Investigation on Non-Isothermal Crystallization Kinetics of Polyethylene Terephthalate-Polyethylene Naphthalate Blends

This study aimed to solve two problems of polyethylene terephthalate (PET) films, namely, their slow crystallization rate and insufficient thermal stability, by using polyethylene naphthalate (PEN) as a modifier to prepare PET-PEN blends with varying PEN contents (0%, 0.9%, 1.8%, and 9%). Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and other methods were used to systematically investigate the effects of the PEN content and cooling rate (5-40 °C/min) on the non-isothermal crystallization behavior and kinetics of the blends. The results indicate that PET and PEN exhibit excellent compatibility. As the PEN content increases, the glass transition temperature (<i>T_g</i>) of the blend increases, while the melting point (<i>T_m</i>) and relative crystallinity decrease. PEN exerts an effect on the crystallization temperature (<i>T_c</i>)-"heterogeneous nucleation-diffusion control-steric hindrance effect". The cold crystallization behavior depends on the PEN content and cooling rate. Samples with PEN content did not exhibit cold crystallization at low cooling rates. The observed non-isothermal crystallization kinetics show that PEN transforms the growth dimension of PET crystals from three-dimensional to two-dimensional, significantly reducing the absolute values of the crystallization rate constant (<i>Z_c</i>) and crystallization activation energy (Δ<i>E</i>). Δ<i>E</i> tends to stabilize when the PEN content reaches or exceeds 1.8%. In summary, PEN achieves precise control of PET non-isothermal crystallization through the mechanism of "heterogeneous nucleation-diffusion control-steric hindrance effect". The research results provide theoretical support for the optimization of processing technology for PET-PEN blend films in high-end fields such as food packaging and electronic insulation.