A novel technique in the foaming process of EPDM/PP via microwave radiation: the effect of blend compatibilization and additive encapsulation

The novel technique of microwave irradiation was used to prepare EPDM/PP cellular foams, together with the novel approach of additive encapsulation.

Foaming behavior of microcellular thermoplastic olefin blends

The influence of reactive compatibilization on the foaming behavior of thermoplastic olefin blends of polypropylene and a metallocene-catalyzed ethylene octene copolymer was investigated. A batch setup was used to foam the samples using carbon dioxide as blowing agent. Solubility measurements were performed to determine the relative amount of gas concentration in the pressurized polymers before foaming. A microscopic method based on the back-scattered electron imaging technique was used to determine the respective locations of the bubbles and the dispersed elastomeric domains in the polypropylene matrix. It was shown that the bubbles are preferentially formed in the dispersed elastomeric domains. A clear relationship was established between the microstructure of the blends prepared with different levels of compatibilizer and the final cellular morphology of the microcellular thermoplastic olefin foams. The initial morphology of the blends was also altered by quiescent coarsening as well as shear-induced phase coalescence, and the impact of the morphological transitions on the cellular structure of the resulting foams was investigated. Dynamic shear and transient measurements of elongation were performed to characterize the viscoelastic behavior of the thermoplastic olefins. It was shown that the addition of a compatibilizer resulted in enhanced viscoelastic properties at low frequencies as well as increased levels of strain hardening, especially at low strain rates. The reactive compatibilization could significantly improve the melt foamability through control of the blend microstructure as well as enhancement of the melt rheological properties.

The foamability of low-melt-strength linear polypropylene with nanoclay and coupling agent

In this work, the feasibility of producing microcellular foam by using homopolymer linear polypropylene with an melt flow index of 18 g/10 min, a high melt flow index coupling agent (G3003, melt flow index of 380 g/min), and different nanoclay (Cloisite 20A) content was investigated. A twin-screw extruder was used to prepare the nanocomposite compounds, and an X-ray diffraction machine was used to characterize the intercalation and exfoliation of nanoclay within the matrix. A rheology test was undertaken to investigate the melt shear viscosity of the samples. A single-screw extruder was employed to produce foam by using 5% supercritical CO2 at various die temperatures. Scanning electron microscopy was used to explore the morphology of the foamed samples, and cell density was calculated by scanning electron microscopy images. Density measurement data was used to calculate the expansion ratio of the foamed samples. Extrusion foaming produced foams with high expansion ratios of about 20 and a high cell density of about 108−9 cells/cm3. The crystallinity behavior of the foamed and unfoamed linear polypropylene and linear polypropylene nanocomposites was also investigated. A high-pressure differential scanning calorimetry was used to investigate the dependency of crystallization behavior on high pressure CO2.