Rigid amorphous fraction versus oriented amorphous fraction in uniaxially drawn polyesters

• Effect of drawing on rigid (RAF) and mobile (MAP) amorphous phases is investigated.
• RAF, MAP and oriented amorphous fraction are quantified by DSC and WAXD.
• RAF appears as soon as a strain induced crystalline phase is developed.
• For PET, a part of the MAP is anisotropic leading to a draw ratio dependence of Tg.
• For PETg, MAP is isotropic leading to constant glass transition parameters.

Structural changes in poly(ethylene terephthalate) PET and the copolyester poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) PETg occurring during uniaxially drawing at 100 °C have been investigated as a function of draw ratio. This work compares the “microstructural” and the “thermodynamic” three phase description of drawn polyester films. Using Wide angle X-ray Scattering, both materials were characterized considering crystals, isotropic and oriented amorphous phases. Temperature Modulated Differential Scanning Calorimetry allows to evaluate the fraction of crystals, mobile and rigid amorphous fractions (MAP and RAF respectively). Above a critical draw ratio, RAF appears as soon as a strain induced crystalline (SIC) phase is developed for both materials. The degree of crystalline phase is lower and takes place at higher draw ratio for PETg than for PET. For PET, the oriented amorphous phase is composed by the RAF and a part of the MAP. For PETg, the SIC takes place in PET-rich regions and the quantity of RAF per crystal is high.

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