Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
Molecular Mobility in Amorphous Biobased Poly(ethylene 2,5furandicarboxylate) and Poly(ethylene 2,4-furandicarboxylate) Aurélie Bourdet,† Antonella Esposito,*,† Shanmugam Thiyagarajan,‡ Laurent Delbreilh,† Frédéric Affouard,§ Rutger J. I. Knoop,‡ and Eric Dargent† †
Groupe de Physique des Matériaux, Normandie Univ, UNIROUEN Normandie, INSA Rouen, CNRS, 76000 Rouen, France Wageningen Food & Biobased Research, P.O. Box 17, 6700 AA Wageningen, The Netherlands § UMET, UMR CNRS 8207, Université Lille 1, 59655 Villeneuve d’Ascq, France ‡
S Supporting Information *
ABSTRACT: Among all the emergent biobased polymers, poly(ethylene 2,5-furandicarboxylate) (2,5-PEF) seems to be particularly interesting for packaging applications. This work is focused on the investigation of the relaxation dynamics and the macromolecular mobility in totally amorphous 2,5-PEF as well as in the less studied poly(ethylene 2,4furandicarboxylate) (2,4-PEF). Both biopolymers were investigated by differential scanning calorimetry and dielectric relaxation spectroscopy in a large range of temperatures and frequencies. The main parameters describing the relaxation dynamics and the molecular mobility in 2,5-PEF and 2,4-PEF, such as the glass transition temperature, the temperature dependence of the α and β relaxation times, the fragility index, and the apparent activation energy of the secondary relaxation, were determined and discussed. 2,5-PEF showed a higher value of the dielectric strength as compared to 2,4-PEF and other wellknown polyesters, such as poly(ethylene terephthalate), which was confirmed by molecular dynamics simulations. According to the Angell’s classification of glass-forming liquids, amorphous PEFs behave as stronger glass-formers in comparison with other polyesters, which may be correlated to the packing efficiency of the macromolecular chains and therefore to the free volume and the barrier properties.
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INTRODUCTION The demand for sustainable alternatives to fossil resources is increasingly motivating both the scientific and industrial communities to pay attention to any polymer that may be obtained from renewable resources.1−6 As a consequence, the number of polymers that are partially or entirely based on renewable resources, and that are already (or soon will be) commercialized, is increasing very fast. 2,5-Furandicarboxylic acid (2,5-FDCA), a monomer obtained from vegetal feedstock, can be used to synthesize poly(ethylene 2,5-furandicarboxylate) (2,5-PEF).7−12 2,5-PEF is nowadays considered as the most promising sustainable alternative to poly(ethylene terephthalate) (PET), as it exhibits improved mechanical and barrier properties, which is essential to process lightweight beverage packaging.4,13,14 O2, CO2, and H2O permeability in 2,5-PEF is decreased by a factor 11,15 19,16 and 2.8,17,18 respectively, as compared to PET.5 Recent studies provided information on the iso- and nonisothermal crystallization kinetics of 2,5PEF.11,12,19−23 The growth of crystalline structures within a polymer induces a progressive reduction of the amorphous phase. In most systems, the presence of crystals considerably modifies the molecular motions in the amorphous phase. The three-phase model and the concept of cooperative rearranging regions (CRR) were used by Codou et al.24 to explain the incomplete decoupling between the crystalline and the © XXXX American Chemical Society
amorphous phases in 2,5-PEF as compared to PET. The motional processes in amorphous 2,5-PEF have been recently examined by Burgess et al.25 and compared to those occurring in PET. The authors proved that the furan ring-flipping in 2,5PEF is limited as compared to the benzene ring-flipping in PET, thus leading to slower chain mobility and a significant reduction in oxygen diffusion. A recent study on the molecular dynamics of semicrystalline 2,5-PEF was done by Dimitriadis et al.26 In this study, they combined dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC) in order to quantify the molecular mobility in each microstructural fraction. However, the molecular-scale motions in 2,5-PEF have not been completely investigated, yet they could greatly help explaining the macroscopic behavior of these polymers, as already reported for other biopolyesters.27 Thiyagarajan et al.28 recently reported that depending on the conditions for the Henkel-type disproportionation reaction, not only the 2,5-isomer (2,5-FDCA) is formed (70%) but also the 2,4-isomer (2,4-FDCA) (30%) and the 3,4-isomer (3,4-FDCA) (
