For purpose of the simplicity, in the present study the viscoelasticity of XHDPE and decrosslinked XHDPE was described by the Lodge model :
However, the crystallization of XHDPE and decrosslinked XHDPE reduces the accessible temperature range of dynamic test leading to an insufficient experimental measurement to construct a master curve.
Therefore, only the relaxation processes of XHDPE and decrosslinked XHDPE in their rubbery plateau and transition region to the glassy state are of interest.
10c and 10d are auxiliary functions describing the relaxation process of XHDPE and decrosslinked XHDPE.
Swelling of XHDPE and decrosslinked XHDPE was performed by following ASTM D 2765, test method C.
A capillary rheometer (Rosand RH7, Malvern Instruments, UK) was used to measure the steady state shear viscosity of decrosslinked XHDPE at a temperature of 200[degrees]C using dies of a diameter of 1 mm and L/D ratio of 8, 16, and 24, respectively.
A stress-controlled Discover Hybrid Rheometer (DHR-2, TA Instruments, New Castle, DE) equipped with 25 mm parallel plates to perform the small amplitude oscillatory shear (SAOS) test of decrosslinked XHDPE at temperatures of 140[degrees]C, 150[degrees]C, and 160[degrees]C.
Figure 2 shows the gel fraction (a) and crosslink density (b) of the decrosslinked XHDPE obtained by ultrasonic TSE as a function of the ultrasonic amplitude at flow rates of 3.
The ultrasonic decrosslinking of XHDPE by means of SSE was performed at flow rates of 4.
The sheet of virgin HDPE and XHDPE and decrosslinked XHDPE were prepared by compression molding in a mold of dimensions of 34 X 16 X 0.
Swelling tests of the XHDPE and decrosslinked XHDPE were performed by following ASTM D 2765, test method C.
A field emission scanning electron microscope (JEOL-7401, Japan Electron Optics Laboratory, Japan) was used to investigate the morphology of cryofractured surfaces of the virgin HDPE, XHDPE, and decrosslinked XHDPE obtained by fracturing of tensile bar moldings in liquid nitrogen.