Ultrasonic decrosslinking of crosslinked high-density polyethylene: effect of degree of crosslinking

Abstract

Decrosslinking of peroxide crosslinked high-density polyethylene (XHDPE) of different degrees of crosslinking by means of an ultrasonic single-screw extruder (SSE) is investigated. Barrel pressure and ultrasonic power consumption during extrusion are recorded. Swelling tests, rheological tests, infrared spectroscopy, thermal analysis and tensile tests are used to elucidate the structure-property relationship of decrosslinked XHDPE. It was found that a more intensive rupture of the crosslinked network occurs in XHDPE of a higher degree of crosslinking. Analysis based on the Horikx function shows that the type of preferential bond breakage during decrosslinking of XHDPE of various degrees of crosslinking is not determined by the bond energy alone but is also influenced by structural characteristics of the network.The activation energy of viscous flow of sols extracted from various decrosslinked XHDPEs supports the analysis based on the Horikx function. The dynamic, thermal and tensile properties of the decrosslinked XHDPE are greatly affected by the type of preferential bond breakage. A significant improvement in the processability and mechanical properties of decrosslinked 2% peroxide cured XHDPE is achieved due to the occurrence of a highly preferential breakage of crosslinks during ultrasonic decrosslinking.

Comparison between decrosslinking of crosslinked high and low density polyethylenes via ultrasonically aided extrusion

“…As shown in Figure It is also seen from Figure 7 that the gel fraction and crosslink density of the decrosslinked XHDPE obtained from SSE and TSE are significantly lower than those of the decrosslinked XLDPE. The previous study on decrosslinking of XHDPE of different levels of crosslink density [17] showed that the lower gel fraction and crosslink density of the decrosslinked XHDPE can be obtained in XHDPE of lower crosslink density. Thus, the lower gel fraction and crosslink density of decrosslinked XHDPE than those of decrosslinked XLDPE cannot be explained in terms of the crosslink density alone.…”

“…A C C E P T E D ACCEPTED MANUSCRIPT 28 In our previous studies [14][15][16][17] Table 2. It is seen from Table 2 that the activation energies of the untreated and ultrasonically treated LDPE differ insignificantly.…”

“…However, a severe thermal degradation occurred due to significant ultrasonic energy dissipation in the ultrasonic treatment zone leading to inferior tensile properties of decrosslinked XHDPE. To overcome this problem, two novel ultrasonically aided extrusion systems with better controlled cooling of ultrasonic treatment zone are developed [13] and used to perform ultrasonic decrosslinking of XHDPE [14][15][16][17]. The effects of ultrasonic amplitude [14][15][16][17], flow rate [14,15], extruder type [15], screw design [16] and degree of crosslinking [17] on ultrasonic decrosslinking of XHDPE are studied.…”

Comparison between decrosslinking of crosslinked high and low density polyethylenes via ultrasonically aided extrusion

“…Also, the gel fraction and crosslink density of the decrosslinked XHDPE obtained from SSE and TSE are significantly lower than those of the decrosslinked XLDPE. The previous study on decrosslinking of XHDPE of different levels of crosslink density [12] showed that the lower gel fraction and crosslink density of the decrosslinked XHDPE can be obtained in XHDPE of lower crosslink density. Thus, the lower gel fraction and crosslink density of decrosslinked XHDPE than those of decrosslinked XLDPE cannot be explained in terms of the crosslink density alone.…”

“…The ultrasonically aided extrusion of XHDPE is studied including the effects of flow rate [8,9], extruder type [10], screw design [11] and degree of crosslinking [12]. It is found that the ultrasonically aided extrusion is a promising technology to obtain a decrosslinked XHDPE exhibiting good processibility and superior mechanical performance.…”