Influence of the Foaming Process on the Burning Behavior of the PET–PEN Copolymer

[Image: see text] The manufacturing process can modify the micromechanical structure, usefulness, and functionality of foams. Although one-step foaming is a simple process, controlling the morphology of the foams is difficult compared to the two-step processing method. In this study, we investigated the experimental differences in thermal and mechanical properties, particularly combustion behavior, between PET–PEN copolymers prepared by the two methods. With an increase in foaming temperature T(f), the PET–PEN copolymers became more fragile, and the breaking stress of the one-step PET–PEN foamed at the highest T(f) was only 2.4% of that of the raw material. For the pristine PET–PEN, 24% of the mass was burned, leaving 76% as a molten sphere residue. The two-step MEG PET–PEN had only 1% of its mass remaining as a residue, whereas the one-step PET–PENs had between 41 and 55%. The actual mass burning rates were similar for all the samples except the raw material. The coefficient of thermal expansion of the one-step PET–PEN was about two orders of magnitude lower than that of the two-step SEG.