Lamellae Evolution of Stereocomplex-Type Poly(Lactic Acid)/Organically-Modified Layered Zinc Phenylphosphonate Nanocomposites Induced by Isothermal Crystallization

Stereocomplex-type poly(lactic acid) (SC-PLA)/oleylamine-modified layered zinc phenylphosphonate (SC-PLA/m-PPZn) nanocomposites are successfully fabricated using a solution mixing process. Wide-angle X-ray diffraction (WAXD) analysis reveals that the structural arrangement of the oleylamine-modified PPZn exhibits a large interlayer spacing of 30.3 angstrom. In addition, we investigate the temperature effect on the real-time structural arrangement of PPZn and m-PPZn. The results indicated that the lattice expansion of m-PPZn with increasing temperature leads to an increase in the interlayer spacing from 30.3 to 37.1 angstrom as the temperature increases from 30 to 150 degrees C. The interlayer spacing decreases slightly as the temperature further increases to 210 degrees C. This behavior might be attributed to interlayer oleylamine elimination, which results in hydrogen bonding destruction between the hydroxide sheets and water molecules. As the temperature reaches 240 degrees C, the in situ WAXD patterns show the coexistence of m-PPZn and PPZn. However, the layered structures of m-PPZn at 300 degrees C are almost the same as those of PPZn, after the complete degradation temperature of oleylamine. The morphology of the SC-PLA/m-PPZn nanocomposites characterized using WAXD and transmission electron microscopy (TEM) demonstrates that most partial delamination layered materials are randomly dispersed in the SC-PLA matrix. Small-angle X-ray scattering reveals that higher crystal layer thickness and lower surface free energy is achieved in 0.25 wt% SC-PLA/m-PPZn nanocomposites. These results indicate that the introduction of 0.25 wt% m-PPZn into SC-PLA reduces the surface free energy, thereby increasing the polymer chain mobility.