The effect of notch preparation technique on the pendulum impact resistance of thermoplastics

The Izod impact test (ASTM D256) uses test specimens which are typically injection molded and then notched using a machining process. It is well documented that the post-molded notching process can impart a significant testing variation. This study compares the Izod impact test results obtained for different materials using the traditional notch preparation method with results obtained using molded-in notch specimens. In addition, different molded notch radii were used to explore their effect on impact resistance. Fifteen materials were chosen for this study to examine the effects of morphology, molecular weight, concentration of filler and concentration of reinforcement.;The results of the study show that the impact resistance increased with increasing molecular weight for the unfilled materials studied for both specimen types. The impact resistance of the molded-in notch samples tended to be higher than that obtained using machined notches. The impact resistance difference between the molded-in and machined-in notches for the unfilled samples became greater with increasing molecular weight. The results also show that increasing the filler concentration in the machined-in notch group increased the impact resistance whereas increasing filler concentration in the molded-in notch group decreased the impact strength. Glass fiber reinforcement reduced impact resistance at low concentrations and increased impact resistance al higher concentrations.;Notch sensitivity was unaffected by increasing molecular weight but decreased with increasing concentration of filler and reinforcement. The method of notching did not have a significant influence on the impact resistance for the filled materials.