Microcellular polyetherimide (PEI) foams were prepared by microcellular injection molding using supercritical nitrogen (SC-N 2 ) as foaming agent. The effects of four different processing parameters including shot size, injection speed, SC-N 2 content, and mold temperature on cell morphology and material properties were studied. Meanwhile, multiwalled carbon nanotube (MWCNT), nano-montmorillonoid (NMMT), and talcum powder (Talc) were introduced into PEI matrix as heterogeneous nucleation agents in order to further improve the cell morphology and mechanical properties of microcellular PEI foams. The results showed that the processing parameters had great influence on cell morphology. The lowest cell size can reach to 18.2 lm by optimizing the parameters of microcellular injection molding. Moreover, MWCNT can remarkably improve the cell morphology of microcellular PEI foams. It was worth mentioning that when the MWCNT content was 1 wt %, the microcellular PEI/MWCNT foams displayed optimum mechanical properties and the cell size decreased by 28.3% compared with microcellular PEI foams prepared by the same processing parameters.

A series of PEI/PP blends were injection molded by conventional and microcellular methods. Polypropylene (PP) was selected as the disperse phase in order to improve the cell nucleation of poly(ether imide) (PEI)/PP blends. The effect of the PP content on the morphology of the PEI/PP blends or foams, the mechanical, thermal and dielectric properties was investigated. In the immiscible PEI/PP blends, the cell density of microcellular PEI/PP foams increased greatly with the increasing of the content of PP because the surface tension effect and interface effect significantly promoted the cell nucleation in the PEI/PP blends. Meanwhile, a large amount of gaps appeared in the interface because the processing temperature of the blends was close to the starting decomposition temperature of PP, which significantly improved the PEI/PP blends toughness because of tiny spherical cells that acted as crack arrestors by blunting the crack tip.

Foaming behaviors of both neat polyetherimide (PEI) and PEI/polypropylene (PP) blends were studied in this article in microcellular injection molding (Mucell) process. The study mainly focused on the comparison of two materials' foaming behaviors under different processing conditions which took a critical effect on the morphologies of foams. The results indicated that the different characteristics of PEI and PEI/PP blends, such as melt strength, gas dissolvability, and solubility, induced different nucleation ability of PEI and PEI/PP blends. The addition of PP could obviously improve the cell density and reduce the cell size. With the processing conditions changing, the morphologies of PEI/PP altered more variously, and their distribution of cell density was wider. This suggested that foaming behaviors of PEI/PP blends was more flexible to be controlled by the processing conditions than neat PEI. The effects of shot size, gas injection, and injection rate on foam morphologies were studied in detail. Shot size determined the weight reduction of samples and affected the cell density and size significantly. Gas dosing time and dosing rate determined the gas ratio which effected on foam morphologies of the PEI and PEI/PP foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41443.

In this study, foaming behaviors of polyetherimide (PEI)/polypropylene-graft-maleic anhydride (PPMA) blends with different fractions of PPMA are investigated by the microcellular injection molding (Mucell) using N2 as the blowing gas. The results indicate that the addition of PPMA can obtain more the interface in blends than PP. Meanwhile, the microcellular PEI/PPMA foams achieve higher void fraction and cell density than that of PEI/PP and neat PEI matrix, and then the cell diameter also significantly decreases from 30 µm to less 10 µm. The excellent cell properties can be attributed to interfacial effect of binary blends. The binary interface decreases the nucleation energy barrier and forms sufficient paths which improve diffusibility of blowing gas, so the microcellular PEI/PPMA foams obtain more nucleating points and paths of supporting cell growth.

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