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

Abstract

Increasing demand for safe, convenient, and affordable packaging has prompted tremendous growth in single-use 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 °C), and the glass transition temperature of poly­(ethylene 2,7-N) was far higher (T g = 121.8 °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 °C. Moreover, the poly­(ethylene 2,7-N) also produced 30% less acetaldehyde under typical processing temperatures at 250–300 °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.

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

“…The samples before annealing are highly amorphous, showing no WAXS diffraction peaks except 27PEN100, which has been discussed in our previous study. 28 After annealing, the 27PENX diffraction peaks match those of PET homopolymer, indicating that 27PENX crystals are comprised solely of PET sequences. At modest substitution rates, sequences containing 2,7-N units are too irregular to crystallize and are relegated to the amorphous phase.…”

“…The high Đ (3.61) of 27PEN100 is likely due to mass transport limitations, which resulted from the high viscosity during polymerization compared to that of PET and 27PEN copolymers, as mentioned in our previous study. 28 The measured IV values of the polymers are consistent with the GPC results, and all polymers were within the range typical for industrially produced PET.…”

“…As shown in Table 5, 27PEN100 shows brittle performance compared to PET, which has been discussed in our previous study. 28 However, the copolymers show ductile deformation with similar yield, plastic deformation, and necking behaviors as compared to PET. Notably, PET fractures after necking with only slight strain hardening, whereas 27PEN copolymers display obvious strain hardening before breaking.…”

“…In contrast, 27PEN100 shows a smooth surface with tiny crystals, which has been discussed in a previous study. 28 Analysis of surface appearance confirmed that 27PENX copolymers possess a similar energy dissipating ability to that of PET.…”

“…19−27 Inspired by these concerns and the potential utility of the naphthalate polyesters, we recently reported a family of biomass-derived poly(ethylene naphthalate) homopolymers as sustainable and potentially lower-cost 26PEN alternatives. 28 Among these, 2,7-naphthalene dicarboxylate (2,7-N) was found to be especially promising. Derived from malic acid, 2,7-N is structurally analogous to 2,6-N in the same manner as meta-substituted isophthalate to para-substituted terephthalate.…”