Enhanced crystallization behaviour and impact toughness of poly(ethylene terephthalate) with a phenyl phosphonic acid salts compound

Abstract

Low crystallization rate and inherent brittleness characteristics limit the wide application of PET. In this paper, it was found that a low molecular weight Phenyl phosphonic acid salts compound (TMC-210) is a very effective nucleator and can enhance the impact strength very much. So, the effect of TMC-210 on the crystallization behaviour and mechanical properties of poly(ethylene terephthalate) were systematically evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), scanning electron microscope (SEM) and mechanical properties test. The results show that TMC-210 obviously improves the crystallization temperature and accelerates the crystallization rate of PET and reflects a significant heterogeneous nucleating effect with a nucleation efficiency of 99.8 % when introducing a low content of 0.6 wt% TMC-210. The spherulites size and number of blended PET are greater than pure PET. The crystal structure of PET does not change but the blends with high TMC-210 content appears new diffraction peaks in x-ray diffraction spectrogram and it may attribute to the agglomeration of TMC-210 particles, which is verified by SEM observation. The impact fracture surface of PET develops a brittle ductile transition and thus the impact strength of PET improves significantly. Additionally, Lauritzen–Hoffman equation was used to discuss the effect of TMC-210 on the fold surface free energy (σ e) of PET in the crystallization process and found that the σ e values of PET/TMC-210 blends is smaller than that of pure PET.