Evidence for the formation of interpenetrated spherulites in poly(butylene succinate-co-butylene carbonate)/poly(l-lactic acid) blends investigated by atomic force microscopy

The spherulitic morphology in poly(butylene succinate-co-butylene carbonate)/poly(l-lactic acid) (PEC/PLLA) blends was investigated by atomic force microscopy (AFM) to obtain direct evidence for the formation of interpenetrated spherulites (IPS), where the spherulites of PEC penetrate into PLLA spherulites. The observation actually revealed that PEC crystals penetrated into interfibrillar regions of edge-on lamellae in a PLLA spherulite. The penetration process was also investigated by AFM with a temperature controller. An edge-on PLLA lamella or a fibril that ran nearly perpendicular to the growth direction of a PEC spherulite obstructed the growth of PEC spherulite. The PEC crystals filled the blocked space after growing around the PLLA lamella. These results showed that the spherulites of PEC and PLLA grow on the same layer instead of forming a layered structure of two spherulites. All the results supported the formation of IPS.