In waterborne bio-based anti-corrosion coatings, the compatibility between bio-based resins and inorganic fillers is a key factor affecting coating performance. Bio-based resins are typically derived from renewable resources such as vegetable oils, cashew nut shells, and lignin, offering advantages such as environmental friendliness and low VOC emissions. However, the polar groups in their molecular structure differ significantly from the surface properties of inorganic fillers, leading to insufficient compatibility and problems such as filler agglomeration and uneven dispersion, which in turn affect the coating's anti-corrosion performance, mechanical strength, and durability. Therefore, improving the compatibility between bio-based resins and inorganic fillers has become an important direction for enhancing the performance of waterborne bio-based anti-corrosion coatings.
Filler surface modification is one of the core methods to improve compatibility. Inorganic fillers, such as nano-silica, graphene oxide, and zinc powder, typically have hydrophilic surfaces, resulting in weak bonding with hydrophobic bio-based resins. Modifying the fillers with surface treatment agents such as silane coupling agents and titanate coupling agents can introduce organic functional groups onto the filler surface, enhancing its interfacial bonding with the resin. For example, the amino or epoxy groups in silane coupling agents can chemically react with the carboxyl or hydroxyl groups in bio-based resins to form chemical bonds, thereby significantly improving the dispersion stability of the filler. Furthermore, grafting polymer chains onto the filler surface is also an effective method; by introducing polymer chains with structures similar to the resin onto the filler surface, the compatibility between the two can be further enhanced.
The design of the resin molecular structure has a decisive influence on compatibility. Functional monomers, such as acrylates and epoxy groups, can be introduced into the molecular structure of bio-based resins to adjust their polarity to match the properties of the filler surface. For example, introducing hydroxypropyl methacrylate into cashew phenol-based epoxy resin can increase the polarity of the resin, making its interfacial bonding with inorganic fillers tighter. In addition, introducing fluorinated or silicon-containing monomers into resin segments through copolymerization can impart hydrophobicity to the resin, reducing the interfacial tension between the filler and the resin, thereby improving dispersibility. The design of core-shell emulsions is also an effective strategy for optimizing compatibility; by encapsulating the filler in a resin shell, stable composite particles can be formed, preventing filler agglomeration.
Optimizing process parameters is equally crucial for improving compatibility. During coating preparation, process conditions such as the order of filler addition, stirring speed, and dispersion time directly affect the filler's dispersion state. For example, high-speed shear dispersion technology can effectively break up filler agglomerates, ensuring uniform dispersion within the resin matrix. Furthermore, adjusting the coating's pH value can alter the surface charge properties of the filler, enhancing its electrostatic interaction with the resin and thus improving dispersion stability. During curing, controlling the curing temperature and time ensures the formation of a complete cross-linked network between the resin and filler, preventing compatibility issues caused by incomplete curing.
The selection and use of additives are important supplementary methods for improving compatibility. Dispersants, wetting agents, and other additives can reduce the surface tension of the coating, enhancing the wettability between the filler and resin, thereby improving dispersion. For example, polyether-modified siloxane dispersants can form an adsorption layer on the filler surface, creating a steric hindrance effect and preventing filler re-agglomeration. In addition, the use of leveling agents can optimize the surface morphology of the coating, reducing defects caused by uneven filler distribution and further improving the coating's corrosion resistance.
The introduction of composite technology offers new insights into improving compatibility. By combining inorganic and organic fillers, the advantages of both can be integrated to enhance the overall performance of the coating. For example, combining nano-silica with graphene can form a filler system with high barrier properties, while the conductivity of graphene enhances the cathodic protection of the coating. Furthermore, the blending modification of bio-based resins with waterborne polyurethanes, acrylates, and other resins can also improve coating performance through synergistic effects.
Environmental adaptability is a crucial indicator for evaluating the effectiveness of compatibility improvements. Waterborne bio-based anti-corrosion coatings need to maintain stable performance under various environmental conditions; therefore, the compatibility between fillers and resins must meet the requirements for use under different temperatures, humidity levels, and corrosive media. For example, in marine environments, coatings need to resist chloride ion penetration; the tight bonding between fillers and resins can effectively block the transport channels of corrosive media, thereby extending the coating's service life. Long-term weather resistance testing can verify the actual effectiveness of compatibility improvement measures, providing a basis for coating optimization.
