Origin of mechanical stress and rising internal energy during fast uniaxial extension of SBR melts
Origin of mechanical stress and rising internal energy during fast uniaxial extension of SBR melts
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DOI：
10.1016/j.polymer.2017.07.041
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发表时间：
2017-08-25
期刊：
影响因子：
4.6
通讯作者：
Wang, Shi-Qing
中科院分区：
文献类型：
--
作者：
Lin, Panpan;Liu, Jianning;Wang, Shi-Qing
我们在单轴拉伸过程中对 SBR 熔体进行同步机械和基于红外热成像的温度测量，以描述观察到的机械响应的性质。利用热力学第一定律，我们评估了与延伸熔体温度上升相关的焓变 h(1)，估计了向周围环境的热损失，并得出结论：在绝热或等温延伸过程中，存在明显的非热焓累积 h(2) = (w - h(1) - q)。 h(2) 随着拉伸比 lambda 单调增加，直到不均匀拉伸或熔体破裂开始，这表明即使在部分链解缠结的情况下屈服后，快速熔体拉伸也基本上是弹性的。在高速率下，链缠结的锁定产生如此高水平的 h(2)，这在交联橡胶的延伸中很少见。当在等温条件下进行熔体延伸时，我们发现时间-温度叠加原理（TTS）无法预测 SBR 熔体在涉及三个温度的固定有效速率下的瞬态响应。 TTS 的失败表明，末端链动力学表现出与控制瞬态应力响应的局部节段动力学不同的温度依赖性。 (C) 2017 Elsevier Ltd. 保留所有权利。
We carry out simultaneous mechanical and IR-thermal-imaging based temperature measurements of SBR melts during uniaxial extension in order to delineate the nature of the observed mechanical responses. Using the first law of thermodynamics, we evaluate the enthalpy change h(1) associated with the temperature rise in the extending melt, estimate the heat loss to the surrounding, and conclude that there is an appreciable non-thermal enthalpic buildup h(2) = (w - h(1) - q) during either adiabatic or isothermal extension. The monotonic increase of h(2) with the stretching ratio lambda until the onset of inhomogeneous extension or melt rupture reveals that fast melt extension is largely elastic even after yielding in presence of partial chain disentanglement. At high rates, the lock-up of chain entanglement produces such a high level of h(2) that is rarely seen in extension of crosslinked rubbers. When melt extension is carried out under isothermal condition, we show that the time-temperature superposition principle (TTS) fails to predict the transient response of a SBR melt at a fixed effective rate involving three temperatures. The failure of the TTS suggests that the terminal chain dynamics show different temperature dependence from the local segmental dynamics that control the transient stress responses. (C) 2017 Elsevier Ltd. All rights reserved.