DSC study of polyethylene terephtalate's physical ageing

Abstract

When we keep an amorphous polymer at a temperature below its glass transition temperature T g or when we vary the cooling rate of the polymer from its melting temperature to a temperature below T g , it is not in a true thermodynamical equilibrium state and many of its properties change such as the free volume, the enthalpy and other properties. This behavior is called Physical ageing. In this paper, the study of this phenomenon in partially crystallized poly (ethylene terephtalate) (PET) (14%) is done by differential scanning calorimetry (DSC). The sample of PET is aged in two different ways: the first one consists on annealing the material at temperatures T a below the glass transition temperature T g for different ageing times ǻt a . The second one consists of cooling the polymer from a temperature higher than T g ( 95°C ) to the room temperature following various cooling rates b. An endothermic peak appears at a temperature situated just above T g . We notice that for a slow cooling rate and higher annealing time, the area's peak increases and the temperature shifts toward a higher value. Examining the results reveals that the influence of the polymer's thermal history is important for a slow cooling rate and a significant annealing time.

Contribution to the Study of the Enthalpy Relaxation of Polyesters by DSC Experiments

“…As in the PET case, [4] these thermograms show that for low cooling rates, an endothermic peak is superimposed on the jump of the heat capacity, located around 124 C, characteristic of the glass transition. Growth and shift of the peak towards higher temperatures are observed when the cooling rate decreases.…”

“…The thermally stimulated currents peak (TSC) resulting from the redistribution of electrical charges due to thermal agitation becomes less intense when aging becomes important. This means that aging is more pronounced when the molecular mobility becomes low, making the sample polarization more limited, resulting in a lower TSC peak [4,11,19] .…”

“…The aim of this work is to study the structural relaxation (physical aging) of polyethylene naphthalate (PEN) by differential scanning calorimetry (DSC) and to compare the obtained results to those obtained within polyethylene terephtalte (PET) published by Doulache et al [4] Poly (ethylene therephthalate) PET and its concurrent poly (ethylene 2,6-naphtalate) PEN are two of the most widely used polymers in packaging applications because of their high performance in such areas as mechanical properties, transparency, and easy processing [7] . The excellent qualities of these materials are opening them up to a wide range of applications.…”

“…[2,3] We note that physical aging involves only reversible changes in materials properties without permanent change in their chemical structure and results either from configuration change by the macromolecular relaxation enthalpy or volume or the phenomenon of transport (penetration of solvent migration of additives). [4][5][6] Its mechanism is summarized as follows:…”

Enthalpy and Volume Relaxation of Core‐Crosslinked Star Polystyrene/Poly(methyl methacrylate) Blends

“…Enthalpy data of the linear/CCS polymer blends obtained from conventional DSC. et al, [37] who determined physical ageing reduced segmental mobility with t a , leading to an increase in DH.…”