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Mechanical, Rheological and Electrical Properties of TPU/Fullerene Nano-composites:
Effect of Surface Modification of Fullerene
Ümit Tayfun,1* Yasin Kanbur, 2 Ufuk Abacı,3 Hasan Yüksel Güney 3 and Erdal Bayramlı 1,4
1 Department of Polymer Science and Technology, Middle East Technical University, Ankara 06531, Turkey
2 Department of Metallurgical and Materials Engineering, Karabük University, Karabük 78050, Turkey
3 Department of Physics, Kocaeli University, Kocaeli 41380, Turkey
4 Department of Chemistry, Middle East Technical University, Ankara 06531, Turkey
Abstract— In this study, thermoplastic polyurethane (TPU) nano-composites with fullerene loadings varying from 0.5 to 2
weight % were prepared by melt mixing. Nitric acid oxidation and silanization were applied to fullerene surface to achieve
better interfacial interactions with TPU matrix. The influence of acid and silane surface modifications of fullerene on
mechanical, rheological and electrical properties of TPU based nano-composites are investigated. Tensile testing, thermal
properties, melt flow index (MFI), dielectric measurements and morphological properties of composites are reported.
Fullerene is a member of carbon nanostructures family
which has a zero-dimensional structure. Research efforts
based on fullerene chemistry with combination of
macromolecular chemistry led to develop easily processable
fullerene-containing polymeric materials [1]. However,
organic modifications required since pristine fullerene tends to
form aggregates very easily and is difficult to handle.
Formation of self-aggregate causes poor miscibility of
fullerenes and limits its applications [2,3].
Polymer nano-composites containing fullerenes have
great potential for versatile applications which include
photodiodes and optical interrupters, polymer
photoconductors, electrodes in lithium batteries, and electro-
optical structures in nano-electronics and nonlinear optics [4].
Incorporating nano-fillers in polymeric matrices is applied in
three different ways such as solution, in-situ and melt mixing.
Many of the lab-scale studies have been made by using mainly
first two methods but melt compounding is the one that is
most practical and compatible for large scale nano-composite
production in industrial applications. The efforts towards
fullerene reinforced composites for practical applications that
have been performed by using melt compounding are very
limited in academic field [5,6,7,8].
Thermoplastic polyurethane (TPU) has desirable
properties for many applications like excellent mechanical
properties, chemical resistance and easy processibility. Beside
these properties, TPU is a fully recyclable polymer that makes
it cost effective. Major of TPU applications are across a range
of markets and applications including automotive, sporting
goods, medical devices, tubes, hoses, wires and cables.
In this study, fullerene is functionalized by using nitric
acid and amino functional silane. The functionalized fullerene
surfaces were characterized with Fourier transform infrared
spectroscopy (FTIR) and Scanning electron microscopy with
energy dispersive X-ray spectroscopy (SEM/EDX).
Pristine and surface functionalized fullerenes were
incorporated at four different compositions of 0.5, 1, 1.5 and 2
weight % in TPU matrix via the melt compounding in counter
rotating twin screw micro-extruder. Test samples were
prepared by injection molding. Mechanical properties, melt
flow characteristics, thermal properties, electrical
conductivities and morphological studies were evaluated by
tensile test, MFI test, Differential scanning calorimetry (DSC)
analysis, Dielectric measurements and SEM, respectively.
Table-I Tensile strength values of 2 wt % fullerene containing composites
Composite Tensile strength
(MPa)
TPU/
Fullerene
30.9
TPU/Ni-
Fullerene
34
TPU/Si-
Fullerene
35.2
Surface oxidation and silanization caused slight increase
in tensile strength values. Percent elongations are higher for
composites that include modified fullerene compared to
pristine fullerene containing composites. DSC analysis reveals
that melting point of the composites increased with
incorporation of surface functionalized fullerene. MFI values
of treated fullerene containing composites are much higher
than that of neat fullerene that attributed to better dispersion of
fullerene in TPU matrix.
Observations from the SEM micrographs of fracture
surfaces of selected composites indicate that nitric acid and
silane treatments improve the interfacial adhesion between
fullerene and TPU matrix. Agglomeration formations
gradually decrease for surface modified loaded composites.
Significant increase in dielectric constant takes place for
composites with the addition of nitric acid and silane modified
fullerene. According to AC-conductivity measurements in the
temperature range of 80-400 K, conductivity increases with
fullerene addition along 80 to 300 K temperature range.
Conductivities of composites drops down beyond the 300 K
due to relaxation of polymer chains.
Surface oxidation and silanization caused better
dispersion due to improved interactions between fullerene and
TPU matrix. These interfacial interactions resulted in
enhancements in mechanical, electrical and thermal properties
of TPU/fullerene nano-composites.
*Corresponding author: tayfun.umit@metu.edu.tr
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