Configuration-Specific Evaluation and Validation Evidence for High-Pressure CO2 Platforms for In Situ Thermomechanical and Optical Characterization of Polymers

The reliable interpretation of polymer plasticization under high-pressure CO2 requires measurements that preserve the polymer–gas state while recording pressure, temperature, and response. This study presents a configuration-specific evaluation and validation evidence framework for in situ thermomechanical and optical polymer characterization. The three-point-bending platform used LVDT displacement monitoring; a separate optical cell provided morphological observation; and a patented compact analyzer screened PS/MMT formulations. A 15-point LVDT calibration gave R2 = 0.9997 and RMSE = 0.073 mm; ambient comparison with corresponding DSC thermal events differed by 0–2 °C across four polymers. For polystyrene, the mechanical response shifted by approximately 45 K from 0 to 120 bar, and heating-rate changes shifted the operational criterion by up to 30 K. Optical observations provided mechanistic corroboration across the pressure-dependent softening boundary. Seven PS/MMT/MAH formulations showed 7.76–11.94 °C reductions at 50 bar. The framework links each result to its platform configuration and transition criterion while explicitly distinguishing demonstrated measurement capability from validation that remains incomplete for the fully integrated architecture.