Thermodynamic Relaxation
Non equilibrium materials like glass or plastic undergo a slow evolution toward a more stable state over time. The physical aging polymer process involves a gradual reduction in the free volume between molecular chains as they pack more tightly together. This change occurs without any chemical reaction or degradation but alters the mechanical properties of the material.
Free Volume
Space between molecules allows for mobility and determines how the material responds to external loads. As the polymer ages, this space diminishes and the chains become more restricted in their movement. This results in an increase in the stiffness and a decrease in the impact resistance of the plastic.
Modulus Change
Shifts in the elastic properties can lead to changes in the calibration of the sensor. Engineers must account for these changes during the design of long life equipment.
Storage Environment
Temperature plays a major role in determining the rate at which these molecular changes occur. Keeping the materials at a consistent temperature below their glass transition point can slow down the process and maintain the stability of the device. High heat can accelerate the aging and cause the sensor to drift away from its original factory settings by reducing the time needed for molecular chains to reach a more densely packed state.
