Among the many environmental problems which mankind faces in the XXI century is the problem of environmental sustainability and management of the tremendous amount of generated polymer waste. Among various polymer wastes, management of crosslinked plastics is a major environmental problem requiring a solution. This study was specifically directed toward the creation of a new, environmentally friendly and science-based technology for the recycling of crosslinked plastics. Uncrosslinked thermoplastics can be easily reprocessed and reused. However, managing crosslinked plastics is a very challenging problem. This is due to the presence of a three-dimensional network, which prevents flow and shaping of crosslinked plastics upon heating and shearing. Our laboratory developed ultrasonic decrosslinking technology for recycling of the crosslinked high density polyethylene (XHDPE) of different levels of crosslink densities and crosslinked LDPE (XLDPE). This is done by using ultrasonically aided single-screw extruder (SSE) operating at a frequency of 20 kHz and twin- screw extruder (TSE) operating at a frequency of 40 kHz at different levels of ultrasonic energy [1]. The experimental studies on the ultrasonic decrosslinking of XHDPE and XLDPE have shown that the ultrasonic extrusion was capable to preferentially break crosslinks rather than main chains in XHDPE. Significant reduction of the extruder torque, die and barrel pressures with the ultrasonic amplitude was observed during decrosslinking of XHDPE and XLDPE. The specific ultrasonic energy decreased with the flow rate and increased with the ultrasonic amplitude, while die pressure increased with the flow rate and decreased with the ultrasonic amplitude [2-5]. Accordingly, application of ultrasonic treatment during extrusion enabled an increase of productivity.
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