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Tenn N.,CNRS Polymers, Biopolymer and Surfaces Laboratory | Follain N.,CNRS Polymers, Biopolymer and Surfaces Laboratory | Fatyeyeva K.,CNRS Polymers, Biopolymer and Surfaces Laboratory | Valleton J.-M.,CNRS Polymers, Biopolymer and Surfaces Laboratory | And 3 more authors.
Journal of Physical Chemistry C | Year: 2012

Poly(ethylene-co-vinyl alcohol) (EVOH) films with two different ethylene contents (29 and 44 mol %) have been treated by hydrophobic plasma (CF 4, tetramethylsilane (TMS), CF 4/H 2, and CF 4/C 2H 2). Conditions of the cold plasma treatment were optimized by the water contact angle measurements as a function of the different plasma parameters (plasma power, gas flow, and treatment time). Chemical changes of the film surface were characterized by X-ray photoelectron spectroscopy. The obtained results revealed the presence of fluorine containing functional groups such as CF, CF 2, and CF 3 in the case of CF 4, CF 4/H 2, and CF 4/C 2H 2 plasma treatment and the presence of SiO xC y compounds after TMS treatment. The morphology of the plasma treated EVOH films was examined by atomic force microscopy, which indicated an increase of the film roughness after treatment. Negligible changes of thermal properties of the modified EVOH films were observed by means of the temperature modulated differential scanning calorimetry. The barrier properties of films were characterized by water permeability measurements. It was found that the hydrophobicity was significantly improved after plasma treatment and for some treated films the water permeability was decreased up to 28%. © 2012 American Chemical Society.


Delpouve N.,CNRS Laboratory for the Characterization of Amorphous Polymers | Stoclet G.,University of Lille Nord de France | Saiter A.,CNRS Laboratory for the Characterization of Amorphous Polymers | Dargent E.,CNRS Laboratory for the Characterization of Amorphous Polymers | Marais S.,CNRS Polymers, Biopolymer and Surfaces Laboratory
Journal of Physical Chemistry B | Year: 2012

Crystallization is among the easiest ways to improve polymer barrier properties because of the tortuosity increase within the material and the strong coupling between amorphous and crystalline phases. In this work, poly(lactic acid) (PLA) films have undergone α∼ thermal crystallization or different drawing processes. Although no effect of α∼ thermal crystallization on water permeability is observed, the drawing processes lead to an enhancement of the PLA barrier properties. This work clearly shows that, in the case of PLA, the crystallinity degree is not the main parameter governing the barrier properties contrary to the crystalline and amorphous phase organizations which play a key role. X-ray analyses confirm that the macromolecular chain orientation in the amorphous phase is the main cause of the improvement of the drawn PLA water barrier property. This improvement is due to the orthotropic structure formation for sufficient draw ratios, particularly when using the Simultaneous Biaxial drawing mode. Moreover, independently of the draw conditions, the drawing process tends to reduce the plasticization coefficient. Consequently, the drawn material barrier properties are not much affected by the water passage. © 2012 American Chemical Society.


Saiter A.,CNRS Laboratory for the Characterization of Amorphous Polymers | Delpouve N.,CNRS Laboratory for the Characterization of Amorphous Polymers | Dargent E.,CNRS Laboratory for the Characterization of Amorphous Polymers | Oberhauser W.,CNR Institute of Chemistry of organometallic Compounds | And 3 more authors.
European Polymer Journal | Year: 2016

The concept of Cooperative Rearranging Region (CRR), an efficient probe of the interaction level in nanocomposites, has been used in Poly(lactic acid) (PLA)-based composites with phyllosilicates prepared in the melt with organomontmorillonite (O-MMT) and using poly(butylene adipate-co-terephthalate) (PBAT) as coupling agent. The samples were crystallized from various thermal treatments in order to obtain a wide range of morphologies and microstructures and accurately characterized by XRD, TEM, standard DSC and MT-DSC with the aim to highlight the effect of lamellae dispersion and distribution at nanoscale onto the thermal features of resulting nanocomposites. The presence of different interaction levels at the interface PLA/O-MMT, even tuned by the presence of PBAT, affects both the crystalline phase structure (by differently promoting crystallization of α and α′ forms) and the distribution between the amorphous fractions (rigid and mobile). The variations of molecular dynamics are classified in two categories depending on the composite microstructure. Only in amorphous materials the cooperativity is driven by the filler/matrix interactions. In semi-crystalline materials, the morphological features linked to the presence of O-MMT and PBAT are overwhelmed by the confinement of the amorphous phase. Comparison between the two crystallization modes evidences a stronger change in the glass transition dynamics for systems exhibiting preponderant nucleation and high percentage of rigid amorphous fraction. © 2016 Elsevier Ltd. All rights reserved.


Delpouve N.,CNRS Laboratory for the Characterization of Amorphous Polymers | Saiter A.,CNRS Laboratory for the Characterization of Amorphous Polymers | Dargent E.,CNRS Laboratory for the Characterization of Amorphous Polymers
European Polymer Journal | Year: 2011

Effects of stereoregularity and crystallization mode on the amorphous phase dynamics are investigated for poly(lactic acid) PLA. An isothermal crystallization from the melt and a cold crystallization are imposed. For each PLA, the cold crystallization leads to the appearance of a less perfect crystalline phase and to an important rigid amorphous fraction RAF content (35%), although only 10% of RAF is generated after crystallization from the melt. Temperature Modulated Differential Scanning Calorimetry is used to determine the Cooperative Rearranging Regions (CRR) size at the glass transition temperature in the mobile amorphous phase MAP. It is shown that the CRR size in the MAP is not modified by the appearance and the spherulite growth. For the intra-spherulite MAP, a confining effect is evidenced, causing an amorphous phase thickness decrease during crystallization, and inducing a drastic CRR size reduction. © 2011 Elsevier Ltd. All rights reserved.


Bahous H.,University of Mostaganem | Soufi M.M.,CNRS Laboratory for the Characterization of Amorphous Polymers | Meuret L.,CNRS Laboratory for the Characterization of Amorphous Polymers | Benzohra M.,CNRS Laboratory for the Characterization of Amorphous Polymers
Macromolecular Symposia | Year: 2014

The aim of this work is to propose a reliable approach to estimate values of the relaxation time constant of polymers at the glass transition temperature. This approach consists of using a new thermo stimulated depolarisation current TSDC protocol which analyzes the relaxation current kinetics obtained after submitting the sample to an electrical field shock at constant temperature. The measurements have been performed on a series of polyethylene terephthalate (PET), polycarbonate (PC) and polyethylene terephthalate glycol (PETg) samples. Different temperatures were needed to explore the range of the glass transition domain of each polymer. The results compared to calorimetric and dielectric data show a good agreement. So we confirm that the value τms = 100 s often used for characterizing the molecular dynamic of the liquid glass former at Tg is not universal. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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