Utilization of Lignin-derived Methoxybisphenols for the Preparation of Bio-based Polyesters for Packaging Applications

The packaging industry faces a shortage of high-strength bio-derived polyesters that can rival polyethylene derivatives, resulting in the overexploitation of fossil resources. By condensing lignin-derived 2-methoxyhydroquinone with methyl 4-chloromethyl benzoate, the diester dimethyl 4,4’-(((2-methoxy-1,4-phenylene)bis(oxy))bis(methylene))dibenzoate (M) was synthesized. Using monomer M and hydroquinone hydroxyethyl ether, aliphatic-aromatic copolyesters P₁-P₄ were prepared via melt polycondensation reaction employing various aliphatic diacids (1,4-butanedioic acid, 1,6-hexanedioic acid, 1,8-octanedioic acid, and 1,12-dodecanedioic acid). The chemical structures of the copolyesters were elucidated using FTIR and ¹H NMR, while their properties were characterized through gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, tensile testing, and dynamic mechanical analysis. GPC analysis revealed that the average molecular weight (M_w) of copolyesters P₁–P₄ ranged from 4.22 to 5.03 × 10⁴ g/mol, while thermal property analysis indicated that the copolyesters thermal stability decreased with increasing aliphatic diacid spacer length unit. Also, the glass transition temperature (T_g) and melting point (T_m) decreased from 90 to 68 °C and 182–158 °C, respectively. Mechanical analysis showed a decrease in tensile modulus from 1740 to 1010 MPa, as well as yield strength from 76 to 54 MPa, but indicated an increase in elongation at break from 236 to 295%, owed to the growth of carbon chains which increases the proportion of flexible units in the polymer chain. The degradability study indicated a modest degradation rate from 3.9 to 5.1% after 30 weeks from P₁–P₄, with low ecotoxicity in all cases. P₄, consisting of 1,12-dodecanedioic acid, exhibited the highest degradation rate, due to its low proportion of benzene units. These findings provide insights into the structure-property relationships of aliphatic-aromatic copolyesters while contributing to the advancement of high M_w polyesters with performance comparable to conventional petroleum-derived polyesters, aligning with the strategy of green low-carbon, energy-saving, reduction, and sustainable development of polymeric materials.