High-Pressure Torsional Braid Analysis (HP-TBA): A new technique for assessment of thermal transitions and changes in moduli of polymers exposed to supercritical or compressed fluids

Abstract

Assessment of thermal transitions and the accompanying changes in the moduli of polymers exposed to supercritical or compressed fluid diluents is of utmost importance in the rational selection of processing temperatures and pressures in polymer modifications.We have developed a new technique to document the Tg and Tm and the relative changes in the rigidity of polymers in supercritical or compressed fluids. It is a supported torsional pendulum in which transitions including melting are traversed without loss of the sample integrity. Transition temperatures or pressures are deduced from analysis of damped sinusoidal oscillations over time (t) described by y = exp(-αt)sin(ωt). The damping coefficient (α), frequency (ω), and the period of the oscillations (2π/ω) are related to storage modulus, loss modulus, and loss tangent. The versatility of the technique is illustrated with amorphous [poly(methyl methacrylate)] and semi-crystalline [poly(ε-caprolactone)] polymers as a function of CO2 pressure and temperature.