The industrialisation of poly(ethylene 2,5-furandicarboxylate) for total replacement of poly(ethylene terephthalate) in the polyester market is under question. Preparation of high-performing polymer blends is a well-established strategy for tuning the properties of certain homopolymers and create tailor-made materials to meet the demands for a number of applications. In this work, the structure, thermal properties and the miscibility of a series of poly(ethylene terephthalate)/poly(ethylene 2,5-furandicarboxylate) (PET/PEF) blends have been studied. A number of thermal treatments were followed in order to examine the thermal transitions, their dynamic state and the miscibility characteristics for each blend composition. Based on their glass transition temperatures and melting behaviour the PET/PEF blends are miscible at high and low poly(ethylene terephthalate) (PET) contents, while partial miscibility was observed at intermediate compositions. The multiple melting was studied and their melting point depression was analysed with the Flory-Huggins theory. In an attempt to further improve miscibility, reactive blending was also investigated.

Aliphatic/aromatic thermoplastic polyesters are a very interesting family of polymers with many applications. Poly(alkylene 2,5-furandicarboxylate)s (PAF)s are the biobased alternatives to poly(alkylene terephthalate)s and are expected to play a key role in bioeconomy. The most important PAFs are poly(ethylene 2,5-furandicarboxylate) (PEF), poly(propylene 2,5furandicarboxylate) (PPF), and poly(butylene 2,5-furandicarboxylate) (PBF), which crystallize slowly. PBF shows a typical PAF thermal behavior but a little faster crystallization compared to that of PPF and PEF. PBF was used in this work as a model material to understand the key parameters of the solidification of PAFs during processing. A detailed study of the kinetics of isothermal and dynamic melt and cold crystallization of PBF at very slow and moderate cooling and heating rates (0.1−20 °C/min) was carried out. Multiple melting was also analyzed. The equilibrium melting temperature was determined (T m o = 196.4 °C). The activation energy of non-isothermal crystallization from the melt decreased with increasing the cooling rate, in accordance with an increasing crystallization rate with supercooling. The cold-crystallization rate increased with increasing the difference between the cold-crystallization temperature (T cc ) and the glass transition temperature (T g ), which in turn increased with the heating rate. Several theoretical models were elaborated for the treatment of the crystallization data. Polarized optical microscopy revealed the formation of ring-banded spherulites at elevated temperatures (T c )s.