Aldehyde-modified Alkyd Resins Based on Waste Poly(ethylene terephthalate) Prepared by in situ Reaction Method for Sustainable Versatile Coating Systems

Abstract

This study aims to develop novel aldehyde-alkyd systems for versatile coating applications from a four-component alkyd resin containing waste poly(ethylene terephthalate) (PET) using a sustainable approach. Post-consumer bottle flakes were depolymerized via a simultaneous hydrolysis-glycolysis reaction. PET-based and reference unmodified alkyd resins were synthesized with and without PET. In the PET-based alkyd formulation, the PET depolymerization product (DP) was used in place of the diol component of alkyd. To produce the modified alkyd resins, the aldehyde resin was incorporated into the reaction medium during the synthesis of the PET-based and reference alkyd resins. Thus, both unmodified and modified alkyds with and without PET were prepared for comparative analysis. The research focused on the effects of aldehyde resin usage and the presence of DP on the coating properties and thermal behavior of the modified alkyd films. The physical/chemical coating properties of both modified and unmodified resins were reasonably sufficient for applications. The hard films obtained from alkyds exhibited superior adhesion strength, excellent impact resistance, and high gloss. Moreover, they were unaffected by water and exhibited remarkable resistance to corrosive agents. Organic solvents did not adversely affect these films. All films demonstrated excellent performance in repeated environmental resistance tests simulating various climatic conditions. The coating and thermal properties of PET-based alkyd films were slightly superior to their reference counterparts due to the incorporation of DP, an oligomer mixture containing aromatic units. Furthermore, in situ aldehyde modification slightly increased alkali resistance and thermal stability and reduced gloss loss in PET-based alkyds.