Rheology-Informed Working Thresholds for HME/FDM Processability in a PVA–Sorbitol–Paracetamol Model System

Background/Objectives: Oscillatory rheology is widely used in hot-melt extrusion (HME) and fused deposition modeling (FDM), but its translation into compact formulation-screening criteria remains limited. This study re-analyzed an existing PVA–sorbitol–paracetamol dataset to derive rheology-informed working thresholds for HME/FDM processability. Methods: Temperature-ramp oscillatory rheology was used to extract formulation-level descriptors: process-temperature complex viscosity (|η*|) at 185 and 200 °C, Processing Window Fraction (PWF) within the 0.8–10 kPa·s corridor, and crossover-related temperature information. These descriptors were interpreted against empirical extrusion at 200 °C and printing at 185 °C. Results: S1.25 and S1.5 showed rheological behavior compatible with successful extrusion, whereas S1.75 showed pronounced softening consistent with over-plasticization and process failure. Paracetamol further reduced complex viscosity while maintaining processability in P5–P15. The lowest successful process-temperature viscosity values, observed for P15, supported working thresholds of approximately 0.460 kPa·s at 200 °C and 0.899 kPa·s at 185 °C. PWF complemented thresholding by describing the practical temperature flexibility of each formulation. Conclusions: Process-temperature |η*|, PWF, and crossover-informed interpretation provided a compact, formulation-specific screening framework for this PVA-based HME/FDM model system. The proposed thresholds are operational derivation outputs and require prospective external confirmation.