Identification of the melting and crystallization temperatures is crucial for effective foaming under compressed fluids. Foaming temperature often falls below melting temperature and above crystallization temperature where the rigidity of the polymer is sufficiently low to allow for bubble expansion but high enough to prevent pore collapse. To assess the thermal transitions in compressed fluids, high pressure torsional braid (HP-TBA) was used.
High pressure torsional braid is a technique that involves an inertial mass suspended from the polymer impregnated glass fiber braid that is subject to initial oscillation. Frequency and amplitude of oscillations allow for the evaluation of changes in relative rigidity and damping as a function of temperature. At transition temperatures, rigidity plateaus and the damping goes through a peak.
Foaming experiments were conducted in isothermal batch cell using the thermal transition data gathered from HP-TBA. The generated foams were characterized with respect to their foam bulk densities and pore morphologies. Comparison of foams generated in carbon dioxide and nitrogen will be made in terms of their expansion ratio and pore size.