Arrigo Rossella, Mascia Leno, Clarke Jane, Malucelli Giulio
Department of Applied Science and Technology and local INSTM Unit, Politecnico di Torino, Viale Teresa Michel 5, 15121 Alessandria, Italy.
Department of Materials, Loughborough University, Loughborough LE11 3TU, UK.
Materials (Basel). 2020 Feb 20;13(4):946. doi: 10.3390/ma13040946.
In this work, time-resolved mechanical spectroscopy (TRMS) was used to accurately characterize the rheological behavior of an epoxidized natural rubber (ENR) containing 25 mol% of epoxy groups. Conventional rheological tests are not suitable to characterize with accuracy the frequency-dependent linear viscoelastic behavior of materials, such as ENR, in a transient configurational state. For this reason, TRMS was used to determine the true rheological behavior of ENR, as well as to gain some insights into the changes of its macromolecular architecture under the dynamic conditions experienced during the measurements. The constructed master curves for the moduli revealed a gradual transition of the ENR rheological state from liquid-like to solid-like through the formation of an "elastic gel" throughout the bulk of the polymer. Furthermore, the evolution of the stress relaxation modulus revealed a slow relaxation mechanism, resulting from thermally activated reactions in the molten state attributed to the formation of crosslinks. Finally, the crosslink density evolution was estimated from the TRMS data and compared with results derived from equilibrium solvent-swelling measurements. These demonstrated the accuracy of the TRMS data in the prediction of the structural changes that can take place in polymers during processing.
在这项工作中，采用时间分辨力学光谱法（TRMS）精确表征了含有25摩尔%环氧基团的环氧化天然橡胶（ENR）的流变行为。传统的流变测试并不适合精确表征材料（如ENR）在瞬态构型状态下与频率相关的线性粘弹性行为。因此，TRMS被用于确定ENR的真实流变行为，并深入了解其在测量过程中所经历的动态条件下大分子结构的变化。构建的模量主曲线显示，通过在聚合物整体中形成“弹性凝胶”，ENR的流变状态从类液态逐渐转变为类固态。此外，应力松弛模量的演变揭示了一种缓慢的松弛机制，这是由熔融状态下热活化反应导致的交联形成所致。最后，根据TRMS数据估算了交联密度的演变，并与平衡溶剂溶胀测量结果进行了比较。这些结果证明了TRMS数据在预测聚合物加工过程中可能发生的结构变化方面的准确性。
