Thermal Behavior of Ring‐Band versus Maltese‐Cross Spherulites: Case of Monomorphic Poly(ethylene adipate)

Abstract

Summary: Two types of spherulites, extinction‐ring and Maltese‐cross, in poly(ethylene 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.DSC curves (10 °C · min−1, scanned from where the trace begins) for: (a) ring‐spherulites in PEA crystallized at 30 °C for 90 min, (b) sample‐(a) heated to 50 °C for 1 min, and (c) sample‐(a) heated to 50 °C, then quenched to 20 °C.magnified imageDSC curves (10 °C · min−1, scanned from where the trace begins) for: (a) ring‐spherulites in PEA crystallized at 30 °C for 90 min, (b) sample‐(a) heated to 50 °C for 1 min, and (c) sample‐(a) heated to 50 °C, then quenched to 20 °C.

Effects of Cyanuric Acid on Crystallization Behavior, Polymorphism, and Phase Transition of Poly(butylene adipate)

“…At T c = 32 o C, two diffraction peaks assigned to β-modification [such as β (110) and β (020)] have disappeared and only three peaks assigned to α-modification can be found, indicating that the pure α-modification formed at T c = 32 o C (this T c is called as T c,α and the WAXD pattern is marked as black). These WAXD results above are in consistence with previous reports [8][9][10][11][12]. Upon loading of 0.5% CA(Figure 4b), T c,e and T c,α of the PBA decreased to 26 and 30 o C, respectively.…”

“…[3][4][5][6][7] Recently, much attention has been focused on the aliphatic polyester (including the PBA) due to the complicated, peculiar and interesting relationship among its polymorphic crystalline structure, multiple melting behavior, morphology, phase transition and property (biodegradability). [8][9][10][11][12][13][14] Depending on the melting-crystallization temperature (T c ), PBA can crystallize into the α modification (T c > 32 o C), β modification (T c < 29 o C), and the mixture of α and β modification ((α + β), 29 o C ≤ T c ≤ 32 o C). 8 The β modification exhibits a faster crystallization rate than the α one, and is considered as the kinetically preferential phase.…”

Uracil as Nucleating Agent for Bacterial Poly[(3‐Hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] Copolymers

“…10–20 °C above the crystallization temperature. This phenomenon is a typical characteristic of the so‐called “annealing peak,” which has been detected for many semicrystalline polymers including PET, isotactic polystyrene (i‐PS), poly(aryl ether ether ketone) (PEEK), poly(ethylene adipate) (PEA), and so forth 46–48. Although the origin of the annealing peak is still under debate, it has been widely accepted that it is associated with the melting of secondary crystals formed upon long‐time annealing during isothermal crystallization.…”

Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review

“…Obviously, the premise for successfully building such nested ring-banded spherulites is that the twisting period should be much narrower than the interval of rhythmic crystallization. It is known that when crystallizing from the melt, PEA can form double-banded spherulites with the quite narrow band spacing under a wide temperature range, and the twisting frequency of PEA lamellae is quite insensitive to the crystallization temperature [54]. By selecting a slow evaporation of PEA/tetrahydrofuran solution-cast films, Li and colleagues have successfully fabricated a nested ring-banded structure of the low molecular weight PEA10.0k [50].…”