In-Situ Visualization of the Cell Formation Process of Foamed Polypropylene under Different Foaming Environments

Abstract

In this paper, the dynamic foaming process of micro-foaming polypropylene (PP) in different foaming environments in real time was obtained via a visualization device. The relationship curve between cell number (n) and foaming time (t) was plotted, and then the nucleation kinetics of foam cells was analyzed. Results showed that the formation rate of cells changed obviously with the variation of melt temperature and the content of the foaming agent. The n-t curves presented a typical “S” shape, which indicated that the appearance of the cell number increased slowly in the initial foaming period, then increased rapidly in a short time, and finally maintained a certain value. When a certain pressure was applied to the PP melt, the external force had a great influence on the n-t curve. With the increasing external force, the rate of cell formation increased rapidly, and the shape of the n-t curve changed from “S” to “semi-S” without an obvious slow increase. The investigation of the n-t relationship in the PP dynamic foaming process under different foaming environments could provide effective bases for improving the foaming quality of injection molding foaming materials.

Cavity pressure profile study during foam injection molding and its effect on cell formation of polypropylene/chemical blowing agent foam

“…Typically, with increase in injection temperature, the viscoelasticity of melt/blowing agent mixture decrease leading to increased free volume and molecular spacing in the polymer with weakened molecular interactions. The fluidity of the melt entering the mold will increase thereby decreasing the surface tension that facilitates the formation of cells by the gas contained in the resin and the expansion of cells results in increased pressure in the cavity 9,41 . It can be realized from the recorded pressure profile that with increase in injection temperature from 165 to 185°C, the maximum cavity pressure increased.…”

“…The fluidity of the melt entering the mold will increase thereby decreasing the surface tension that facilitates the formation of cells by the gas contained in the resin and the expansion of cells results in increased pressure in the cavity. 9,41 It can be realized from the recorded pressure profile that with increase in injection temperature from 165 to 185 C, the maximum cavity pressure increased. However, further increasing the temperature resulted in a decreased cavity pressure that can be attributed to the inhomogeneous nucleation due to higher local stress variations in the melt resulting in low cell nucleation rate.…”

Experimental and simulation analysis of bubble deformation in foaming polypropylene

“…Polypropylene (L5E89) with an MFR=3.1g 10 min −1 was provided by China National Petroleum Corporation (Beijing, China). The foaming agent masterbatch was self-prepared [22].…”