Meaning
Amorphous materials kept below their glass transition temperature undergo a slow, spontaneous densification that alters their mechanical and thermal properties over time. The physical aging of polymers represents this process, during which the material loses excess free volume and relaxes toward a more stable thermodynamic state. This change establishes the long-term limits of product performance by increasing yield stress and stiffness while decreasing ductility and fracture toughness.
It is a fundamental factor in the long-term degradation of polymer parts.
Structural Progression
Polymer chains slowly pack closer together, which restricts their mobility and reduces the material’s free volume. During physical aging, the material moves toward its equilibrium volume at a rate that depends on temperature and processing history. If a component is deployed in an application without accounting for this structural shift, it may become brittle and crack under normal load.
This progression must be modeled to predict lifespan.
Thermal Boundary
Heating a polymer above its glass transition temperature erases all previous aging effects and resets the material’s structure. This thermal treatment restores the original ductility and volume. It allows for material rejuvenation.
Product Evaluation
Quality control protocols must include accelerated aging tests to evaluate how the polymer behaves after years of storage. These tests expose the material to slightly elevated temperatures to speed up the densification process. It ensures the part remains functional throughout its intended service life.
