Relations between microstructural development and ... between microstructural development and rheological properties in polymer nano-composites thse mahi hassanabadi hojjat doctorat

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  • RELATIONS BETWEEN MICROSTRUCTURAL DEVELOPMENT AND RHEOLOGICAL PROPERTIES IN POLYMER NANO-

    COMPOSITES

    Thse

    MAHI HASSANABADI HOJJAT

    Doctorat en gnie chimique Philosophiae Doctor (Ph.D.)

    Qubec, Canada

    Mahi Hassanabadi Hojjat, 2013

  • iii

    Rsum

    Cette thse porte principalement sur la comprhension des relations entre la microstructure

    et les proprits rhologiques des nano-composites base dun copolymre dthylne-

    actate de vinyle (EVA).

    La premire partie de l'tude concerne les nano-composites dEVA avec de la cellulose

    nanocrystalline (NCC). Cette partie cherche infrer la structure dchantillons inconnus

    laide de mesures rhologiques. En analysant les proprits obtenues par des mesures

    rhologiques en cisaillement et en longation, les principaux mcanismes tant lorigine

    du renforcement de ces nano-composites sont tudis en dtail.

    Dans la deuxime partie du travail, on sintresse aux nano-composites contenant des

    particules isomtriques (CaCO3) et anisomtrique (argile). L'objectif est de dterminer

    l'effet de variables structurelles comme les interactions polymre-particule et particule-

    particule, l'tat de dispersion, et en particulier la forme des particules sur les proprits

    finales. Les mcanismes par lesquels ces paramtres influencent les proprits rhlogiques

    ont t abords en lien avec les prdictions par un modle de fonction molculaire de

    contrainte (MSF). Il a t constat que plus les particules sont non-isomtriques, plus les

    interactions polymre-particule et les interactions entre les particules sont leves. Ainsi,

    l'effet de largile est beaucoup plus important que celui du CaCO3, et ce pour presque tous

    les comportements rhologiques tudis. La plupart des paramtres rhologiques ont

    montr une divergence autour du seuil de percolation. Par consquent, les modles bass

    sur la dynamique des chanes (modle MSF) ne peuvent prdire le comportement aprs la

    percolation. Pour les systmes percols, les modles bass sur le rseau fractal, qui

    considrent les interactions entre les particules, ont t utiliss.

  • v

    Abstract

    The main objective of this thesis is to understand the relations between microstructure and

    rheological properties of polymer nano-composites based on ethylene vinyl acetate (EVA)

    copolymer.

    The first part of the study is related to EVA-nano crystalline cellulose (NCC) composites.

    As a first step, determination of the unknown structure of the samples using rheological

    methods was investigated. By analyzing the properties obtained under shear and

    extensional deformations, the mechanisms leading to polymer reinforcement were

    investigated in details.

    In the second part, nano-composites containing isometric (CaCO3) and anisometric (clay)

    particles were used. The focus here was to determine the effect of structural variables such

    as polymer-particle and particle-particle interactions, state of dispersion, and in particular

    particle shape on the final properties of these nano-composites. The mechanisms involving

    these parameters were investigated through rheological properties and discussed with

    respect to experimental data. Predictions via the molecular stress function (MSF) model are

    also presented. It was found that higher particle anisomety led to greater polymer-particle

    and particle-particle interactions. Therefore, the effect of clay was much higher than CaCO3

    on almost all the rheological parameters studied. But, lower predictability was found

    around the percolation concentration. Consequently, while a model based on chain

    dynamics could predict the behavior below percolation, such model failed to predict the

    response at higher concentrations. For percolated systems, models based on fractal

    networks, which include particle-particle interactions, were used.

  • vii

    Foreword

    This dissertation is composed of six chapters. In the first chapter, a general introduction on

    nano-composites and rheology is presented. The importance of rheological analysis for

    understanding structure-property relationships of nano-composites is highlighted and

    reviewed according to the literature. Then, Chapters 2-5 report on the results of the project

    which were published as four scientific articles as follows:

    Chapter 2

    H. Mahi, D. Rodrigue, Linear and non-linear viscoelastic properties of ethylene vinyl

    acetate/nanocrystalline cellulose composites, Rheol. Acta, 51, 127-142 (2012).

    In this part of the work, for the first time, the linear and non-linear rheological behavior of

    melt blended cellulosic nano-composites was discussed with the aim to get some

    information about the structure of nano-composites by rheological measurements. Because

    of the carbon-based structure of both nano-cellulose and polymeric matrix, it was not

    possible to distinguish the particles and the matrix by typical microscopic techniques like

    TEM and SEM. Therefore, rheological analysis was used to capture some structural

    parameters and to discuss on the molecular origin of the observed responses under different

    deformations.

    Chapter 3

    H. Mahi, D. Rodrigue, Relationships between linear and non-linear shear response of

    polymer nanocomposites, Rheol. Acta, 51, 991-1005 (2012).

    While in chapter 2, rheology was used for a system in which nano-particles and matrix

    were indistinguishable by typical microscopic methods, the rheology of two nano-

    composites (based on clay and CaCO3) for which the particles are distinguishable inside the

    polymer matrix (EVA) was studied. Three main objectives were achieved in this work.

    First, since the structure of the systems was analysed by TEM and SEM, investigations

    relating rheology to structure were validated by morphological analyses. Second, the effect

  • viii

    of particle shape on the rheological properties was studied with an emphasis to distinguish

    the effect of particle-particle and polymer-particle interactions. Finally, the relations

    between nano-composite structure (data under SAOS) and material flow (data obtained in

    shear transient tests) were studied in detail.

    Chapter 4

    H. Mahi, D. Rodrigue Effect of nano-particles on flow and recovery of polymer

    nanocomposites in the melt state, Int. Polym. Proc., 28, 151-158 (2013).

    This part of the work is a continuation of the work presented in chapter 3. In chapter 3, the

    effect of two geometrically different nano-particles was studied and discussion about the

    importance of particle-particle network was made. In this chapter, in order to validate the

    statements in chapter 4, as well as to study the recovery behavior of the nano-composites,

    the behavior of the pre-sheared systems was studied.

    Chapter 5

    H. Mahi, M. Abbasi, M. Wilhelm, D. Rodrigue Validity of the modified molecular stress

    function theory to predict the rheological properties of polymer nanocomposites, J. Rheol.,

    57, 881-899 (2013).

    Considering the wide applicability of models based on the tube concept to predict the

    rheological properties of polymeric systems, it was tried to examine to what extent a model

    based on the tube theory can predict the rheology of nano-composites. In this context, a

    modified version of the molecular stress function (MSF) theory was used to predict the

    non-linear flow behavior under extension and shear. The validity and the limits of the tube

    theory for polymer nano-composites were investigated. In order to better understand the

    molecular origin of the behavior observed for nano-composites, the observed response of

    the systems under LAOS was quantified by FT-rheology.

    Finally, in chapter 6, the general conclusions are given and completed by suggestions for

    future works.

  • ix

    It should be mentioned that for all papers, I performed the experimental work including

    data analysis and wrote the first draft of the papers which were revised by all co-authors. In

    chapter 5, the MSF calculations were performed by M. Abbasi.

    Furthermore, in addition to the above mentioned papers, some other results in this work

    were presented in conferences/presentations as:

    H. Mahi, D. Rodrigue, Rheology, and microstructure in polymer nanocomposites,

    Karlsruhe Institute for Technology (KIT), Karlsruhe, Germany, (2013/06).

    H. Mahi, D. Rodrigue, Effect of MWNTs on Rheological Properties of Polymer

    Nanocomposites: A Comparison between Different Nano-Particle Shapes, SoR 84th

    Annual Meeting, Pasadena, California, USA (2013/02).

    H. Mahi, M. Abbasi, M. Wilhelm, D. Rodrigue, Effect of Nano-Particle Geometry on

    Rheological Properties of Nanocomposites Using SAOS and LAOS Deformations, XVIth

    International Congress on Rheology, Lisbon, Portugal (2012/08).

    H. Mahi, D. Rodrigue, Effect of nano-particles on the recovery of polymer

    nanocomposites in the melt state, PPS Regional meeting, Kish Island, Iran (2011/10).

    H. Mahi, D. Rodrigue, Effect of nano-particle shape on linear and non-linear rheological

    properties of polymer nano-composite, SoR 83rd

    Annual Meeting, Cleveland, Ohio. USA

    (2011/09).

    H. Mahi, D. Rodrigue, Shear rheology of nanocomposites based on cellulose, clay and

    CaCO3, Karlsruhe Institute for Technology (KIT), Karlsruhe, Germany, (2011/09).

    H. Mahi, D. Rodrigue, Rheological analysis as a tool to