Organometal catalyst promoted Mechano-chemical depolymerization of post-consumer Polyethylene terephthalate to non-ortho phthalate plasticizer for PVC flexibility

Abstract

Plastic waste mismanagement poses a serious threat to the ecosystem and human beings. Depolymerization through Chemical recycling (Alcoholysis) is an emerging solution. Plastic waste particularly, PET has been depolymerized through an intensified reactor system to a non-ortho phthalate green plasticizer, dioctyl terephthalate (DOTP). Different catalysts were synthesized for effective conversion with butyl stannic acid (0.5 %) resulting in 100 % conversion and 90 % yield within 180 min at refluxing 2-ethyl hexanol conditions (185–190 °C) at 1:3 feed to solvent ratio. The intensified reactor configuration reduced the PET dissolution time to 30 min by overcoming the mass transfer limitations which otherwise take 120–180 min for reaction homogenization. Product purity, DOTP was characterized by ¹H NMR with an ester content of 99.20 % by mass, acid value 0.04 mg KOH/g, APHA (<5 %), and refractive index of 1.5110. A side product, terephthalic acid was formed during the product purification steps and was purified using glacial acetic acid as recrystallization media. The synthesized DOTP is further tested as a plasticizer with PVC resins in different parts per hundred (phr) to break its interstrand-dipole and soften it for specific applications. The plasticized material shows better thermal stability and more flexibility than pure PVC with a maximum tensile strength of 18.74 ± 0.4155 MPa for 33.3 phr. This work provides a sustainable pathway from a linear to a circular economy using an organometal catalyst for PET depolymerization.