Investigation On High Melt Strength Polypropylene And Its Foamability

1,6-hexanediol diacrylate (HDDA), pentaerythrithyl tetramethacrylate (PETMA) and triallyl-isocyanurate (TAIC) were used as representative monomers to modify polypropylene (PP) in the presence of dicumyl peroxide (DCP) in a mixer. The resuts of torque curves and grafting degree measurement indicated that the end torque value and grafting degree of the grafted products were increased with the increase of monomer, and followed the order as below:TAIC<PETMA<HDDA.In the presence of DCP, HDDA was used as the monomer to modify PP in the molten state. Dynamic rheological measurement showed that, with the increase of HDDA, PP-g-HDDA possessed higher G’ and lower tanδ at low frequency, displaying an increase in η*and shear-thinning shifted to lower frequency in η*-ω plot, as well as significant changes in VGP and Han plot. The results also indicated the formation of more branching and/or crosslinking structures, and the improvement of mechanical property of PP-g-HDDA. Thermal properties of PP-g-HDDA showed that the increased crystalline temperature and melting point and the improvement of thermostability.RAFT agent, zinc N, N-dimethyldithiocarbamate (ZDMC) was used to restrain the side reactions during the melt modification of polypropylene (PP) with1,6-hexanediol diacrylate (HDDA) in the presence of dicumyl peroxide (DCP). FTIR, DSC and rotational Rheometer were used to characterize the performance of modified samples. FTIR results suggested the absence of ZDMC on PP backbone. With the addition of ZDMC, the end-torque value and grafting degree increased, while the gel content decreased, indicating that ZDMC mediate melt modification of PP and favored the formation of more long chain branching. Dynamic rheological measurement further confirmed the formation of more long chain branching on PP backbone in the presence of ZDMC.Finally, the effect of ZDMC on the foamability of the PP, using DCP and HDDA as initiator and monomer respectively, was also investigated by one-step compression-molding process. The characterization of the foam was presented based on cellular structure and bulk density. The results showed that the addition of ZDMC would favor the formation of foams with low bulk density, well-defined closed cell structure, high cell density and expansion ratio.