A New Era in Engineering Plastics: Compatibility and Perspectives of Sustainable Alipharomatic Poly(ethylene terephthalate)/Poly(ethylene 2,5-furandicarboxylate) Blends

Abstract

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.

Keywords: blends; crystallization; poly(ethylene furanoate); poly(ethylene terephthalate).

Scheme 1

The chemical structures of poly(ethylene terephthalate) (PET) (a) and PEF (b).

Figure 1

Wide-angle X-ray diffractometry (WAXD) patterns for the blends and for the PEF and PET homopolymers and their blends at different compositions as indicated.

Figure 2

Differential scanning calorimetry (DSC) thermograms (a) for the semicrystalline blends recorded upon heating at 20 °C/min and (b) total Modulated Temperature DSC (MTDSC) signal for the fast-cooled samples upon heating at 5 °C/min.

Figure 3

Modulated Temperature DSC (MDSC) thermograms for the fast-cooled upon heating at 5 °C/min: (a) reversing signals and (b) non-reversing signals.

Figure 4

Power compensation DSC thermograms of melt quenched blends at 20 °C/min (a) full temperature scale and (b) details of the glass transition temperature range; the black dotted line corresponds to the T_g of PEF and the red dotted line corresponds to the T_g of PET. (c) First derivative of the heat flow plotted as a function of temperature for several PET/PEF compositions. Red and blue arrows indicate glass temperatures of PEF and PET segments, respectively.

Figure 5

DSC heating scans at 20 °C/min for PET-PEF 95-5 blend samples after crystallization at the indicated temperature.

Figure 6

(a) Hoffman-Weeks plot for the determination of the equilibrium meting temperature of PET within the PET-PEF 95-05 blend, (b) Plots of $\frac{\Delta H^0{V}_1}{R{V}_2}\left(\frac{1}{T_{m(blend)}^0}-\frac{1}{T_{m(pure)}^0}\right)$. against ${\varphi }_1^2$ using equilibrium melting temperatures.

Figure 7

(a) Evolution of the relative degree of crystallinity with time for the PET-PEF 95-5 blend at various temperatures and (b) dependence of the isothermal crystallization half-time on the temperature for blends with high PET content.

Figure 8

Lauritzen Hoffman-plots for PET and the blends.

Figure 9

(a) DSC traces of non-isothermal crystallization of PET-PEF 95-05 at various cooling rates, (b) DSC traces of the non-isothermal crystallization of all blends under cooling at 10 °C/min, (c) peak crystallization temperatures versus cooling rate for the blends that were crystallized.

Figure 10

(a) Effect of blending time on the DSC curves of a PET-PEF 60-40 copolymer, (b) zoom-in of the glass transition temperature region of the blend at different blending times.

Figure 11

PLM photos recorded at 210 °C for the blends: (a) neat PET, (b) PET-PEF 90-10, (c) PET-PEF 80-20, (d) PET-PEF 60-40, (e) PET-PEF 50-50, (f) PET-PEF 40-60, (g) PET-PEF 30-70, (h) neat PEF.