Tzourtzouklis Ioannis, Kardasis Panagiotis, Papageorgiou George Z, Floudas George
Department οf Physics, University οf Ioannina, Ioannina 45110, Greece.
Department of Chemistry, University of Ioannina, Ioannina 45110, Greece.
Macromolecules. 2024 Oct 4;57(24):11395-11406. doi: 10.1021/acs.macromol.4c01962. eCollection 2024 Dec 24.
We report the pressure-temperature (-) phase diagram, the origin of the subglass dynamics, and the crystallization kinetics of the biobased polyester poly(ethylene 2,5-furanoate) (PEF), through dielectric spectroscopy (DS) measurements performed as a function of temperature and pressure. The phase diagram comprises four different "phases"; glass, quenched melt, crystalline, and normal melt. The cold crystallization temperature, , increases linearly with pressure (according to the Clausius-Clapeyron equation) as / ∼ 240 K·GPa and is accompanied by a small change in specific volume (Δ = 0.028 cm/g). This contrasts with the stronger dependence of the glass temperature, , with a pressure coefficient, / , of 383 K·GPa, typical of rigid polymers. With the application of pressure, we address the molecular origin of the subglass β-process through the apparent activation volume, a quantity accessible only by pressure experiments. Moreover, increasing pressure densifies the segmental process but blocks the β-process, with possible implications in the gas-barrier properties. The crystallization kinetics from the quenched melt to the cold-crystallized state was explored by thermodynamics (differential scanning calorimetry, DSC), dynamics (DS), and structure (via simultaneous X-ray scattering at small (SAXS) and wide (WAXS) angles) following different routes within the phase diagram. Interestingly, all probes followed the same sigmoidal kinetics (of the Avrami type) with comparable time scales. Inspection of the evolution of the dielectric strength for the different dynamic processes during isothermal crystallization (at = 402 K; = 0.1 MPa) revealed the absence of the (RAF) at the early stages of crystallization. This observation is in line with the proposed -an intermediate phase formed during crystallization in the absence of chain folding, as suggested by G. Strobl. Subsequent growth of the RAF followed the same Avrami kinetics as identified by the thermodynamic and structural probes. Shallow quenches within the - phase diagram identified experimental routes for keeping PEF in the metastable quenched amorphous state for long times.
我们通过作为温度和压力函数进行的介电谱（DS）测量，报告了生物基聚酯聚（2,5 - 呋喃二甲酸乙二酯）（PEF）的压力 - 温度（-）相图、亚玻璃动力学的起源以及结晶动力学。相图包含四个不同的“相”：玻璃态、淬火熔体态、晶态和正常熔体态。冷结晶温度(T_{cc})随压力线性增加（根据克劳修斯 - 克拉佩龙方程），(dT_{cc}/dP ∼ 240 K·GPa)，并且比容有小的变化（(\Delta v = 0.028 cm^3/g)）。这与玻璃化温度(T_g)对压力更强的依赖性形成对比，(T_g)的压力系数(dT_g/dP)为(383 K·GPa)，这是刚性聚合物的典型特征。通过表观活化体积研究了压力作用下亚玻璃β过程的分子起源，表观活化体积是一个只有通过压力实验才能获得的量。此外，压力增加使链段过程致密化，但阻碍了β过程，这可能对气体阻隔性能有影响。通过在相图内不同路径下的热力学（差示扫描量热法，DSC）、动力学（DS）和结构（通过小角（SAXS）和广角（WAXS）同步X射线散射）研究了从淬火熔体到冷结晶态的结晶动力学。有趣的是，所有探针都遵循相同的S形动力学（阿弗拉米类型），时间尺度相当。在等温结晶过程中（(T = 402 K)；(P = 0.1 MPa)）对不同动态过程的介电强度演变进行检查，发现在结晶早期不存在松弛活化峰（RAF）。这一观察结果与G. Strobl提出的 - 在没有链折叠的结晶过程中形成的中间相一致。随后RAF的生长遵循与热力学和结构探针确定的相同的阿弗拉米动力学。在 - 相图内的浅淬火确定了将PEF长时间保持在亚稳态淬火非晶态的实验路径。
