Time dependent properties of polymer blends and composites: a review
Polymer blends and composites play crucial roles across aerospace, automotive, energy and structural applications, yet their long-term performance governed by complex time‐dependent properties and performance. Existing reviews often isolate chemical aging, mechanical behavior or characterization techniques, leaving a gap in understanding how molecular‐scale changes translate into macroscopic property loss. This review provides an integrated, mechanism‐driven synthesis of time‐dependent behavior in polymers, linking degradation chemistry, morphology evolution and property deterioration. We critically examine physical aging, photo‐oxidation, hydrolysis, viscoelastic relaxation, interfacial decay in composites and the role of environmental stressors. Quantitative trends from the literature are consolidated to clarify how mechanical strength, elongation, thermal transitions, dielectric response, and optical performance evolve. We also evaluate advanced analytical methods, including DMA, dielectric spectroscopy, thermally stimulated depolarization current and nanoscale dielectric tools that reveal molecular mobility and relaxation phenomena. Finally, we outline design guidelines and future directions, emphasizing predictive modeling, nanofiller‐based stabilization and the development of sustainable, long‐life polymer systems.