Synthesis and characterization of cathodic electrodeposition coatings based on octadecyl-modified cationic waterborne po
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Synthesis and characterization of cathodic electrodeposition coatings based on octadecyl-modified cationic waterborne polyurethanes Xiaoling He, Yu Zhang, Jingwei He, Fang Liu
Ó American Coatings Association 2020 Abstract Aimed at increasing the hydrophobicity of cathodic electrodeposition (CED) coatings based on cationic waterborne polyurethanes (WPUs), a series of cationic WPUs with hydrophobic octadecyl side chains were successfully synthesized by introducing 1-monostearoyl-rac-glycerol as a diol chain extender. ATRFTIR spectra and SEM images showed the degree of phase separation between soft segments and hard segments of cationic WPUs clearly increased by incorporating octadecyl groups. The water contact angle and water absorption studies showed that the water-resistance property of modified CED coatings was obviously enhanced because of the incorporation of a low surface energy unit and the formation of a more sophisticated surface induced by hydrogen bonds. The International Standardization test of paints and varnishes revealed that the CED films possessed excellent hardness, adhesion, flexibility, and impact resistance. Optical transmittance tests showed that the sample films possessed excellent optical transmittance of about 90%, and meanwhile, the thermostability of the film was promoted. Keywords Cathodic electrodeposition coatings, Cationic waterborne polyurethanes, Octadecyl side chains, Synthesis, Characterization
Introduction Corrosion prevention of metallic substrates is an ongoing research topic for the use of metals in outdoor applications.1 Organic protective coatings are comX. He, Y. Zhang, J. He, F. Liu (&) School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, Guangdong, China e-mail: [email protected]
monly used as a dense barrier to postpone the contact of moisture and oxygen from the surrounding environment with the metal surface. To apply organic coatings on the metal surface, electrophoretic deposition method exhibits obvious advantages (e.g., electric automated controlled character, higher utilization of paint, lower pollution, as well as the ability to coat recessed areas of complex workpiece shapes) compared with dipped or sprayed coatings.2,3 Under the applied external electric field, the charged particles migrate and deposit on oppositely charged electrodes to form a uniform film either by cathodic or anodic processes.4,5 Whereas, considering the drawbacks of substrate dissolution and film discoloration caused by anodic process, cathodic electrodeposition (CED) should be a more appropriate process.6 Cationic waterborne polyurethanes (WPUs) are a promising and well-researched polymer system for the CED coatings. Numerous attempts using modified inorganic nanoparticles and curing processes have been made to improve the corrosion resistance of CED coatings.7–14 Incorporation of zinc oxide nanoparticles into the cationic WPUs could significantly enhance corrosion resistance of the CED coatings due to the improvement of stability of UV radiatio
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