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

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.