Utilizing Furfural-Based Bifuran Diester as Monomer and Comonomer for High-Performance Bioplastics: Properties of Poly(butylene furanoate), Poly(butylene bifuranoate), and Their Copolyesters

Abstract

Two homopolyesters and a series of novel random copolyesters were synthesized from two bio-based diacid esters, dimethyl 2,5-furandicarboxylate, a well-known renewable monomer, and dimethyl 2,2′-bifuran-5,5′-dicarboxylate, a more uncommon diacid based on biochemical furfural. Compared to homopolyesters poly­(butylene furanoate) (PBF) and poly­(butylene bifuranoate) (PBBf), their random copolyesters differed dramatically in that their melting temperatures were either lowered significantly or they showed no crystallinity at all. However, the thermal stabilities of the homopolyesters and the copolyesters were comparable. Based on tensile tests from amorphous film specimens, it was concluded that the elastic moduli, tensile strengths, and elongation at break values for all copolyesters were similar as well, irrespective of the furan:bifuran molar ratio. Tensile moduli of approximately 2 GPa and tensile strengths up to 66 MPa were observed for amorphous film specimens prepared from the copolyesters. However, copolymerizing bifuran units into PBF allowed the glass transition temperature to be increased by increasing the amount of bifuran units. Besides enhancing the glass transition temperatures, the bifuran units also conferred the copolyesters with significant UV absorbance. This combined with the highly amorphous nature of the copolyesters allowed them to be melt-pressed into highly transparent films with very low ultraviolet light transmission. It was also found that furan–bifuran copolyesters could be as effective, or better, oxygen barrier materials as neat PBF or PBBf, which themselves were found superior to common barrier polyesters such as PET.

Tuning the Properties of Furandicarboxylic Acid-Based Polyesters with Copolymerization: A Review

“…In all studies described above where two acids and one diol were used for the synthesis of the copolymers, incorporating 2,5-FDCA in the polymer’s structure results in higher T g compared to the respective homopolymer, whether derived from an acid with cyclic moieties such as 2,4-FDCA, TPA, and cyclohexane dicarboxylic acid or a linear one such as succinic, adipic, sebacic, etc. The only instance where the T g was reduced was in a study by Kainulainen et al [ 63 ], where the bifuran diester was used as a comonomer, and it was due to the reduced mobility of the bifuran ring compared to the furan ring. On the other hand, when two diols are used to prepare copolymers from 2,5-FDCA, two main strategies can be singled out.…”

“…The authors investigated the activation energy (E a ) for thermal degradation via modulated-temperature–TGA measurements, and the defining factor for calculating E a was found to be the length of the diol used. Finally, 1,4 cyclohexane dicarboxylic acid and bifuran dicarboxylic acid were used as comonomers in materials derived from PEF [ 33 ], PPF [ 61 ], and PBF [ 63 ]. The synthesized materials presented excellent thermal stability, with decomposition initiation temperatures above 360 °C that were between those of the respective homopolymers.…”

“…The combination of PEF, PPF, and PBF with other FDCA-based polymers has been reported as an approach to improve their mechanical properties [ 37 , 45 , 63 ]. Interestingly, small contents of PPeF and PHF yielded copolymers with tensile properties better than those of bottle-grade PET [ 37 , 45 ].…”

“…Finally, for random copolymers, the rigidity of the structure can be evaluated from the shifting of α relaxation to higher temperatures. Usually, it is derived from the introduction of furan moieties, but other cyclic monomers were also found to have the same effect on increasing the polymers’ storage modulus [ 36 , 63 , 84 ]. For example, the shifting of the α relaxation with the insertion of furan [ 84 ] and CBDO [ 36 ] are shown in Figure 20 .…”

“…PBF- co -PBbF amorphous films exhibited improved permeability to O 2 in comparison with PBF, PBbF, PET, and PBT [ 63 ]. PBC units in PBF deteriorated the barrier properties while improving the ε b [ 84 ].…”