Next-Generation High-Performance Biobased Naphthalate-Modified PET for Sustainable Food Packaging Applications

Abstract

We report a series of novel poly(ethylene terephthalate) (PET) copolymers with improved properties through the incorporation of bioadvantaged dimethyl 2,7-naphthalenedicarboxylate (2,7-N) as a comonomer. PET is among the most commonly used engineering thermoplastics, ubiquitous in the food packaging industry. However, its application is limited by poor thermal (low Tg) and oxygen barrier performance. A series of poly(ethylene terephthalate-stat-2,7-naphthalate) copolymers were synthesized from ethylene glycol (EG), terephthalic acid (TPA), and 2,7-N via a standard two-step melt polycondensation reaction. The 2,7-N significantly improved the thermal, mechanical, and barrier properties. The glass transition temperature (Tg> 75.4 °C) and thermal stability (Td,5%> 405.1 °C) of the copolymers increase monotonically with 2,7-N content, exceeding those of PET (Tg= 69.7 °C, Td,5%= 401.4 °C). Moreover, the mechanical properties and the crystallization behaviors are tunable through the 2,7-N loading. Composition-optimized copolymers showed an increase of 70% and 200% in elongation at break and tensile strength, respectively. In addition, the oxygen permeability value of the copolymers containing 20% 2,7-N loading fell to PO2 = 0.0073 barrer, a 30% improvement over that of PET. These results illustrate that the novel substitution patterns offered by biobased chemicals can translate to performance advantages in packaging materials. Finally, the fundamental structure-property relationships connecting the bioadvantaged chemicals as the comonomers to the product performance were constructed as a guide for value-added renewable polymers in the future.