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The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass transition particles. Part I: Mathematical modeling and numerical simulation
Author(s) -
Ramesh N. S.,
Rasmussen Don H.,
Campbell Gregory A.
Publication year - 1994
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760342206
Subject(s) - materials science , nucleation , glass transition , polymer , composite material , computer simulation , polymer science , mechanics , thermodynamics , physics
The existing models based on classical nucleation theory are not able to explain satisfactorily the nucleation phenomenon of microcellular foams in thermoplastics. Here, we extend the analysis of Kweeder (24), who developed a new model that considers the presence of microvoids, resulting from the thermal processing history of the polymer, as potential nucleation sites. The nucleation model “concentrates” on the stresses and thus void formations in the rubber particles. Since these are pre‐existing microvoids, bubble nucleation depends on the survival of these voids to grow rather than the formation of a new phase as modeled by classical nucleation theory. The population of viable microvoids with a sufficiently large radius to survive and overcome surface and elastic forces has been modeled to yield the cell density. A log‐normal distribution, which relates to the rubber particle size, has been used to model the distribution of microvoids in the polymer composite material. The model depends on various process parameters such as saturation pressure, foaming temperature, concentration of nucleating agents, solubility of the blowing agent in the polymer, and the modulus. High impact polystyrene (HIPS) was added to polystyrene to obtain polymers with different concentrations of rubber gel particles, the nucleating agent, and used here for this study.