Injection Processing and Foaming Behaviors of Polypropylene Composite Foams

A volume-adjustable cavity of molding machine for polymer foaming was fabricated with renovation of an ordinary injection molding machine. Polypropylene （PP） composite foams were prepared by chemical foaming method via the volume-adjustable cavity of the molding machine. The decompressing and short shot processes in preparing the samples were carded out to adjust the cell structure of the foamed samples. The structures that foamed insufficiently, moder- ately, and excessively were observed in these two foaming processes. The foamed PP composite samples generated in decompressing pro- cess have more desirable cell s^cture than those generated by short shot process, specifically, the cell structure with the cell size of 46.97 IJxn, cell density of 3.18x 106 cell/cm3, and cell size dispersion of 10.76 ~m was achieved in the decompressing process. A controlled foaming process was realized through the decompressing process using the injection foaming equipment with a volume-adjustable cavity. The foamed PP composite has the insufficient, moderate, and excessive foamed structures in these two foaming processes.

Polydimethylsiloxane assisted supercritical CO2 foaming behavior of high melt strength polypropylene grafted with styrene

Foamable high melt strength polypropylene （HMSPP） was prepared by grafting styrene （St） onto polypropylene （PP） and simultaneously introducing poly- dimethylsiloxane （PDMS） through a one-step melt extru- sion process. The effect of PDMS viscosity on the foaming behavior of HMSPP was systematically investigated using supercritical CO2 as the foaming agent. The results show that the addition of PDMS has little effect on the grafting reaction of St and HMSPP exhibits enhanced elastic response and obvious strain hardening effect. Though the CO2 solubility of HMSPP with PDMS （PDMS-HMSPP） is lower than that of HMSPP without PDMS, especially for PDMS with low viscosity, the PDMS-HMSPP foams exhibit narrow cell size distribution and high cell density. The fracture morphology of PDMS-HMSPP shows that PDMS with low viscosity disperses more easily and uniformly in HMSPP matrix, leading to form small domains during the extrusion process. These small domains act as bubble nucleation sites and thus may be responsible for the improved foaming performance of HMSPP.

Synergistic effects of expandable graphite and dimethyl methyl phosphonate on the mechanical properties, fire behavior, and thermal stability of a polyisocyanurate-polyurethane foam

In this study, a series of flame-retardant polyisocyanurate-polyurethane (PIR-PUR) foams were prepared using various concentrations (0-25% by weight) of expandable graphite (EG) and dimethyl methyl phosphonate (DMMP) (0-7% by weight). The effect of these additives on the properties of the PIR-PUR foams, including physico-mechanical, morphological, flame retardancy, and thermal stability, was studied. Increasing amounts of EG in the PIR-PUR foam caused a significant drop in the compression strength. However, DMMP caused the mechanical properties of PIR-PUR foam to improve compared to foam filled with EG alone. The flame retardancy of PIR-PUR foams containing both EG and DMMP was enhanced significantly compared to EG filled foams. Thermogravimetric analysis (TGA) indicated that EG enhances the thermal stability of PIR-PUR foams but that DMMP decreased it. The morphology of the residual char provided conclusive evidence for the weak thermal stability of foams filled with DMMP.