Experimental and theoretical investigation on polystyrene/n-pentane foaming process

摘要

At the present work, foaming process (bubbles nucleation and growth) of Polystyrene (PS)/n-pentane batch foaming system was studied experimentally and theoretically. Synthesized PS was characterized by rheological measurements and the foaming dynamics was studied using a designed in-situ observation apparatus. The saturation time at the lowest mass diffusivity conditions was determined to ensure that all experiments would be performed at saturation state. Dissolved content and Henry's constant of n-pentane in PS at foaming conditions were also determined. The effects of temperature and sorption pressure as operation parameters on the foaming dynamics of PS/n-pentane system were investigated and it was found that temperature had a dramatic effect on the foaming dynamics and other parameters such solubility, diffusivity and melt strength were affected by temperature. Moreover, the bubble growth behavior of PS/n-pentane system was simulated and it was compared to the experimental results. To calculate concentration profile in the shell, mass diffusion equations were solved by implicit method with considering gas escape from the outer layer of the viscoelastic shell around the bubble. Furthermore the effect of mass diffusivity and viscosity on the bubble growth behavior was examined simultaneously and it was emphasized that the bubble growth behavior was a mass diffusion controlled phenomenon.