Next-Generation High-Performance Bio-Based Naphthalate Polymers Derived from Malic Acid for Sustainable Food Packaging

Increasing demand for safe, convenient, and affordable packaging has prompted tremendous growth in singleuse plastics, with attendant increases in carbon dioxide emissions and environmental waste. This study presents a family of engineering polyesters featuring biobased naphthalate rigid segments. The proposed polyesters can serve as an eco-friendly substitute for existing packaging materials, such as poly(ethylene terephthalate) (PET). Bio-PET analogs using 2,7-naphthalate-based rigid segments of dimethyl 1,2,3,4-tetrahydronaphthalene-2,7-dicarboxylate (THN) or dimethyl 2,7-naphthalene dicarboxylate (2,7-N) were synthesized via transesterification with ethylene glycol to the bis-hydroxy ester followed by polycondensation. The proposed bionaphthalate polyesters provide unique performance advantages. In experiments, the glass transition temperature of poly(ethylene THN) was comparable to that of PET (T-g = 67.7 degrees C), and the glass transition temperature of poly(ethylene 2,7-N) was far higher (T-g = 121.8 degrees C). The thermal stability of poly(ethylene 2,7-N) far exceeded that of PET, as evidenced by its char yield of 33.4 wt % at 1000 degrees C. Moreover, the poly(ethylene 2,7-N) also produced 30% less acetaldehyde under typical processing temperatures at 250-300 degrees C. Finally, the oxygen permeability values of these naphthalate-based polymers were less than P-O2 = 0.0034 barrer, which represents a 3-fold improvement over PET (0.0108 barrer). Overall, biobased naphthalate rigid segment polyesters are promising candidates for sustainable packaging materials, particularly those requiring high gas barrier performance.