Solvent‐Free Upcycling Vitrimers through Digital Light Processing‐Based 3D Printing and Bond Exchange Reaction

Abstract

Vitrimers, a type of dynamically crosslinked polymers that combine the solventand heat-resistance of thermosets with the reprocessability of thermoplastics, offer a new solution to the problem of plastic pollution. However, the current recycling approaches of vitrimers greatly constrain the shapes of recycled vitrimers to simple geometries, thus significantly limiting the application scopes of recycled vitrimers. Here, a simple but universal method for upcycling vitrimer wastes is reported by developing a UV curable recycling (UVR) solution system. Conventional unprintable vitrimer powders can be mixed with the UVR solution, and the resulting mixture is compatible with digital light processing based 3D printing to fabricate 3D structures with high resolution (up to 20 µm) and high geometric complexity. Heat treatment triggers bond exchange reactions in the printed structures, and greatly enhances the mechanical properties. This method allows to cyclically print vitrimer wastes multiple times. Moreover, the UVR-vitrimer mixture solution can work as an adhesive to bond printed small parts together to build a larger and more complex structure which cannot be printed. The upcycling method reported in this work extends the application scope of recycled vitrimers and provide a practical solution to address environmental challenges associated with plastic pollution.

Photocurable Glycerol- and Vanillin-Based Resins for the Synthesis of Vitrimers

“…According to the data from the literature, the greater part of the resin prepared for vitrimer synthesis by optical 3D printing generally consists of the monomer and the smaller part consists of the cross-linker. 15 Therefore, the resin 20D/80H with the lowest viscosity of 405 mPa·s and the highest amount of glycerol monomer HPPA was selected for further investigation of vitrimeric properties. Figure 2 b shows that the gelation of resin 20D/80H started at 2 s after resin irradiation, indicating a growth of the chain size and network formation, and the values of G ′, G ″, and η * increased immediately, reaching values of 13.55 MPa, 6.16 MPa, and 237.07 MPa·s, respectively.…”

“…The shrinkage of the resins containing the glycerol fragment was higher (11.5–14.5%) than the neat DGEVADMA resin (10.5%) because the lower viscosity and the t gel values had no influence since the gelation of all resins started after 2 s of irradiation. According to the data from the literature, the greater part of the resin prepared for vitrimer synthesis by optical 3D printing generally consists of the monomer and the smaller part consists of the cross-linker . Therefore, the resin 20D/80H with the lowest viscosity of 405 mPa·s and the highest amount of glycerol monomer HPPA was selected for further investigation of vitrimeric properties.…”

“…According to the data from the literature, the greater part of the resin prepared for vitrimer synthesis by optical 3D printing generally consists of the monomer and the smaller part consists of the crosslinker. 15 Therefore, the resin 20D/80H with the lowest S1. The intensity of the C�C group signal, which was present at 1636 cm −1 in the FT-IR spectra of DGEVADMA and HPPA, was reduced in the polymer spectrum.…”

“…Acrylate- and methacrylate-based resins are the most commonly used for 3D printing due to the high polymerization rate and commercially available monomers . Acrylate-based resins having hydroxyl and ester groups have been used to prepare vitrimers by optical 3D printing, which after the 3D printing process can undergo thermoactivated transesterification reactions. ,,− These vitrimers were reshapable, repairable, and recyclable, which contributed to alleviating the environmental challenges associated with the continuous increase in the consumption of 3D printing materials. The most commonly used monofunctional acrylates in the 3D printing of vitrimers are 2-hydroxy-2-phenoxypropyl acrylate (HPPA), as has hydroxyl and ester groups that are essential in the transesterification reactions, and benzene ring, which can increase thermal and mechanical properties.…”

One-shot transformation of ordinary polyesters into vitrimers: decomposition-triggered cross-linking and assistance of dynamic covalent bonds

“…11,12 In addition to reprocessability, vitrimers can exhibit various useful functions, such as recyclability, healability, and strong adhesion. 13–15 In the most recent situation, the vitrimer concept has been applied to bio-based materials 16–19 and advanced technology, such as 3D printers, 20,21 strain sensors, 22 and functional coatings. 23…”