Toughening of polyamides by the in situ generation of elastomeric phases

Abstract

 Samples of a commercial Trogamid polyamide (an aromatic “nylon”) were modified with two silane coupling agents. In the case of the epoxysilyl agent, the silane was incorporated as a side chain by reacting it with the sample at 50–60 °C for 3 days, with triethylenediamine as catalyst. In contrast, an isocyanatosilyl compound was added only to the polyamide end groups (carboxylic acid and amine groups). The polyamide–epoxy composites were linked with a difunctional silane and were then dried into films. They exhibited some improved ultimate properties, including toughness, at the lower epoxysilane contents. In particular, the tensile strengths of the samples that were annealed at 120 °C were greatly improved. Also, the maximum extensibility was increased by increasing the amount of difunctional silane, but at the cost of decreased tensile strengths. The Trogamid isocyanatosilyl materials, on the other hand, showed properties similar to those of polyamides reinforced with silica generated in situ by the hydrolysis of tetraethoxysilane. Specifically, the tensile strengths of these composites increased slightly, but at the cost of decreased toughness. Although it was not possible to improve all the mechanical properties of either type of composite simultaneously, it was possible to identify the conditions for maximizing at least one or two of them at a time. Thus, the results provided guidance on how to optimize the properties of an important class of polyamides for any particular application.