Experimental and numerical studies on bubble dynamics in nonpressurized foaming systems

Abstract

This work explores the influence of rheological properties on polymer foam development in nonpressurized systems. To understand the complex contributions of rheology on the mechanism of bubble growth during different stages of foam processing, visualization studies were conducted by using a polymer-foaming microscopy setup. The evolving cellular structure during foaming was analyzed for its bubble surface density, bubble size, total bubble projected area, and bubble size distribution. Morphological analysis was used to determine the rheological processing window in terms of shear viscosity, elastic modulus, melt strength and strain-hardening, intended for the production of foams with greater foam expansion, increased bubble density and reduced bubble size. A bubble growth model and simulation scheme was also developed to describe the bubble growth phenomena that occurred in nonpressurized foaming systems. Using thermophysical and rheological properties of polymer/gas mixtures, the growth profiles for bubbles were predicted and compared to experimentally observed data. It was verified that the viscous bubble growth model was capable of depicting the growth behaviors of bubbles under various processing conditions. Furthermore, the effects of thermophysical and rheological parameters on the bubble growth dynamics were demonstrated by a series of sensitivity studies.

Effect of silica nanoparticles on the impregnation process, foaming dynamics and cell microstructure of styrene-methyl methacrylate copolymer/n-pentane foams

“…One of the main objectives in the production of the polymeric foams is to increase the cell density or decrease the average cell size. For this purpose, some techniques such as rapid pressure drop, 11–15 high sorption pressure at low temperature, 16 selecting of high melt strength polymeric matrix, 17 polymer blending, 18–20 and incorporation of nucleating agents are used. 21–26 Furthermore, among nucleating agents, the nanoparticles are of more interest since they have high specific surface area and can create more heterogeneous nucleation sites into polymer matrix.…”

“…Emami et al. 17 investigated the effect of rheological properties of polymer matrix on the foaming dynamics of polyethylene (PE) with chemical blowing agent as well. Their results showed that with increasing PE melt strength, the nucleation rate reduced while the bubbles coalescence was decreased as well.…”

Development of a bubble growth model for natural rubber‐based foams

“…Some comparative studies have been conducted on the bubble growth model results experimental observation in thermoplastics. [ 29–33 ] The effect of temperature, viscosity, and other materials function on the bubble growth in thermoplastics foaming process was simulated by other researchers. [ 34–37 ]…”

The effect of copolymer composition, gas content, and temperature on the bubbles nucleation and growth of styrene–methyl methacrylate copolymer/n-pentane foaming process

“…Rapid pressure drop method is mostly used to study the foaming process, 11 –14 but some researchers such Iliev et al 15 and Emami et al 16 used temperature increasing method at nonpressurized conditions to examine the foaming dynamics. Generally, the rapid pressure drop method has been used more than temperature increasing method to study the foaming dynamics.…”