Comprehensive study of the steam-aging degradation behaviors and its correspondence to aging mechanism of PET monofilaments under artificially accelerated environment

Abstract

Polyethylene terephthalate (PET) monofilament is extensively utilized in various industries due to its exceptional properties. However, PET monofilament is apt to hydrolysis when exposed to moisture and heat, and the corresponding steam-aging mechanism is not clearly, which severely affects its properties and service life. Hence, the pure PET and modified anti-hydrolysis PET monofilament by introducing hydrolysis stabilizers (polycarbodiimide, PCDI) were subjected to the pressure cooker test, and the resultant changes in mechanical properties were studied. Additionally, the varying length scales structural changes were compared to assess the effectiveness of the hydrolysis stabilizers and to reveal the steam-aging mechanisms of PET monofilaments. The results indicated that both PET monofilaments underwent three distinct aging processes, including pre-aging, steady-aging stage, and rapid failure aging stage. The disorientation of the molecular chain within the oriented amorphous region occurred in the pre-aging stage, giving rise to a subtle increment in breaking strain. Competitive recrystallization and hydrolysis reactions then took place simultaneously in the amorphous region, with the generation of small crystals acting as cross-linking points during the steady-aging stage, forming a more stable lamellar structure that delayed mechanical property loss due to hydrolysis-induced molecular chain breakage. The hydrolysis degradation reaction predominates in the rapid failure aging stage, resulting in a significant decrease in intrinsic viscosity, breaking stress and strain, and causing macroscopic defects. The degradation of molecular chains and the morphology damage induced by steam-aging are the main reasons for the decline of mechanical properties. Moreover, the addition of hydrolysis stabilizers (PCDI) predominantly influenced the molecular chain arrangement in the amorphous region, effectively prolonging the duration of the steady-aging stage and enhancing resistance to hydrolytic degradation conversely.