A study of the glass transition in the amorphous interlamellar phase of highly crystallized poly(ethylene terephthalate)

Abstract

Poly(ethylene terephthalate) (PET) is a semi-crystalline polymer that can be crystallized up to different degrees heating from the amorphous state. Even when primary crystallization has been completed, secondary crystallization can take place with further annealing and modify the characteristics of the amorphous interlamellar phase. In this work we study the glass transition of highly crystallized PET and in which way it is modified by secondary crystallization. Amorphous PET samples were annealed for 4 hours at temperatures between 140 • C and 180 • C. The secondary crystallization process was monitored by differential scanning calorimetry and the glass transition of the remaining interlamelar amorphous phase was studied by Thermally Stimulated Depolarization Currents measurements. Non-isothermal window polarization is employed to resolve the relaxation in modes with a well-defined relaxation time that are subsequently adjusted to several standard models. Analysis of experimental results reveal that cooperativity is so diminished in crystallized samples with respect to the amorphous material that it can be neglected in the modellization of data. The evolution of the modes during secondary crystallization, once primary crystallization has been completed, gives more weight to lower energy modes. As a consequence, secondary crystallization tends to lower the glass transition temperature of the amorphous interlamellar phase, although remaining noticeably higher than in amorphous samples. Evolution of calorimetric scans of the glass transition are simulated from the obtained results and show the same behavior. It can be concluded that primary and secondary crystallization act in opposite directions on the glass transition temperature of the material even though the effect of secondary crystallization is much slighter. The interpretation of these results in terms of current views about secondary crystallization is discussed.

Dielectric study of the glass transition of PET/PEN blends

“…It has been found that the dielectric strength and the width of the relaxation time distribution are sensible to the processing parameters but molecular coupling does not change significantly with the blend composition or the degree of transesterification [4]. The α relaxation, the dielectric manifestation of the glass transition [5], depends strongly on the thermal history [6] because crystallization and physical aging affects the amorphous phase that is where this phenomenon takes place [7]. The relative content of PET and PEN also affects the α relaxation.…”

“…The cristallinity degree was estimated from differential scan calorimetry (DSC) measurements and found to be less than 10% in all cases. Also, it should be noted that a small degree of crystallinity poses no problem since the α relaxation of the interspherulitic amorphous phase is analogous to the α relaxation of the amorphous material and is easy to distinguish from the α relaxation of the amorphous interlamellar phase (α c ) [7].…”

The investigation of the growth and perfection of the poly(ethylene terephthalate) crystalline region from amorphous state during annealing using a controlled temperature gradient

“…Poly(ethylene terephthalate) (PET) is one of the most important engineering plastics， which has been widely used as a raw material in the manufacture of fibers, packaging, optical devices, and appliances due to its excellent film‐forming property, weather resistance, and transparency (amorphous PET) 1 . The processing of PET involved many physical transformation, such as glass transition, 2,3 crystallization, 4–6 recrystallization, 7,8 double melting 9 and so on. These physical transformation will have effects on the dimensional stability (bending, creeping, softening and so on) and mechanical properties on the resultant PET products.…”

Dielectric and optical properties of a poly(ethylene terephthalate) membrane in the temperature interval 150–400 K

“…The results of different dielectric property measurements of PET materials of various structures can be found in the literature . Some of the optical characteristics of PET materials have been reported in literature .…”

“…The results of different dielectric property measurements of PET materials of various structures can be found in the literature. [11][12][13][14] Some of the optical characteristics of PET materials have been reported in literature. 15,16 However, the relation between the optical characteristics of the PET track membrane and the temperature has been studied very little.…”