Interphase epoxy-amine

Properties of the Interphase Epoxy-Amine/Metal Influences from the Nature of the Amine and the Metal... 

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]. 

Epoxy-amine liquid prepolymers are extensively appHed to metallic substrates and cured to obtain painted materials or adhesively bonded stractures. Overall performances of such systems depend on the interphase created between the organic layer and the substrates. When epoxy-amine Hquid mixtures are appHed to a more or hydrated metaUic oxide layer (such as Al, Ti, Sn, Zn, Fe, Cr, Cu, Ag, Ni, Mg, or E-glass), amine chemical sorption concomitant with metaUic surface dissolution appear, leading to the organometaUic complex or chelate formation [1, 2]. Furthermore, when the solubility product is exceeded, organometaUic complexes may crystaUize. These crystals induce changes of mechanical properties (effective Young s modulus, residual stresses, practical adhesion, durability, etc.). 

When liquid epoxy-amine prepolymers were applied and cured on metallic substrates, interphases were created within the organic layer in the vicinity of the metal surface. 

When epoxy-amine prepolymers were applied on metallic substrates, interphases between the coating part, having the bulk properties, and the metallic surface were created. Amine chemisorption onto oxidic or hydroxidic metallic surfaces, concomitantly with partial dissolution of the surface oxide (and/or hydroxide) on the metal substrate, was observed, according to the basicity characteristics of the amine monomers (pfC,>10). Then it could be assumed that either ... 

The interphase in PE fibre/epoxy resin matrix composites was studied by FTIR microspectroscopy using a set-up for investigation of the matrix as close to the fibre as a few microns or less. It was shown that moisture present on the fibre surface could influence the polymerisation reaction of the epoxy/anhydride matrix in an irreversible manner. This effect was enhanced for composites from the more hydrophilic PVAl fibre. The fibre/matrix interaction in these thermoplastic fibre composites was also studied by DSC through characterisation of the fibre melting. A decreased DSC interaction parameter was found if the composition of the interphase was changed by moisture. For a composite with an epoxy/amine matrix, on the other hand, the DSC interaction parameter was unaffected by moisture from the fibre surface. 22 refs. (Pt.I, ibid, p.83-100)... 

Exposure to 70 °C gives similar results for the surface treated fiber (Fig. 24). That is, a complete reversibility in noted. The finished fiber (i.e. the fiber with the interphase consisting of the amine deficient brittle interlayer) experiences a nonrecovery of interfacial shear strength after moisture exposure and dehydration. Parallel surface spectroscopic investigation of the fiber surfaces show that under these conditions the fiber surface chemistry is not permanently altered by this exposure. Model studies of epoxies with the amine deficient composition of the interphase show that, the wet Tb of this material is about 70 °C. Therefore, the interphase is at or above its wet Tg and therefore because of the compliant nature of this material, stresses cannot be transfered efficiently and the interface is permanently distorted. 

Cu-DETA complexation in the epoxy, especially in the interphase, reduces the concentration of reactive amine hydrogen and this causes slower kinetics and a smaller degree of conversion. 

A study by Comyn et al. [8] indicated that low (or no) cure took place in the interphase between an amine cured epoxy and aluminum because the amine was preferentially adsorbed onto the aluminum oxide on the aluminum. Garton et al. [9] showed that the acidic surface of a carbon fiber selectively adsorbed amine and catalyzed the reaction between the amine and an epoxy resin. Nigro and Ishida [10] found that homopolymerization of epoxy resin was catalyzed by a steel surface. Zukas et al. [11] discovered, in a model system of an amine cured epoxy resin and an activated aluminum oxide, a change in the relative rates of the reactions leading to crosslinking of the epoxy, so that the material in the interphase was structurally different from that in the bulk. 

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