Document Abstract
ANTEC Papers: 2001
0908: Formulating Foamable Resins for Achieving a Given Volume Expansion Ratio in Rotational Foam Molding
Remon Pop-Iliev, Ghaus M. Rizvi, and Chul B. Park* Microcellular Plastics Manufacturing Laboratory Department of Mechanical & Industrial Engineering University of Toronto Toronto, Ontario, Canada M5S 3G8 * park@mie.utoronto.ca
The rotational foam molding process is suitable for fabricating rotational moldings intended for applications that require their internal volume to be entirely or partially occupied with a cellular structure. Whether the outcome of this process will result in articles having a fully foamed core or just a foamed layer with a given thickness depends on the volume expansion ratio for which the foamable resin has been formulated and the shot size the mold has been charged with. Although the amount of chemical blowing agent (CBA) that should be introduced into the polymer in order to prepare a foamable resin that would be suitable for satisfying the required expansion characteristics can be theoretically calculated, in practice, due to various reasons, a portion of the generated blowing gasses during the rotational foam molding cycle is often inevitably lost via the mold’s vent(s). As a consequence of this unaccounted loss of blowing gas, a discrepancy exists between the theoretically calculated and the practically achievable volume expansion ratio of a particular foamable resin. Thus, in order to compensate for the loss of the blowing gas that takes place during the foaming stage, the amount of CBA introduced into the polymer while preparing the foamable resin should be greater than the theoretically calculated. This paper establishes the relationship between the theoretically calculated level of CBA concentration in the foamable resin formulation and the actual experimentally-obtained volume expansion ratio in order to predict the necessary CBA concentration correction factor for a given volume expansion ratio and polymer material-blowing agent combination.