Influences of material and processing conditions on the depolymerization speed of anhydride-cured epoxy during the solvent-assisted recycling

Abstract

Thermosetting polymers with permanent crosslinking networks have been intensively used in high-performance applications requiring thermal stability, chemical resistance, and structural integrity. However, they are extremely hard to be reprocessed and recycled using conventional techniques. The recently developed solvent-assisted recycling technique is shown to depolymerize and recycle thermoset wastes using low-toxic solvents and mild processing conditions. The macromolecular polymer chains can be cleaved at target covalent bonds on the chain backbone through bond exchange reactions with solvent molecules. In this study, the influences of various material and processing conditions on the network depolymerization speed are studied from both experimental and theoretical points of view. A diffusion-reaction chemomechanics modeling framework is defined to link the physical properties of organic solvent and microscale reaction kinetics to the overall depolymerization speed of thermosets at various material and processing parameters. The study reveals how the temperature, network crosslinking density, and physical properties of the solvent, in particular, the solvent diffusivity and solvent/polymer interactions would affect the depolymerization speed. It enhances our understanding of the underlying fundamentals of thermoset recycling using organic solvents, which provides valuable insights for industrials to optimize the recycling conditions and develop appropriate strategies for waste management. • Influencing mechanisms of various material and processing parameters are revealed. • A theory is defined to link solvent properties to the depolymerization speed. • There is an optical content of good solvent to maximize the depolymerization speed. • There are threshold values for solvent hydroxyl-hydrocarbon ratio and interaction parameters.