Epoxy silane functionalization

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

Figure 24.3 Silane functionalization of epoxy resins. Top Functionalization with y-mercapto-propyltrimethoxysilane. Bottom Functionalization with amino-bis-(y-propyltrimethoxysilane).

Prezzi, L and Mascia. L. (2005) Network density control in epoxy-silica hybrids by selective silane functionalization of precursors. Adv. Polym. Technol., 24, 13. 

Ma, P.C., Kim, J.-K., Tang, B.Z., 2007. Effects of silane functionalization on the properties of carbon nanotube/epoxy nanocomposites. Composites Science and Technology 67, 2965-2972. 

As is well known to all, chemical functionalization disrupts the extended n conjugation of CNTs and consequently reduces the electrical conductivity of functionalized CNTs. Silane-functionalized CNT/epoxy nanocomposites exhibited lower electrical conductivity than did untreated CNT composites at the same content of CNTs. In 2005, Cho and co-workers observed that the electrical conductivity of the surface-functionalized MWNT composites was lower than that of the untreated MWNT composites with the identical content of CNTs. This is attributed to the increased defects in the lattice stmaure of carbon-carbon bonds on the surface of CNTs due to the acid treatment. Generally, the severe functionalization of CNTs can sigrtificantly lower the conductivity of the composites. However, several researchers have foimd that the fimaionalization of CNTs could improve the electrical conductivity of the composites. In 2005, Tambutri and co-workers reported that the functionalization of SWNTs with -COOH and -OH groups enhanced the conductivity of composites compared to untreated SWNTs. 

Urethane sealants have good inherent adhesion to most substrates, but silane adhesion promoters are often used to improve this adhesion. Epoxy-, amino-, and mercapto-functional silanes are the most common because of their dual reactive nature. The silane end can react with surface hydroxyls the epoxy, amino, or mercapto end can react with the isocyanate. 

Adhesion promoting silanes are often added to improve adhesion to various substrates. As is the case with urethane sealants, silanes with a dual-reactive nature are typically used. Examples of such silanes are mercapto- and epoxy-functional silanes. Organic titanates may also be used. 

Formulated Melamine resin + epoxy-functional silane... 

In primer formulations for adhesive bonding of metals, the coupling agents that are most frequently used are those based on epoxy and amine functionalities. Aqueous solutions of aminosilanes have been successfully used for obtaining stable adhesive bonds between epoxy and steel [10] and epoxy and titanium [11,12], while epoxy functional silanes are preferable for applications involving aluminum substrates [13,14], A simple solution of % epoxy functional silane in water is currently used for field repairs of military aircraft [15] where phosphoric acid anodization would be extremely difficult to carry out, and performance is deemed quite acceptable. 

Silane coupling agents may contribute hydrophilic properties to the interface, especially when amino functional silanes, such as epoxies and urethane silanes, are used as primers for reactive polymers. The primer may supply much more amine functionality than can possibly react with the resin at the interphase. Those amines that could not react are hydrophilic and, therefore, responsible for the poor water resistance of bonds. An effective way to use hydrophilic silanes is to blend them with hydrophobic silanes such as phenyltrimethoxysilane. Mixed siloxane primers also have an improved thermal stability, which is typical for aromatic silicones [42]. 

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