Polymer–filler interactions in kaolin/nylon 6,6 composites containing a silane coupling agent

Abstract

The properties of calcined and hydrous kaolin filled nylon 6,6 composites have been investigated with respect to particle size and surface treatment with an amino-silane coupling agent (A1100). The mechanical properties of untreated kaolin filled nylon 6,6 composites are kaolin type (hydrous and calcined) independent. However, A1100 surface treatment leads to a distinction between calcined and hydrous kaolin composites, promoting adhesion only with calcined kaolin. Treated calcined kaolin filled nylon 6,6 exhibits improved strength and elongation properties, which are influenced by the silane loading level relative to the filler surface area. At high silane loading levels a plasticing effect was observed with impact strength decreasing. The wet strength of A1100 treated calcined kaolin composites is almost double that of the untreated condition. As A1100 does not promote adhesion with hydrous kaolin wet and dry strength properties are relatively unaffected, with the mode of failure being interfacial. Evidence of interfacial chemical bonding was found only in A1100 treated calcined kaolin. It is thought that the interaction is controlled by an acid base interaction between surface free primary amines and carboxylic acid polymer end groups with amide formation at the interface. The distinction between treated calcined and hydrous kaolin composites is due to the availability of surface free amines. Calcined kaolin has a relatively neutral surface on which the amines are not inhibited in their interaction with nylon functional groups. Hydrous kaolin has an acidic surface with bronsted activity that protonates surface amines inhibiting their interaction with nylon 6,6.