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

The manufacturing process can modify the micromechanicalstructure,usefulness, and functionality of foams. Although one-step foamingis a simple process, controlling the morphology of the foams is difficultcompared to the two-step processing method. In this study, we investigatedthe experimental differences in thermal and mechanical properties,particularly combustion behavior, between PET-PEN copolymersprepared by the two methods. With an increase in foaming temperature T (f), the PET-PEN copolymers became morefragile, and the breaking stress of the one-step PET-PEN foamedat the highest T (f) was only 2.4% of thatof the raw material. For the pristine PET-PEN, 24% of the masswas burned, leaving 76% as a molten sphere residue. The two-step MEGPET-PEN had only 1% of its mass remaining as a residue, whereasthe one-step PET-PENs had between 41 and 55%. The actual massburning rates were similar for all the samples except the raw material.The coefficient of thermal expansion of the one-step PET-PENwas about two orders of magnitude lower than that of the two-stepSEG.