Polymer Initiators

Polypropylene (PP)

Isotactic PP is a semi-crystalline polymer which is produced with Ziegler Natta catalyst on a continuous process (up to 300 kT/y). This polymer cannot be polymerized by free radical chemistry.

Free radicals degrade the polypropylene backbone through a reaction called beta-scission. This phenomenon is used by most polypropylene producers to adjust the melt flow, grade, and narrow molecular weight distribution during the final step. The benefits for producers are higher rationalization of the plant and much higher production flexibility, allowing them to provide the market with a wider range of products.

This operation is commonly called "vis breaking" or "PP controlled rheology."

The organic peroxide can be (1) added in hopper of the extruder or (2) injected in the extruder as:

• a liquid (pure or diluted in a solvent)
• a solid (peroxide + PP carrier)

click to enlarge

Generally the residence time in the machine is approximately 20-50 seconds and processing temperature is between 200 and 240°C. See figure above.

• Breaking Mechanism
• Key Parameters