Amorphous-Phase Miscibility and Crystal Phases in Blends of Polymorphic Poly(hexamethylene terephthalate) with Monomorphic Poly(pentamethylene terephthalate)

Abstract

ABSTRACT:Annealing or heat scan-induced lamellar thickening and factors influencing crystal unit cells in polymorphic poly(hexamethylene terephthalate) (PHT) were probed using polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), synchrotron small-angle X-ray scattering (SAXS). The DSC and WAXD results show that post-scanning or annealing (up to 140 C) on 110 C-crystallized PHT neither transform crystal cell types nor does thin lamella into thick lamella. Rapid lamellar thickening in PHT could take place during DSC scanning, which was proven by comparing SAXS data. T max (final temperature of heating); within a range of 180 up to 220 C) does not influence the polymorphism or multiple melting peaks in PHT. All evidence suggests that kinetic factors are less influential on the polymorphism in PHT. Further, polymorphic poly(hexamethylene terephthalate) (PHT) was blended with monomorphic poly(pentamethylene terephthalate) (PPT) to form a crystalline/ crystalline blend system. The semicrystalline PPT and PHT are miscible in the melt state or quenched amorphous phase. The miscibility, via weak intermolecular interactions, in the amorphous phase of the PHT/PPT blends exerts almost no influence on the crystalline domains, where PPT does not interfere with the formation of or crystal forms in PHT, and vise versa, PHT does not interfere with the sole -crystal form in PPT.

Influence of Rigid Segment Type on Copoly(ether-ester) Properties

“…Whilst PHF has the lowest value of melting temperature. In turn, PHT has two melting temperatures, resulting from two crystal structures: α and β [ 13 ]. Moreover, all investigated polyesters were found to be semi-crystalline polymers, wherein the crystallization temperatures at heat rate of 10 °C/min of PHF (T c = 96.8 °C) and PHT (T c = 105.9 °C) appear to be very similar, while PHN has the highest value of crystallization temperature of 169.0 °C.…”

“…In the case of PHT, the polymorphism, suspected from DSC analysis, was confirmed. The α structure signals can be observed at 2θ = 16.29°, 19.55°, 20.70°, 21.44°, 25.54° [ 13 ] and signals that are coming from β structure can be observed at 2θ = 18.18°, 23.64° [ 13 ]. The WAXS diffractogram proves different crystal structures of all synthesized polyesters.…”

“…PHT is polymorphic polyester, which has three crystal structures: α, β, and γ. The γ is the rarest form because this crystal structure is converted to the other structures by annealing or orientation [ 12 , 13 ]. Replacement of TPA with FDCA, or its derivatives, results in achieving polyesters fully made from renewable materials.…”