Effect of EVA on the Unnotched Impact Toughness of PP/HDPE/EVA Blends

Beverage bottle caps are usually made from two primary materials: PP and HDPE. In this study, the evaluation criteria were the unnotched impact toughness and the microstructure of PP/HDPE/EVA samples produced by injection molding. The samples were tested according to ASTM D256. PP/HDPE/EVA blends were prepared with various ratios: 47.5/47.5/5, 45/45/10, 42.5/42.5/15, 40/40/20, and 37.5/37.5/25. The results showed that adding EVA to the PP/HDPE blend significantly increased the unnotched impact toughness: from 84.03 kJ/m² (PP/HDPE/5% EVA) to 85.06 kJ/m² (PP/HDPE/10% EVA), then decreased to 70.3 kJ/m² (PP/HDPE/15% EVA), followed by an increase to 83.32 kJ/m² (PP/HDPE/20% EVA) and 89.42 kJ/m² (PP/HDPE/25% EVA). The discrepancy in value between the samples with the highest and lowest EVA content was 19.12 kJ/m². Overall, as the EVA content increased, the unnotched impact toughness also tended to increase. However, the sample with PP/HDPE/15% EVA showed a noticeable decrease.