Poly(alkylene 2,5-Furanoate)s Thin Films: Morphology, Crystallinity and Nanomechanical Properties

Abstract

Poly(alkylene 2,5-furanoate)s are considered as the most attractive and interesting alternatives to replace oil-based terephthalic polymers. These furan-based polyesters can be synthesized using fully bio-based synthetic strategies, allowing to reduce the environmental impact of plastics. At the same time, these polymers have shown outstanding thermal, mechanical and gas-barrier properties. All these results envisage their industrial use in the near future. Now, considering the downscaling of the products’ size towards the nanometer scale, we present a study of the morphology and nanomechanical properties of poly(alkylene 2,5-furanoate) thin films. Using Atomic Force Microscopy, we report the development of nanostructures upon crystallization, following different thermal treatments, for thin films with thicknesses below 200 nm. Moreover, we studied the impact of crystal growth in the nanomechanical properties of these materials. We found that the polymer thin films preserve their excellent mechanical response even in the confined geometry, as proved by the Young’s moduli values close to the GPa, accompanied by high surface stiffness, and low indentation depths. The poly(alkylene 2,5-furanoate) thin films were found to have nanomechanical properties comparable to those of the oil-based poly(ethylene terephthalate), a further evidence that in the future they could replace traditional polymers in several applications.

Broadband Dielectric Spectroscopy Study of Biobased Poly(alkylene 2,5-furanoate)s’ Molecular Dynamics

“…This result is in line with previous works where PTF, PBF, and PHF showed a cold crystallization [24,28,[31][32][33], while PPeF remained in an amorphous state regardless of the thermal treatments [26,31,32]. In fact, this particular material only showed crystallization after being stored at room temperature for over 6 months [39,40]. On the contrary, in the case of SL samples, the melt crystallization occurring while slowly cooling showed an odd/even effect.…”

Evidence of Nanostructure Development from the Molecular Dynamics of Poly(pentamethylene 2,5-furanoate)

“…This result is in line with recent AFM observations of PPeF crystallization in thin film geometry, where crystalline structures started appearing after 3 months of storage at room temperature. 55 To provide further information about the crystallization behavior of bulk PPeF, in our current work we performed DSC and XRD studies of a freshly prepared sample as a function of the storage time, as presented in Figure S1. There, it is observed that the PPeF film requires about 4 months to develop some detectable crystalline structures.…”

“…23,25 Specifically, the different number of methylene groups has a direct effect on the chain mobility and crystallizing capability. 23,[55][56] These characteristics allow to obtain from amorphous to semicrystalline polymers, which at room temperature can be in the glassy or in the rubbery state. According to these features, a different microstructure can develop, having a direct effect on the macroscopic properties.…”

“…24 PPeF is characterized by a glass transition temperature below room temperature and shows crystallization kinetics so slow that, under normal conditions, it can be considered completely amorphous. 24,[55][56] Despite these characteristics, PPeF can be processed as films and, very surprisingly, it exhibits an elastic mechanical response at room temperature, as well as exceptional barrier properties. 24,55 This behavior has been explained on the basis of particular inter-chain interactions, 24 also proposed for the other polymers of the family.…”

“…24,[55][56] Despite these characteristics, PPeF can be processed as films and, very surprisingly, it exhibits an elastic mechanical response at room temperature, as well as exceptional barrier properties. 24,55 This behavior has been explained on the basis of particular inter-chain interactions, 24 also proposed for the other polymers of the family. 25 These interactions give rise to a microstructure responsible for the exceptional performances that make PPeF an excellent candidate for the realization of flexible mono-material devices, with outstanding gas barrier capabilities.…”