【摘要】 以IUPAC-LDPE熔体在150℃下详细的流变学表征实验和毛细管挤出实验为基础考察了该熔体在挤出实验中的滑动问题。根据相对滑动特性给出了判断相对滑动存在和计算相对滑动速度的方法.用Wagner模型,PSM模型和Osaki模型计算的表现剪切速率,在10s-1时的毛细管壁面剪切应力比毛细管挤出实验给出的应力值高出约15%-17%,这个结果意味着IUPAC-LDPE熔体在挤出实验中存在滑动现象.在表观剪切速率为0.1,1.0和10s-1时,挤出实验条件下的流动与根据在旋转流变仪上测定的流变特性用PSM模型计算的流动相比,它们之间存在的相对滑动速度分别为0.004,0.071和1.343mm/s.用Wagner模型和Osaki模型计算的相对滑动速度与PSM模型的结果相近.更多还原

【Abstract】 The question of slip in the IUPAC-LDPE melt extrusion for sample A was examined on the basis of the available extrusion experimental data and the detailed characterization of the rheological properties of the LDPE melt at 150℃. The methods of judging the existence of the relative slip and calculating the relative slip velocity were given in the paper in terms of the relative slip characteristic, which has been noticed in considerable amount of experimental researches on the occurrence of slip. The stress deviation among different experiments for the same material and temperature was used to identify whether there maybe exists the relative slip in the experiments. The precondition of applying the relative slip characteristic to judge the existence of slip is to get the reliable experimental results and to conduct the precise theoretical description between the shear stress and the shear rate. The results obtained by using the judgment method of relative slip demonstrate that slip may occur in the extrusion of the IUPAG-LDPE sample A melt through a long die. The direct manifestation of slip is that the true shear stress in the die wall calculated by using the theoretical models, including Wagner model, PSM model, and Osaki model, based on Laun’s rheological characterizations is approximately 15%-17% higher than that given in the extrusion experiments at the highest apparent shear rate of 10 s-1. Such magnitude of stress relative deviation noted for the IUPAC-LDPE melt can also be found in other investigations on slip. For example, the results of the stress relative deviations are in the range of about 7%-22% when Kalika and Denn (1987) and Hatzikiriakos and Dealy (1992) calculated the slip velocities occurring in their capillary extrusion experiments, which were obtained in the present paper in terms of their reported experimental data. No enough experimental evidence is available for illuminating that the stress deviation of 15%-17% is caused by errors in the experiments of the IUPAC-LDPE melt The slip velocities of the extrusion condition relative to the test condition of obtaining the rheological properties are 0.004, 0.071 and 1.343mm·s-1 at the apparent shear rates of 0.1. 1.0 and 10s-1, respectively, which were obtained by using PSM model. The magnitudes of the relative slip velocities obtained by using Wagner model and Osaki model have similar values. The ratios of the relative slip velocity over the mean velocity upstream at the highest rate of 10.0 s-1 are 35.8%, 31.7% and 30.2%. respectively, for PSM model, Wagner model with k=0.18 and Osaki model.更多还原