Ketone modification of alkyd synthesized from waste PET as a sustainable option: A comparative study of coating and thermal properties of alkyd–melamine–ketone resin systems

Abstract

This study aims to prepare alkyd–melamine–ketone combinations from short‐oil alkyd resins synthesized using coconut oil fatty acid and waste poly(ethylene terephthalate) (PET) intermediate (bis(2‐hydroxyethyl) terephthalate, BHET) for coating applications with a green technology approach. For this aim, waste PET flakes obtained from post‐consumer water bottles were depolymerized by the glycolysis reaction. Purified depolymerization intermediate (BHET) was incorporated into the formulation of the four‐component alkyd resin, completely instead of the diol. For comparison, reference alkyds without waste PET were also synthesized. Then, ketone modifications of alkyd resins were carried out using cyclohexanone formaldehyde (CHF) resin by blending method. For this, firstly, melamine formaldehyde (MF) resin was added to the alkyd resin at a ratio of 40% by weight to obtain alkyd–melamine formaldehyde (Alkyd–MF) resin. Then, ketone‐modified blends were prepared at ratios of Alkyd–MF/CHF of 80/20, 70/30, 60/40, and 50/50 by weight. The effect of using ketone (CHF) resin at different ratios and the presence of BHET on the coating properties and thermal behaviors of alkyd–ketone blend films were investigated. At the end of the study, high‐gloss (151–154 GU) and medium‐hard (71–120 König second) films exhibiting excellent adhesion (100%) were obtained from alkyd–ketone blends. In both the reference and PET‐based blend series, adding CHF resin to the alkyd–amino (Alkyd–MF) resin improved all physical coating properties. Moreover, with increasing CHF resin ratios, hardness, gloss, and abrasion properties increased in both series. Although acceptable and usable results have been obtained in all ratios of CHF resin (20%, 30%, 40%, and 50%), the optimum CHF resin ratio for each physical coating properties has changed depending on the desired properties and expectations. These blend films resisted corrosive chemicals such as concentrated alkali, acid, and salt solutions for 72 h without damage, and at the end of the 18 h not affected by water. Acetone, toluene, methanol, and ethyl acetate did not affect these films in any way. All films performed excellently in repeated environmental resistance testing over 10 cycles, simulating changing climate conditions. In the chemical coating tests, superior results were obtained with all CHF resin ratios. The thermal resistance of Alkyd–MF/CHF blend films was found to be quite high. The incorporation of CHF resin into the alkyd–amino (Alkyd–MF) resin improved thermal resistance, and as the amount of CHF resin increased the thermal stability increased in both blend series. Moreover, the thermal resistance of PET‐based blend films was higher than their counterparts in reference blends due to the use of long‐chain BHET having an aromatic unit.Highlights Alkyd–MF/CHF blends using alkyds with and without PET were prepared. Good physical/excellent chemical coating properties/high thermal resistance. Incorporation of CHF into Alkyd–MF improved coating/thermal properties. CHF significantly improved the individual alkali resistances of the alkyd. As CHF increased, physical coating properties/thermal resistance increased. The thermal stabilities of the PET‐based blend were even higher.