Laboratory MAPIEM, Université du Sud Toulon Var, Avenue Georges Pompidou - BP56, 83957, La Garde, France.
ACS Appl Mater Interfaces. 2013 Jul 24;5(14):6751-61. doi: 10.1021/am401689s. Epub 2013 Jul 3.
We describe the possibility of using γ-aminopropyltriethoxysilane (γ-APS) to increase the durability of epoxy powder coating/steel joints. The curing temperature of epoxy powder coatings is frequently above 200 °C, which is seen so far as a major limitation for the use of the heat-sensitive aminosilane coupling agent. Despite this limitation, we demonstrate that aminosilane is a competitive alternative to traditional chromate conversion to enhance the durability of epoxy powder coatings/steel joints. Fourier-transform reflection-absorption infrared spectroscopy (FT-RAIRS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) were used to identify the silane deposition conditions that influence the adhesion of epoxy powder coatings on steel. We show that AFM analysis provides highly sensitive measurements of mechanical property development and, as such, the degree of condensation of the silane. The joint durability in water at 60 °C was lower when the pH of the γ-APS solution was controlled at 4.6 using formic acid, rather than that at natural pH (10.6). At the curing temperature of 220 °C, oxidation of the carbon adjacent to the amine headgroup of γ-APS gives amide species by a pseudofirst-order kinetics. However, a few amino functionalities remain to react with oxirane groups of epoxy resin and, thus, strengthen the epoxy/silane interphase. The formation of ammonium formate in the acidic silane inhibits the reaction between silane and epoxy, which consequently decreases the epoxy/silane interphase cohesion. We find that the nanoroughness of silane deposits increases with the cure temperature which is beneficial to the wet stability of the epoxy/steel joints, due to increased mechanical interlocking.
我们描述了使用γ-氨丙基三乙氧基硅烷（γ-APS）来提高环氧粉末涂层/钢接头耐久性的可能性。环氧粉末涂层的固化温度通常高于 200°C，这被认为是使用热敏氨基硅烷偶联剂的主要限制。尽管存在这种限制，但我们证明氨基硅烷是增强环氧粉末涂层/钢接头耐久性的传统铬酸盐转化的一种有竞争力的替代品。傅里叶变换反射吸收红外光谱（FT-RAIRS）、X 射线光电子能谱（XPS）和原子力显微镜（AFM）用于确定影响环氧粉末涂层在钢上附着力的硅烷沉积条件。我们表明，AFM 分析可提供对机械性能发展的高度敏感测量，因此也是硅烷缩合程度的敏感测量。当使用甲酸将γ-APS 溶液的 pH 值控制在 4.6 而不是自然 pH 值（10.6）时，在 60°C 的水中，接头耐久性较低。在 220°C 的固化温度下，γ-APS 中与胺头基相邻的碳通过准一级动力学氧化生成酰胺物种。然而，一些氨基官能团仍然与环氧树脂的环氧化物基团反应，从而增强环氧/硅烷界面。在酸性硅烷中形成甲酸铵抑制了硅烷与环氧的反应，从而降低了环氧/硅烷界面的内聚强度。我们发现硅烷沉积物的纳米粗糙度随固化温度的升高而增加，这有利于提高环氧/钢接头的湿稳定性，因为机械互锁增加。
