Dynamic networks for recycling thermoset polymers
Methods for recycling thermoset polymers, particularly by changing them into dynamic networks with the use of an appropriate catalyst solution which transforms the thermoset polymer into a vitrimer-like composition. The methods include the step of swelling a crosslinked thermoset polymer in a solution including a catalyst, whereby the catalyst diffuses into the thermoset polymer, in particular into the thermoset network. Upon removal of the liquid portion of the solution, such as solvent, the catalyst facilitates the occurrence of exchange reactions at elevated temperatures, rendering the system a dynamic network. The vitrimerized composition having the thermoset polymer and catalyst is recyclable and processable and thus suitable for many end uses.
1. A method for producing a recyclable thermoset composition, comprising the steps of:
obtaining a crosslinked polymer;
dissolving a catalyst in a liquid to form a solution;
contacting the crosslinked polymer with the solution such that: (i) the crosslinked polymer swells without dissolving and (ii) the catalyst becomes infused in at least a portion of the crosslinked polymer; and
removing the liquid from the crosslinked polymer and solution.
2. The method according to claim 1 , wherein the crosslinked polymer comprises one or more of polyurethane and epoxy.
3. The method according to claim 2 , wherein the catalyst comprises tin(II) 2-ethylhexanoate or zinc acetylacetonate.
4. The method according to claim 3 , wherein the polyurethane is derived from a composition comprising polycaprolactone triol and 1,4-phenylene diisocyanate, and wherein the epoxy network is derived from diglycidyl ether of Bisphenol-A and a fatty acid.
5. The method according to claim 1 , wherein the contacting step comprises placing the crosslinked polymer in the solution.
6. The method according to claim 3 , wherein removing the liquid from the crosslinked polymer and solution comprises placing the crosslinked polymer in a vacuum oven at 80° C. for at least 12 hours.
7. The method according to claim 1 , further including the step of incorporating nanoparticles into a composition comprising the crosslinked polymer after the liquid is removed from the crosslinked polymer and solution.
8. The method according to claim 7 , wherein the nanoparticles are present in an amount from about 1 to about 30 parts by weight based on the total weight of the composition.
9. The method according to claim 8 , wherein the nanoparticles comprise carbon nanotubes.
10. The method according to claim 1 , wherein at least 10 wt. % of the solution consists of the catalyst.