Rheological Assessment of Polymer Melts and Networks: From Degradation to Recyclability

Polymer degradation occurs throughout the material lifecycle, from manufacturing and service to end-of-life, involving chemical transformation, performance deterioration, and microplastic release. Uncontrolled degradation presents significant challenges to the performance stability, operational safety, and sustainable management of polymer products. Rheology provides a sensitive and efficient approach for assessing degradation-induced changes in polymer structure and thermomechanical behavior, complementing conventional measurements of molecular weight, mass loss, and mechanical properties. This review discusses how rheological methods have been applied to the assessment and analysis of degradation and stability in polymer melts and cross-linked networks with an emphasis on structural evolution, degradation kinetics, and the effects of processing conditions. Linear and nonlinear rheological measurements offer complementary insights into structural changes and material stability under high temperatures and large deformations, which are particularly relevant to polymer processing and recycling. Recent advances in in-process rheological characterization, combined with optical and morphological analyses, enable real-time monitoring of structural degradation and performance evolution during melt-processing. The review also identifies key challenges in interpreting rheological signatures, distinguishing degradation mechanisms, and establishing reliable structure-property relationships, highlighting opportunities to develop rheology-based approaches for degradation diagnosis, lifetime prediction, and recycling process optimization.