Influence of Rubber Annealing on Behavior of the Three-Phase Model in PET Study by the Thermally Stimulated Current (TSC) Method

Abstract

Polymers are generally formed by two phases: a crystalline phase where chains are arranged in parallel, one over the other, and an amorphous phase where there is absence of order. Several recent works have supposed the existence of a three-phase model where there coexist simultaneously a crystalline phase, a rigid amorphous phase, and a mobile amorphous phase. The objective of our work is to put in evidence the existence of three phases separately within polyethylene terephtalate (PET). This polymer is widely used in electrical insulation and especially in packaging. To this effect, samples of PET have undergone a heat treatment of isothermal annealing time from 10 to 240 min. The samples thus treated were studied by the thermally stimulated current method, which tracks the variation of the depolarization current as a function of sample temperature. Recordings of thermocurrent are made after increasing temperature with a linear heating rate of 7°C/min. Then we can calculate the areas under the thermocurrent peak and hence estimate the corresponding degrees for the various phases present in the annealed material, χc and χam. Analysis of the values obtained for these degrees introduce a third component, denoted χar, which characterizes the rigid amorphous phase. Monitoring the evolution of these degrees with duration of annealing is realized. It is clear from all results that PET annealed rubber has a three-phase behavior with simultaneous presence of three phases, a crystalline phase χc, an amorphous mobile phase χam, and a rigid amorphous phase χar.