Study and modeling of high-density polyethylene coalescence under the extrussion conditions

During the extrusion of thermoplastic particulates, the major problem is to adjust and optimize the experimental conditions of temperature and rotational speed of the screw, to decrease porosity defects, resulting from the coalescence of the polymer grains. In this work, a study of high-density polyethylene (HDPE) coalescence as a function of temperature and shear rate is conducted, with modeling of this phenomenon by the Bellehumeur model. The effect of applying a shearing force to get closer to the conditions of extrusion is also evaluated using the equations of Yao-Yuan Chang and Shi-Yow Lin, which represent the latest version of the changes to the Laplace equation. Results show that the coalescence changes as a function of time despite the slight increase in the shear rate between 1 to 7 s −1 , it tends clearly to reduce the rate of coalescence up to 60% and thus promotes deformation and rupture. In addition, the studied Bellehumeur modeling of coalescence reveals only a mild deviation respected to experimental data even the complicated measurement conditions.