Abstract
Amorphous glassy polymers are widely used as structural materials. However, their mechanical properties continuously evolve with physical aging, which significantly influences their applications. In this work, we investigate the effects of aging on stress response of poly(ethylene terephthalate)-glycol (PETG). The PETG specimens are either quenched or annealed around or below the glass transition temperature (Tg) for a period of time. The uniaxial compression tests are then performed at Tg-40 °C and strain rate 0.001/s. The quenched polymers exhibit the smallest yield strength and strain softening, indicating that negligible structural relaxation occurs for the quenched condition. For annealed polymers, the yield strength increases with aging time. The results also show that there exists an optimal temperature to achieve the highest structural relaxation rate, which is around Tg-20 °C. Compared with annealing at a single temperature, annealing at multiple temperatures in discrete steps is a more efficient method for structural relaxation. The same experiments are also performed on specimens with 30% predeformation. The optimal aging temperature does not change with predeformation. However, at the same annealing condition the yield strength of specimens with 30% predeformation is around 5 MPa less than that of undeformed specimens.
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