Thermal Processing Window Evaluation of an Uncompatibilized PET/HDPE Blend for Sustainable Applications: A Factorial Mechanical Characterization

Mechanical recycling of post-consumer poly(ethylene terephthalate)/high-density polyethylene (PET/HDPE) streams is limited by immiscibility and processing-sensitive behavior. A nominal 30 wt% PET/70 wt% HDPE blend was evaluated using a 2 × 3 factorial matrix combining maximum extrusion setpoints (Te: 235 and 260 °C) and maximum injection setpoints (Tinj: 200, 230, and 260 °C). Each processing combination was represented by one run from common bulk feedstocks. Tensile (n = 54) and flexural (n = 53) responses were compared using within-campaign specimen-level contrasts and descriptive multi-response scoring. The Te= 260 °C/Tinj= 200 °C condition produced the highest observed strength–stiffness response, with tensile strength of 32.5 ± 2.23 MPa, flexural strength of 49.2 ± 6.35 MPa, and flexural modulus of 1550 ± 143 MPa. At Tinj= 200 °C, phase-agnostic SEM analysis showed finer fracture-surface texture after extrusion at 260 °C. Charpy impact followed a different trend, with Te= 235 °C/Tinj= 200 °C giving the highest observed blend impact response. These results indicate distinct processing–performance relationships for static and impact behavior in the uncompatibilized post-consumer PET/HDPE blend and establish a baseline for further processing and compatibilization studies.