High Heat Resistance, Barrier Property, and Low Carbon Emission PET for Sustainable Food Packaging Applications Based on Biobased Functional Monomers

PET has a wide range of applications in human life. To address the issues including low glass transition temperature, inadequate oxygen barrier properties, and slight brittleness that limit certain applications of PET, 1,4-cyclohexanedimethanol (CHDM) and isosorbide (IS) were incorporated into the PET main chains using a one-pot two-step method, resulting in the formation of PETGI copolymers. Dynamic mechanical and melt rheological properties revealed that the V-shaped fused ring structure of isosorbide hinders the free movement of the polymer chains, which significantly enhanced the heat resistance of the PETGI copolymers. The glass transition temperature of the PETGI copolymers ranges from 80 to 106 °C. Furthermore, CHDM and IS facilitate the amorphous structure of PETGI, yielding a transparency of 98% and superior toughness, with an elongation at break of 234%. The incorporation of isosorbide markedly increases the molecular chain rigidity of the copolymer while reducing the free volume of the polymer. Time-temperature superposition (TTS) provided insight into the structural influence of different monomers in the molecular chain on the fractional free volume (f_g). As a result of these combined factors, the oxygen barrier performance of the PETGI copolymer containing 40% mol of isosorbide was improved by 41% compared to standard PET. The results of sustainability assessment showed that the equivalent PETGIE₆C₀I₄ reduces carbon dioxide emissions by nearly 15.4% compared to PET.