Modeling flow and cell formation in foam sheet extrusion of polystyrene with CO₂ and co‐blowing agents. Part I: Material model

Abstract

In foam extrusion, process parameters, material properties, and the blowing agent have an influence on the resulting foam properties. For safety and environmental reasons, carbon dioxide (CO2) has gained importance as a physical blowing agent for the production of low‐density polystyrene foam sheets. The sole use of CO2 often leads to corrugation, open cell structures, or surface defects on the foam sheet. As an alternative, blowing agent mixtures based on CO2 and organic solvents such as ethanol, acetone, or ethyl acetate can be used, changing solubility and flow behavior of the gas‐loaded melt. Modeling of the foaming process in the extrusion die could help to reduce experimental effort and accelerate the development of novel blowing agent mixtures. A model approach to describe the melt behavior of polystyrene loaded with various blowing agent mixtures in the extrusion die is developed. Part I of the article describes the modeling of material properties, that is, rheological behavior by a Carreau‐WLF approach with shift factors for temperature, pressure, and blowing agent effects on the glass transition temperature. Solubility behavior is modeled by a combined Henry solubility coefficient approach, showing good agreement with experimental data. Based on the material model, a process model is developed in Part II of this work.

A Review of Rigid Polymeric Cellular Foams and Their Greener Tannin-Based Alternatives

“…The introduction of CO 2 as an inexpensive and safe blowing agent has also been investigated recently, with the possibility of creating microcellular epoxy foams with cell densities of about 100 cells/cm 3 [ 171 ]. However, corrugation and surface defects have often been reported due to the use of CO 2 , which is why Breuer et al tested mixtures of CO 2 and organic solvents such as acetone, ethyl acetate or ethanol [ 172 ].…”

Calculating diffusion coefficients from molecular dynamics simulations for modelling foam processes of polypropylene: Investigating different process conditions and blowing agents

“…1 Therein, the development of a process model that can describe the melt flow in an extrusion die concerning the foam process, requires, amongst others, the knowledge of the diffusion coefficients for the different blowing agents. 2,3 The diffusion coefficient for a blowing agent is often difficult to measure experimentally, especially in the range of elevated temperatures which are used in the foam process. Here molecular dynamics simulations (MD) can be of assistance, since these enable the determination of diffusion coefficients on a computer aided level as well as many other parameters.…”

Effects of reactive diluent on processing, structure, and properties of epoxy foams and their sandwich composites

“…The chemical foaming method has many ways to control the bubble size, which is the most promising. Chemical foaming uses a chemical foaming agent to react or decompose gas under certain conditions 17,18 . The process generally mixes the chemical foaming agent and the resin matrix evenly and then raises the temperature to decompose or react with the chemical foaming agent.…”

“…Chemical foaming uses a chemical foaming agent to react or decompose gas under certain conditions. 17,18 The process generally mixes the chemical foaming agent and the resin matrix evenly and then raises the temperature to decompose or react with the chemical foaming agent. The gas generated by decomposition or reaction forms bubble holes in the resin matrix and the foam preparation is completed after curing.…”