Visual Observation of Physical Batch Foaming for Polymer Blends and Composites
Kentaro Taki, Kazuhide Tabata, Tatsunori Yanagimoto, Masahiro Ohshima
Department of Chemical Engineering, Kyoto University
Japan
Keywords: Polymeric foam, Visual observation, blend
In the physical foaming processes, the bubbles are created in polymers by dissolving physical foaming agent (PFA) such as CO2 and then releasing pressure or increasing the temperature to induce phase separation of PFA in the polymer. The foaming procedure is simple, however, making the fine cellular structure in a specified polymer is not easy. Foaming basically involves bubble nucleation, bubble growth and cell coalescence. One has to understand such foaming mechanisms and identify the cause-and-effect relationship among polymer properties and operating conditions of the processing unit in order to produce high quality foamed products.
In this study, using a newly developed high-pressure autoclave, which had two sapphire windows on the walls, the visual observation of polymeric batch foaming of polymer blends and composite was conducted to understand the foaming mechanisms. Using CO2 as physical blowing agents, polypropylene/ethylene-propylene-diene rubber (PP/EPDM) blends, polyethylene/TiO2 (PE/TiO2) composites and polypropylene/clay nano-composite were foamed by varying pressure release rate in the range from 0.4 to 1.5 MPa/s and temperature in the range from 150 to 200oC. Five PP/EPDM samples were prepared by changing the PP composition from 0, 25, 50, 75 to 100 wt%, three PE/TiO2 samples were made by changing the TiO2 composition 0, 10 and 20% and three PP/Clay nanocomposites were prepared at different clay compositions levels, i.e., 0, 2.7, and 7.5 wt%.
A magnetic suspension balance measured the solubility and diffusivity of CO2 in blends and composites. CCD camera with a microscope observed the bubble nucleation and bubble growth behavior in-situ. The series of micrograph taken by the CCD camera were analyzed so as to reveal the effect of composite weight percentage and blend ratios as well as morphology on the bubble nucleation and growth rate. The visual observation together with solubility and diffusivity data made it possible to elucidate the mechanism responsible for the foam formation in blend and composites.