Kilogram-scale preparation of sustainable PETG modified with a biobased cyclic diol derived from 5-hydroxymethylfurfural: From synthesis to properties

Poly(ethylene terephthalate-co-cyclohexanedimethanol terephthalate) (PETG) which could perform good mechanical and transparency properties have been commercialized for decades. While, such good properties presented only when the copolyesters is unable to crystallize for a narrow window of compositions. Moreover, considering the unsustainability of 1,4-cyclohexanedimethanol (CHDM) which was mainly obtained from fossil resources, incorporating novel biobased monomer into poly(ethylene terephthalate) (PET) to obtain the excellent properties have arisen researchers’ attentions. Novel biobased 2.5-tetrahydrofurandimethanol (THFDM), an alicyclic diol containing similar structure with CHDM, was successfully introduced into PET and obtained a series of copolyesters with outstanding tunable properties. The process was conducted in 5L stainless steel reactor, which maintained the stability of properties of samples and provided the prospect of being large scale production. The cyclic structure and ether group contained by THFDM reached a balance to the influence on the Tg of copolyesters, resulting only slight change of Tg (ranging from 76.1 °C to 69.4 °C). Three equations, namely Fox’s, Gordon–Taylor’s and Kwei’s equations, were employed to evaluate the Tg of copolyesters. According to the statistics analysis, the value calculated by Kwei’s equation performed the best fitting the experimental results comparing to the other two theories, due to the peculiar dielectric properties. The (co)polymers performed as amorphous materials with excellent transparency at room temperature. As expected, the introduction of highly electronegative ether-oxygen atoms increased the hydrophilicity. It was worthy noting that the rheology property determining the processability was significantly influenced by the polarity which could be adjusted by the content of THFDM. As for the mechanical property, the yield strength increased form 52.7 MPa (PET) to 63.6 MPa (poly(tetrahydrofurandimethanol terephthalate), PTT), while the elongation at break decreased from 205.0% (PET) to 43.3% (PTT) in consistent with the decrease tendency of impact strength (200.6–78.0 J/m). Overall, the PETTs copolyesters performed outstanding transparency, comparable Tg, broader processing window and better mechanical properties comparing with PETG, and it could be potentially used in sheet material, high-performance shrink film, bottle and profile markets. Therefore, the PETT copolyesters is an ideal candidate in replacing PETG to realize the concept of “carbon neutral” and “sustainable development”.