Mechanochemistry: An Efficient Way to Recycle Thermoset Polyurethanes

Area of Science:

• Materials Science
• Polymer Chemistry
• Sustainable Engineering

Background:

• Thermosetting polyurethane (PU) plastics pose recycling challenges due to their rigid cross-linked structure.
• Effective methods for degrading and repurposing waste thermosetting PU are crucial for sustainability.

Purpose of the Study:

• To develop and optimize a mechanochemical recycling process for waste thermosetting polyurethane plastics.
• To characterize the recycled material and evaluate the properties of composite plates made from it.

Main Methods:

• Mechanochemical degradation using an adjustable speed test machine with optimized crushing parameters (speed, time, feed amount) determined via orthogonal experimental design.
• Characterization of degraded thermosetting PU using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD).
• Preparation of recycled composite plates via hot pressing, incorporating thermoplastic resin, followed by mechanical and thermal insulation property testing.

Main Results:

• Mechanochemical action successfully destroyed the cross-linked molecular structure of thermosetting PU, decomposing methyl and aldehyde groups.
• A reactive and plastic recycled powder was generated, enhancing regeneration ability.
• Recycled composite plates exhibited improved mechanical properties (max tensile strength 9.913 MPa) and formability but reduced thermal insulation (min thermal conductivity 0.056 W/m·K).

Conclusions:

• The mechanochemical method effectively recycles thermosetting polyurethane plastics by breaking down the polymer network.
• The addition of thermoplastic resin enhances the mechanical performance and processability of the recycled composite plates.
• This study presents a viable approach for the valorization of waste thermosetting polyurethane materials.