Fracture behavior of nylon 6/ABS blends compatibilized with an imidized acrylic polymer

The fracture behavior of blends of nylon 6 and acrylonitrile-butadiene-styr ene (ABS) compatibilized with an imidized acrylic (IA) polymer was examined by Izod impact testing and single-notch three-point bend (SEN3PB) instrume nted Dynatup tests. The effects of the method of fracture surface measureme nt, ABS content, specimen thickness, compatibilizer content and fracture zo ne geometry were investigated. Blends containing a fixed (5 wt.% IA) compat ibilizer content were tough over a broad range of ABS contents; the optimum toughness occurred near 50 wt.% ABS. A dual-mode of fracture was observed in SEN3PB specimens whose Izod impact samples with the same composition had ductile-brittle transition temperatures near room temperature. In these SE N3PB samples, ductile deformation occurred in samples with shorter ligament lengths, whereas brittle failure prevailed in samples with longer ligament lengths. The critical Ligament length at which the ductile-to-brittle tran sition occurs was shown to be dependent on the compatibilizer content and s pecimen thickness. These dual modes of fracture were rationalized in terms of a plane-strain to plane-stress transition. For blends that were super to ugh and had good low temperature toughness as judged by Izod impact testing , the toughness of SEN3PB specimens was generally insensitive to specimen t hickness; these blends were fully ductile over the entire range of ligament lengths. The size of the stress-whitened zone was examined for fractured S EN3PB specimens that were fully ductile over the entire range of ligament l engths. Among specimens of a given composition, the size of the stress-whit ened zones was geometrically similar and independent of the size of the ori ginal ligament. However, when ductile samples of different composition were compared, the size of the stress-whitened zone was not necessarily proport ional to the energy dissipated during plastic deformation. This may be a re sult of the presence of different modes of energy absorption in the nylon 6 or SAN matrix phase. (C) 1999 Elsevier Science Ltd. All rights reserved.