MATHEMATICAL MODELS AND NUMERICAL SIMULATIONS OF THERMALLY-EXPANDABLE MICRO-BALLOON FOR PLASTIC FOAMING

摘要

A thermally expandable microcapsule, often called micro-balloon, has been utilized in compression, injection moldings and extrusion processes to foam several polymers. The microballoon consists of polymer shell and liquid hydrocarbon in core. The hydrocarbons are used as a physical blowing agent. A mathematical model was developed in this study to describe the expansion behavior of the microballoon in air as well as in polymer matrix so as to find the key factors of improving the expandability of the balloon. The viscoelastic properties of the polymer shell, evaporation of hydrocarbons in balloon, diffusion behavior of the blowing agent through the polymer shell were taken into account in the models. The developed model showed quite good agreements with the visually-observed thermally-expansion behavior of the microballoon.