Fracture toughness characterizations of compatibilized polyamide-6 (PA6)/poly(phenylene ether) (PPE) blends

Under the plane-strain condition, the material properties, K_IC and G_IC, of the blends, brittle or with small-scale yielding, increase with increasing elastomer content. To evaluate the critical J-integral for the ductile blends, several methods have been compared to understand the influence of elastomer content and different thicknesses using single-edge notch-bend specimens, For a given thickness, the fracture toughness increases with increasing elastomer content. Moreover, the slope of the R-curve becomes gradually steeper with increasing elastomer content and decreasing specimen thickness. J_IC values determined from ASTM E813-89 and modified ASTM E813-81 methods always give the highest and the lowest values, respectively. J_IC values determined from three other methods are comparable and can be employed to characterize the fracture toughness of the compatibilized PA6/PPE blends. It is noted that J_IC values determined from the modified ASTM E813-89 and the hysteresis energy methods are apparently independent of thickness. Therefore, these two methods may be considered as potential alternative techniques to evaluate the critical J-integral for toughened polymer blends.