Upcycling of Polyethylene Terephthalate to Continuously Reprocessable Vitrimers through Reactive Extrusion

Abstract

Vitrimers are expected to combine features of thermosets and thermoplastics but their continuous reprocessing is still a challenge; poly­(ethylene terephthalate) (PET) has been widely used in our daily life, while its cross-linking upcycle contradicts with processability. Herein, we combined polyol with a tertiary amine structure and diepoxy to transform PET to continuously reprocessable vitrimers through an industrial twin-screw extruder. The cross-linking of PET was determined by swelling and rheology experiments, and the vitrimer feature was characterized by stress relaxation and oscillatory frequency sweep experiments. Creep resistance and mechanical properties of PET vitrimers were improved greatly relative to neat PET. Meanwhile, PET vitrimers exhibited excellent reprocessability via compression, extrusion, and injection molding suitable for industrial production. According to this work, any thermoplastics containing ester bonds should be able to be upgraded to vitrimers for additional advantages such as creep resistance, dimensional stability, insolubility, etc., without sacrificing the original processability.

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

“…Vitrimers were also produced from PET waste by a reactive mixing and extrusion method. [155] A polyol with a tertiary amine structure was used to catalyze the transesterification reaction and a diepoxy was used to crosslink the PET chain after incorporation of reactive groups through reactive extrusion.…”

Sustainability performance of polyethylene terephthalate, clarifying challenges and opportunities

“…An additional recent example of upcycling is described in J. Qiu, et al's paper discussing reprocessable vitrimers 81 . Therein they describe a method to melt blend PET with 2,2‐bis(hydroxymethyl)‐2,2′, 2″‐nitrilotriethanol, a polyol with a tertiary amine structure and used diepoxy (D.E.R.)…”

Sustainability of Synthetic Plastics: Considerations in Materials Life-Cycle Management

“…Additionally, one can incorporate triggerable chemistries to generate associative (vitrimer) or dissociative networks that theoretically can be re-formed numerous times without a loss in thermomechanical performance. 86 − 88 Yet still, the tradeoff between mechanical performance and recyclability is an important conundrum in vitrimer design. Long relaxation times at the recycling temperatures and creep/deformation at the application temperatures also prevent broader utility, although with proper material design the issue can sometimes be mitigated.…”