Improved crystallization behavior and enhanced impact strength of melt processed poly(ethylene terephthalate)/UiO-66 nanocomposites

Abstract

The present research aimed to investigate the influence of Zr-based metal-organic framework, i.e. UiO-66, on the performance of poly(ethylene terephthalate) (PET) by the melt mixing method. PET/UiO-66 nanocomposites were prepared at 0.25, 0.5, 1, and 2 wt% of UiO-66. FESEM microphotographs showed the success of the melt mixing method in the fine dispersion of UiO-66 within PET. Additionally, XRD patterns confirmed that UiO-66 retained its structure after melt mixing at 260 °C. DSC analysis suggested that UiO-66 acted as a nucleating agent with a best performance at 1 wt% loading, i.e. 45 % decrease in the crystallization half-time and 11 % increase in the crystallization temperature. Furthermore, the PET/UiO-66 nanocomposites exhibited an improvement in char formation and resistance to complete thermal degradation at high temperatures compared to neat PET. The inclusion of UiO-66 in PET increased the impact strength with a maximum value at 0.5 wt% loading, e.g. more than twice neat PET. In addition, DMTA results indicated that UiO-66 acted as a strengthening agent in PET. Rheological investigations revealed that PET/UiO-66 exhibits the non-Einstein-like viscosity behavior in which the complex viscosity decreased by increasing UiO-66 content. We reasoned that behavior mainly to the flexible nature of the UiO-66 particles. Although all the samples showed almost Newtonian behavior at 260 °C in frequencies between 0.03 Hz and 100 Hz, PET/UiO-66 (0.5) presented the shear thinning behavior. This was ascribed to the good dispersion with the strong interfacial interaction, leading to a microstructure with yield stress.