Preparation Of High Melt Strength Polypropylene By ～(60)Co-γ Radiation

The polypropylene of commerce is a semi-crystalline polymer. Although the polypropylene of commerce has many desirable and beneficial properties, it is deficient in melt strength. Thus it has a variety of melt processing shortcomings, including the onset of edge weave during high speed extrusion coating of paper or other substrates, sheet sag and local thinning in melt thermoforming and flow instabilities in co-extrusion of laminate structure. This research provided a process for converting the linear PP into the PP having an amount of free-end long branches of propylene units. Results obtained in the research have indicated that in the linear polypropylene treated by V -ray radiation, the long chain free end branching is confined for the most part to the amorphous fraction of the semi-crystalline polypropylene. The melt strength of the commercial polypropylene has been increased greatly.High melt strength polypropylene was prepared by the initiation of 60Co- V radiation in nitrogen environment, polyfunctional acrylate monomers used as the radiation sensitizer. Influences of the functionalities and amount of the radiation sensitizer, and dose of radiation on the gel content were investigated, and the sol-gel curve was analysed according to Charlesby-Pinner equation. The melt flow rate and melt strength of the radiated polypropylene were measured. The results show that the high melt strength polypropylene was got by 60Co- Y radiation with 1 kGy dose and 6 kGy/h dose rate in nitrogen environment. Adding plasticizer, antioxidant or styrene/methyl acholol mixed additives, and thermal treatment before or after irradiation can enhance the melt strength of the irradiated polypropylene in different degree repectively.The effect of radiation on structure and properties of polypropylene were studied by GPC, DSC and DMA. GPC shows that the weight average molecular weight and Z average molecular weight of the radiated polypropylene are maximal and the molecular weight distribution is the widest when the content of sensitizer is one part by weight. DSC reveals that the crystalline temperature of the radiated polypropylene is enhanced obviously and the crystallinity keeps stable. Tg and T-E' curve of the radiated polypropylene were measured by DMA. The results show that Tg of radiated polypropylene decreases greatly. E' of the radiated polypropylene is lower than that of the common polypropylene in cryogenic temperature and similar to that of the commercial polypropylene in evaluated temperature.High melt strength polypropylene was prepared by 60Co- y radiation and its molecular weight and molecular weight distribution, thermal properties and dynamic mechanical properties were characterized. This research broke a path to expand applied fields of Polypropylene and to prepare high melt strength polypropylene at home.