Dielectric study of the glass transition of PET/PEN blends

Abstract

An analysis of the glass transition of four materials with similar chemical structures is performed: PET, PEN and two PET/PEN blends (90/10 and 70/30 w/w). During the melt processing of the blends transesterification reactions yield block and random PET/PEN copolymers that act as compatibilizers. The blends obtained in this way have been characterized by 1 H-NMR and DSC. A degree of randomness of 0.38 and 0.26 has been found for the 90/10 and 70/30 copolymers. It is shown by DSC that this copolimerization is enough to compatibilize the blends. The α relaxation, the dielectric manifestation of the glass transition, has been studied by thermally stimulated depolarization currents (TSDC). The relaxation has been analyzed into its elementary modes by means of a relaxation map analysis. The activation energies of the modes of the glass transition do not change significantly between the four materials: in all cases the modes with a larger contribution have around 3 eV and modes with less than 1 eV are not detected. The change in the pre-exponential factor accounts entirely for the relaxation time change from material to material, that is larger as the PEN content increases. The compensation law is fulfilled and compensation plots converge for high-frequency modes. The polarizability decreases as the PEN content increases due to the increased stiffness of the polymer backbone. An analysys of the cooperativity shows that the central modes of the distribution are the most cooperative while highfrequency modes tend to behave more as Arrhenius. The low-frequency modes are difficult to study due to the asymmetry of the distribution of relaxation times. PEN turns out to be the less cooperative material. It is demonstrated how the parameters obtained from the dielectric study are able to reproduce calorimetric data from DSC scans and are, therefore, a valid description of the glass transition.

Influence of internal flexibility on the double glass transition in a series of odd non-symmetric liquid crystal dimers characterised by dielectric measurements

“…A complex relaxation, as that commonly related to the glass transition, can be resolved by this poling procedure into more elementary spectra because in the subsequent heating ramp only the contribution of this small fraction of the relaxation will be detected. The whole relaxation results then from the superposition of the elementary contributions obtained at different polarization temperatures in the so called 'Relaxation Map Analysis' study (RMA) [26,36].…”

“…Several empirical models of τ (T ) can be checked in this way by fitting TSDC data according to equation 2. A more detailed explanation of this procedure can be found elsewhere [25,26]. We have checked the obtained TSDC data against two phenomenological models for τ (T ) usually applied to calorimetric and dilatometric measurements: the Arrhenius model and the ToolNarayanaswamy-Moynihan model (TNM).…”

“…Some thermal parameters used for each material in the TSDC experiments. 338 288 15 338 5 443 315 278 15 323 7 448 330 278 15 330 9 443 315 273 15 327 in studying the glass transition [25][26][27][28].…”

Chemical Structure and Microstructure of Poly(alkylene terephthalate)s, their Copolyesters, and their Blends as Studied by NMR

“…Several examples of blends of PET with polyesters, polycarbonates, or polyamides, and other polymers, whose microstructure was studied by NMR, have been reported in the literature. One outstanding case is the blend made from PET and poly(ethylene naphthalate) (PEN), which has been thoroughly studied for the high potential that this material has in the bottling field . PET is blended with PEN in order to increase its glass transition temperature and to improve its barrier properties to gases.…”

Synthesis and Properties of Thermotropic Copolyesters Based on Poly(ethylene terephthalate) and 4′-Acetoxy-4-biphenyl-carboxylic Acid

“…The thermal and mechanical properties of PET can be improved by physical and chemical modifications: (1) mixing with other polymers and (2) copolymerization [ 2 ]. In the first case, mixing PET with other polyesters, for example, polytrimethylene terephthalate [ 3 ], polyethylene naphthalate [ 4 ], or bisphenol A polycarbonate [ 5 ], is not a completely physical process since their monomeric units are exchanged between macromolecules up to complete randomization. Such a type of interaction is also known as transesterification or ester–ester exchange, and resulting products are copolyesters rather than blends.…”