Quantitative analysis of cell distribution in injection molded microcellular foam

Abstract

The microstructure of cellular materials, in particular microcellular polymers, is commonly characterized by the mean cell size and cell population density. Although the physical properties of foamed polymers are highly dependent on cell distribution, very insignificant work has been carried out to quantify the distribution of cells. This experimental study correlates the influential processing parameters of microcellular injection molding with the cell distribution, mean cell size and population density. For the first time, “Cell Distribution Index (CDI)”, a quantitative parameter for characterization of foams has been defined in this paper. Foamed samples of polystyrene were prepared via microcellular injection molding process. The design of experiment includes five influential processing parameters (factors) at five different levels. Molded samples were fractured cryogenically and micrographs were obtained using a table top scanning electron microscope. With the help of image processing package, mean cell size, cell population density, frequency and newly defined term CDI were calculated for each micrograph. Finally, the effect of processing parameters on cell distribution was analyzed by plotting the CDI against the processing parameters.

Formation mechanism and structural characteristics of unfoamed skin layer in microcellular injection-molded parts

“…For quantitatively characterizing polymer foams, Rizvi et al. 13 defined a parameter named “Cell Distribution Index (CDI)” and studied the mean cell size, cell population density, frequency of foamed polystyrene (PS) samples. Using standard ASTM D 638-02 tensile bars, Chandra et al.…”

Characterization of microcellular plastics for weight reduction in automotive interior parts

“…Gómez-Gómez et al [134] reported that the effect of injection speed on the cell density of PETG plates is inconclusive. Rizvi et al [194] pointed out a decrease in cell diameter and CDI parameter with the injection speed. In the present study, the maximum cell size decreased, however, the CDI increased, that is, the cell size distribution became more heterogeneous.…”

“…where n is the number of cells in the micrograph, A is the analyzed area (cm 2 ) and ρs and ρf are the density of solid and foamed material, respectively. The Cell Distribution Index (CDI) was proposed by Rizvi et al [194] to assess the uniformity of cell size distribution, and it is defined as:…”

Injection-moulding of nitrogen-foamed bio-based microcellular poly(butylene succinate): Processing conditions/foam structure/flexural properties relationship

“…9 Most of studies have been focused on conventional polymers such as polypropylene, polyethylene or polystyrene. [10][11][12] The relationships between the injection moulding process and the properties were also discussed, but most were limited to the laboratory scale for standardized specimens (simple plate or dog bone specimen). 13,14 Thus, Gong et al 10 reported the effect of cell structure parameters on the mechanical properties of PP materials, which indicated that small and uniform cells result in improvements of the foam tensile and impact strengths.…”