Single‐catalyst reactions from depolymerization to repolymerization: Transformation of polyethylene terephthalate to polyisocyanurate foam with deep eutectic solvents

Abstract

Polyisocyanurate (PIR) has been used as a flame retardant insulation material because of its improved thermal insulation and flame-retarding effects due to its cyclic structure with an isocyanate trimer group. When a deep eutectic solvent (DES) is used as a catalyst, PET glycolysis produces bis(2-hydroxyethyl terephthalate) (BHET) and its derivatives. These recycled polyols react with isocyanate to form PIR foam (PIRF) in the presence of a physical blowing agent. DES-based glycolysis is a low-energy process with a relatively low temperature and short reaction time. In this study, a potassium-based DES system was applied for the sequential depolymerization and repolymerization of waste PET into PIRFs. Potassium-based DESs were used as hydrogen bond acceptors (HBAs), and ethylene glycol (EG), glycerol, and urea were used as hydrogen bond donors (HBDs). The PIRF was obtained through one-pot depolymerization and repolymerization with a single-catalyst DES system. All DES catalyst systems effectively decomposed PET; the PET conversion efficiency reached 95% after 2 h reaction. The recycled PIR was more thermally stable (approximately 26.9% limiting oxygen index (LOI) and approximately 68.8 W/g heat release rate (HRR)). This paper presents an environmentally friendly and robust upcycling process for the transformation of waste PET into PIRF.

Polyurethane‐polyisocyanurate (PUR‐PIR) foams based on castor oil modified with tire rubber waste: Statistical‐based analysis

“…Alves et al 28 observed similar bands between 3600 and 3200 cm −1 referring to –OH, and urethane and urea absorptions at peaks of 1709 cm −1 and 1597 cm −1 . In addition, Lee and Jung 45 reported that the peaks of 1594–1595 cm −1 correspond to the elongation vibrations of the CC aromatic bonds of diphenyl methylense diisocyanate.…”

Depolymerization within a Circular Plastics System

“…181 Similarly Lee et al screened a range of potassium-based DESs for the depolymerization of PET and one-pot synthesis of polyisocyanurate foams which are used as flame-retardant insulation. 182 DESs have also been applied to catalyze PET hydrolysis and aminolysis. 183,184 Other efforts have used DESs on polyester/ cotton fibers.…”

“…Zhou et al prepared dioctyl terephthalate, an alternative to the commercial plasticizer dioctyl phthalate, by alcoholysis in 2-ethyl-1-hexanol . Similarly Lee et al screened a range of potassium-based DESs for the depolymerization of PET and one-pot synthesis of polyisocyanurate foams which are used as flame-retardant insulation …”

Use of Deep Eutectic Solvents in Plastic Depolymerization

“…Among these processes, the recent work by Lee and Jung emerged as a robust upcycling process for the transformation of waste PET into polyisocyanurate foam (PIRF), as reported in Scheme 12 [50].…”