Ultrasonic decrosslinking of peroxide crosslinked HDPE in twin screw extrusion: Part II simulation and experiment

The simulation of ultrasonic decrosslinking of the peroxide crosslinked high‐density polyethylene (XHDPE) under static (no flow) condition and during flow in a twin‐screw extruder (TSE) is carried out. The simulation under the static condition provides dependences of the ultrasonic bubble oscillation dynamics, gel fraction, and crosslink density of the decrosslinked XHDPE on the ultrasonic amplitude, hydrostatic pressure, bubble volume fraction, and treatment time. For the decrosslinking using TSE, the simulation provides distributions of temperature, velocity, gel fraction, crosslink density, and pressure in the ultrasonic treatment zone on the ultrasonic amplitude. The simulation results of ultrasonic decrosslinking of XHDPE using TSE are compared with the experimental data. A quantitative agreement for the ultrasonic power consumption is achieved using assigned values of the initial bubble radius and volume fraction. Only a qualitative agreement on the dependence of gel fraction and crosslink density on the ultrasonic amplitude is achieved. The effect of the flow rate on the gel fraction and crosslink density of the ultrasonically decrosslinked XHDPE is overpredicted due to the absence of a suitable theory to correctly model the ultrasonic bubble nucleation. POLYM. ENG. SCI., 57:1047–1061, 2017. © 2016 Society of Plastics Engineers