Continuous supercritical decrosslinking extrusion process for recycling of crosslinked polyethylene waste

Abstract

This work demonstrates that extrusion process can be used as a continuous reactor for the recycling of crosslinked polyethylene (XLPE) via supercritical methanol decrosslinking reaction. The multistage single screw extruder (L/D = 36, D = 40 mm) with methanol injection pump was customized for the continuous supercritical decrosslinking reaction. Reaction temperature was ranged from 360°C to 390°C. The amount of methanol was varied from 0 to 7 mL/min. The extruder provided the crosslinked polymers with the supercritical conditions of methanol during continuous process. The gel content of XLPE decreased with the increase in the reaction temperature and methanol content. Although XLPE experienced supercritical methanol for less than 2 min retention time in the continuous supercritical extruder, it was completely decrosslinked above 390°C at the methanol feeding rate of 7 mL/min. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41442.

Chemical Recycling of High-Molecular-Weight Organosilicon Compounds in Supercritical Fluids

“…The authors of Refs. [ 66 , 67 , 68 ] present various options for implementing a continuous process using extrusion technologies. The study [ 67 ] shows the possibility of efficient processing of silane-XLPE in sc 1-propanol on a pilot industrial plant, consisting of two extruders and providing a processing volume of 20 kg/h.…”

“…Baek and co-workers studied the kinetics of the selective de-crosslinking of silane-XLPE in sc alcohols in a batch process [ 69 ] and in a continuous process [ 68 , 70 , 71 ]. For example, in their Ref.…”

Selective Decomposition Process and Mechanism of Si–O–Si Cross-Linking Bonds in Silane Cross-Linked Polyethylene by Solid-State Shear Milling

“…Other studies had shown that XLPE could be pulverized into a fine powder and used as a polymer filler . Besides, XLPE waste could also be converted into oil or PE wax by thermal and catalytic splitting decomposition. , However, they had some disadvantages such as high energy consumption, high cost, and secondary pollution. , Interestingly, supercritical fluids including methanol and alcohol could be used to selectively break cross-linking points of XLPE to obtain materials with thermal processability. − Unfortunately, the critical temperature and pressure of supercritical fluids which were most easy to burn and explode were high and required specific equipment, making commercial applications of supercritical fluids expensive and dangerous. Therefore, it is important to develop an effective, clear, and low-cost method to recycle waste XLPE materials.…”

Recycling of crosslinked high‐density polyethylene through compression molding

“…One of the recycling methods, studied by the majority of these studies, was on decrosslinking of XHDPE and XLDPE followed by shaping using compression molding, injection molding, and extrusion. Prior to shaping, the crosslinked polyethylene was decrosslinked using solid‐state shearing (milling), melt state shearing, supercritical fluids such as water, methanol, propanol, ethanol, and ultrasonic aided melt state shearing . These studies were concerned with evaluating the efficiency of the decrosslinking process, while the three shaping processes, identified above, were used to manufacture test coupons for evaluation of tensile mechanical properties of coupons made with the decrosslinked polyethylene in comparison to those coupons manufactured with the crosslinkable polyethylene (virgin) or polyethylene without any initiator.…”