RELATIONS BETWEEN MICROSTRUCTURAL DEVELOPMENT AND RHEOLOGICAL PROPERTIES IN POLYMER NANO-
MAHI HASSANABADI HOJJAT
Doctorat en gnie chimique Philosophiae Doctor (Ph.D.)
Mahi Hassanabadi Hojjat, 2013
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.
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)
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.
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:
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
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
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.
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.
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
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
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