Depuis maintenant plusieurs années les nano-composites font l’objet de nombreuses études qui traitent de la fonctionnalisation des nanomatériaux. Parmi ces travaux publiés récemment, de très nombreux auteurs se sont intéressés à l’amélioration de la conductivité électrique de polymères thermoplastiques par introduction de nanotubes de carbone dans l’objectif de leur conférer de nouvelles propriétés ou fonctions spécifiques. Le principal but de notre étude est de produire un matériau qui verrait ses propriétés mécanique et électriques améliorées par l’incorporation de NTC bien dispersés. Les NTC sont donc dans un premier temps mélangés à la matrice thermoplastique puis broyés de manière à obtenir différents mélanges de granulés chargés à 0.01, 0.1 et 1%wt. Des testes rhéologiques et d’homogénéisations ont été réalisés pour détecter la qualité finale des mélanges obtenus et la variation de la distribution des NTC. Des informations supplémentaires ont été obtenues grâce à l’étude du comportement visqueux à des températures différentes comprise entre 25 à 120°C. Après injection, des éprouvettes ont été obtenues à partir de ces mélanges de manière à pouvoir les caractériser mécaniquement et électriquement. Une caractérisation mécanique et une analyse MEB ont été aussi effectuées de manière à étudier la microstructure du nano-composite, mais également d’estimer la distribution spatiale des NTC

GELIN, Jean-Claude

SAHLI, Mohamed

ZHANG, Jie

I-Revues

21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
Polymer nanocomposites based on functionalized carbon 
nanotubes: Improvement of dispersion, mixing and 
composite properties  
J. Zhang
a, b
, M. Sahli
a
, J-C. Gelin
a
 
a. Institut FEMTO-ST, Départ. Mécanique Appliquée, 24, chemin de l’épitaphe, Besançon France. 
b. Institut FEMTO-ST, Départ. MN2S, 32 avenue de l’observatoire, 25000 Besançon France. 
Résumé: 
Le but principal de notre étude est de produire un matériau qui verrait ses propriétés mécanique et 
électriques améliorées par l’incorporation de NTC bien dispersés. Les NTC sont donc dans un 
premier temps mélangés à la matrice thermoplastique puis broyés de manière à obtenir différents 
mélanges de granulés chargés à 0.1, 1 et 10%wt. Des testes d’homogénéisations et d’observation 
microscopique ont été réalisés pour déterminer la qualité finale des mélanges obtenus et la variation 
de la distribution des NTC. Des informations supplémentaires ont été obtenues grâce à l’étude du 
comportement rhéologique à différentes températures comprise entre 180 à 210°C. Après injection, 
des éprouvettes de traction ont été obtenues à partir de ces mélanges de manière à pouvoir les 
caractériser sous sollicitations mécaniques.  
Abstract: 
The main purpose of this study is to produce the materials which have the mechanical and electrical 
properties improved by the incorporation of CNTs well dispersed. The CNTs are initially mixed with 
the thermoplastic matrix and then crushed so as to obtain different mixtures of pellets loaded at 0.1, 1 
and 10wt%. Homogenization of the testes and microscopic observation were performed to determine 
the final quality of the resulting mixtures and variation in the distribution of CNTs. Additional 
information was obtained through the study of the rheological behavior at different temperatures 
between 180-210 °C. After injection molding process, the tensile specimens were obtained from these 
mixtures to be able to characterize under mechanical stress. 
Mots clefs: nano-composites, nanotubes de carbone, polymères chargés, dispersion, 
électromécanique.  
1 Introduction 
In recent years, carbon nanotubes (CNTs) have been more and more widely used in various fields; As 
a novel material, the carbon nanotubes have attracted the large attention of researchers after its first 
discovery in 1991 [1] because of its remarkable characteristics. CNTs are allotropes of carbon made of 
graphite; they have a tubular shape with a diameter in nanometer scale, and a length in micrometer 
scale. Due to this structure, carbon nanotubes possess some excellent physical, mechanical, thermal 
and electrical properties [2-5], these properties make them a very unique material with a whole range 
of promising applications including in nanocomposite (material reinforcement), nanotube-based field 
emitters, chemical sensing, biomedical (drug delivery), and nano electromechanical system (NEMS).  
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
Owing to the extremely high stiffness and strength, carbon nanotubes are usually used as a 
reinforcement material to improve the mechanical performance of composite; a lot of research works 
have been carried out to develop the CNTs/Polymers composites and investigate the evolution of their 
properties such as mechanical and rheological properties [6-8], it is discovered that a little content of 
CNTs can improve evidently the various physical properties of composites [9]. Moreover, through 
extensive research, one can also find that for the elaboration of CNTs/Polymers composites, the 
dispersion of carbon nanotubes is a key who can affect the final mechanical and electrical properties of 
nanocomposites [10]. However, actually the homogeneous dispersion of CNTs in polymer is difficult 
because of the inherently inert (hydrophobic) nature and tendency to agglomerate and entangle due to 
their size and shape [11], which lead to the decline of the composites mechanical and electrical 
properties; therefore, the research for improving the dispersion of CNTs is also very significant.  
In this paper, we focused on the application of carbon nanotubes in the polymer based nano-
composites systems (CNTs/Polymer). Firstly, we have investigated the dispersion of CNTs in different 
solution by using a particle size distribution analyser, and then the optimal solution has been used to 
realize CNTs/PP composite by melt mixing process; the rheological and mechanical properties of 
obtained nanocomposites have been investigated; the evaluation of homogenization for the composite 
have been executed by TGA (Thermogravimetric analysis). At last, the suitable dispersion of CNTs in 
polymer was realised and CNTs based homogenous nanocomposites were obtained with desired 
quality. 
2 Materials and Methods 
2.1  Materials  
Commercially isotactic polypropylene (PP - EP548N) were supplied by Sabic company® with melt 
flow Index (MFI) = 11g/10min (230 ºC/2.16 kg) and density = 0.892g/mm3. Multi-walled carbon 
nanotubes (MWNTs) - NC7000 were purchased from Nanocyl Company (Belgium) and were 
produced with purity higher than 90% and diameter range of 15-30 nm with a typical length of 1-10 
um. The morphology of carbon nanotubes was observed by scanning electron microscopy (figure 1). 
 
Table 1. Material characteristics of Polypropylene 
Material Polypropylene (PP), EP548N 
density [g/mm3] 0.892 
Transition temperature [°C] -10 
Melting temperature [°C] 160 
Thermal conductivity [W/mK] 0.14 
Melt flow index (MFI) [g/10min] [230°C/2.16kg]:11 
 
FIG. 1 – SEM Photo of carbon nanotubes – NC7000. 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
2.2  CNTs dispersion process 
In this work, the used CNTs are powdery; they have been dried in an oven at 80 °C for 24h before 
using. Before mixing process, particle-size distributions of multi-walled CNTs were measured using a 
Horiba model LA-950V2 laser scattering particle size analyzer. The dried powders of multi-walled 
CNTs were dispersed either in distilled water containing a Sodium dodecyl sulfate (SDS dispersions) 
or in acetone (act), and with dishwashing liquids (v) added later. The conditions of dispersions were 
circulation speed (C), ultrasound frequency (US) and agitation speed (A). 
2.3  Elaboration of CNTs/PP composites 
All Prior to the preparation of nanocomposites, all of the materials were dried in an oven for 24h at 
80ºC. PP/MWNT nanocomposites were carried out in a Brabender® mixer with a pair of rotor blades. 
The rotation speed and temperature of the mixing chamber were set at 30 rpm and 180 ºC, respectively, 
and blending continued for 30 min. During the mixing process, the PP was firstly introduced in the 
mixing chamber, then the solution containing CNTs was gradually introduced; because of the high 
mixing temperature, the water and all the other dispersion agents will be evaporated during the process. 
After pelletizing, blend granules were injection-molded into standard test specimen using Billon 
injection molding machine. The mould temperature was kept at 25°C and the barrel temperature 
ranged from 200 to 220 ºC. The injection pressure and injection speed 100bar and 40rpm, respectively.  
3 Results and discussion 
3.1  Analysis of particle size distribution 
With the help of the particles size distribution analyzer, we can investigate the dispersion stat of CNTs 
in solution with different solvents. The figure 2 demonstrates the CNTs size distribution in four 
different solutions, we can observe that the measured CNTs median diameter and average diameter are 
respectively 8.80, 8.29, 43.10, 3.48μm and 9.38, 8.39, 49.28, 3.64μm in four solutions: dishwashing 
liquids, dispersions (SDS), acetone, and solvent mixed with acetone and dishwashing liquids. 
Comparing to the average diameter (1.5μm) provided by CNTs supplier, one can conclude that the 
solvent mixed with acetone and dishwashing liquids can improve effectively the dispersion of CNTs in 
the solution; the measured high values of CNTs average diameter in the other solutions are due to the 
agglomeration of CNTs, these values are actually the diameters of the agglomeration of CNTs.   
 
FIG. 2 – The CNTs particles size distribution in solution for different solvents. 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
3.2  Mixing characterization 
The curves in figure 3 shows the final mixing torque variation of the PP and CNTs/PP composite 
(loading ratio between 0.1 to 10 wt.%), vs. mixing time. Uniform mixing is achieved when the torque 
reaches a steady state value.  From the results, it reveals that: 1) adding the CNTs can increase the 
final mixing torque of the composites; 2) increasing the CNTs content can increase the final mixing 
torque, when the CNTs content is below to 1wt.%, there is no evident difference comparing to the pure 
PP; when the CNTs content is beyond 1wt.%, an evident increase of the mixing torque for the 
composite is observed.                  
 
FIG. 3 – Mixing torque vs. time for PP and PP loaded CNTs at 180°C during 30 mins.  
3.3  Homogeneities analysis 
In order to investigate the homogeneity of the CNTs/PP composite, the electronic scanning 
microscopy (SEM) has been used to observe the dispersion state of the CNTs in the polypropylene. 
The result is illustrated in figure 4a, it can be observed that the carbon nanotubes have been almost 
dispersed homogenously in the polypropylene. Besides, the thermo gravimetric analysis (TGA) was 
also carried out to investigate composites homogeneity from 20°C to 500°C, the figure 4b 
demonstrated the TGA results of same nanocomposite for three tests, we can see that the TGA curves 
decreased from about 400°C, which means the beginning of the degradation for PP; it can be also 
found that the TGA curves of the tree tests are almost superimposed; thence one can conclude that the 
obtained composite by melt mixing process is homogenous. 
  
FIG. 4 – (a) SEM photo of the composite loaded with 10wt.% of CNTs, (b) mass loss of the 
nanocomposite loaded with 0.1 wt% of CNTs for three tests. 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
3.4  Rheological characterizations 
In our work, the viscosity of CNTs/PP composites have been measured by a rheometer HAAKE 
MARS III with a cone-and-plate geometry of a diameter 35mm and an angle 2°. The test temperature 
is set from 180 to 210°C beyond the melting temperature of polypropylene and below its degradation 
temperature. The shear rate has been chosen in a range from 10-1 to 102s-1. Figure 5a shows the 
dependence of the melt shear viscosity of the PP loaded with 0.1wt.% CNTs on shear rate, it can be 
seen that the viscosity of CNTs/PP composite decreases with an increase of shear rate. It can also be 
observed that the melt shear viscosity decreases with a rise of temperature when shear rate is constant. 
The conclusion that increasing the temperature and shear rate can decrease the viscosity of CNTs/PP 
composite and improve their fluidity can be obtained.  
3.5  Mechanical properties 
For investigating the influence of the CNTs to the composites mechanical properties, some specimens 
with dumbbell shaped were obtained by injection molding with the mixed CNTs/PP composites. The 
results of tensile tests are shown in figure 5b, it describes the evolution of the tensile stress as a 
function of strain for PP and CNTs loaded PP. One can observe that the increasing of CNTs loading 
ratio leads to a rapid increase in the Young's modulus; for 1wt.% and 10 wt.% CNTs loading, the 
Young’s modulus of composites increases respectively 13% and 40% comparing to the no-loaded PP. 
One conclusion is obtained that the addition of carbon nanotubes can significantly increase the 
mechanical properties of the final composites. 
 
FIG. 5 – (a) The shear viscosity of PP loaded with 0.1wt% CNTs vs. shear rate at different 
temperature, (b) Evolution of tensile stress vs. strain for PP and CNTs loaded PP at ambient 
temperature. 
4 Conclusion 
In this work, the multi-walls carbon nanotubes (MWCNTs) have been mixed with polypropylene to 
realize the CNTs/PP composites. Firstly, the dispersion state of CNTs in different solutions has been 
investigated; the optimal solvent has been selected and used in the mixing process to improve the 
CNTs homogenous dispersion in PP. Then, the CNTs/PP composites with different loading ratio from 
0.1 to 10.wt% have been obtained by melt mixing process; the homogeneity of elaborated composite 
has been evaluated by the micro observation and thermo gravimetric analysis; more over their 
rheological and mechanical properties were also characterized. Finally, the results indicate that the 
solvent mixed with acetone and dishwashing liquids can improve effectively the dispersion of CNTs in 
solution and the addition of CNTs in the polypropylene can effectively increase the polypropylenes 
mechanical property.        
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
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Polymer nanocomposites based on functionalized carbon nanotubes: Improvement of dispersion, mixing and composite properties

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