| Summary: | 碩士 === 義守大學 === 化學工程學系暨生物技術與化學工程研究所 === 103 === The purpose of this research is to study the corrosion protection effectiveness of waterborne polyurethane (WPU) coatings modified with a silane, nano-SiO2 particles and a crosslinking agent on galvanized steel sheets.
In the first part, 3-aminopropyltrimethoxysilane (APTMS), was used to bind the WPU particles and the metal substrate by reacting simultaneously with the COOH moiety of WPU and the pedant OH group on metal surface. The silane was used to promote the adhesion between the organic polymer and the inorganic galvanized steel sheet. The coatings were dried at room temperature and then cured at a high temperature. The coatings with various amounts of APTMS were then subjected to a series of corrosion protection tests.
In the second part, additional nano-SiO2 particles were added to the WPU/APTMS mixtures. SiO2 particles were reported in many papers to be able to improve moisture resistance, hardness and abrasion resistance of WPU. SiO2 particles were added after mixing WPU with APTMS. The fabrication steps and tests were similar to those for WPU/TMPMA mixtures.
In the third part, a carbodiimide crosslinker, XL-29SE, was further added into the WPU/APTMS/SiO2 mixtures. The crosslinker was to promote the crosslink density to further improve moisture resistance, abrasion resistance, adhesion and solvent resistance. The fabrication steps and tests were similar to those for the above mixtures.
The gel content results show that the highest gel content value reaches 46.7% at the highest APTMS dosage, the value increases to 60.7% with the further addition of SiO2, then the value further increases to 62% with the further addition of XL-29SE. The pencil hardness value for the WPU coating is 6B, it increases to HB with the addition of APTMS, it further increases to H with the addition of SiO2 and/or XL-29SE. In the aqueous copper sulfate solution drop tests, the penetration time is 25 min for the WPU/APTMS coating, it improves to 30 min for the WPU/APTMS/SiO2 coating, it further improves to 35 min for the WPU/APTMS/SiO2/XL-29SE coating. In the contact angle tests, the value is 70.8° for WPU, 75.1° for WPU/APTMS, 77.2° for WPU/APTMS/SiO2 and 78.4° for WPU/APTMS/SiO2/XL-29SE. The salt spray tests show that the surface of WPU-coated sheet deteriorate after 24h, while the surfaces of WPU/APTMS- and WPU/APTMS/SiO2-coated sheets show little sign of deterioration after 72h.
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