Visual Studies of Model Foam Development for Rotational Molding Processes

This work explores the foam development process under atmospheric pressure as applicable to rotational molding, investigating the influence of the processing parameters, and characterizing the morphology of the foamed structure. Detailed understanding of the bubble transformation during foaming of nonpressurized polymer melts provided an accurate basis for predicting the morphological structure and macroscopic properties of foams produced by rotational molding. The experimental results are based on visualization studies using a hot stage microscopy setup. The cellular structure developed during the foaming was analyzed for its bubble density, bubble size, and statistical parameters considering the combined effect of these two factors. It was found during this investigation that the foaming mechanism comprises four distinct stages. It included two major stages of bubble nucleation, primary nucleation in interstitial regions, and secondary nucleation in the polymer melt. Statistical analysis of the developing foamed structure revealed that primary nucleation in the interstitial regions was the controlling stage in determining the final cellular structure. Subsequently, the nucleation stages were followed by bubble growth and bubble coalescence/shrinkage. The microscopic observations were complemented by actual rotational foam molding experiments. (c) 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E809E821, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21323