Thermal behavior of ring-band versus maltese-cross spherulites: Case of monomorphic poly(ethylene adipate)

Two types of spherulites, extinction-ring and Maltese-cross, in polyethylene adipate) (PEA) were identified, isolated, and separately characterized using DSC and polarized-light optical microscopy (POM). Ring-band spherulites in PEA occurred only in a very narrow temperature range roughly between 25 and 30°C, while Maltese-cross spherulites at 35°C and above or at 20°C and below. Thermal behavior of ring-spherulites is interpreted, analyzed, and compared to that of Maltese-cross spherulites. The thermal behavior, like the morphology, was found to be significantly different between these two types of spherulites. Among the three multiple melting peaks in PEA, the highest P₃ is proven to be related to melting of lamellae in the ring-band spherulites; P₁ and P₂, whose relative extent of overlapping is dependent on the temperature of crystallization, are related to melting of lamellae in the regular ringless spherulites. This study has provided urgent and timely evidence for one major step further in the interpretation of relationships between the thermal behavior, melting, and extinction-ring versus Maltese-cross spherulites in semi-crystalline polymers.