Reactive compatibilization of nylon 6/styrene-acrylonitrile copolymer blends. Part 1. Phase inversion behavior

The phase morphology and phase inversion behavior of nylon 6 (PA)/styrene-acrylonitrile (SAN) compatibilized blends have been studied using an imidized acrylic polymer (IA) and a styrene/acrylonitrile/maleic anhydride terpolymer (SANMA) as compatibilizers. PA/SAN blends can be considered as a simpler version of industrially important PA/ABS blends; therefore, this study is useful for the better understanding of the morphology development for PA/ABS blends with compatibilizers. Compared to binary blends of nylon 6 and SAN, addition of IA causes the phase inversion composition to shift to a higher nylon 6 volume fraction; whereas, addition of SANMA slightly changes the phase inversion composition to a lower nylon 6 volume fraction. The use of IA results in a significant increase of the nylon 6 phase viscosity due to the in situ formation of graft polymers during the melt processing; whereas, the addition of SANMA only slightly increases the nylon 6 phase viscosity. The significant change in the nylon 6 to SAN25 viscosity ratio due to the formation of PA-IA graft polymer may be partially responsible for the shift of the phase inversion composition observed as addition of IA. The method of the mixing also affects the phase inversion composition. The composition range where the nylon 6 forms a continuous phase extends to a lower nylon 6 volume fraction for blends mixed in an extruder compared to those prepared in a Brabender. The stabilization of blend morphology by Formation of graft copolymers was studied for compositions near phase inversion as well as at compositions away from this region. Accordingly, it has been shown that IA does not stabilize the morphology near the phase inversion composition, but it is very effective at compositions where either of the components forms a clearly defined dispersed phase. The factors affecting the critical composition where phase inversion occurs have been established. (C) 2000 Elsevier Science Ltd. All rights reserved.