A Step Forward in Thermoplastic Polyesters: Understanding the Crystallization and Melting of Biobased Poly(ethylene 2,5-furandicarboxylate) (PEF)

Abstract

Three samples of biobased poly(ethylene 2,5furandicarboxylate) (PEF) with various molecular weights (MWs) were synthesized. Their crystallization was studied by using differential scanning calorimetry (DSC), modulated temperature DSC (MDSC), wide-angle X-ray diffractometry (WAXD), and polarized light microscopy (PLM). The rates of isothermal crystallization from the melt decreased with increasing MW. One up to three melting endotherms were observed in DSC heating thermograms of samples crystallized isothermally. This behavior was interpreted in the context of recrystallization/reorganization phenomena. Recrystallization and multiple melting were associated with low stability samples crystallized at low crystallization temperatures (T c 's) and with low molecular weight. However, the multiple melting of PEF crystallized after self-nucleation was attributed to a dual morphology. As PEF crystallized slowly, its melt crystallization on cooling at 15 different slow rates ranging from 0.1 to 5.0 °C/min was studied, while the crystallization from the glass was investigated upon heating at 15 different rates from 0.25 to 10 °C/min. A large amount of the collected data was treated using various models. But most importantly, critical observations were made by combining all the available raw data and results from different techniques and methods, allowing for better understanding of the crystallization and melting of thermoplastics under various conditions. The limitations of the experimental techniques and data treatments were evaluated.

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“…An almost exponential decrease can be seen. Also, PBF showed faster crystallization compared to PEF since a smaller degree of supercooling was needed compared to that of PEF for a given cooling rate …”

“…The degree of crystallinity further decreased to 33% with the further increase in the cooling rate to 20 °C/min. For comparison, the degree of crystallinity values for PEF ranged between 35 and 9%, for slow cooling rates ranging from 0.1 to 5 °C/min …”

“…This is in accordance with our earlier observations on PBF and PEF. 33,46 In general, PBF showed faster crystallization rates than those of PEF and could attain a significant degree of crystallinity even upon heating scans at 20 °C/min. In contrast, for PEF, much slower heating scans are needed to arrive to sufficient crystallinity values.…”

“…Also, PBF showed faster crystallization compared to PEF since a smaller degree of supercooling was needed compared to that of PEF for a given cooling rate. 46 The crystallization temperature, T c , can be converted to crystallization time, t. 47,48 Figure 7c,d shows the evolution of the relative degree of crystallinity with temperature and time. Figure 8a shows the melting endothermic peaks of PBF samples upon subsequent heating after cooling from the melt at the indicated cooling rates.…”

“…For comparison, the degree of crystallinity values for PEF ranged between 35 and 9%, for slow cooling rates ranging from 0.1 to 5 °C/min. 46 Avrami theory as modified by Jerziorny 48 was used for the study of the non-isothermal crystallization of PBF. The Avrami plots are constructed by plotting log[−ln(1 − X)] versus log t. From the slope and the intercept of each Avrami plot, the Avrami parameters n and K A can be calculated (Figure 9a).…”