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Sustainable multifunctional coating resins for scavenging applications

Final Report Summary - SUSCOAT (Sustainable multifunctional coating resins for scavenging applications)

The main research objective of the SUSCOAT project was to use the thiolactone chemistry platform developed in Ghent University to develop multifunctional polymer coatings and non-isocyanate polyurethane materials in collaboration with Dow Benelux B.V.

Development of multifunctional thiolactone building blocks and establishment of a general, efficient, sustainable synthetic route

New thiolactone building blocks were synthesized, providing different chemical functionalities in the molecules, enabling a variety of physical properties and post-processing modification.
Once a library of monomers was established, an optimization and generalization of the synthetic procedure was performed, leading to a generic, upscalable protocol. Of interest were the use of benign solvents, i.e. water and ethyl acetate, and the avoidance of the most hazardous chemicals or excesses of chemical compounds.
Another benefit of thiolactone chemistry proven within the SUSCOAT project is the implementability in established industrial materials. As alternative crosslinking method for polyurethanes, current advantages of different non-isocyanate PU formation processes are combined in novel polyurethane resins, which will facilitate the transition towards more sustainable consciousness in industry

Development of sustainable coatings using thiolactone chemistry

Sustainable multifunctional isocyanate-free polyurethane UV-cured coating resins were developed using the N-(allyloxy)carbonyl homocysteine thiolactone monomer. Different amine compounds were incorporated into the polymers by the aminolysis of the thiolactone group and the effect of the amine structure and the monomer:amine molar ratio on the coating properties was investigated. The two-step amine-thiol-ene conjugation was optimized for coating applications resulting in high conversion of functional groups. UV-initiated thiol-ene polymerization was used to prepare coatings in an energy-efficient manner and the use of thiol precursors excluded oxygen inhibition that can hinder photopolymerization of acrylates.

Properties of new thiolactone-based coatings

According to the results of the standard ASTM tests for coatings, thiolactone-based coatings with different functionalities maintained high impact resistance of 2 kg▪m and high transparency of 90% and low haze (<5%). The good transparency and low haze of the thiolactone-based coatings could be further utilized for optical applications, where additional functionalities could be easily incorporated (ex. antibacterial). Coatings with multifunctional amines and monomer:amine ratios >1 exhibited higher glass transition temperatures and greater pencil hardness, due to the cross-linking effect of the multifunctional amines. The screening of the new thiolactone-based coatings has established a foundation for the future development of multifunctional renewable coatings via thiolactone chemistry.

Application of thiolactone-based coatings for reduction of formaldehyde emissions

Thiolactone chemistry was used to prepare polymer coatings with amine functional groups that could trap formaldehyde emissions. Formaldehyde is an indoor air pollutant that can cause harmful health effects, such as respiratory irritation. Formaldehyde can be emitted from the adhesives used to produce particleboard products. A multifunctional polymer coating applied on products could prevent harmful emissions by acting as a barrier as well as chemically locking in pollutants via specialized functionalities. Formaldehyde readily reacts with amine groups, so amino-functionalized thiolactone-based coating is a promising approach for reducing emissions.

Results of the European standard formaldehyde release test by the flask method indicated that the thiolactone-based polymers with higher amine loadings resulted in a greater reduction in formaldehyde. Urea-formaldehyde adhesives were overcoated with scavenging polymers, which resulted in a significant reduction in formaldehyde emissions. Polymers were tested before and after exposure to formaldehyde, which confirmed that formaldehyde was bound to the polymers. In conclusion, thiolactone chemistry enables simple and efficient introduction of different functionalities into polymers, which could be further extended for the abatement of a variety of pollutants.