CROSS-LINKING OF POLYPROPYLENE BY PEROXIDE AND MULTIFUNCTIONAL MONOMER DURING REACTIVE EXTRUSION

Polypropylene (PP) powder was extruded in the presence of peroxide and multifunctional monomers at varying concentrations. With increasing peroxide concentration, MFI increased almost linearly, whereas hardness, modulus, and impact strength decreased, and the results were interpreted in terms of decreased molecular weight and its distribution by chain scission. On the other hand, triacrylate type multifunctional monomers (PETA and TMPTA) reduced the MFI of PP upon extrusion, and led to increase of Tm and Tc followed by increased modulus, yield strength, and elongation as well. TAIC and PBQ exerted effects smaller than triacrylate type. When the multifunctional monomers were added to the 0.01 phr peroxide containing system, MFI decreased below that of peroxide, and increased above that of multifunctional monomer of the same concentration, and synergistic physical properties were generally obtained, especially at low content of coagent. However, at higher peroxide concentration (0.05 and 0.1 phr) MFI increased with PETA and TMPTA, and decreased with PBQ. In general, increase and decrease of MFI were respectively followed by the decrease and increase of modulus, strength, and impact strength as well. (C) 1993 John Wiley & Sons, Inc.