聚合物流变参数拟合及主曲线的生成
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摘要
聚合物流变学有助于了解聚合物的加工特性,确定适宜的加工条件,制取最佳性能的制品;借助流变学的概念和方法,可以研究与聚合物流变性质有关的一些分子参数,为合成具有预期性能的聚合物提供理论依据。
     围绕聚合物熔体流变参数拟合及主曲线的生成,本文主要开展了如下工作:
     (1)将近百种材料不同温度下的剪切速率~粘度数据对Cross—Arrhenius粘度模型进行最小二乘拟合,计算其中的参数B、T_b、τ~*和n。分子量不同结构相似的聚合物有相同的温度依赖性,根据时温等效原理生成与温度无关的(η/η_0~η_0(?))主曲线,结果表明ABS、SAN、PS、PP、HIPS、HDPE、POM迭加效果较好。
     (2)给出了基于熔融指数的(η·MFI~(?)/MFI)主曲线生成方法。用熔融指数仪测定三个牌号PP不同温度、不同载荷下的熔融指数,生成(η·MFI~(?)/MFI)主曲线,该曲线与温度、聚合物等级无关。利用主曲线可计算材料一定温度、一定剪切速率下的粘度,该方法能满足工程计算和模具CAE分析的精度要求,有一定的实用性。克服了由于η_0不易获得,(η/η_0~η_0(?))主曲线使用不方便的缺点。
     (3)给出了由动态数据(频率~损耗角正切、复合模量~损耗角正切)拟合水平活化能及垂直活化能,计算水平移动因子α_T垂直移动因子b_T,从而对不同温度下的动态数据进行水平、垂直移动生成主曲线的方法。该方法有较广泛的适用性,由动态数据计算的结果可应用到稳态数据的迭加,生成的主曲线效果比较理想。
     (4)将动态频率扫描实验的储能模量和耗能模量数据,用线性、正则、非线性最小二乘法拟合材料的离散松弛时间谱。并讨论不同松弛单元数目、松弛时间范围、测试温度对松弛谱的影响。
Rheology helps to understand the polymer's good processing properties, make the proper processing conditions and fabricate the best goods. Rheology is the theoretic foundation to get the desired goods through the rheological parameters.
    The main work of this paper is as following about the polymer rheological parameters fitting and master curve:
    (1) Calculate the parameters (B, Tb, τ~* and n) of about one hundred kinds of materials by data fitting. Polymers with similar structure and different molecular weight have the same dependence on temperature. Get the master curve on the basis of time-temperature superposition, and master curves of ABS, SAN, PS, PP, HIPS, HDPE, POM are good from the experiment results
    (2) Draw the master curve η-MFI - ηIMFI. Get the material's MFI at different temperature and loading from experiment for master curve. The master curve has nothing to do with temperature and grades. Although there is error in calculation from master curve, the curve is ideal for engineering calculation. It overcome the fault that the zero viscosity is difficult to get for (η0 ) master curve.
    (3) Get dynamic data at different temperature and frequency with ARES which is strain-controlled rotational rheometer. Respectively extract the horizontal and vertical activation energy from loss tangent vs. frequency and loss tangent vs. complex modulus data, calculate the horizontal and vertical shift factors, then there is a good master curve not only for dynamic data but also for steady data.
    (4) The discrete relaxation time spectrum is calculated from the store modulus and the loss modulus which are got from the dynamic frequency test. In the calculating process the results are get from different relaxation numbers of the Maxwell unit, relaxation time ranges, temperatures and different materials.
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