Study on Crystallization Behavior and Foaming Property of Polypropylene Blend System
Foaming of polypropylene homo polymer(PP-H),polypropylene block copolymer(PP-B) and PP-H/PP-B blend system by using supercritical CO2 as foaming agent at a typical condition were studied. The crystallization behavior,crystal structure and morphology were characterized using differential scanning calorimetry and polarized optical microscope. The melt strength was characterized indirectly using meltflow rate tester. The morphology of the foams was observed by scanning electron microscope . The foaming behaviors of them were compared. Results show that PP-B is not only used as crystallization nucleating agent to make the spherocrystalfine and increase the density of crystallization,but also used as physical cross-link point to enhance the melt strength in the PP-H/PP-B blend system at the rate of 70∶30. The changes of the two aspects improve the foaming property of the blend system effectively,resulting in much smaller cell size,higher cell density and unbroken cells.
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