Crystallization Behavior and Molecular Dynamics Simulation of Poly(Lactic Acid) Film Toughened by Poly(Ethylene Glycol)-Modified Carbon Dots

In order to improve the crystallization properties and toughness of PLA film, poly(ethylene glycol) (PEG)-modified carbon dots (CDs) were synthesized as nanofillers to achieve this goal. PEG-CDs were characterized by Fourier transform infrared spectrometer (FTIR), static contact angle measurement, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analyzer (TGA), and the results demonstrated that the PEG chains were successfully grafted onto the surface of CDs. PEG-CDs/PLA composite films were prepared by extrusion blow molding technology, and their mechanical properties, thermal stability, anti-aging performance, and water vapor barrier properties were investigated. The results showed that the elongation at break of PEG-CDs/PLA composite films (0.05 wt%) increased from 19.43% (for pure PLA film) to 107.75%, and the water vapor barrier properties, thermal stability, and anti-aging properties of PEG-CDs/PLA composite films were improved to varying degrees compared with those of pure PLA film. The rheological behavior analysis of the PEG-CDs/PLA composite film revealed that PEG-CDs had a plasticizing effect on PLA, which is one possible cause for the increased toughness of the PEG-CDs/PLA composite films over pure PLA film. Moreover, the results of the crystallization behavior proved that PEG-CDs could not only improve the crystallinity of PLA but also accelerate its crystallization rate. Molecular dynamics simulations confirmed the presence of strong interactions between PEG-CDs and PLA, thereby enhancing the overall performance of PLA films. Graphical DSC and POM analyses indicate that PEG-CDs can effectively enhance the crystallinity of PLA. The results of isothermal and non-isothermal crystallization behavior show that PEG-CDs not only promote the crystallization of PLA but also accelerate its crystallization rate. Additionally, MD analysis demonstrates that there is a strong interaction between PEG-CDs and PLA. These factors collectively explain the effectiveness of PEG-CDs in improving the overall performance of PLA-based films.