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

Abstract

Poly(2,5-alkylene furanoate)s are bio-based, smart, and innovative polymers that are considered the most promising materials to replace oil-based plastics. These polymers can be synthesized using ecofriendly approaches, starting from renewable sources, and result into final products with properties comparable and even better than those presented by their terephthalic counterparts. In this work, we present the molecular dynamics of four 100% bio-based poly(alkylene 2,5-furanoate)s, using broadband dielectric spectroscopy measurements that covered a wide temperature and frequency range. We unveiled complex local relaxations, characterized by the simultaneous presence of two components, which were dependent on thermal treatment. The segmental relaxation showed relaxation times and strengths depending on the glycolic subunit length, which were furthermore confirmed by high-frequency experiments in the molten region of the polymers. Our results allowed determining structure-property relations that are able to provide further understanding about the excellent barrier properties of poly(alkylene 2,5-furanoate)s. In addition, we provide results of high industrial interest during polymer processing for possible industrial applications of poly(alkylene furanoate)s.

Keywords: 2,5-furandicarboxylic acid; bio-based polymers; broadband dielectric spectroscopy; molecular dynamics; poly(2,5-alkylene furanoate)s.

Scheme 1

Chemical structure of the investigated poly(alkylene 2,5-furanoate)s. n refers to the number of methylene groups: 3, 4, 5 and 6 for PTF, PBF, PPeF and PHF, respectively.

Figure 1

Broadband dielectric spectroscopy (BDS) results at 228 K. Circles correspond to ε″ and squares correspond to ε′. The fittings were carried out following Equation (1). Solid pink lines correspond to the total fit, while blue and green lines show the components of β₁ and β₂, respectively. The data corresponding for fast-cooled (FC)-PBF was adapted from Ref [28].

Figure 2

(a) Relaxation plot, (b,c) fitting parameters, and (d) full width at half maximum (FWHM) as a function of temperature for the local relaxations of poly(alkylene furanoate)s: PTF (light pink), PBF (yellow), PPeF (light purple), PHF (light green). Solid symbols correspond to the β₁ (■) and β₂ (●) contributions of FC samples, while empty symbols (Δ) correspond to the β₁ contribution in SL samples. In the specific case of SL PBF, the contribution of β₂ is shown by crossed triangles. The results for FC PBF were taken from Ref [28].

Figure 3

BDS results showing the segmental relaxation of the polymers. Circles correspond to ε″ and squares correspond to ε′. Solid symbols show the results for FC samples, while empty ones show the results for SL samples. Continuous lines correspond to fittings, as detailed in the main text. The data corresponding for FC PBF was adapted from Ref [28].

Figure 4

(a) Relaxation plot, (b,c) fitting parameters, and (d) FWHM, as a function of temperature for the segmental relaxations of FC poly(alkylene furanoate)s: ■ PTF, + PBF, ▲ PPeF, ● PHF. The low-temperature data for PBF (blue crosses) were adapted from Ref [28].

Figure 5

Relaxation strength ($T\Delta \epsilon$) and FWHM as a function of the relaxation time (${\tau }_{\mathrm{MAX}}$). Solid symbols correspond to: ■ PTF, + PBF, ▲ PPeF, ● PHF. Empty symbols show the FWHM data: □ PTF, × PBF, Δ PPeF, ○ PHF.