Fast Upcycling of Poly(ethylene terephthalate) into Catalyst-Free Vitrimers

Abstract

We reported a catalyst-free technique to fabricate transesterification-based poly(ethylene terephthalate) (PET) vitrimers via melt reacting PET with N,N′-tetraglycidyldiaminodiphenyl methane (TGDDM) in several minutes. We investigated the effect of TGDDM content on the reaction mechanism and chemical structure of the final products in detail. At low TGDDM content (≤0.5 wt %), branched thermoplastic PET was obtained by the chain-extension reaction between carboxyl groups of PET and epoxy groups of TGDDM. At medium TGDDM content (0.7−1.0 wt %), PET vitrimers with relatively low cross-link density were achieved through the cross-linking reaction between original carboxyl plus hydroxyl groups of PET and epoxy groups of TGDDM. At high TGDDM content (1.2−2.0 wt %), soluble chain-extended products were first formed through reacting original carboxyl and hydroxyl groups of PET with part of epoxy groups of TGDDM, and PET vitrimers were then obtained after the excess epoxy groups were consumed by the newly formed functional groups, which were generated by thermal decomposition of ester groups of PET under catalyzation of tertiary amines of TGDDM moieties. The cross-linked network structure endowed the PET vitrimers with enhanced heat resistance and creep resistance. The obtained PET vitrimers could relax stress rapidly and showed excellent processability and weldability, owing to the fast transesterification between hydroxyl and ester groups under catalyzation of internal tertiary amines. We believe that the facile fabrication technique showed great potentiality for upcycling of PET into vitrimers in large-scale production.

Upcycling Recycled Epoxy-Based Vitrimer for Enhancing Toughness of Poly(ethylene terephthalate)

“…Moreover, the copolymerization contributes to the crosslinking form in the structure, which may also limit crystallization as a result. [49,51,52] addition, the Tan δ curves reveal that the peak temperatures of samples containing the vitrimer are slightly higher than that of the neat PET. This result can be attributed to the crosslinking structure formed while incorporating the vitrimer, which limits the flexibility of the molecular chain.…”

“…Moreover, the high elongation value may be also attributed to the relatively lower crystallinity. [52] As a result, the effective toughness behaviors of the copolymers were observed. However, as the content of the vitrimer increased, the elongation values reduced gradually.…”

“…[51] Wu et al converted PET into catalyst-free vitrimers using N,N-tetraglycidyldiaminodiphenyl methane (TGDDM) via melt reaction; the dynamic crosslinked structure endowed the vitrimers with improved heat resistance, creep resistance, processability, and weldability. [52] To the best of our knowledge, no previous report discusses the potential high-value reuse pathway of a depolymerized vitrimer matrix from abandoned composites as a functionalized modifier via melt polymerization. In the present study, we aim to improve the toughness of the brittle PET material by introducing a degraded epoxy vitrimer collected from CFRP composites as a modifier.…”

Circularity in polymers: addressing performance and sustainability challenges using dynamic covalent chemistries

“…51,147 For example, PET was reactively extruded via an autocatalyzed NGP transesterication in the presence of a polyol crosslinker containing an adjacent tertiary amine. 51,52,192 The resultant PET vitrimer displayed enhanced creep resistance vs. the neat PET and was reprocessable to yield transparent and uniform products via compression molding, extrusion molding, and injection molding for 3 cycles with mechanical property (e.g., storage modulus) retention greater than 90%. 51,52,192 In contrast, as mentioned earlier, PET recycled through conventional reprocessing suffered from property deterioration (e.g., brittleness, decreased melt viscosity) aer two cycles of mechanical recycling and extrusion.…”

“…51,147 For example, PET was reactively extruded via an autocatalyzed NGP transesterification in the presence of a polyol crosslinker containing an adjacent tertiary amine. 51,52,192 The resultant PET vitrimer displayed enhanced creep resistance vs. the neat PET and was reprocessable to yield transparent and uniform products via compression molding, extrusion molding, and injection molding for 3 cycles with mechanical property ( e.g. , storage modulus) retention greater than 90%.…”