Structure and Property Gradation from Surface to Bulk of Poly( l -lactic acid)/Poly( d -lactic acid) Blended Films as Estimated from Nanoscratch Tests Using Scanning Probe Microscopy

Structure and property gradation from surface to bulk of poly( l -lactic acid)/poly( d -lactic acid) (PLLA/PDLA) blended films was estimated from nanoscratch tests using scanning probe microscopy (SPM). The PLLA/PDLA blended film was prepared by melting, following isothermal crystallization at 150 °C due to the formation of stereocomplex crystal (sc-crystal). Grazing-incidence X-ray diffraction measurements revealed that the fraction of sc-crystal on the surface was higher than that of bulk. Two types of morphologies were observed in an SPM nanoscratch test conducted under a higher applied load: a less-deformed morphology and a plowed-up morphology. These results demonstrate that a hierarchical structure with an sc-microcrystallite networked surface could be developed by optimizing the processing conditions.