Rheological characterization of degradation and polycondensation of poly(ethylene terephthalate) melt in air and in nitrogen
Rheological characterization of degradation and polycondensation of poly(ethylene terephthalate) melt in air and in nitrogen
复制标题
聚对苯二甲酸乙二醇酯熔体在空气和氮气中的降解和缩聚的流变表征
DOI：
10.1063/1.4802616
复制
发表时间：
2013
影响因子：
5.9
通讯作者：
M. Wagner
中科院分区：
文献类型：
--
作者：
M. Kruse;V. H. Rolón;M. Wagner
研究了三种不同的基于对苯二甲酸二甲酯或对苯二甲酸的聚对苯二甲酸乙酯（PET）样品在流变表征过程中因热暴露引起的改变和突变。在280°C的熔融状态下进行了热稳定性和频率扫描实验，并研究了气氛（空气或氮气）的影响以及样品制备的影响（在流变仪的板之间直接熔融的颗粒与从压模板上切割的样品）。热稳定性测试揭示了在空气中测量的储存（G '）和损耗（G″）模量与在纯氮气氛中测量的完全不同的行为。在空气中测量的样品显示，由于热降解，两个模量都减少了，而由于缩聚，在氮中观察到意想不到的强烈增加。加载时间对试样流变特性已经产生了明显的影响，这种影响可以外推到加载时间为零时进行重构。分子结构的快速变化对频率扫描试验有显著影响。频率扫描是双向进行的，即首先将角频率从0.05 rad.s−1增加到500 rad.s−1，然后从500 rad.s−1降低到0.05 rad.s−1，反之亦然。这些试验证实了所施加的大气（空气或氮气）分别造成降解和凝结的影响。然而，除了这些主要的变化，即由于空气中的链断裂而导致的分子量降低和由于氮中的缩合反应而导致的分子量增加外，还检测到相反的影响。这清楚地表明了双峰分子量分布的形成，其存在得到了压缩模压板流变特性的支持，发现压缩模压板表现出更多的降解，但也增强了双峰性。研究了三种不同的基于对苯二甲酸二甲酯或对苯二甲酸的聚对苯二甲酸乙酯（PET）样品在流变表征过程中因热暴露引起的改变和突变。在280°C的熔融状态下进行了热稳定性和频率扫描实验，并研究了气氛（空气或氮气）的影响以及样品制备的影响（在流变仪的板之间直接熔融的颗粒与从压模板上切割的样品）。热稳定性测试揭示了在空气中测量的储存（G '）和损耗（G″）模量与在纯氮气氛中测量的完全不同的行为。在空气中测量的样品显示，由于热降解，两个模量都减少了，而由于缩聚，在氮中观察到意想不到的强烈增加。试样的加载时间已经引起了流变学性质的显著变化。
Three different poly(ethylene terephthalate) (PET) samples based on dimethyl terephthalate or terephthalic acid, were studied in terms of alterations and mutations caused by thermal exposure during rheological characterization. Thermal stability and frequency sweep experiments were performed in the melt state at a temperature of 280°C, and the influence of the atmosphere (air or nitrogen) as well as the effect of sample preparation (pellets molten directly between the plates of the rheometer vs. samples cut from compression molded sheets) were studied. Thermal stability tests reveal a fundamentally different behavior of the storage (G′) and the loss (G″) modulus for measurements in air compared to measurements in a pure nitrogen atmosphere. Samples measured in air show a decrease of both moduli due to thermal degradation, while an unexpected strong increase was observed in nitrogen due to polycondensation. The loading time of the samples caused already a significant change of the rheological properties, which could be reconstructed by extrapolation to zero loading time. Frequency sweep test were significantly affected by the rapid changes of the molecular structure. Frequency sweeps were conducted bidirectional, i.e. by first increasing the angular frequency from 0.05 rad.s−1 to 500 rad.s−1, which was then followed by a decrease from 500 rad.s−1 to 0.05 rad.s−1, and vice versa. These tests confirm the effects of the atmosphere applied, air or nitrogen, causing degradation and condensation, respectively. However, besides these dominating alterations, i.e. reduction of the molecular weight due to chain scission in air and increase of the molecular weight due to condensation reactions in nitrogen, also the opposite effects were detected. This indicates clearly the formation of a bimodal molecular weight distribution whose existence was supported by the rheological characterization of compression molded plates, which were found to show more degradation but also enhanced bimodality.Three different poly(ethylene terephthalate) (PET) samples based on dimethyl terephthalate or terephthalic acid, were studied in terms of alterations and mutations caused by thermal exposure during rheological characterization. Thermal stability and frequency sweep experiments were performed in the melt state at a temperature of 280°C, and the influence of the atmosphere (air or nitrogen) as well as the effect of sample preparation (pellets molten directly between the plates of the rheometer vs. samples cut from compression molded sheets) were studied. Thermal stability tests reveal a fundamentally different behavior of the storage (G′) and the loss (G″) modulus for measurements in air compared to measurements in a pure nitrogen atmosphere. Samples measured in air show a decrease of both moduli due to thermal degradation, while an unexpected strong increase was observed in nitrogen due to polycondensation. The loading time of the samples caused already a significant change of the rheological properties, w...