Polypropylene (PP) foams with double crystal melting peak structure were prepared using supercritical CO 2 as blowing agent. Such structure was induced by the b-nucleating agent (NA) and dissolved CO 2 in a lab-scale autoclave system. From the dynamic rheological behaviors, one can see that long chain branching polypropylene (LCBPP) possess better melt elasticity than linear polypropylene (LPP). In order to improve the foamability, LPP was blended with LCBPP. The results of differential scanning calorimeter and wide-angle X-ray diffraction indicated that NA was helpful for the introduction of b-crystal in LPP, but not for LCBPP and PP blends. Therefore, the foamability and the content of b-crystal of various PP foams can be effectively controlled by adjusting the ratio of LPP and LCBPP. Meanwhile, both the cooling rate and the content of NA affected the formation of b-crystal in various PP samples.

Environmentally-friendly flame retardant, PolyFR, has an excellent effect on the flame retardancy and foaming behavior of polystyrene.

It is of great interest and importance to design and fabricate the double crystal melting peak (DCMP) structure for the expanded polypropylene (EPP) bead foams during sintering. Two kinds of methods with different mechanisms were proposed to prepare long-chainbranched polypropylene (LCBPP) samples with a DCMP structure: One was that the DCMP structure was prepared by generating crystals of different perfection degrees and the other one was that the DCMP structure was prepared by adding β-NA to produce various crystal forms. In addition, zeolite molecular sieve (ZMS) as the synergist was introduced into LCBPP/β-NA system to increase the efficiency of β-NA. The crystallization behaviors of various PP and their foams were tested by differential scanning calorimetry and wide-angle X-ray diffraction, as well as the cellular morphologies of various LCBPP foams were observed by scanning electron microscope. The results showed that a DCMP structure was formed in pure LCBPP in the presence of CO 2 at 168-172 C. The content of β-crystal in LCBPP/β-NA system was the highest when the content of β-NA optimized as 1.5 phr. The percentage of β-crystal in LCBPP/β-NA system was further increased when a small content (0.045 phr) of ZMS was added. Compared with that in unfoamed LCBPP, the percentage of β-crystal in LCBPP foams was obviously enhanced, due to the coupling effect of crystal nucleation and cell nucleation. In the LCBPP foams, the cell size became smaller and the cell density became larger, owing to the addition of ZMS.

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