The Effect of the Silane Deposition Conditions on the Durability of Aluminium Joints Pretreated using 3-Aminopropyltrimethoxysilane

The interfacial adhesive fracture energies and durabilities of aluminium/polyurethane joints pretreated with 3-aminopropyltrimethoxysilane using a range of deposition conditions has been investigated using the blister test. For substrates that were rinsed in order to remove the excess silane, the initial adhesive fracture energy was found to increase markedly compared with the unpretreated joints, but was not affected by changes in the pretreatment solvent (water and toluene), time (five and twenty minutes), or, for substrates pretreated from aqueous solutions, pH (6.8 and 10.4). However, the durability of these rinsed silane pretreated joints varied considerably with the silane pretreatment conditions. The most durable joints were formed when the aluminium was pretreated from aqueous solutions at pH 6.8 for five minutes. XPS analysis of the failed fracture surfaces revealed that the failure was associated with the very thin silane film, occurring at the metal/silane/polymer interface. When the excess silane was not removed by rinsing, the initial adhesive fracture energy was approximately half that obtained from the rinsed joints and the durability was also very poor. XPS analysis of the fracture surfaces showed that failure had occurred within a thick silane film.