Macromolecular NanotechnologyMorphological and structural characterization of polypropylene/conductive graphite nanocomposites
Introduction
Polyolefins can be compounded with a variety of common and special fillers, reinforcements, and modifiers to yield specific properties in a wide range of applications. Among these additives are electrically and thermally conductive modifiers that can provide protection against static accumulation, electrostatic discharge and molding cycle reduction. Various fillers, some of them metallic, are used to produce the modification of conductive properties of the neat polymer. However, high concentrations of filler (e.g. 30% carbon black), are needed, that can take a toll on physical and esthetical properties of the polymer: selection of conductive material has often involved compromises. The preparation of polymer composites by dispersion of small loadings of nanosized fillers in a polymeric matrix has lately attracted much attention in the academia and the industry for its potential in improving the performance of macromolecular materials [1]. Nanoparticles may confer to the matrix physical–mechanical properties much improved with respect to traditional micron-sized fillers, due mainly to a maximization of the polymer-filler interfacial region [2], [3]. Although considerable success was achieved with polymer-layered silica composites [1], reports on the use of graphite, another common type of layered filler with a high aspect ratio, are comparatively rare [4], [5], [6], [7]. Natural occurring graphite consists of graphene layers formed by sp2 hybridized carbon atoms. Van der Waals forces bind the layers one to each other. Single graphite sheets are stacked in aggregates, in which they have a spacing of 0.335 nm [5], [8]. The electrical conductivity of graphite arises from the delocalized π bonds, resulting from the sp2 hybridization. The weak van der Waals forces that keep neighboring layers together allow the possibility of intercalating molecules in the interlayer space, thus increasing the interplanar spacing and achieving a thorough mixing of the filler in the matrix. The production of polypropylene/graphite composites is especially difficult because hardly any interaction occurs between polypropylene (PP) and chemically inert graphite layers [7]. In order to do so, conductive expanded graphite (CG) can be used instead of naturally occurring graphite. A number of methods have been reported [9], [10], [11], [12], [13], [14], [15] to intercalate atoms and molecules between graphene layers, increasing the interlayer spacing by a distance determined by the size of the guest. Intercalation is known to occur along with a charge transfer between the intercalate species and the graphene layers [10]. The obtained compounds are called graphite intercalation compounds (GIC) and can exhibit the staging phenomenon [10], [11], [13], in which each intercalated layer is separated by a definite number of graphene layers. The stage number n designates the number of graphene layers that separate adjacent intercalate layers.
The aim of this work was the study of the structure of PP/CG composites as a function of the filler content, using small-angle X-ray scattering (SAXS), wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM).
Section snippets
Samples and sample preparation
The polymeric matrix employed for the preparation of the composites was a propylene–ethylene random copolymer (ethylene 1.5% w/w) produced by Basell Polyolefins. Seven samples were manufactured with increasing quantities of filler: 0.02%, 0.2%, 2%, 4%, 8%, 12% and 20%. The CG powder used as filler was Conductograph® (SGL Carbon Group) (density 0.14 g/cm3). All the composites were prepared by melt mixing in a camera mix (Brabender) at 200 °C. The obtained materials were processed by compression
Results and discussion
Preliminarily, a characterization of the filler was carried out. SEM pictures of CG are shown in Fig. 1(a) and (b). It can be seen that graphite was completely fragmented, resulting in graphite sheets with diameters ranging from about 1 to 10 μm. WAXD and SAXS analysis was also carried out on pristine CG, obtaining the diffractograms shown in Fig. 2, Fig. 3.
As may be seen in Fig. 2, a very intense signal appeared at 26.5° 2θ. This peak is ascribable to the stacking of single graphene layers at a
Conclusions
The structure and morphology of CG and of PP/CG composites were studied by WAXD, SAXS and SEM. The composites obtained by melt mixing of different amounts of CG with PP were characterized. An effect of graphite on the crystallization behavior was observed and the opposite influences of enhanced thermal conductivity and hinder of chain mobility on the formation of γ-phase were discussed. An understanding of the dependence of the structure and morphology of PP/CG composites is critical for the
Acknowledgement
This work was carried out in the context of the European Network of Excellence Nanofun-Poly. V.C. gratefully acknowledges financial support by Basell Italia S.p.A., through a Federchimica grant and by the University of Padova. The authors thank Dr. Claudio Furlan of Centro Universitario Grandi Apparecchiature Scientifiche (CUGAS) of the University of Padova for the SEM micrographs.
References (44)
- et al.
Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials
Mater Sci Eng
(2000) Interfaces and interphases in multicomponent materials: past, present, future
Eur Polym J
(2005)- et al.
Framework for nanocomposites
Mater Today
(2004) - et al.
Preparation of polystyrene/graphite nanosheet composite
Polymer
(2003) - et al.
Mechanical and thermal properties of graphite platelet/epoxy composites
Polymer
(2004) The interactions of two chemical species in the interlayer spacing of graphite
Synth Met
(2000)- et al.
Transport behavior of PMMA/expanded graphite nanocomposites
Polymer
(2002) - et al.
Exfoliation of graphite flakes and its nanocomposites
Carbon
(2003) - et al.
Facile synthesis of highly conductive polyaniline/graphite nanocomposites
Eur Polym J
(2004) - et al.
Exfoliation process of graphite via intercalation compounds with sulfuric acid
J Phys Chem Solids
(2004)
Development of the γ-crystal form in random copolymers of propylene and their analysis by DSC and X-ray methods
Polymer
Small-angle X-ray scattering from high-density polyethylene: lamellar thickness distributions
Polymer
Charakterisierung von graphit-FeCl3-verbindungen als teilweise geordnete schichtstrukturen
Carbon
Small-angle X-ray scattering of graphite–ferric chloride intercalation compounds
Synth Metals
Electrical properties of composites based on conjugated polymers and conductive fillers
Carbon
Influence of stereoirregularities on the formation of the γ-phase in isotactic polypropene
Polymer
Morphology, structure and properties of a poly(1-butene)/montmorillonite nanocomposite
Polymer
Fabrication and characterization of nylon 6/foliated graphite electrically conducting nanocomposite
J Polym Sci Polym Phys Ed
Polypropylene/graphite nanocomposites by thermo-kinetic mixing
Polym Eng Sci
Ultrathin graphite oxide-polyelectrolyte composites prepared by self-assembly: transition between conductive and non-conductive states
Adv Mater
Exfoliation of graphite
J Mater Sci
Dispersion of graphite nanosheets in a polymer matrix and the conducting property of the nanocomposites
Polym Eng Sci
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