CHAPTER 2
THERMAL PROPERTIES OF THE
POLYPROPYLENE/MULTI-WALLED
CARBON NANOTUBE COMPOSITES
G. E. ZAIKOV, A. D. RAKHIMKULOV, S. M. LOMAKIN,
I. L. DUBNIKOVA, A. N. SHCHEGOLIKHIN, E. YA. DAVIDOV, and
R. KOZLOWSKI
CONTENTS
2.1 Introduction .......................................................................................................20
2.2 Experimental ..................................................................................................... 21
2.2.1 Materials ..............................................................................................21
2.2.2 Nanocomposite Processing ..................................................................21
2.2.3 Investigation Techniques ......................................................................23
2.3 Discussion and Results .....................................................................................24
2.3.1 Nanocomposite Structure .....................................................................24
2.4 Thermal-Oxidative Degradation of PP/MWCNT Nanocomposites .................26
2.4.1 Kinetic Analysis of Thermal Degradation of PP/MWNT .................... 28
2.5 Combustibility of PP/MWCNT Nanocomposites .............................................32
Keywords ...................................................................................................................35
References ..................................................................................................................35
20 Engineering of Polymers and Chemical Complexity
2.1 INTRODUCTION
Studies of thermal and fire resistant properties of the polypropylene/multi-walled car-
bon nanotube composites (PP/MWCNT) prepared by means of melt intercalation are
discussed. The sets of the data acquired with the aid of non-isothermal thermogravi-
metric (TG) experiments have been treated by the model kinetic analysis. The ther-
mal-oxidative degradation behavior of PP/MWCNT and stabilizing effect caused by
addition of multi-walled carbon nanotube (MWCNT) has been investigated by means
of thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR)
spectroscopy.
The results of cone calorimetric tests lead to the conclusion that char formation


MWCNT which determine high performance carbonization during thermal degrada-
tion process.

-
composites under high temperature tests.
At present time the great attention is given to the study of properties of polymeric
nanocomposites produced on the basis of well known thermoplastics (PP, PE, PS,
PMMA, polycarbonates, and polyamides) and carbon nanotubes (CN). The CNs are
considered to have the wide set of important properties like thermal stability, reduced
combustibility, electroconductivity, and so on [1-7]. Thermoplastic polymer nanocom-
posites are generally produced with the use of melting technique [1-12].
Development of synthetic methods and the thermal characteristics study of PP/
MWCNT nanocomposites were taken as an objective in this chapter.
A number of papers pointed at synthesis and research of thermal properties of
nanocomposites (atactic polypropylene (aPP)/MWCNT) were reported [10-12]. It is
remarkable that PP/MWCNT composites with minor level of nanocarbon content (1–
5% by weight) were determined to obtain an increase in thermal and thermal-oxidative
stability in the majority of these publications.
Thermal stability of aPP and aPP/MWCNT nanocomposites with the various con-
centrations of MWCNT was studied in the chapter [10]. It was shown that thermal
degradation processes are similar for aPP and aPP/MWCNT nanocomposites and ini-
tial degradation temperatures are the same. However, the maximum mass loss rate
temperature of PP/MWCNT nanocomposites with 1 and 5% wt of MWCNT raised by
40–70°C as compared with pristine aPP.
Kashiwagi et al. published the results of study of thermal and combustion prop-
 
rate of heat release (RHR) was detected during combustion research with use of cone
calorimeter. A formation of char network structure during the combustion process was
considered to be the main reason of combustibility decrease. The carbonization in-
 

abnormal dependence of maximum RHR upon MWCNT concentration is closely re-
Thermal Properties of the Polypropylene/Multi-Walled 21
lated with thermal conductivity growth of PP/MWCNT nanocomposites during high
temperature pyrolysis and combustion.
2.2 EXPERIMENTAL DETAILS
2.2.1 MATERIALS
Isotactic polypropylene (melting flow index = 0.7 g/10 min) was used as a polymer
matrix in this chapter. The MWCNT (purchased from Shenzhen Nanotechnologies
Co. Ltd.) were used as a carbon-containing nanofillers. This product contains low
amount of amorphous carbon (less than 0.3 wt%) and could be produced with differ-
ent size characteristics - different length and different diameter and therefore different
diameter to length ratio. Size characteristics for three MWCNT used in this chapter are
given in Table 1. Sizes and structure of initial MWCNT were additionally estimated by
scanning electron microscopy (SEM) (Figure 1).
TABLE 1 Properties of MWCNT
Designation D, nm L,
μm
Density, g/cm
3
Specific
surface area,
m
2
/g
  5–15 2 40–300
 40–60 1–2 2 40–300
 40–60 5–15 2 40–300
2.2.2 NANOCOMPOSITE PROCESSING
Compositions were prepared by blending CN with melted polymer in a laboratory
mixer Brabender at 190°C. TOPANOL
®
(1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphe-
nyl)butane) and dilaurylthiodipropionate (DLTP) were added in the amount of 0.3
wt% and 0.5 wt% as antioxidants to prevent thermal-oxidative degradation during
polymer processing.
         -

therefore greater nanotube distribution in a polymer matrix [14-23]. In order to func-
tionalize MWCNT we used preliminary ozone treatment of MWCNT followed by
ammonolysis of epoxy groups on the MWCNT surface. The selective ozonization of
MWCNT was carried out with ozone-oxygen mixture (ozone concentration was 2.3 ×
10
–4
mol/L) in a bubble reactor. Then the ammonolysis of oxidized MWCNT has been
carried out by tert-butylamine in the ultrasonic bath (35 kHz) at 50
o
C for 120 min with
following evaporation of tert-butylamine excess. Infrared (IR) transmission spectra
of tablet specimens of MWCNTs in KBr matrix was analyzed by using Perkin-Elmer

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