Although the performance of the polyurethane-acrylate composite emulsion is significantly better than that of a single emulsion, its hardness, water resistance, and chemical resistance still fall short of the requirements for high-grade waterborne wood coatings. To address these limitations, researchers at the College of Chemistry and Chemical Engineering, Hunan University, have incorporated epoxy resins into polyurethane-acrylate composite emulsions using both physical blending and chemical copolymerization methods. This resulted in the development of polyurethane-acrylate-epoxy resin composite emulsions (PUEA). The study focused on how the addition method and dosage of epoxy resins affect the properties of the emulsion and the resulting coating film.
The findings revealed that the inclusion of epoxy resins significantly improved the hardness, water resistance, and chemical resistance of the final coating. It was also found that an optimal epoxy resin mass fraction of 3 to 4% provided the best results. In recent years, many researchers have explored the complementary properties of polyurethane (PU) and polyacrylate (PA) emulsions, leading to the development of polyurethane-acrylic ester (PUA) composite emulsions. Building upon this research, the addition of epoxy resins to PUA systems led to the creation of epoxy-modified polyurethane-acrylate (PUEA) composite emulsions, which showed marked improvements in water resistance, hardness, and other key properties.
With growing environmental awareness, governments around the world have implemented strict regulations to limit volatile organic compounds (VOCs) in coatings. As a result, environmentally friendly coatings have become a major trend in the industry. Waterborne coatings are considered one of the most effective solutions for reducing VOC emissions and have seen rapid development in recent years. Currently, the main base materials for waterborne coatings include polyacrylate (PA) and polyurethane (PU) emulsions. While these materials offer advantages such as safety, non-flammability, and low toxicity, they each have their own limitations. PA emulsions often suffer from poor film-forming properties, abrasion resistance, and adhesion, while PU emulsions may exhibit issues with stability, self-thickening, and water resistance.
To overcome these challenges, researchers have combined the strengths of PU and PA emulsions through copolymerization, leading to the production of PUA composite emulsions. Although PUA has shown significant improvements in performance, it still faces issues like high water absorption and low hardness when used as a base material for waterborne wood coatings. To further enhance its properties, epoxy resins were introduced into the PUA system, resulting in the development of PUEA composite emulsions. Testing showed that the water absorption of the PUEA coating was significantly reduced, and the hardness, luster, and chemical resistance were all improved.
The preparation process involved two methods: chemical copolymerization and physical blending. Experimental materials included toluene diisocyanate (TDI-80), epoxy resin (CYD-012), polyether glycol (PPG-10), dimethylol propionic acid (DMPA), 1,4-butanediol (BDO), triethylamine (TEA), and ethylenediamine (EDA). Results indicated that the addition of epoxy resin greatly enhanced the stability of the PUEA emulsion. The optimal epoxy resin content was found to be between 3% and 4%, leading to smaller and more uniformly sized particles. The particle size of PUEA latex increased compared to PUE/MMA dispersion, but the distribution became more uniform.
In terms of thermal stability, PUEA emulsion performed better than PUE/MMA dispersion. Emulsions prepared via chemical copolymerization showed superior pencil hardness, gloss, water resistance, and chemical resistance compared to those made by physical blending. Therefore, the chemical copolymerization method was more effective in producing PUEA emulsions. Additionally, the PUEA emulsion containing epoxy resin exhibited improved purity and enhanced mechanical properties, particularly in water resistance, chemical resistance, and hardness. These improvements make PUEA a promising candidate for advanced waterborne wood coatings.
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