FUSION BONDING OF MALEIC-ANHYDRIDE GRAFTED POLYPROPYLENE-POLYAMIDE-6 BLENDS TO POLYAMIDE-6

Bond formation between maleic anhydride grafted polypropylene-polyamid e 6 (PPg-PA) blends and polyamide 6 (PA) has been investigated. The fr acture energy, G(c), of joints formed at various bonding temperatures was measured using a wedge test in a double cantilever beam geometry a nd compared with that obtained between homopolymers of the constituent s. Optical and transmission electron microscopy was used to study the morphology of the blends in the bulk and at the interface, in an effor t to understand how the microstructure influences the fracture behavio ur. For bonding temperatures, T-b, below the melting temperature of PA , the fracture energy G(c) of the bonds between PPg-PA adherends and t he PA adherends is low. G(c) nevertheless increases with increasing T- b, reaching a maximum for T-b congruent to 225 degrees C, which approx imately coincides with the melting temperature of PA, and then falling off at higher T-b. Observations of the fracture surfaces using electr on spectroscopy for chemical analysis (ESCA) show that fracture occurs cohesively in the blend within a thin layer close to the interface. I n the case of blends in which the PP, is the continuous phase, the pre sence 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 < 225 degrees C, PA is still solid, which prevents intimate contact and interdiffusion across the i nterface. G(c), is low, and decreases with increasing PA content. For T-b greater than or equal to 225 degrees C, melting of PA allows inter diffusion of PA chains to occur across the interface, leading to a str ong bond. The experimental observations suggest that the crack propaga tes by jumping between PPg domains. In this temperature range, G(c) is high, and increases with increasing PA content. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.