The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China; Institute of Physics, University of Freiburg, 3 Hermann-Herder-Street, Freiburg 79104, Germany.
The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China.
Int J Biol Macromol. 2020 Mar 15;147:1301-1308. doi: 10.1016/j.ijbiomac.2019.09.256. Epub 2019 Nov 18.
Shear-induced crystallization plays a crucial role in the manufacturing process of polymers. In this work, crystallization kinetics of biosynthesized polyhydroxyalkanoates (PHA) under different shear conditions were systematically investigated by rheometers. First, rheological properties of PHA melts were performed at different temperature to obtain mastercurves via the time-temperature superposition principle at 170 °C as a reference temperature. Then the stretch relaxation time and corresponding critical shear rate at different temperatures for the flow regime transition were calculated via the discrete Maxwell relaxation time spectrum and Arrhenius equation. Finally, the influence of shear temperature (T), shear time (t) and shear rate (γ̇) on the crystallization process of PHA were discussed. The results showed the crystallization rate of PHA was improved significantly under high shear rate and long shear time. Interestingly, the t reached the minimum value when the γ̇ or the t was large enough, which reached around 450 s at isothermal crystallization condition of 100 °C. Moreover, the nucleation density for PHA increased by appx.100 times than that under quiescent conditions. Therefore, this work may provide a useful theoretical guidance on the shear-induced crystallization of PHA.
剪切诱导结晶在聚合物的制造过程中起着至关重要的作用。在这项工作中，通过流变仪系统地研究了生物合成聚羟基烷酸酯（PHA）在不同剪切条件下的结晶动力学。首先，在不同温度下进行 PHA 熔体的流变性能测试，通过时温叠加原理在 170°C 作为参考温度获得主曲线。然后，通过离散 Maxwell 松弛时间谱和 Arrhenius 方程计算了不同温度下流动状态转变的拉伸松弛时间和相应的临界剪切速率。最后，讨论了剪切温度（T）、剪切时间（t）和剪切速率（γ̇）对 PHA 结晶过程的影响。结果表明，在高剪切速率和长剪切时间下，PHA 的结晶速率显著提高。有趣的是，当 γ̇或 t 足够大时，t 达到最小值，在 100°C 的等温结晶条件下约为 450 s。此外，PHA 的成核密度比静止条件下提高了约 100 倍。因此，这项工作可能为 PHA 的剪切诱导结晶提供有用的理论指导。
