Effect of Isobutane Content on the Properties of PET Foam Sheets Produced With a Biodegradable Polymer Based Chain Extender for Food Tray Applications

The influence of isobutane loading on the properties of extruded PET foam sheets for food tray applications is investigated. A biodegradable polymer‐based chain extender is used as a sustainable alternative to conventional PET‐based carriers, supporting more sustainable PET foam production. Five formulations with isobutane contents from 0.6 to 1.4 wt% are prepared under constant conditions, and characterization is performed before and after thermal treatment at 250°C for 90 s to simulate thermoforming. The 1.2 wt% formulation delivers maximum thickness (2.31 mm before oven, 3.91 mm after) and minimum density (177.3 kg/m 3 before, 116.9 kg/m 3 after), achieving an 87% density reduction relative to solid PET. This formulation also exhibits the most uniform cellular architecture, with an average cell diameter of 211.1 ± 25.7 μm. The tensile behavior, characterized by reduced strength and modulus alongside increased elongation up to 1.2 wt%, is consistent with the reduced density and increased cell expansion at higher isobutane loadings. At 1.4 wt%, cell coalescence and collapse occur. Thermal analysis shows amorphous character before oven exposure, while post‐treatment X‐ray diffraction indicates crystallization enhancement. The optimal formulation is successfully thermoformed into a tray, demonstrating industrial processability and distinguishing this work from previous laboratory‐scale PET foaming studies. This study highlights isobutane as a key parameter for tailoring PET foam properties and supports PET foam as a nontoxic, recyclable alternative to polystyrene trays.