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

Abstract

Please cite this article as: Huang K, Isayev AI, Comparison between decrosslinking of crosslinked high and low density polyethylenes via ultrasonically aided extrusion, Polymer (2015), AbstractAmong various polymer wastes, management of crosslinked plastics is a major environmental problem requiring a solution. Among various crosslinked plastics, recycling of crosslinked polyethylenes is of a great importance due to the presence of a three-dimensional network. To solve this problem, novel environmentally friendly technologies for decrosslinking of the crosslinked polymers are developed based on ultrasonically assisted single (SSE) and twin screw (TSE) extruders. In particular, decrosslinking of peroxide crosslinked high-density polyethylene (XHDPE) and low-density polyethylene (XLDPE) by means of an ultrasonic SSE and TSE is investigated. Barrel pressure, die pressure and ultrasonic power consumption during extrusion are recorded. Swelling, rheological, thermal analysis and tensile tests are used to elucidate the structure-property relationships of decrosslinked XHDPE and XLDPE. The frequency dependencies of the storage and loss moduli, complex viscosity and tangent loss of XHDPE, XLDPE and their decrosslinked networks are described by the post critical gel model with its parameters correlated with gel fraction and crosslink density. The dynamic, thermal and tensile properties of the decrosslinked XHDPE and XLDPE are greatly affected by the type of preferential bond breakage. It was found that the decrosslinking of XLDPE is more difficult than that of XHDPE. An analysis based on the Horikx function reveals a highly preferential breakage of crosslinks during decrosslinking of XHDPE. In contrast to decrosslinking of XHDPE, the presence of long-chain branching in XLDPE is found to lead to the breakage of its main chains during decrosslinking. An improvement and a reduction in mechanical properties of decrosslinked XHDPE and XLDPE are, respectively, observed in comparison with those of virgin XHDPE and XLDPE. Such differences in behavior are due to the occurrence of a highly preferential breakage of crosslinks in XHDPE and the breakage of main chains in XLDPE during ultrasonic decrosslinking. Graphic AbstractStress-strain curves of HDPE, LDPE, XHDPE and XLDPE (a) and decrosslinked XHDPE (b) and XLDPE (c) by SSE and TSE with and without ultrasonic treatment.

Ultrasonic treatment of polycarbonate/carbon nanotubes composites

“…A cylinder temperature of 330 °C and a mold temperature of 130 °C were used for HPC composites, and a cylinder temperature of 300 °C and a mold temperature of 110 °C were used for LPC composites. [32]. Higher power consumption indicated that more energy was transmitted to polymer melt.…”

A reactive extrusion process with the aid of ultrasound for preparing cross-linked polypropylene

“…In particular, at the frequency zone lower than 0.5 Hz, value of loss tangent of CPP was almost independent on frequency. By comparison with CPP‐0, CPP‐300 possessed lower loss tangent, demonstrating the effect of the ultrasound on formation of branching and crosslinked structure .…”

“…In particular, at the frequency zone lower than 0.5 Hz, value of loss tangent of CPP was almost independent on frequency. By comparison with CPP-0, CPP-300 possessed lower loss tangent, demonstrating the effect of the ultrasound on formation of branching and cross-linked structure [49,50]. Figure 5 shows the plots of complex viscosity, which depended on the molecular weight and structure, as a function of frequency for all samples at 2008C.…”

Mechanochemical modification of crosslinked low‐density polyethylene: Effect of solid‐state shear pulverization on crosslinks, branches, and chain lengths

“…[14][15][16] Efforts to handle XLLDPE waste in an environmentally responsible manner have been sparse. While earlier work focused on reducing its size for downcycling into a filler material, [15,17] more recent reports included batch pan-milling, [14,18,19] supercritical fluid-assisted reactions in batch and continuous modes, [16,20,21] and ultrasonic melt extrusion [22,23] to chemically or mechanochemically decompose the crosslinks. The development of LDPE vitrimers led to a material with reversible crosslinks.…”