This paper examines the effect of high-pressure carbon dioxide on the foaming process in polystyrene near the glass transition temperature. The foaming was studied using a cylindrical high-pressure view cell with two optical widows. The chemical structure of polymers greatly impacts CO2 solubility and diffusivity. The CO2-philic groups such as carbonyl or ether groups in the backbone or on side chains of a polymer interact with CO2 and help with the dissolution of CO2 within the polymer. This technique has potential applications in the shape foaming of polymers at lower temperatures, dye impregnation and polystyrene foaming. Three sets of experiments were carried out at operating temperatures of 50, 70 and 100oC each over a range of pressures from 24 to 120 bar. Foaming was not observed when the polymer was initially at conditions below Tg but was observed above Tg. The nucleation appeared to occur randomly leading to subsequent bubble growth from these sites, with a maximum radius of 0.02 - 0.83 mm. Three models were applied to the foaming experimental data. Bubbles appeared in all the experiments without exception. The nucleation appeared to occur randomly leading to subsequent bubble growth from these sites. With time, more bubbles nucleate and grow, and the bubbles initially appear to be circular. Model C was applied to assess whether a varying viscosity and diffusivity model with the WLF equation. The model shows very good agreement by using realistic parameter values. The expansion occurs by diffusion of a dissolved gas from the supersaturated polymer envelope into the bubble. Many theories have been proposed for the nucleation radial growth of a single bubble in an infinite expanse of melt.
Author(s)
Details
Salah
Al-Enezi
Petroleum Research & Studies Centre (PRSC), Kuwait Institute
for Scientific Research (KISR), Kuwait.
Please see the book here:- https://doi.org/10.9734/bpi/cmsdi/v5/1555
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