Alkyd resins (ARs) represent a significant development in synthetic polymers, being among the oldest ones and playing a crucial role in numerous applications, especially within the coating sector. The trend is moving towards replacing non-renewable resources in the production of ARs with bio-based alternatives, with the goal of creating more sustainable binder materials as part of the transition to a bioeconomy. 2,5-Furandicarboxylic acid (FDCA) serves as a promising biomass-derived “building block” to replace non-renewable petroleum-derived aromatic diacids and anhydrides in AR synthesis. Various vegetable oils, including sunflower seed (SFO) and linseed oils (LSO), were utilized along with pentaerythritol (P) and glycerol (G) as polyols. FTIR and ¹H NMR spectroscopies were conducted for the verification of alkyd structures. The synthesized ARs were assessed for their physico-chemical properties, including acid value, hydroxyl value, color, density, and viscosity. The performance of the resulting alkyd coatings, which are crucial for their commercial applications, was examined. Key factors such as drying time, hardness, adhesion, wettability, chemical and corrosion resistance, and UV stability were analyzed. All synthesized FDCA-based alkyd coatings demonstrate outstanding adhesion, good thermal stability up to 220 °C, and barrier properties for steel with |Z|_0.02Hz ~10⁶–10⁷ Ohm cm⁻², which render them suitable for the processing requirements of indoor coating applications. The higher temperature at 50% mass loss (T₅₀) for SFO-P (397 °C) and LSO-P (413 °C) as compared to SFO-G (380 °C) and LSO-G (394 °C) indicated greater resistance to thermal breakdown when pentaerythritol was used as a polyol. Replacing glycerol with pentaerythritol in FDCA-based ARs resulted in a viscosity increase of 1.2–2.4 times and an enhancement in hardness from 2H to 3H. FDCA-based ARs exhibited decreased tack-free time, enhanced thermomechanical properties, and similar hardness as compared to phthalic anhydride-based ARs, underscoring the potential of FDCA as a sustainable alternative to phthalic anhydride in the formulation of ARs, integrating a greater proportion of renewable components for wood coating applications.

Chemical recycling of polyethylene terephthalate (PET) with decomposition into monomers suitable for resynthesizing primary polymer is a critical task for achieving carbon neutrality in the polyester industry. This paper presents a study comparing PET depolymerization solvolysis in tetrahydrofuran medium using a series of metal octoates (Co, Mn, Zn, Ca, Ba, Li, Zr, Cu, Pb). The resulting terephthalic acid (TPA) was characterized using a combination of methods (¹H NMR, thermogravimetric analysis, differential scanning calorimetry, and Raman spectroscopy). In an aprotic tetrahydrofuran (THF) medium, a comparative performance of commercial metal octoates under fixed metal-mass loading was conducted for the first time: the leadership of Co (83.7%) and Pb (78.4%) is explained by the lability of their coordination sphere, while the anomalously low activity of Zr (17.5%) is associated with steric blocking of the metal active center. In the present work, the influence of technological parameters on the depolymerization process using the most active catalyst, cobalt octoate, was studied. It was found that increasing the reaction time from 1 to 6 h leads to an increase in PET conversion from 27% to ~85%, and in TPA yield from 14% to ~84%. A study of the influence of water content in the reaction mixture showed that increasing the water concentration to 20 wt.% intensifies hydrolysis, promoting an increase in the yield of TPA to ~80%; however, a further increase in the water content (up to 30 wt.%) does not lead to a significant change in the yield, which indicates the achievement of conditions providing the highest observed isolated TPA yield within the tested range for the reaction in this system. The obtained results create a scientific basis for the rational design of catalytic systems for the depolymerization of PET, adapted to the different qualities of secondary raw materials and the technological requirements of industrial chemical recycling.