parts: automobiles, household goods, furniture, containers, etc.