In recent years, there has been growing interest in exploring new and innovative ways to create sustainable and environmentally friendly paints. In collaboration with the Eindhoven University of Technology (TU/e) and a major player in the coating industry, PTG/e supported the development of an environmentally friendly way of generating polycarbonate coating resins by copolymerization of limonene oxide with carbon dioxide (CO2).
To explore more about this sustainable coating, let us first discuss some important aspects of powder coatings. Unlike conventional coatings like paints, which are films that are formed via the evaporation of a solvent, powder coatings typically are dry powders that are applied electrostatically and cured via temperature or with ultraviolet light and require no volatile components. Nowadays, these coatings are intensively used in industry to provide protection against aggressive environmental conditions and/or for decorative purposes. Some examples of powder-coated products can be seen in Figure 1. The binder or resin is the main constituent of a typical thermoset powder coating (TPC) and is the film-forming element of the product. It provides adhesion to a substrate, binds pigments and other additives together, and determines important properties such as durability, flexibility, and hardness. In addition, colors, additives, and fillers can be added to modify certain properties of the coating like gloss, opacity, and stability.
Figure 1: Examples of powder-coated applications which are applied for decorative and protective purposes, such as parts for the automotive industry and powder-coated metal objects like pipelines.
Several types of thermoset powders, derived from epoxies, acrylics, hydroxyls (polyester), and carboxyl(polyurethane) groups can be used in the synthesis of TPCs. Some of these types suffer from poor exterior durability or moderate chemical resistance. Therefore, an alternative could be a polycarbonate-based resin which is typically amorphous, and usually exhibits properties like high transparency and low UV absorption, particularly suitable for outdoor use. However, the downside of commercially synthesized polycarbonate is the use of phosgene (Cl2C=O), which is a highly toxic gas that requires serious environmental and safety considerations. The co-monomer bisphenol A (BPA) is also debated for its potential adverse health effects.
Limonene oxide is a potential biobased epoxide derived from limonene and could be a good alternative to phosgene / BPA. Limonene is a major component that can be found in the oil of citrus peels, like oranges. It is a colorless liquid that is often used as a flavoring agent in food manufacturing. Its abundance and its multiple functionalities make it an attractive, renewable building block for polymer synthesis. Via a chemical reaction that involves carbon dioxide (CO2), a fully recyclable poly(limonene carbonate) (PLC) can be synthesized, carrying functional groups that can be modified or crosslinked to introduce new functionalities such as antibacterial activity, hydrophilicity, and water solubility. This makes CO2, also known as the primary driver of climate change, a useful molecule that can be used as a monomer to create a sustainable polycarbonate powder coating. This pathway is shown schematically in Figure 2. As a result, this fully limonene-derived PLC has great potential as a TPC binder, which can deliver good exterior durability and chemical resistance. These two properties make this type of renewable binder a great alternative for the manufacturing of powder coatings, avoiding any concerning reactants.
Figure 2: Simplified overview that involves the reaction mechanism of a limonene-based coating. Here, first limonene is epoxidized to limonene oxide. The latter is used for the synthesis of poly(limonene carbonate) (PLC) in the presence of carbon dioxide. With the use of a crosslinking molecule (thiol-based) and radical initiator, under the influence of ultraviolet light, a crosslinked network (TEN) is formed via a thiol-ene reaction with the pendant isoprenyl groups of PLC and results in the formation of a thin layer on a particular surface.
Whether you’re looking to enhance material sustainability, develop new materials, or material research, our team has the knowledge, expertise, and state-of-the-art infrastructure to help you achieve your goals. And, with a large network within the TU/e, we’re able to tap into a wealth of knowledge and resources. Contact us to learn more about how we can help you!
For additional technical details about this topic, feel free to visit the main article via the following link: Limonene-derived polycarbonates as biobased UV-curable (powder) coating resins