Visualization of Polymer Foaming Using a Batch Foaming Simulation System With a High Pressure-Drop Rate

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Abstract

An innovative batch foaming simulation system was designed and constructed in order to elucidate the mechanisms of bubble formation and growth during polymer foaming. A theoretical model to simulate the pressure and pressure-drop in the batch foaming chamber was derived. The system was experimentally verified using polystyrene (PS101) and CO₂.

Using the batch foaming simulation system, the bubble formation and growth occurring inside specific polymer samples (PS685D) and at the interface between the samples and a sapphire window were studied. It was found that bubble formation inside the polymer required a higher supersaturation than bubble formation at the interface because of the smaller critical radius induced by the higher degree of supersaturation. Finally, the bubble formation and life span of polymer with chemical blowing agent (CBA) blown under atmospheric and high pressure were studied.

The system was further used to investigate the foaming of polystyrene (PS 101) with carbon dioxide (CO₂), polystyrene (PS685D) with CO 2 and nitrogen (N₂), and linear polypropylene (PP) (HE351F) and branched PP (WB130HMS) with CO₂ and N₂. The results showed that gas content and pressure-drop rate were the two most significant factors governing bubble formation and growth during foaming processes. Moreover, the foaming temperature and branching of the polymer had some effects on maximum cell density. Nucleating agent (talc) played a significant role under processing conditions with a low gas content and low pressure-drop rate, but it did not show any obvious effect at high gas content and high pressure-drop rate. Under the same initial foaming condition, the maximum cell densities of PS685D/CO₂ and PP/CO₂ foams were higher than those of PS685D/N 2 and PP/N₂ foams, respectively; while the maximum cell density of PS685D/CO₂ and PP/CO₂ foams were lower than those of PS685D/N₂ and PP/N₂ foams, respectively, if the same mole number of gas in unit polymer was used. In addition, experimental results show that branched PP foamed with N₂ generated slightly higher cell density than linear PP, while linear PP foamed with CO₂ generated slightly higher cell density than branched PP under the same initial saturation condition.

Finally, the bubble formation and life span of polymer with chemical blowing agent (CBA) blown under atmospheric and high pressure were studied.

Cited Works (2)

Year	Entry
2002	Naguib HE, Park CB, Panzer U, Reichelt N. Strategies for achieving ultra low-density polypropylene foams. Polym Eng Sci. July 2002;42(7):1481-1492.
1999	Sato Y, Fujiwara K, Takikawa T; Sumarno, Takishima S, Masuoka H. Solubilities and diffusion coefficients of carbon dioxide and nitrogen in polypropylene, high-density polyethylene, and polystyrene under high pressures and temperatures. Fluid Phase Equilib. August 1999;162(1-2):261-276.