Enhancing the impact resistance of PET copolyesters by rubber toughening

Abstract

Glassy thermoplastic polymers are prone to brittle fractures. To enhance their mechanical properties and, consequently, their durability, it is imperative to focus on toughness, specifically impact resistance, which determines the material’s mechanical failure limit. This thesis focuses on improving the impact resistance of PET copolyesters through rubber toughening. It delves into the impact and tensile properties of PET copolyesters (PET1, PET2, and PET3), aiming to unravel the structure-property relationship. The study involved the preparation of tensile and impact specimens via melt extrusion and injection molding. A DSC analysis confirmed the nature of these copolyesters, revealing PET3 as semi-crystalline, distinct from the amorphous PET1 and PET2. Impact tests indicated that PET2 achieved an improvement of impact properties at 15 wt.% rubber concentration, while PET1 accomplished this at 20 wt.%. Tensile tests yielded similar results for PET1 and PET2 but showed reduced deformability as the impact modifier concentration increased from 15 wt.% to 20 wt.%. In its unmodified state, PET3 exhibited remarkable plastic deformability, which decreased with an increase in rubber concentration. PET3’s impact properties showed no enhancement with increased modifier concentration. Morphological analysis of modified PET copolyesters revealed increasing amounts of cavitation in PET1 and PET2 as the concentration increased from 15 wt.% to 20 wt.%, whereas PET3 exhibited cleavage brittle fractures regardless the modifier concentration. The presence of cavitation indicates that shear yielding is the dominant deformation mechanism.