Early‐Stage Thermal Aging of Soybean Oil at 150°C: Coupling DGA ‐Derived Scission Gas Markers With GPC ‐Resolved High‐Molecular‐Weight Tail Growth

Triglyceride‐based oils undergo concurrent chain scission and intermolecular coupling during high‐temperature exposure, resulting in time‐dependent redistribution of molecular weights and the formation of volatile/gaseous products. Here, refined soybean oil was thermally aged at 150°C for 0–96 h, and its degradation behavior was characterized using physicochemical indices (acid value, viscosity, and moisture), dissolved gas analysis (DGA) as scission‐related gaseous markers, and gel permeation chromatography (GPC) to track the evolution of the high‐molecular‐weight (high‐MW) tail. Over the studied window, DGA‐measured gases exhibited rapid accumulation (e.g., ethylene reached ~65 ppm at 96 h), whereas the GPC high‐MW tail reflected a slower, lagging oligomerization/coupling contribution. To enable integrated interpretation of these heterogeneous observables, we propose a cross‐metric mapping N ( M ) that links ethylene concentration ( N ) to the high‐MW tail area increment ( M ), using M as a time‐proxy coordinate ( R 2 = 0.968). The derived time‐scale parameter λ ≈107 quantifies the pronounced curvature mismatch between cracking and growth, confirming that the two processes evolve on distinctly different apparent time scales. This mapping provides a practical, time‐scale‐free yardstick for comparing the relative cracking‐versus‐growth tendency of different oil systems or under different contaminant conditions (e.g., copper catalysis), offering a chemically grounded, application‐oriented approach for short‐term thermal stability assessment of triglyceride‐based liquids under controlled heating conditions.