From Waste PET to Highly Transparent Unsaturated Polyester Resins: A Cost-Effective Strategy without Specialty Monomers

Authors:
Publisher website
Google Scholar
Abstract
Chemical recycling of polyethylene terephthalate (PET) waste through glycolysis has emerged as an attractive strategy for producing value-added polymeric materials. However, conventional PET-derived unsaturated polyester resins (UPRs) often suffer from reduced optical transparency owing to structural heterogeneity, increased crystallinity, and side reactions that occur during depolymerization and repolymerization processes. Although transparent recycled polyesters can be obtained using specialty monomers such as 1,4-cyclohexanedimethanol (CHDM) and isosorbide, their high cost limits large-scale industrial implementation. In this work, a cost-effective approach was developed for the synthesis of transparent UPRs from waste PET. PET waste was glycolyzed for different reaction times (0.5 and 3 h) to produce hydroxyl-terminated oligomers, which were subsequently repolymerized and converted into unsaturated polyester resin. The influence of depolymerization duration on molecular structure, morphology, transparency, thermal stability, and processing characteristics was systematically investigated using FTIR, NMR, GPC, SEM, UV–vis spectroscopy, XRD, TGA, and DSC analyses. GPC results demonstrated successful depolymerization followed by molecular-weight recovery after polyesterification, while FTIR confirmed the incorporation of maleate unsaturation into the polymer backbone. XRD analysis revealed the predominantly amorphous nature of the synthesized resins, while UV–vis spectroscopy showed exceptionally high optical transparency, with transmittance values exceeding 99% at 550 nm. The cured resins also exhibited suitable viscosity, gel time, hardness, and heat distortion temperature for practical applications. The combined use of sterically hindered neopentyl glycol (NPG) and meta-substituted isophthalic acid (IPA) effectively suppressed crystallization and preserved optical clarity, enabling the production of highly transparent recycled UPRs without the use of expensive specialty monomers. This study demonstrates a sustainable and economically viable route for converting PET waste into transparent, high-performance polyester resins for coating, composite, and decorative applications.
Funding Information
  • University Grants Commission

This publication has 21 references indexed in Scilit: