Experimental and numerical investigation of bubble nucleation and growth in supercritical CO₂-blown poly(vinyl alcohol)

Bubble nucleation and growth was experimentally and numerically investigated in polyvinyl alcohol (PVA) while using supercritical carbon dioxide (scCO₂) as a blowing agent. The solubility and diffusivity of CO₂ in PVA were first evaluated using a magnetic suspension balance (MSB). Bubble nucleation and growth during foaming was then examined using a batch foaming setup equipped with a visualization system. It was observed that the increase in depressurization rate during the foaming increased the average bubble density. The average bubble size during the foaming was also evaluated through three different numerical models based on the integral method. Moreover, according to the bubble pressure profile, the PVA viscosity and CO₂ diffusion control the bubble growth. According to the sensitivity analysis, the bubble growth seems to be more affected by the changes of thermodynamic parameters than the PVA rheological properties. Eventually, the average CO₂ concentration and the critical free energy were numerically calculated using the classic nucleation theory.