The Narrow Thickness Distribution of Lamellae of Poly(butylene succinate) Formed at Low Melt Supercooling

Abstract

Crystallization of poly(butylene succinate) (PBS) at 100 °C, about 30 K below the equilibrium melting temperature, allowed the preparation of crystals, which were analyzed regarding their zero-entropy-production melting temperature. Irreversible melting occurs in a rather narrow temperature window of only around 8 K, between 101 and 109 °C, revealing a narrow distribution of the thickness of isothermally formed lamellae and a rather low thickening/stabilization factor of less than 1.4. Quasiisothermal temperature-modulated differential scanning calorimetry suggests significant reversible melting and crystallization during and after crystallization, proving the existence of a large fraction of crystalline phase being at the stability limit at the crystallization temperature. Heating of crystals formed at 100 °C to above their zero-entropy-production melting temperature, followed by isothermal annealing, permitted the analysis of the kinetics of irreversible melting, yielding superheating-dependent rate constants of the order of magnitude of 10 2 s −1 5−10 K above the zero-entropy-production melting temperature. The advanced analysis of the melting behavior of polymer crystals isothermally grown at low melt supercooling allows one to draw conclusions about their (inherently) low thermodynamic stability.

Melting Kinetics of Superheated Polymer Crystals Examined by Isothermal and Nonisothermal Fast Scanning Calorimetry

“…The temperature dependence is stronger than linear, suggesting a kinetic barrier for melting. These results reconfirm our recent reports on isothermal melting kinetics, 28 which correspond to other prior results of the nonisothermal melting kinetics 6,18 and microscopic observations of isothermal crystal melting. 16 It is also noted that the obtained results in Figure 5 are not sensitive to the choice of starting time t 0 = 2 or 3 ms.…”

“…For the isothermal measurements in Figures 2−9 and 13, after isothermal (incomplete) melting at preset times t, the integrated heat of melting on subsequent heating at a fixed rate of 1000 K s −1 was examined. 28 The starting temperature of subsequent heating was set at T c . For the T c dependence in Figures 10−12, the real-time isothermal heat flow data during melting were examined in order to reduce the number of repetition cycles of crystallization and melting.…”

“…12,16 However, in the case of a synthetic polymer having an inherently broad melting temperature range, it is not easy to evaluate the dependence from isothermal measurements by calorimetry at different temperatures; it is noted that the isothermal melting behaviors of ultrahigh-molecular-weight PE seem to be exceptional in this respect. 2,26,27 In a recent report, 28 for poly(butylene succinate) (PBS) with a narrow melting temperature range, isothermal melting was measured after a fast temperature jump in an FSC. We used the melting end time as the characteristic time to describe the isothermal melting kinetics and examined the temperature dependence.…”

Insertion‐Crystallization‐Induced Low‐Temperature Annealing Peaks in Melt‐Crystallized Poly(l‐Lactic Acid)

“…Though using an even higher heating rate is advantageous for increasing the signal/noise ratio, it is detrimental regarding thermal‐lag effects, quantified elsewhere for the used instrument. [ 67–69 ] Data obtained on samples annealed at 140 °C for less than about 100 s reveal on subsequent heating the glass transition at around 68 °C, being slightly higher than typically observed in conventional differential scanning calorimetry (DSC) experiments, [ 70,71 ] due the higher heating rate, [ 72–74 ] and no further events. Annealing the sample longer than about 100 s permits crystallization as indicated with the melting event at temperatures close to 200 °C and the decrease of the heat‐capacity step at T g due to the reduced liquid fraction.…”

Bulk Enthalpy of Melting of Poly (l‐lactic acid) (PLLA) Determined by Fast Scanning Chip Calorimetry

“…These sections were afterward reduced in their lateral size to 50-100 μm, using a stereomicroscope and a scalpel. Such samples had a mass of ≈100 ng, assuring negligible thermal lag, as analyzed by the heating ratedependence of T g , [38,39] and sufficient signal-to-noise ratio on cooling and heating at a rate of 1000 K s −1 . Before loading the sample onto the UFS 1 chip sensor, the latter was conditioned and temperature-corrected according to the instrument specifications.…”