Visual Studies of Model Foam Development for Rotational Molding Processes

Abstract

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: E809-E821, 2013; View this article online at wileyonlinelibrary.com.

Bubble nucleation in nonpressurized polymer foaming systems

“…The foaming experiments were repeated at least five times to determine accuracy and reproducibility of the experimental results and offset the effect of any possible inconsistency in the sample preparation. The observed results in microscopic experiments through the discussed foaming method in this work have shown strong correlations to the foaming performance of the tested materials at higher production scales and under actual processing conditions in our previous research study, conducted in a lab-scale rotational foam molding machine [13].…”

“…Densification of the sintering polymer continued until the onset of decomposition for the blowing agent at 166°C. A detailed explanation of the sintering stage has been discussed in our previous work .…”

“…In this study, the mechanisms involved in the nucleation in such foaming systems have been experimentally investigated, which follows our previous work on visualization studies of the foam development process in nonpressurized conditions . It was found that the nucleation process is comprised of two distinct stages: primary and secondary nucleation.…”

“…5a, d, g, j, and m). Densification of the sintering polymer continued until the onset of decomposition for the blowing agent at 166 C. A detailed explanation of the sintering stage has been discussed in our previous work [13]. The sintering process is significantly affected by material properties, including powder particle size, thermal transitions, and rheology of the polymer matrix [24][25][26].…”

Skin‐Foam‐Skin TP‐Seal® Rotomolded Structures: A New Concept for the Production of Car Bodies for Urban Mobility

“…This pressure difference is the main driving force for the growth of the bubble nuclei. 4 The interest in foaming in rotomolding is driven by the possibility to produce thick layers of a very low density: from 150 to 300 kg/m 3 . This allows the production of thick parts that will give much more strength with a good weight balance.…”