Numerical and experimental studies of bubble growth during the microcellular foaming process

Abstract

A new experimental technique for studying the dynamics of bubble growth in thermoplastics using scanning electron microscopy is developed. The influence of temperature, saturation pressure, molecular weight, and the nature of physical blowing agent are investigated. The experimental results show that, the above, process variables control the growth of foams during processing. The existing Newtonian model for the growth of a single bubble in an infinite amount of polymer has been modified to account for the non‐Newtonian effects by modeling the polymer as a power law fluid. The experimental data has been compared with the appropriate viscoelastic cell model which considers the growth of closely spaced spherical bubbles during the foaming process. The simulation results indicate that the predictions of the cell model are in qualitative agreement with the trends of the experimental data and the quantitative agreement is reasonable. The cell model also gives an equilibrium radius which agrees with the experimental data. Other viscous models do not predict the equilibrium radius of the bubble and underpredict the experimental data.

Nucleation and growth in microcellular materials: Supercritical CO2 as foaming agent

“…To apply this cell model to the generation of polymeric foams, it has been modified by Upadhyay (1984) and Arefmanesh and Advani (1991) to accommodate the viscoelastic nature of polymers. This latter model has previously been shown by Ramesh et al (1991) to describe the growth of microcells during a thermal-induced generation of microcellular foams. We have used a modified framework of the cell model to describe the growth of cells during pressure-induced generation of microcellular polymeric foams, where the initial matrix consists of a polymer swollen by supercritical C02, and changes in temperature during depressurization are significant.…”

Transport analysis of diffusion‐induced bubble growth and collapse in viscous liquids

“…8-11, 34 and 40 constitute a TBL approximation model derived using the integral model of Rosner and Epstein (1972). As discussed in the previous section, several studies on bubble growth have used both the TBL approximation based on the integral method and the IDS approximation (Patel, 1980;Han and Yoo, 1981;Ramesh et al, 1991). In order to reproduce these models, Eq.…”

“…It should be noted, however, that the model developed by Payvar (1987) excluded viscous, inertial and surface tension effects. More recently, Ramesh et al (1991) used a model similar to Han and Yo0 (1981) to describe bubble growth in power law and Maxwell model fluids.…”

“…Moreover, a number of models where more complicated effects such as fluid elasticity have been included (Han and Yoo, 1981;Ramesh et al, 1991), and a model for predicting bulk flow in polymer foam processing (Arefmanesh et al, 1990), are based on transport models using both approximations, neither of which have been justified. Intuitively, one would expect viscous effects in the liquid surrounding the bubble to retard the rate of growth or dissolution in comparison with the diffusion-controlled case.…”

A new insight into foaming mechanisms in injection molding via a novel visualization mold

“…Therefore, the foaming phenomena were not tracked during the process. Additionally, most of hypotheses or theoretical simulations were not experimentally verified [5,6]. In this context, the in-situ observation of foaming phenomena drew significant attention amongst researchers [7][8][9][10].…”