Thermal Treatment
Differential scanning calorimetry reference enthalpy curves establish baseline thermal history in glassy polymers. A sub tg anneal holds material below its glass transition temperature to relieve internal stresses without causing bulk dimensional distortion. Processing times extend from several hours to days depending on molecular weight and crosslinking density.
Enthalpy Recovery
Subjecting components to a sub tg anneal drives structural densification, which manifests as an endothermic peak during subsequent reheating scans. Yield stress and brittle fracture susceptibility increase as molecular mobility drops. Mechanical property changes track physical aging kinetics inside non-crystalline polymer networks.
Process Qualification
Metrology protocols verify physical property stabilization by measuring density variations and dimensional tolerances after heat treatment. Thermal treatment recipes specifying a sub tg anneal require precise temperature uniformity within processing ovens to ensure homogenous physical aging across entire component lots. Optical polarimetry assesses residual birefringence reduction inside transparent optical elements following thermal processing.
Micro-hardness measurements track surface mechanical property evolution across extended annealing durations.
Stress Relief
Molded plastic optics retain anisotropic stresses induced by rapid cooling during injection molding. Executing a sub tg anneal mitigates internal refractive index variations caused by residual stress patterns. Dimensional stability during operational service improves following thermal conditioning.
