Peroxides in polypropylene
Last update on Nov 15, 2000
Part I. Viscosity breaking of PP (vis-breaking)
Molecular weight adjustment of polypropylene after polymerization is today intensively practiced by producers in order to offer a wide range of grades to customers and rationalise polymerization operations. This operation, commonly called "vis-breaking" or "controlled rheology", is generally performed at the finishing step into an extruder by addition of peroxide. Viscosity reduction is controlled by the amount of peroxide introduced.
Figure 1 shows impact of peroxide on MFI of PP at 230°C.
Figure 1 : MFI versus peroxide(DHBP) content after extrusion at 230C
This approach is not only used by PP producers but also by converters particularly where high fluidity is required like :
- PP Non wovens by melt blown
- PP composites , Glass Mat Thermoplastic (GMT)
- PP recycling to adjust viscosities