Relationships between impact performance and structures of rotationally molded crosslinked high-density polyethylene

Crosslinked high-density polyethylene (XL-HDPE) is a preferred material for chemical and fuel tanks due to its superior environmental stress crack resistance and impact strength. The impact performance of rotationally molded specimen is important for final products. In the research the drop weight impact strength (defined as ARM impact strength) of rotationally molded XL-HDPE is tested between -40 degrees C and 25 degrees C. The crosslinking content, crystallization characteristics, and dynamic mechanical properties (DMA) of different thickness gradients are examined to illustrate the relationships between the impact strength, brittle-ductile transition (BDT) and microstructures. The innermost surface layer (about 0.3 mm) has lower gel content, higher crystallinity, and average lamellar thickness compared with the body part. The ARM impact strength is about 1 J/mm at -40 degrees C and -30 degrees C, and about 29 J/mm at -20 degrees C similar to 25 degrees C. There is a BDT between -30 degrees C and - 20 degrees C. After removing the innermost surface layer, the sample breaks in ductile manner in the entire tested temperature range, and the ARM impact strength is about 24 similar to 26 J/mm. The DMA results show that the BDT is consistent with the structure transition of the innermost surface layer. The microstructures of rotationally molded XL-HDPE in the innermost surface layer dominate the low temperature impact performance.

Automated summary

The research demonstrates that crosslinked high-density polyethylene (XL-HDPE) has good impact strength and environmental stress crack resistance. The microstructures of the innermost surface layer after rotational molding play a dominant role in low temperature impact performance and are closely related to the brittle-ductile transition of the material.