超声波速表征聚合物熔体黏度的方法

Viscosity of Polymer Melts Characterized by Ultrasonic Wave

应用S-S状态方程和笔者前文的比容与超声波声速关系,建立自由体积与超声波声速关系。进而应用Doolittle方程中黏度和自由体积关系建立了黏度和超声波声速之间定量模型。将实验拟合的参数值代入声速-自由体积模型计算黏度,计算值与实验值基本符合,说明模型有较好的适用性。进一步直接拟合声速-黏度试验曲线,获得了幂律函数模型。这2个模型为超声波在线检测熔体黏度提供了条件。在不同剪切应力下,测试聚丙烯(PP)、聚乙烯(HDPE)和聚苯乙烯(PS)的热膨胀系数(αf)及声速温度系数(kv)。随剪切应力增大,不同聚合物的αf和kv上升趋势不相同(HDPE>PP>PS)。

Simha-Somcynsky （S-S） state equation was combined with specific volume-ultrasonic velocity relationship to develop free volume-ultrasonic velocity equation, which was further coupled with modified Doolittle equation to establish viscosity-ultrasonic velocity model. Free volume from PVT data and the tested ultrasonic velocity were used in this model to calculate viscosity. The agreement between predicted value and experimental data confirms such rationality of the model. Fitting the experimental data suggests one power law model between viscosity- ultrasonic velocity. These models provide a basis for on-line measuring viscosity by ultrasonic wave. Thermal expansion coefficient （af） and ultrasonic velocity- temperature coefficient （kv） were obtained from the process equations for melts of PP, HDPE and PS with different shear stress. Increasing of af and kv with shear stress exhibits a different tendency for different polymers （HDPE 〉 PP 〉 PS）.