Rigid amorphous fraction versus oriented amorphous fraction in uniaxially drawn polyesters Florian Hamonic a , Valérie Miri b , Allisson Saiter a , Eric Dargent a,⇑ a AMME-LECAP EA 4528 International Laboratory, Normandie Univ., Université et INSA de Rouen, 76801 Saint Etienne du Rouvray, France b Unité Matériaux Et Transformations (UMET), CNRS, Bât C6, Université Lille 1, F-59655 Villeneuve d’Ascq, France article info Article history: Received 8 February 2014 Received in revised form 15 May 2014 Accepted 19 June 2014 Available online 28 June 2014 Keywords: Polyester Drawing Microstructure Amorphous phase abstract 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 polyes- ter 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 amor- phous 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. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction It has been recognized that semi-crystalline polymers cannot be described very well in terms of a simple two phase crystalline–amorphous model. Different kinds of phases have been proposed in literature [1]. Appearance of mesophases during the thermo-mechanical treatment of polymers was evidenced using Wide angle X-ray Scat- tering WAXS method for various polymers such as poly(ethylene terephthalate) (PET) [2] or poly(lactic acid) (PLA) [3]. The mesophase is an intermediate state between amorphous and crystalline phases; it possesses some degree of medium-range order. In a recent work [4], Cebe et al. demonstrate that combinations of thermal analysis and WAXS are the key techniques to characterize the phase structure of polyester fibers. They quantified for the first time the PLA mesophase in as-spun nanofibers. Wu et al. [5] claimed that there are two types of non-crystalline domains in PET fibers: an isotropic amorphous phase and a highly oriented noncrystalline region. They estimated the amount of these two phases from two-dimensional WAXS patterns. Similarly, from X-ray diffraction of PET fibers, Wunderlich separated the non-crystalline scattering into an amorphous phase and an oriented intermediate phase [6,7]. In the case of Nylon-6 fibers, Murthy et al. have proposed a method for evaluating the isotropic and non- isotropic non crystalline phases from X-ray diffractograms [8]. Three phase model was also developed to describe the isotropic microstructure of thermally crystallized poly- mers. The incomplete decoupling due to tie molecules between crystalline and non-crystalline phases leads to a decrease for the amorphous phase chain mobility [9], and implies to describe most of the quiescent crystallized poly- mers with a three phase model: the crystalline phase, the mobile amorphous phase (MAP), and the rigid amorphous fraction (RAF) [1,10,11]. The RAF is the result of strong http://dx.doi.org/10.1016/j.eurpolymj.2014.06.014 0014-3057/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +33 232955080; fax: +33 232955082. E-mail address: eric.dargent@univ-rouen.fr (E. Dargent). European Polymer Journal 58 (2014) 233–244 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj