Viscosity curves of two commercial polymer melts: high density polyethylene (HDPE 5306J and 2300J) were studied by using a capillary rheometer with twin bores at different temperatures. It was found that the viscosity curves at different temperatures overlapped when the shear rate reached and exceeded a critical value. It was supposed to be high shear rate that caused orientation of the polymer chains along flow direction which weakened the random thermal motion of the polymer chains influenced by variation of the temperature. Various viscosity models were used to regress the viscosity curve of HDPE 2300J at 210 -C. The results showed that the Cross equation and Carreau equation fit the data well, the former was better than the latter. The power law equation fit the data well in the shear thinning zone only. The parameters Ai or A2 of Vinogradov—Malkin equation were prone to be negative or zero when used to regress the viscosity data. Based on the Vinogradov—Malkin equation a modified 3 — parameter — equation was proposed which fit the data fairly well.%用双筒毛细管流变仪研究了2种商用高密度聚乙烯熔体(HDPE 5306J和2300J)的黏度曲线,发现当剪切速率超过一个临界值后,不同温度下的黏度曲线发生重叠,而且分子量大的材料对应的临界剪切速率较小.分析认为高剪切速率导致分子链沿流动方向取向,这种效应减弱了由于温度变化对于分子链段无规则热运动的影响.应用各种黏度曲线经验模型对HDPE 5306J在210℃下的流动曲线进行了回归分析,其中Cross方程能够较好地拟合实验数据,Carreau方程次之,但方程更简单,幂律方程适于拟合剪切变稀区的实验数据,不适于拟合零剪切黏度区的实验曲线,普适V-M方程在拟合过程中A1或A2容易出现负值,而且方程复杂,在普适V-M方程基础上得到修正的方程式,参数减少为3个,而且拟合效果较好.
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