Polyurethane Vitrimerization for Recyclable Thermoset Reprocessing
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Solution Overview
Problem
The recycling of polyurethane (PU) thermosets is limited due to their permanent crosslinked structure, leading to inefficient mechanical and chemical recycling methods that result in decreased mechanical properties and high energy consumption.
Innovation Solution
The use of organocatalysts like triazabicyclodecene (TBD) in a vitrimerization process to convert the permanent crosslinked structure of PU thermoset foam into a dynamic network through a carbamate exchange reaction, allowing for reprocessing without loss of mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mechanical recycling is used to crush PU thermoset waste, then the material can be reused as filler, but the mechanical properties decrease and processing becomes difficult due to increased viscosity
Solution Approach 1:
The patent changes the chemical parameter of the crosslinked structure by introducing dynamic covalent bonds that can exchange and rearrange. This transforms the permanent crosslinked structure into a dynamic network that allows reprocessing while maintaining mechanical properties, resolving the contradiction between recyclability and strength retention
Solution Approach 2:
The patent introduces dynamic covalent bonds that enable the crosslinked network to reconfigure and flow under stress. This dynamic behavior allows the material to be reprocessed like thermoplastics while maintaining the crosslinked structure's mechanical advantages, eliminating the need to compromise strength for recyclability
2Productivity
If chemical degradation via catalyzed glycolysis is used to recycle PU thermosets, then the material can be converted into polyols or small molecules, but the process has low efficiency and high energy requirements
Solution Approach 1:
The patent changes the chemical reactivity parameter by incorporating dynamic covalent bonds that can exchange at moderate temperatures. This allows the recycling process to proceed at lower temperatures and with higher efficiency compared to conventional glycolysis, reducing energy consumption while improving recycling efficiency
Solution Approach 2:
The patent uses catalysts as intermediaries to facilitate the exchange reactions of dynamic covalent bonds. These catalysts enable the recycling process to proceed under milder conditions with lower energy input, resolving the contradiction between recycling efficiency and energy consumption
3Productivity
If solvents are used to dissolve catalysts for inducing swelling in thermoset, then the recycling process is expedited, but solvent handling and environmental concerns arise
Solution Approach 1:
The patent extracts and eliminates the solvent component from the recycling system by using solid catalysts that can be mechanically mixed with the ground thermoset. This removes the harmful environmental factor of solvent handling while maintaining the expedited recycling process through efficient solid-state catalysis
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The vitrimerized network retains high mechanical strength and can be reprocessed multiple times, with rapid stress relaxation at low temperatures, and can be foamed under pressure, eliminating the need for solvent use and reducing environmental impact.
Implementation Method 1
The topology rearrangement happens through the carbamate exchange reaction, mainly via a dissociative mechanism
Implementation Method 2
The vitrimerized network can rapidly relax the stress in 10 seconds at temperatures as low as 120° C.
Implementation Method 3
organocatalysts, such as triazabicyclodecene (TBD), can be used in a vitrimerization process to recycle and reprocess thermoset rigid PU foams
Data Source
AI summary
A vitrimerized polymer composition includes a polyurethane with partially broken down crosslinking ligands, a catalyst, and a dynamic recyclable network in which a portion of the catalyst forms ligands with a portion of the polyurethane.