Molecular Design Strategies of Nucleating Agents with Synergistic Effects for Upcycling Polyethylene Terephthalate

The nucleating agents with different alkyl chain lengths sodium 4-[(benzyl)amino] benzoate (SAB-Be), sodium 4-[(heptanoyl)amino] benzoate (SAB-7C), and sodium 4-[(stearoyl)amino] benzoate (SAB-18C) were synthesized via chemical to improve the crystallization and mechanical properties of recycled polyethylene terephthalate (rPET) that had been damaged during mechanical recycling. The rPET/nucleating agent blends were prepared by melt blending. The molecular structure and thermal stability of the nucleating agents were characterized using the utilization of fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). The differential scanning calorimetry (DSC) results showed that the crystallization properties of the rPET had been improved. In addition, the glass transition temperatures (<i>T</i>_g) of rPET, rPET/SAB-Be, rPET/SAB-7C, and rPET/SAB-18C were 80.3 ± 0.3 °C, 80.4 ± 0.9 °C, 77.0 ± 1.2 °C, and 69.7 ± 0.9 °C, respectively, demonstrating that the length of the alkyl chain in the nucleating agents was essentially proportional to the lubrication effect on rPET. Meanwhile, the rheological properties also supported the conclusion. The isothermal thermodynamic analysis indicated that the compatibility between nucleating agents and rPET was related to the length of the alkyl chain in the nucleating agents. The scanning electron microscopy (SEM) results of the fracture surfaces of the rPET/nucleating agent blends showed that the longer the alkyl chain in the nucleating agent, the greater the compatibility with rPET. Furthermore, the rPET/SAB-18C exhibited the best mechanical properties of the samples used in this research, with flexural strength and impact strength increased by 5.1% and 58.9%, respectively, compared to rPET. Overall, this work provided the new approach for rPET upcycling by combining molecular design strategies.