Fusion bonding of maleic anhydride grafted polypropylene-polyamide 6 blends to polyamide 6

Abstract Bond formation between maleic anhydride grafted polypropylene–polyamide 6 (PP g –PA) blends and polyamide 6 (PA) has been investigated. The fracture energy, G c , of joints formed at various bonding temperatures was measured using a wedge test in a double cantilever beam geometry and compared with that obtained between homopolymers of the constituents. Optical and transmission electron rnicroscopy was used to study the morphology of the blends in the bulk and at the interface, in an effort to understand how the microstructure influences the fracture behaviour. For bonding temperatures, T b , below the melting temperature of PA, the fracture energy G c of the bonds between PP g –PA adherends and the PA adherends is low. G c nevertheless increases with increasing T b , reaching a maximum for T b ≅225°C, which approximately coincides with the melting temperature of PA, and then falling off at higher T b . Observations of the fracture surfaces using electron spectroscopy for chemical analysis (ESCA) show that fracture occurs cohesively in the blend within a thin layer close to the interface. In the case of blends in which the PP g is the continuous phase, the presence of the PA domains alters the crack propagation path, leading to an increase in G c , with increasing PA content. In the case of blends where the PA is the continuous phase, the fracture behaviour depends strongly on bonding temperature. For T b G c , is low, and decreases with increasing PA content. For T b ≥225°C, melting of PA allows interdiffusion of PA chains to occur across the interface, leading to a strong bond. The experimental observations suggest that the crack propagates by jumping between PP g domains. In this temperature range, G c is high, and increases with increasing PA content.