Nanocomposites Synthesis, Structure, Properties and New Application Opportunities
Nanocomposites Synthesis, Structure, Properties and New Application Opportunities
Nanocomposites Synthesis, Structure, Properties and New Application Opportunities
1, 1-39, 2009
Review Article
2009
1. Introduction
Nanocomposites are composites in which at least one of the
phases shows dimensions in the nanometre range (1 nm = 109 m)1.
Nanocomposite materials have emerged as suitable alternatives to
overcome limitations of microcomposites and monolithics, while posing
preparation challenges related to the control of elemental composition
and stoichiometry in the nanocluster phase. They are reported to be the
materials of 21st century in the view of possessing design uniqueness and
property combinations that are not found in conventional composites.
The general understanding of these properties is yet to be reached2, even
though the first inference on them was reported as early as 19923.
The number of published papers containing words such as nanoscience, nanotechnology, nanomaterials, etc., doubled in 1.6 years4 in
the late 1990s. Also, a literature survey made by the authors reveals
that about 13.420 papers (of which 4028 contain the keywords nanocomposite and polymer in Web of Science-ISI: updated on 10February
2009) have been published on nanocomposites in the last two decade
(19882008). Similarly, patents with complete document on nanocomposites account for about 4663 during the same period as per Scirus
(www.scirus.com). Additionally, specific conferences and special issues
of some journals have been devoted exclusively to the emerging science
and technology of nanomaterials.
It has been reported that changes in particle properties can be observed when the particle size is less than a particular level, called the
critical size (Table 1)5. Additionally, as dimensions reach the nanometre
level, interactions at phase interfaces become largely improved, and
this is important to enhance materials properties. In this context, the
surface area/volume ratio of reinforcement materials employed in the
preparation of nanocomposites is crucial to the understanding of their
structureproperty relationships. Further, discovery of carbon nanotubes
(CNTs) in 19916 and their subsequent use to fabricate composites
exhibiting some of the unique CNT related mechanical, thermal and
electrical properties7-9 added a new and interesting dimension to this
area. The possibility of spinning CNTs into composite products and
textiles10 made further inroads for the processing and applications of
CNT-containing nanomaterials. Nowadays, nanocomposites offer new
*e-mail: kgs_satya@yahoo.co.in
Camargo et al.
Table 1. Feature sizes for significant changes in properties reported in nanocomposite systems [reproduced from reference 5 with the kind permission
of the author and the Japan Society of Powder and Powder Metallurgy].
Properties
Class
Metal
Ceramic
Polymer
Examples
Fe-Cr/Al2O3, Ni/Al2O3, Co/Cr, Fe/MgO, Al/CNT,
Mg/CNT
Al 2O 3/SiO 2, SiO 2/Ni, Al 2O 3/TiO 2, Al 2O 3/SiC,
Al2O3/CNT
Thermoplastic/thermoset polymer/layered silicates, polyester/TiO2, polymer/CNT, polymer/
layered double hydroxides.
from the matrix and the potential of these composites for possible macro
scale CNT-polymer production. Here, problems encountered so far are
considered, and hints given regarding a critical volume fraction of CNTs
to get appropriate strengthening (as observed in microcomposites);
possible failure mechanisms in such composites are also presented.
Finally, to the best of our knowledge, and in view of the very limited
work on metal-based nanocomposites including the ones with CNT
reinforcements, no review is available to-date on this system.
Considering these facts and also the absence of a more general
review comprising the three different kinds of nanocomposites (metal-,
ceramic- and polymer-based), this paper gives an overview of them,
including those with incorporation of CNTs. However, while doing so
only a few relevant publications2,4,7-9,11,14-308 are considered here. The
main features, current status and recent developments in the area are
provided, focussing on the preparation methods, structure, properties
and applications of these systems to avoid repetition. Also, the potential uses of nanocomposites and the opportunities they provide, along
with perspectives for the future and market and safety aspects are also
presented. Nanocomposite coating is not covered, in order to keep the
focus of the review.
Materials Research
addition, the incorporated phase undergoes phase transition in conjunction with the volume expansion initiated by the stress field of a
propagating crack, contributing for the toughening and strengthening
processes, even in nanocomposites36.
The potential of ceramic matrix nanocomposites (CMNC),
mainly the Al2O3/SiC system, was revealed by the pioneering work of
Niihara37,38. Most studies reported so far have confirmed the noticeable
strengthening of the Al2O3 matrix after addition of a low (i.e. ~10%)
volume fraction of SiC particles of suitable size and hot pressing of the
resulting mixture. Some studies have explained this toughening mechanism based on the crack-bridging role of the nanosized reinforcements39.
Consequently, the incorporation of high strength nanofibres into ceramic
matrices has allowed the preparation of advanced nanocomposites with
high toughness and superior failure characteristics compared to the
sudden failures of ceramic materials40.
Metal matrix nanocomposites (MMNC) refer to materials consisting of a ductile metal or alloy matrix in which some nanosized reinforcement material is implanted. These materials combine metal and
ceramic features, i.e., ductility and toughness with high strength and
modulus. Thus, metal matrix nanocomposites are suitable for production of materials with high strength in shear/compression processes
and high service temperature capabilities. They show an extraordinary
potential for application in many areas, such as aerospace and automotive industries and development of structural materials41. Both MMNC
and CMNC with CNT nanocomposites hold promise, but also pose
challenges for real success.
Polymer materials are widely used in industry due to their ease of
production, lightweight and often ductile nature. However, they have
some disadvantages, such as low modulus and strength compared
to metals and ceramics. In this context, a very effective approach to
improve mechanical properties is to add fibres, whiskers, platelets
or particles as reinforcements to the polymer matrix. For example,
polymers have been filled with several inorganic compounds, either
synthetic or natural, in order to increase heat and impact resistance,
flame retardancy and mechanical strength, and to decrease electrical
conductivity and gas permeability with respect to oxygen and water
vapour25. Furthermore, metal and ceramic reinforcements offer striking routes to certain unique magnetic, electronic, optical or catalytic
properties coming from inorganic nanoparticles, which add to other
polymer properties such as processibility and film forming capability42.
Using this approach, polymers can be improved while keeping their
lightweight and ductile nature31,43-47. Another important aspect is that
nanoscale reinforcements have an exceptional potential to generate
new phenomena, which leads to special properties in these materials as
will be seen later. It may be pointed out that the reinforcing efficiency
of these composites, even at low volume fractions, is comparable to
40-50% for fibres in microcomposites34.
Addition of reinforcements to a wide variety of polymer resins
produces a dramatic improvement in their biodegradability. This underlines a good example of polymer matrix nanocomposites [PMNC]
as promising systems24 for ecofriendly applications. Besides, future
space mission concepts involve large ultra lightweight spacecrafts
termed Gossamer48. The materials required for such spacecrafts
should possess and maintain a specific combination of properties for
over a long period (10-30 years) in relatively harsh environments such
as 173 to 373 K for satellites and cycling temperatures of 1273K for
re-entry vehicles, exposure to atomic O2 and solar radiation. Some of
the Gossamer spacecraft devices are movable mechanical parts such as
gears and gyroscopes, and others include solar arrays/sails, antennae
and drives, sunshields, rovers, radars, solar concentrators, and reflector
arrays. It is reported48 that these parts will have to be fabricated from
flexible, appropriate materials, which can be folded or packaged into
small volumes, similarly to those available in conventional launch vehicles, and should possess many of the common mission concepts. This
is needed since the structure consisting of ultra lightweight parts would
2. Processing of Nanocomposites
2.1. Raw materials
As with microcomposites, CMNC matrix materials include Al2O3,
SiC, SiN, etc., while metal matrices employed in MMNC are mainly
Al, Mg, Pb, Sn, W and Fe, and a whole range of polymers, e.g. vinyl
polymers, condensation polymers, polyolefins, speciality polymers
(including a variety of biodegradable molecules) are used in PMNC.
In general, it is the reinforcement that is in the nanorange size in these
materials. Both synthetic and natural crystalline reinforcements have
been used, such as Fe and other metal powders, clays, silica, TiO2 and
other metal oxides, although clays and layered silicates are the most
common176. This is so due to their availability with very low particle
sizes and well-known intercalation chemistry18,50,51, in addition to
generating improved properties even when they are used at very low
concentrations252. Most of these reinforcements are prepared by known
techniques: chemical, mechanical (e.g. ball milling), vapour deposition,
etc.; details of these may be found in many of the references given in
the following sections.
Similarly, CNTs are prepared mostly by chemical/vapour deposition methods and details are available elsewhere319-327. A bibliometric
analysis of CNTs made in 2000335 revealed that about 49% of the patents
filed between 1992-1999 were related to the processing of CNTs and
about 14% to their structure, properties and models. CNTs consist of
graphene cylinders and are available in two varieties, as single walled
(SWCNT) and multi walled (MWCNT), with about 70% yield in the
case of SWCNT317. While SWCNTs are single graphene cylinders,
MWCNTs consist of two or more concentric cylindrical sheets of
graphene around a central hollow core. Both types exhibit physical
characteristics of solids, either metallic or semiconducting in nature,
with microcrystallinity and very high aspect ratios of 103.
Surface modifications of reinforcements are carried out to give
homogeneous distribution with less agglomeration, and to improve
interfacial bonding between the matrix and the nanosized reinforcements. Details on these can be found in the references given for each
type of nanocomposites in later Sections. In the case of CNTs, use of
surfactants, oxidation or chemical functionalization of surfaces are
some of the techniques employed27. Chemical methods may be more
effective, particularly for polymer and ceramic matrices. Physical
blending and in situ polymerization are used for improving dispersion
in the case of CNT-reinforced polymer composites, while alignment
of CNTs could be achieved by techniques such as ex-situ techniques
(filtration, template and plasma-enhanced chemical vapour deposition,
force field-inducements, etc.)33.
Method
Powder Process
Polymer Precursor
Process
Sol-Gel Process
System
Al2O3/SiC
Al2O3/SiC, SiN/SiC
SiO 2 /Ni, ZnO/Co, TiO 2 /
Fe 2O 3, La 2O 3/TiO 2, Al 2O 3/
SiC, TiO2/Al2O3, Al2O3/SiO2,
Al2O3/SiO2/ ZrO2, TiO2/Fe2
TiO5, NdAlO3/Al2O3
Procedure
Ref.
i) Selection of raw materials [mostly powders - small average size, uniformity 38, 53
and high purity]; ii) Mixing by wet ball milling or attrition milling techniques
in organic or aqueous media; iii) Drying by heating, using lamps and/or ovens, or by freeze-drying; iv) consolidation of the solid material by either hot
pressing or gas pressure sintering or slip casting or injection moulding and
pressure filtration.
Mixing a Si-polymeric precursor with the matrix material Pyrolysis of the
16,
mixture using a microwave oven, generating the reinforcing particles.
54-57
Hydrolysis and polycondensation reactions of an (in)organic molecular pre- 58-73
cursor dissolved in organic media. Reactions lead to the formation of threedimensional polymers containing metal-oxygen bonds (sol or gel) drying
to get a solid material and further consolidation by thermal treatment.
Materials Research
Camargo et al.
and Chemical methods, which include the sol-gel process, colloidal and
precipitation approaches and the template synthesis. While Table3a
lists systems prepared by some of these methods, Table 3b shows their
advantages and limitations. Scheme 1a depicts the conventional powder
method and Scheme 1b illustrates the polymer precursor route used in
the synthesis of an Al2O3/SiC nanocomposite.
A large variety of parameters affecting the sol-gel process, such
as type of solvent, timing, pH, precursor, water/metal ratio, etc., allow a versatile control of structural and chemical properties of the
final oxide materials61. Regarding the processing of carbon nanotubes
(CNT)-reinforced ceramic nanocomposites, many approaches have been
described20,74-112. Several of these are listed in Table 3c.
Method
Advantages
Powder Process
Limitations
Ref.
Simple
Polymer
Precursor
Process
Sol-Gel Process
Process
Hot pressing
System
SiO2/CNT,
SiC/CNT
Al2O3/CNT
Catalytic decomposition
Solvothermal process
Al2O3/CNT
Fe3O4/CNT
Procedure
Ref.
Dispersion of CNTs and SiO2 glass powders into ethanol, stirring and ultrasonic treatment, 20, 74
drying and hot pressure sintering in pure N2 atmosphere. Mixing of nanoparticles of SiC
and carbon nanotubes
Preparation of the alumina matrix by anodizing growth of CNTs into its porous walls. 75, 77
CNTs grow into hexagonal array of straight pores extending from the substrate to the
matrix surface.
Use of acetylene over Al2O3 powder impregnated with iron catalysts.
76
Dispersion of CNTs in EDA (ethylenediamine) using ultrasonic treatment; addition of
78
an iron(III)-urea complex; heating in a Teflon-lined autoclave maintained at 200 C for
50hours, followed by cooling to room temperature.
A-Al2O3 + B-SiC
Ultrasonic bath
Coating/drying
mbols.
aixa
em.
Al2O3/SiC nanocomposite
(a)
Scheme 1. a) Conventional Powder Processing, and b) Polymer Precursor route.
Al2O3/SiC nanocomposite
(b)
Process
Spray Pyrolysis
System
Procedure
Fe/MgO, W/Cu i) Dissolution of the inorganic precursors (starting materials) in a suitable solvent to get the
liquid source; ii) Generation of a mist from this liquid source using an ultrasonic atomizer;
iii) Use of a carrier gas to carry the mist into a pre-heated chamber. iv) Vaporisation of the
droplets in the chamber and trapping with a filter, promoting their decomposition to give the
respective oxide materials; v) Selective reduction of the metal oxides to produce the respective metallic materials.
Liquid Infiltration
Pb/Cu, Pb/Fe, i) Mixing of fine reinforcement particles with the matrix metal material; ii) Thermal treatW/Cu/ Nb/Cu, ment, whereby the matrix melts and surrounds the reinforcements by liquid infiltration; iii)
Nb/Fe, Al-C60
Further thermal treatment below the matrix melting point, to promote consolidation and
eliminate internal porosity.
Rapid Solidification Al/Pb, Al/X/Zr i) Melting of the metal components together; ii) Keeping the melt above the critical line
Process(RSP)
(X = Si, Cu, Ni), of the miscibility gap between the different components to ensure homogeneity; iii) Rapid
Fe alloy
solidification of the melt by any process, such as melt spinning.
RSP with
Al/SiC
Use of ultrasonics for mixing and for improving wettability between the matrix and the
ultrasonics
reinforcements.
High Energy
Cu-Al2O3
Milling the powders together till the required nanosized alloy is obtained NanocomposBall Milling
ite.
CVD/PVD
Al/Mo, Cu/W, PVD: i) Sputtering/evaporation of different components to produce a vapour-phase; ii)
Cu/Pb
Supersaturation of the vapour phase in an inert atmosphere to promote the condensation of
metal nanoparticles; iii) Consolidation of the nanocomposite by thermal treatment under
inert atmosphere.
CVD: Use of chemical reactions to get vapours of materials, followed by consolidation.
Chemical Processes Ag/Au, Fe/SiO2, Colloidal Method: i) Chemical reduction of inorganic salts in solution to synthesize metal
(Sol-gel, Colloidal) Au/Fe/Au
particles; ii) Consolidation of the dry material; iii) Drying and thermal treatment of the resulting solid in reducing atmosphere, such as H2, in order to promote selective oxide reduction
and generate the metal component.
Sol-gel process: i) Preparation of two micelle solutions using mesoporous silica containing
0.1 M HAuCl4 (aq.) and 0.6 M NaBH4 (aq.); ii) Mixing under ultraviolet light till complete
reduction of the gold.
For Fe/Au-containing nanocomposites: i) Synthesis of the iron shell; ii) Preparation of the
second shell and drying of the powders after second gold coating; iii) Pressing of the mixture
to get the final material..
Ref.
11
11,
114-117
118-122
123
124
125-129
130-134
Materials Research
Camargo et al.
Table 4b. Advantages and limitations of processing methods for metal-based nanocomposites.
Process
Spray Pyrolysis
Liquid Infiltration
Rapid Solidification
Process (RSP)
RSP with ultrasonics
High Energy Ball
Milling
CVD/PVD
Chemical Processes
(Sol-Gel, Colloidal)
Advantages
Effective preparation of ultra fine, spherical and
homogeneous powders in multicomponent systems,
reproductive size and quality.
Short contact times between matrix and reinforcements; moulding into different and near net shapes
of different stiffness and enhanced wear resistance;
rapid solidification; both lab scale and industrial
scale production.
Simple; effective.
Limitations
High cost associated with producing large quantities
of uniform, nanosized particles.
Ref.
11
Capability to produce highly dense and pure materials; uniform thick films; adhesion at high deposition
rates; good reproducibility.
Simple; low processing temperature; versatile; high
chemical homogeneity; rigorous stoichiometry
control; high purity products.
Process
Electroless
Coating
Electroless
Coating
Hot Pressing
Nanoscale
Dispersion
PM/Infiltration
System
Co-CNT
Procedure
Ref.
i) Use of electroless plating bath containing the activated CNTs, the cobalt precursor, the reducing 135
agent CoSO4.7H2O, the complexing agent and a buffer. CNT with deposit of Co coating results;
ii) Thermal treatment at 873 K, 200 torr, under a 10% H2/N2 flow gas.
Sn / CNTs, SnSb0.5/ Reduction of SnCl2 and SbCl3 precursors by KBH4 in the presence of CNTs.
136,
CNT and Sn 2 Sb/
137
CNT
Al/CNT
Mixing of powders through grinding for 30 minutes and hot pressing at 793 K under a pressure 138
of 25 MPa.
Al/CNT
Preparation of the precursor of MWCNT (13 nm dia and 10-50 m long) with natural rubber and 139
ethyl propylene; mixing with Al powder; rolling into sheets by compression moulding at 353 K;
placing of this precursor on an Al (99.85%) plate of 28 m grain size; heating to 1073 K in N2
atmosphere for one hour; final cooling.
Mg-Al2O3f-CNT
a) Mechanical mixing of Mg powders with MWCNT (1 vol. %) using alcohol and acid; sinterisa- 141
tion at 550 C under 25 MPa pressure;
b) Infiltration of molten Mg through performs of Al2O3 fibers (25 vol. %; 40-100 m long) covered
with MWCNTs under gas pressure.
Silicate layer
Polymer
Heat
Aliphatic chains
Intermolecular interactions
Figure 1. Melt intercalation synthesis of polymer/clay nanocomposites [reproduced from ref. 165 with the kind permission of the authors, the American
Chemical Society, USA].
Process
Intercalation /
Prepolymer from
Solution
In-situ Intercalative
Polymerization
Melt Intercalation
Template Synthesis
(a) Mixing
(b) In situ
polymerization
Sol-Gel Process
System
Procedure
Ref.
Clay with PCL, PLA, HDPE, PEO, Employed for layered reinforcing material in which the polymer may 5, 18,
PVA, PVP, PVA, etc.
intercalate. Mostly for layered silicates, with intercalation of the polymer 151or pre-polymer from solution. Use of a solvent in which the polymer or 157
pre-polymer is soluble and the silicate layers are swellable.
Montmorillonate with N6/PCL/ Encasing of the layered silicate within the liquid monomer or a mono- 158PMMA /PU/Epoxy
mer solution formation of polymer between the intercalated sheets. 164
Polymerization by heat or radiation, by diffusion of a suitable initiator or
by a catalyst fixed through cation exchange inside the interlayer, before
the swelling step.
Montmorillonate with PS/PEO/PP/ Annealing of a mixture of the polymer and the layered host above the 165PVP, Clay-PVPH
softening point of the polymer, statically or under shear. Diffusion of 169
polymer chains from the bulk polymer melt into the galleries between
the host layers during annealing (Figure 1).
Hectorite with PVPR, HPMC, In situ formation of the layered structure of the inorganic material in an 170PAN, PDDA, PANI
aqueous solution containing the polymer. The water soluble polymer acts 175
as a template for the formation of layers. Widely used for the synthesis of
LDH nanocomposites, but less developed for layered silicates.
PVA)/Ag; PMMA/Pd Polyester/ (a) Mixing of either polymer or monomer with reinforcing materials;
178TiO2
(b1) Dispersion of inorganic particles into a precursor of the polymeric 183
PET/CaCO3, Epoxy vinyl ester/ matrix (monomer); (b2) Polymerization of the mixture by addition of
Fe3O4 ; Epoxy vinyl ester/-Fe2O3; an appropriate catalyst;
Poly (acrylic acid)(PAA)/Ag, PAA/ (b3) Processing of this material by conventional moulding technoloNi and PAA/Cu
gies.
AgNO3, NiSO4 and CuSO4;
Use of ultrasonics for dispersion in epoxy systems. Exposition of AG
systems to 60 Co -ray to promote simultaneous polymerization and
metal nanoparticle formation.
Polyimide/SiO2; 2-hydroxyethyl Embedding of organic molecules and monomers on sol-gel matrices; 24,
acrylate (HEA)/SiO2, polyimide/ introduction of organic groups by formation of chemical bonds In- 184silica. PMMA/ SiO2, polyethylacr- situ formation of sol-gel matrix within the polymer and/or simultaneous 186
ylate/ SiO2, polycarbonate / SiO2 generation of inorganic /organic networks.
and poly (amide-imide)/TiO2
Process
Intercalation /
Prepolymer from
Solution
In-situ Intercalative
Polymerization
Melt Intercalation
Template Synthesis
Advantages
Synthesis of intercalated nanocomposites based
on polymers with low or even no polarity. Preparation of homogeneous dispersions of the filler.
Easy procedure, based on the dispersion of the
filler in the polymer precursors.
Environmentally benign; use of polymers not
suited for other processes; compatible with industrial polymer processes.
Large scale production; easy procedure.
Sol-Gel Process
Limitations
Industrial use of large amounts of solvents.
Ref.
5, 18,
151-157
Process
Direct Mixing
Solution Mixing
System
Thermoset Resins
Thermoplastic Resins
(PS/Epoxy)
Procedure
Dispersion of CNTs; Cure.
Dispersion of 0.2-1% CNTs, (100 nm
dia, 10 m long); Removal of solvent
or precipitation of polymer; Cure.
Melt Mixing
Polymers, N6
Mechanical mixing of CNTs with prepolymer melt followed by extrusion,
injection or compression moulding.
In-situ Polymerization Polyaniline-CNT,
Use of ultrasonics for dispersion in
MMACNT, Epoxy-CNT, monomer/matrix; Cure.
Poly(ether-ester)
Others
PP-CNT, PVK-SWCNT, Solid-state mechanochemical pulverizaiPP-SWCNT, PANi
tion; blending + sonication; melt blendSWCNT
ing; VDP.
Remarks
Modification of polymer behaviour;
synergistic effect; shape memory
nanocomposites.
Use of 0.2-2.0% MWCNT, twin screw
mixer.
Ref.
187
188-193
49, 194,
195
196-202
203-206
Materials Research
Camargo et al.
Table 6a. Summary of processing methods for conducting polymer nanocomposites [reproduced from ref. 19 with the permission of the authors and the
American Chemical Society, USA]
Polymer of interest
(Shell)
PPy and PAn
WO3
Table 6b. Categorization of processing methods for conducting polymer nanocomposites [reproduced from reference 19 with the permission of the authors
and the American Chemical Society, USA].
Conducting polymer nanocomposites
Inorganic-in-organic
Organic-in-inorganic
mbols.
aixa
em.
Chemical preparation
Nanocomposites with colloidal stability (SiO2, SnO2, BaSO4, etc., as
core)
Nanocomposites with improved physical and mechanical properties
(Fe2O3, ZrO2, TiO2, etc., as incorporated materials)
Electrochemical preparation
Nanocomposites with charge storage, optical and electrochromic activities
(incorporation of MnO2, SnO2, CB, PB, WO3, SiO2, etc.)
Nanocomposites with catalytic activities (incorporation of catalytically
active Pt, Pd, Cu, etc. microparticles and some bimetallic couples like
Pd/Cu, etc.)
Nanocomposites with magnetic susceptibility (using Fe2O3, -Fe2O3, Nanocomposites with magnetic susceptibility
etc., magnetic particles)
(-Fe2O3 magnetic macroanion)
Nanocomposites with dielectric, energy storage, piezoresistive and
catalytic activities (with BT, POM, PtO2, TiO2, Pd, Pt, etc., incorporation)
Nanocomposites with grafted surface (NH2/COOH functional groups
on surface and colloidal silica as core)
ls.
After mixing, the polymer chains intercalated and displace
the solvent within the interlayer of the silicate
Layered silicate
Polymer
ls.
Phase separated
(microcomposite)
(a)
Intercalated
(nanocomposite)
(b)
Exfoliated
(nanocomposite)
(c)
Properties
Density (Mgm3)
SWNT
0.8
150-1587 (Expt.)
3000 (Theor.)
1.2
50-500
Can sustain bending to large angles
and restraightening without damage.
1109
50-500
6000 at 273 K
3073 in vacuum and 823 in air
500 (Parallel)
22 x 103 (Perpendicular with plane)
MWNT
Corresponding values in other known materials
1.33-1.40
One sixth of steel and one-half of the density of
(Expt.)
aluminium.
1.8 (Theor.)
Much higher than known materials.
0.4-3.7
10-60
-
10
Materials Research
Camargo et al.
Matrix/Reinforcements
Si3N4/SiC
MoSi2/ZrO2
B4C/TiB2,
Al2O3/SiC
MgO/SiC
Mullite/SiC
Al2O3/ZrO2
Al2O3/Mo, Al2O3/W
Al2O3/NdAlO3
Properties
Improved strength
and toughness
Improved
photoluminescence
Reference
97
98
99
38
37
100
101
102
73
39, 103
Properties/Material
Vickers Hardness [GPa]
Youngs Modulus [GPa]
Fracture Strength [MPa]
Fracture Toughness [MPam1/2]
Al2O3/SiCp
composite
106-283
2.4-6.0
Table 10. Fracture strength and fracture toughness for Si N /SiC nano- and
3 4
microcomposites106, 107.
Properties/Material
Si3N4/SiC
composite
700
5.3
Si3N4/SiC
nanocomposite
1300
7
Al2O3/SiCp
nanocomposite
22
383
549-646
4.65.5
500 nm
500 nm
(a)
(b)
50 nm
(c)
11
ls.
4 Mm
5.00 k 1.0.2.6
0.2 Mm
11 5 k 0.1.0.8
(c)
(b)
(a)
Figure 4. a) SEM, b) TEM images of Al2O3/SiC nanocomposites; and c) TEM (high magnification) showing a SiC grain [reproduced from references 103, 104
with the kind permission of the authors, Elsevier].
SiC
Intragranular SiC
(Roman), tamanho 8.
nhas com 0.5 de Stroke.
centes a "Dados grficos" com 0.6 de Stroke.
ouver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
o de barras com 10% de preto quando houver texto e 50% quando no.
ela ou figura devem estar todos em Ingls.
em estar dentro de caixas de texto com 2 mm de distncia nas extremidades.
ra ou grfico deve estar em "Sentence case".
pas dever ter 1 ponto de Stroke.
fias, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
arte inferior da imagem, fundo preto).
presentam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
Al2O3
Intergranular
SiC
A = Si3N4
0.5 Mm
0.1 Mm
(a)
(b)
Figure 6. TEM images of Si3N4/SiC nanocomposites [reproduced from Reference107 with the kind permission of the authors, Elsevier, the American
Institute of Chemical Engineers @ 1997, AIChME].
(Roman), tamanho 8.
SiC
nhas com 0.5 de Stroke.
centes a "Dados grficos" com 0.6 de Stroke.
ouver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
o de barras com 10% de preto quando houver texto e 50% quando no.
ela ou figura devem estar todos em Ingls.
em estar dentro de caixas de texto com 2 mm de distncia4 nas
nm extremidades.
ra ou grfico deve estar em "Sentence case".
Figure 5. HRTEM image of the interface region between Al2O3, SiC particles
pas dever ter 1 ponto
de Stroke.
in the Al
O /SiC nanocomposite [reproduced from reference 39 with the kind
2 3
permission
of the authors,
Elsevier].
fias, seguir padro correto (respeitando
estilo
de escala, posio dos dados, caixa
arte inferior da imagem, fundo preto).
presentam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
(a)
(b)
(c)
90
2.2
70
2.0
60
1.8
50
1.6
1.4
40
1.2
30
2.4
80
1.0
20
10
15
20
25
30
CNT volume content %
Figure 8. Effect of CNT volume content on the mechanical properties of SiO2/
CNT nanocomposites [reproduced from reference 74 with the kind permission
of the authors, Elsevier].
2400
2200
2000
1800
Table 11. Electrical conductivity of CNT ceramic nanocomposites [reproduced from reference 110 with permission of the authors and the American
Institute of Physics, USA].
Materials
Electrical conductivity
(S/m)
1012
15
1050
1510
3345
40-80
280-400
Pure Al2O3
Friction coefficient
Materials Research
Camargo et al.
1600
1400
1200
1000
800
600
0.6
3.0
0.5
2.5
0.4
2.0
0.3
1.5
0.2
1.0
0.1
0.5
12
400
0.0
200
0
6
8
4
CNT content (wt. (%))
(a)
10
12
14
4
6
8
CNT content wt.
Friction coefficient
10
12
0.0
14
Wear loss
(b)
Figure 9. Variations of a) microhardness, and b) friction coefficient, wear loss as a function of CNT content in Al2O3/CNT materials [reproduced from reference 76 with the kind permission of the authors, Elsevier].
13
Matrix/reinforcement
Ag/Au
Ni/PSZ and Ni/YSZ
Cu/Nb
Al/AlN
ls.
Al/SiC
CNT/Sb and CNT/SnSb0.5
-Fe/Fe23C6/Fe3B
1 Mm
Figure 10. TEM image of CNT, SiO2 nanocomposite mixture [reproduced
from reference 74 with the kind permission of the authors, Elsevier].
Cu/Al2O3
CNT/Fe3O4
Properties
Reference
Improvement in catalytic
96
activity
Improved hardness and
5, 13
strength
Improved microhardness
123
Higher compression
95
resistance and low strain
rate
Improved hardness and
143
elastic moduli
Improvements in Li+
136, 137
intercalation properties
Drastic improvement
122
in hardness
Improved microhardness
124
Improved electrical
78
conductivity
Table 13. Hardness values (GPa) of the ingot and ribbon samples prepared
from the Fe/Fe23C6/Fe3B nanocomposite [reproduced from reference 122 with
the permission of the Authors and Elsevier].
ls.
1 Mm
(a)
100 nm
(b)
Figure 11. SEM micrographs of Al2O3/CNT materials: a) at low magnification, and b) at high magnification [reproduced from reference 76 with the
kind permission of the authors, Elsevier].
Sample
As-solidified
600 C
650 C
700 C
750 C
800 C
850 C
Ingot
10.3
8.0
6.6
6.5
-
Ribbon
11.0
11.0
15.6
16.2
12.2
12.0
10.5
14
Materials Research
Camargo et al.
as - Materials Research
14
s, seguir padro
corretooccurred
(respeitando
escala,released
posio from
dos dados,
changes
dueestilo
to O2deatoms
Fe2O3caixa
during reduce inferior da imagem,
fundo16b,
preto).
tion. Figure
c presents TEM micrographs of uniformly distributed
95,96
ceramic
particles
in Al and
Ag metal
matrices
respectively.
sentam figurasnanosize
ex: (a), devem
estar
centralizadas
na parte
inferior
da imagem.
12
Tiwari et al.
10
Wear volume
Roman), tamanho
8.
distributed
over the entire material122.
as com 0.5 de Stroke.
In the case of Al/SiC nanocomposites (Figure 15), only two
ntes a "Dadosphases
grficos"
0.6 deinStroke.
arecom
visible
the TEM images: SiC (granular fine grains) and
Al (overall
matrix).
No substituir
more sharp
have appeared
ver rosa do ventos
na imagem
original,
pelaring-spot
padro dapatterns
paleta symbols.
in
the
electron
diffraction
pattern
(SAED),
indicating
the
formation of
de barras com 10% de preto quando houver texto e 50% quando no.
147
fine,
nanosized
powders
containing
the
brittle
SiC
phase
embedded
ou figura devem estar todos em Ingls.
in the ductile Al matrix.
m estar dentro de caixas de texto com 2 mm de distncia nas extremidades.
Other metal-ceramic nanocomposites are shown in the SEM and
ou grfico deve estar em "Sentence case".
TEM photographs of Figure 16. Figure 16a is a SEM micrograph of Fe/
s dever ter 1 ponto
Stroke. heat treated at 873 K and reduced at 1073 K11. Volume
MgO de
composite
8
6
4
Present study
2
0
10
20
30
40
50
60
Load (N)
Figure 13. Wear loss of nanosized vs. microsized leaded Al alloys [reproduced
from reference 78 with the kind permission of the authors, the American
Chemical Society, USA].
Properties / Material
as - Materials Research
Al/SiC
composite
88.4
78
Al/SiC
nanocomposite
100
160
Roman), tamanho 8.
Youngs modulus (GPa)
as com 0.5 de Stroke.
Hardness (H ) (Kg/mm2)
ntes a "Dados grficos" com v0.6 de Stroke.
ver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
3.0preto quando houver texto e 50% quando no.
de barras com 10% de
ou figura devem estar todosSiC
em Ingls.
Al100-x composites
3
m estar dentro de caixas de texto com 2 mm de distncia nas extremidades.
ou grfico deve estar2.5
em "Sentence case".
s dever ter 1 ponto de Stroke.
Fe3B
Fe23C6
100 nm
200 nm
A-Fe
Figure 14. TEM images, corresponding SAED for the nanocomposite -Fe/
Fe23C6/Fe3B ribbons heat-treated at 850 C [reproduced from reference 122
with the kind permission of the authors, Elsevier].
s, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
2.0fundo preto).
e inferior da imagem,
sentam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
(b)
SiC
Al
matrix
crografias, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
50
95imagem, fundo preto).
o na parte inferior da
que representam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
90
45
85
Youngs modulus
Shear modulus
80
75
4
6
8
SiC content, x (vol. %)
10
40
35
12
(a)
20 nm
Figure 15. a) TEM image, b) the corresponding SAED of mechanically solid
state mixed Al/SiC nanocomposite [reproduced from reference 147 with the
kind permission of the author, Elsevier].
ta symbols.
ades.
Al
500 nm
Al + AIN
1 Mm
40 nm
200 nm
(a)
(b)
(c)
Figure 16. TEM micrographs of a) Fe/MgO; b) Al/AlN and c) Ag/SiO2 nanocomposites [reproduced from references 11, 95, 96 respectively, with the
kind permission of the authors, Elsevier].
gurascaixa
- Materials Research
dos,
5
4
3
2
1
0
15
stage of wear, while the behaviour at late stages was affected by the
processing technique. In addition, some elongation of particles was also
observed, along with coarsening of Pb particles during sliding, due to
dislocation-aided diffusion.
ls.
50
100
150
(a)
200
250
300
7
6
Resistivity, 10 6 .cm 1
(Roman), tamanho 8.
5
imagem.
nhas com 0.5 de Stroke.
4 0.6 de Stroke.
centes a "Dados grficos" com
3 original, substituir pela padro da paleta symbols.
ouver rosa do ventos na imagem
o de barras com 10% de preto2 quando houver texto e 50% quando no.
ela ou figura devem estar todos
1 em Ingls.
em estar dentro de caixas de texto com 2 mm de distncia nas extremidades.
0
ra ou grfico deve estar em "Sentence
case". 100
0
50
150
200
250
300
(b)
pas dever ter 1 ponto de Stroke.
Resistivity, 10
6 .cm
1
3
(Roman), tamanho 8.
nhas com 0.5 de Stroke.
2
centes a "Dados grficos" com 0.6 de Stroke.
1
ouver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
o de barras com 10% de preto0 quando houver texto e 50% quando no.
0
50
100
150
200
250
300
ela ou figura devem estar todos em Ingls.
(c)
em estar dentro de caixas de texto com 2 mm de
distncia nas
Temperature
(K)extremidades.
ra ou grfico deve
estar 17.
em Dependence
"Sentence case".
Figure
of electrical resistivity in Al/CNT composites with tempas dever ter 1 ponto
de a)
Stroke.
perature:
Al/CNT 1 wt. (%), b) Al/CNT 4 wt. (%), and c) Al/CNT 10wt.(%) [reproduced
referenceestilo
138 with
the kindposio
permission
of theacaixa
uthors,Elsevier].
fias, seguir padro corretofrom
(respeitando
de escala,
dos dados,
30 nm
(b)
250 nm
(a)
(b)
143002
20.0 kV
x35.0 k
514 nm
Figure 19. a) TEM images of CNTs, and b) SEM image of Al/CNT 1 wt.(%) [reproduced from reference 138 with the kind permission of the authors,Elsevier].
16
Materials Research
Camargo et al.
3.3. Polymer
matrix nanocomposites
s (Roman), tamanho
8.
inhas com 0.5 de Stroke.
Structure-property correlations in polymer nanocomposites have
ncentes a "Dados
com 0.6
de Stroke.
beengrficos"
extensively
dealt
with in a recent book292, which describes the
properties
of polymers
based
on nanostructure
and morhouver rosa domechanical
ventos na imagem
original,
substituir pela
padro
da paleta symbols.
phology.
Table
presents
examples
of these
properties.
to de barras com
10% de
preto15
quando
houver
texto e 50%
quando
no.
ela ou figura devem
todos em
Ingls.- discontinuous reinforcement
3.3.1.estar
Polymer
matrix
vem estar dentro
de
caixas
de
texto
com
2 mm de distncia nas extremidades.
(non-layered) nanocomposites
ra ou grfico deve estar em "Sentence case".
The de
reinforcing
apas dever ter 1 ponto
Stroke. materials employed in the production of polymer
18
grain
boundaries of the aluminium matrix.
guras - Materials
Research
0.9
0.8
0.7
0.6
0.5
0.4
1
afias, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
example, when the three dimensions are in the nanometre scale, they are
parte inferior da imagem, fundo preto).
called isodimensional nanoparticles. Examples include spherical silica,
presentam figuras
(a), devem
centralizadasnanoclusters
na parte inferior
219 da imagem.
metalex:particles
andestar
semiconductor
. The second kind of
1.0
2
vol. (%) TiO2
(a)
(c)
1000 nm
1000 nm
(b)
(d)
1000 nm
1000 nm
Figure 21. TEM micrographs depicting the level of TiO2 nanoparticle dispersion
within the polyester matrix in the polyester/TiO2 nanocomposite. Volume fraction of particles: a) 1 vol. %; b) 2 vol. %; c) 3 vol. %; and d) 4 vol. % [reproduced
from reference 180 with the kind permission of the authors, Elsevier].
Matrix/reinforcement
Polypropylene/montmorillonite
Nylon-6/Layered-silicates
Polylactide/Layered-silicates
Epoxy/Layered-silicates
Polyimide/montmorillonite
Polystyrene/Layered-silicates
Polyethylene oxide/Layered-silicates
Poly(methyl methacrylate)/Pd
Polyester/TiO2
Epoxy/SiC
Properties
Improved tensile strength, strain at break, stiffness, Youngs modulus and tensile stress
Improved storage modulus, tensile modulus, HDT, tensile stress and reduced flammability.
Improved bending modulus, bending strength, distortion at break, storage modulus, gas barrier
properties and biodegradability.
Improved tensile strength and modulus.
Improved tensile strength, elongation at break and gas barrier properties.
Improved tensile stress and reduced flammability.
Improved ionic conductivity.
Improved thermal stability.
Improved fracture toughness and tensile strength.
Improved microhardness, storage modulus and elastic modulii.
In the majority of publications on clay and layered compounds [e.g. R. Schllhorn, Angew. Chem. Int. Ed. Engl., 19 (1980) 983], layered structures are classified
as two-dimensional (grown preferentially in two dimensions). This is opposite to the usual interpretation given by polymer nanocomposite scientists, who consider
the number of nanodimensions of the reinforcing agents to classify them. In the case of layered structures, they are in the nanorange in only one dimension, though
they may possess three dimensions and hence the material is termed as one-dimensional. On the same line, nanoparticles and nanotubes, which have three and two
nanorange dimensions respectively, are classified as isodimensional and two-dimensional respectively. Following the majority of the papers dealing with polymer
nanocomposites, which use the nomenclature adopting the number of nanorange dimensions, the same terminology will be followed throughout this paper.
Reinforcing material
Polymer chains
ls.
100 nm
500 nm
(a)
17
(b)
(Roman), tamanho 8.
nhas com 0.5 de Stroke.
centes a "Dados grficos" com 0.6 de Stroke.
ouver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
o de barras com Acc.V
10% deSpot
preto
quando houver texto e 50% quando no.
Magn WD
500 nm
450 nm
1-0001 10.0kV x40.0k
30.0estar
kV 2.0
50000x
ela ou figura devem
todos
em Ingls.
6.1 CNR IRT eMR
(c) 2 mm de distncia nas extremidades.
(d)
em estar dentro de caixas de texto com
Figure
photograph
ra ou grfico deve
estar 23.
em TEM
"Sentence
case". of a) PAA/Ag; b) PVP/Fe2O3; c) PET/CaCO3, and
d) PMI/SiO nanocomposites.
PAA = polyacrylic acid, PVP = 4-polyvinylpy2
pas dever ter 1 ponto de Stroke.
ridine, PET = poly(ethylene terephthalate), PMI = polymaleimide [reproduced
fias, seguir padro
correto
(respeitando
estilo
escala,
posio dos
caixa
from
references
183, 223,
181,de224
respectively,
withdados,
the kind
permission of
arte inferior da imagem,
fundo
preto).Springer Science, Business Media].
the authors,
Elsevier,
presentam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
500 nm
200 nm
(a)
(b)
Figure 24. TEM images of the PSM/CdSe nanocomposite (PSM =
poly(styrene-alt-maleic anhydride) [reproduced from reference 225 with the
kind permission of the authors, Elsevier].
18
Materials Research
Camargo et al.
nA
nA
A-Z
nM
140
nM
140
120
100
120
100
80
60
40
20
0
(a)
20
40
(b)
60
80
100
120
140
80
60
40
20
0 0
20
40
60
80
100
120
140
(c)
Figure 25. a) Phase-contrast AFM image of poly-para-xylylene/Pd nanocomposite. Dark regions are polymer spherulites; light spots are Pd nanoparticles situated at the boundary between polymer spherulites; b) AFM phase contrast image of poly-para-xylylene/Sn 8 vol. % nanocomposite; and c) AFM phase contrast
image of the poly-para-xylylene/Sn 16 vol. % nanocomposite [reproduced from reference 47 with the kind permission of the authors, Elsevier].
ganic phase with spherical globules of ~200 nm size. In the case of tin,
separated Sn particles localized on polymer spherulites (Figure 25b)
and aggregates of Sn nanoparticles connected in continuous chains are
evident. The ionic conductivity of these nanocomposites is reported to
have improved when compared with that of the pure polymer.
secondary, tertiary and quaternary alkylammonium or alkylphosphonium. In organosilicates, these alkylammonium or alkylphosphonium
cations lower the surface energy of the inorganic host and improve
the wetting characteristics of the polymer matrix, resulting in a larger
interlayer spacing. Moreover, these cations provide functional groups
that can react with the polymer matrix or initiate the polymerization of
monomers to improve the strength of the interface between the inorganic
component and the polymer matrix50,245,248,249.
Montmorillonite, hectorite and saponite are the most commonly
used layered silicates. Their structure is presented in Figure 26 and their
formulae in Table 16235. When the hydrated cations are ion-exchanged
with bulkier organic cations, a larger interlayer spacing is usually
obtained (Figure 26).
The main reason for the remarkable improvements observed in
polymer/layered-silicate nanocomposites is the stronger interfacial interaction between the matrix and the silicate, compared to conventional
filler-reinforced systems. Some examples will be given below in order
to illustrate this statement.
The incorporation of MMT (montmorillonite) into a Nylon-6 matrix
has led to a significant improvement in its mechanical properties. The
Youngs modulus (or tensile modulus), for example, of pure Nylon-6
(1.11 GPa) was strongly improved when the nanocomposite was
formed. The Nylon-6/MMT with a filler content of 4.1 wt. (%) gave a
value of 2.25 GPa, which corresponds to an increase of 102.7%208,209.
Figure 27 represents the dependence of tensile modulus E, at 393K
(120 C), on clay content for organo-modified montmorillonite- and
saponite-based nanocomposites208. Results clearly show that the increase in Youngs modulus in these systems is related to the average
length of the layers and, consequently, to the aspect ratio of the dispersed
nanoparticles as well as the extent of their exfoliation. Also, regarding
Nylon-6 nanocomposites, a strong interaction between matrix and
silicate layers occurs via formation of hydrogen bonds.
This behaviour can also be supported by maleic anhydride modified by propylene (PP-MA)/LS anocomposites. Table 17 represents
the variation of the Youngs modulus as a function of filler and maleic
anhydride contents for both the nano and the microcomposite. These
results indicate that the nanocomposite shows higher Youngs modulus
than the pure PP matrix. Also, a significant increase, as compared to
the PP microcomposite, was observed as the amount of MA added to
the polymer matrix was increased250.
Important improvements on the stress at break were also observed
in Polymer/LS systems. In thermoplastic-based nanocomposites, the
stress at break, which expresses the ultimate strength that the material can bear before breaking, varies depending on the nature of the
interactions between the matrix and the filler. Table 18 shows some
Tetrahedral
Octahedral
Tetrahedral
ols.
Exchangeable hydrated
cations (Li, Na, Rb, Cs)
O
O, OH
Al, Fe, Mg, Li
O, OH
Si, Al
Figure 26. Schematic representation of the structure of 2:1 phyllosilicates.
examples of tensile stress in different nanocomposite systems. According to these results, some important conclusions can be drawn,
as discussed below.
Exfoliated Nylon-6 and intercalated PMMA nanocomposites exhibited a great increase in the stress at break251. This can be due to the
polar (PMMA) and ionic interactions (Nylon-6 grafted onto the layers)
between the matrix and the silicate layers. This increase is larger in
Nylon-6 nanocomposites250-252. On the other hand, propylene-based
nanocomposites showed only a slight enhancement in tensile stress,
which can be explained by the lack of interfacial adhesion between
non-polar PP and polar-layered silicates. However, addition of maleic
anhydride-modified polypropylene to the polypropylene matrix has
confirmed to be effective in the intercalation of the PP chains and the
maintenance of the ultimate stress at an acceptable level18. Finally,
regarding PS-intercalated nanocomposites, the ultimate tensile stress
is significantly decreased compared to that given by the PP matrix and
drops down at higher filler contents252. The authors have attributed
this finding to the weak interactions at the polystyrene-clay interface.
It is important to note that in previous compositions in which polar
interactions were developed, strengthening at the filler matrix interface
was observed18.
Table 16. Chemical formulae of 2:1 phyllosilicates [reproduced from reference 26 with permission of the authors and Elsevier].
0.8
E (120 C) (GPa)
ls.
19
0.6
2:1 Phyllosilicate
Montmorillonite
Hectorite
Saponite
L = 1000
0.4
Chemical formula
Mx(Al4-xMgx)Si8O20(OH)4
Mx(Mg6-xLix)Si8O20(OH)4
MxMg6(Si8-xAlx)O20(OH)4
L = 500
0.2
0
6
4
Clay content wt. (%)
Table 17. Youngs modulus for PP-MA based micro- and nanocomposites as a
function of filler and maleic anhydride contents [reproduced from reference 250
with permission of the authors and the American Institute of Physics, USA].
Sample
Montmorillonite
Saponite
Nylon
L= average length of silicate layers
PP
microcomposite
nanocomposite
nanocomposite
nanocomposite
Filler
content
(wt. (%))
0
6.9
7.2
7.2
7.2
MA content
(wt. (%))
0
0
7.2
14.4
21.6
Youngs
modulus
(Mpa)
780
830
838
964
1010
Table 18. Tensile stress evolution for nanocomposites based on various thermoplastic matrices [reproduced from ref. 18 with permission of the authors and
Elsevier].
Matrix
Nylon-6
Nylon-6
Nylon-6
PMMA
PMMA
PP-MA 7.2 wt. (%)
PP-MA 21.6 wt. (%)
PS
PS
PS
PS
Structure
68.6
68.6
68.6
53.9
53.9
31.4
32.6
28.7
28.7
28.7
28.7
4.7
5.3
4.1
12.6
20.7
5.0
4.8
11.3
17.2
24.6
34.1
Exfoliated
Exfoliated
Exfoliated
Intercalated
Intercalated
Intercalated
Intercalated
Intercalated
Intercalated
Intercalated
Intercalated
97.2
97.3
102
62.0
62.0
29.5
31.7
21.7
23.4
16.6
16.0
20
60
50
Materials Research
Camargo et al.
Epoxy/Magadiite exfoliated
40
30
Epoxy/Magadiite intercalated
20
10
Epoxy/Magadiite conventional
0
0
5
10
Magadiite loading (wt. (%) SiO2)
15
Table 19. Mechanical properties of some N6/(HE)2M1R1 nanocomposites [reproduced from ref. 257 with permission of the authors and Elsevier].
N6/(HE)2M1R1
LMW
0.0 wt. (%) MMT
3.2 wt. (%) MMT
6.4 wt. (%) MMT
MMW
0.0 wt. (%) MMT
3.1 wt. (%) MMT
7.1 wt. (%) MMT
HMW
0.0 wt. (%) MMT
3.2 wt. (%) MMT
7.2 wt. (%) MMT
Modulus
(GPa)
Yield strength
(MPa)
Strain (%)
2.82
3.65
4.92
69.2
78.9
83.6
4.0
3.5
2.2
232
12
2.4
2.71
3.66
5.61
70.2
86.6
95.2
4.0
3.5
2.4
269
81
2.5
101
18
5
39.3
38.3
39.3
2.75
3.92
5.70
69.7
84.9
97.6
4.0
3.3
2.6
3.4
119
4.1
129
27
6.1
43.9
44.7
46.2
28
11
4.8
Izod impact
strength (J/m)
36.0
32.3
32.0
The substituents on the quaternary ammonium compound used to form the organoclay are identified in this shorthand notation where R = rapeseed, HE = hydroxyethyl,
M = methyl. Rapeseed is a natural product composed predominantly of unsaturated C22 alkyl chains (45%)257.
21
This figure compares the values of the storage moduli for two sets of
samples in which the reinforcement content varied from 0 to 30 wt.(%).
Values were recorded for nanocomposites filled with organomodified
clay and for composites prepared by melt-blending the SBS matrix
and Na-montmorillonite under the same conditions. There is a sharp
increase in elastic modulus for nanocomposites, while microcomposites
do not present any improvement in this property.
DMA properties were also studied for the widely used bifunctional
diglycidyl ether of bisphenol-A (DGEBA) containing different amounts
(2-10 wt. (%)) of layered silicate, and prepared by a two steps chemical
method (173 to 323 K and from 323 to 573 K). Results indicated that,
with increasing organic clay content in the composite, the relaxation
temperatures of the cured system decreased, while the presence of
modified layered silicate improved both toughness and stiffness of
the matrix260. AFM phase contrast images (Figure 31) show stacked
layers of silicates in the product, even though they are not distributed
homogeneously throughout the material. The high magnification shown
in Figure 31(b) reveals the striated structure in the 5 wt. (%) layered
silicate-containing nanocomposite, with increasing phase intervals at
the top of the surface. However, no individual layers could be seen
by TEM.
The dependence of the storage modulus for polyimide-based
nanocomposites filled with 2 wt. (%) of organic clays and for the
unfilled matrix is shown in Figure 32. At any temperature, higher storage moduli result from the better nanofiller dispersion. Moreover, the
large difference between exfoliated montmorillonite- and exfoliated
mica-based nanocomposites can be explained by the respective aspect
600
(a)
s (Roman), tamanho 8.
inhas com 0.5 de Stroke.
ncentes a "Dados grficos" com 0.6 de Stroke.
houver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
100 nm
nm no.
100 nm
to de barras com 10% de preto quando
houver texto e 50%100
quando
(a)
(b)
(c)
ls.
ela ou figura devem estar todos em Ingls.
Figure 29. Bright field TEM images of melt compounded nanocomposites
vem estar dentrocontaining
de caixas de
comMMT
2 mmbased
de distncia
nas extremidades.
3 texto
wt. (%)
on a) HMW,
b) MMW, and c) LMW
ura ou grfico deve
estar
em
"Sentence
case".
Nylon-6 [reproduced from reference 257 with the kind permission of the
apas dever ter 1 authors,
ponto deElsevier].
Stroke.
4
Nanocomposite
2
xa
m.
E (Pa)
bols.
107
8
6
4
Microcomposite
2
106
200
3.31 0
MM
200
400
600
.M
Figure 31. Phase contrast AFM images of DETDA (diethyltoluenediamine)cured DGEBA (diglycidylether of bisphenol) containing 5 wt. (%) organoclay
[reproduced from reference 260 with the kind permission of the authors,
Elsevier].
3.0
Storage elastic modulus (GPa)
afias, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
parte inferior da imagem, fundo preto).
108 estar centralizadas na parte inferior da imagem.
presentam figuras ex: (a), devem
8
6
400
2.5
2.0
1.5
Synthetic mica
1.0
Montmorillonite
Saponite
Hectorite
no Clay
0.5
0.0
0
10
15
20
25
Clay wt. (%)
30
35
Figure 30. Trend of the Storage Modulus (E) at 531 K for SBS-based nanocomposites, microcomposites as a function of the filler level [reproduced
from reference 259 with the kind permission of the authors, the Materials
Research Society, USA].
Figure 32. Temperature dependence of storage elastic modulus for polyimidebased nanocomposites filled with 2 wt. (%) of organomodified synthetic mica,
montmorillonite, saponite, hectorite [reproduced from reference 255 with the
kind permission of the authors, John Wiley & Sons Inc.]
22
Materials Research
Camargo et al.
ratio of the dispersed silicate layers, with lengths of 0.218 and 1.23mm
for montmorillonite and synthetic mica respectively, as observed by
TEM studies.
From Figure 32, it is also evident that the glass transition temperature decreases (~288 K) with increasing clay content for this
nanocomposite. The influence of dispersion and length of the layered
particles has thus been demonstrated in the case of these nanocomposites using various organoclays (hectorite, saponite, montmorillonite
and synthetic mica)210,255. Mica and montmorillonite clays lead to
exfoliated-structures, while a partially exfoliated-intercalated structure
was obtained for saponite and a mainly intercalated morphology was
attributed to the hectorite-based nanocomposite.
Furthermore, DMA studies carried out on organoclays exfoliated
within cross-linked matrices revealed a very noticeable improvement in
storage modulus, especially above Tg. For example, the epoxy/montmorillonite 4 vol. % nanocomposite below Tg showed a 58% increase164.
In this case, a well-ordered exfoliated nanocomposite (silicate layers
separated by approximately 100 ) was formed. At 331 K, E equals
2.44 and 1.55 GPa for the nanocomposite and the unfilled cross-linked
matrix, respectively. At 423 K, which is above Tg, the reported E values
are 11 and 50 MPa for the unfilled and filled epoxy, respectively. This
enhancement corresponds to a storage modulus improvement by a factor
of 4.5. Also, an interesting result could be observed in nitrile rubber/
organoclay nanocomposites258. A three-fold increase in the storage
modulus was described through the simple dispersion/exfoliation of
10parts of organoclay per 100 parts of rubber, with a modulus as high
as 8.8 MPa. This value is similar to what can be obtained with the same
matrix filled with 40 parts of carbon black per 100 parts of rubber. As a
result, the amount of filler can be reduced by a factor of four. Overall,
the storage elastic modulus appears to be substantially enhanced at
temperatures above Tg for exfoliated nanocomposites filled with layered
silicates. A possible explanation for such an improvement could be the
as - Materialscreation
Researchof a three-dimensional network of interconnected long silicate
layers, strengthening the material through mechanical percolation.
Roman), tamanho 8.Mechanical properties of layered nanocomposites typically reas com 0.5 desemble
Stroke. those of ceramic materials. Flocculated nanocomposites are,
same
as intercalated nanocomposites. Silicate layers
ntes a "Dadosconceptually,
grficos" com the
0.6 de
Stroke.
are sometimes flocculated due to hydroxylated edgeedge interaction
ver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
of the silicate layers, and when they are completely and uniformly
de barras com 10% de preto quando houver texto e 50% quando no.
dispersed in a continuous polymer matrix, an exfoliated or delaminated
ou figura devem
estar todos
em Ingls.
structure
is obtained.
The individual clay layers are separated in a conm estar dentro de
caixas
de
texto
2 mm
extremidades.
tinuous polymer com
matrix
by de
andistncia
averagenas
distance
that depends on clay
ou grfico deve
estar emUsually,
"Sentence
loading.
thecase".
clay content of an exfoliated nanocomposite is
muchde
lower
(4-5 wt. (%)) than that of an intercalated (11-34 wt.(%))
s dever ter 1 ponto
Stroke.
200 nm
200 nm
Exfoliated
(b)
Intercalated
(a)
Figure 33. TEM images showing a) intercalated, and b) exfoliated polymerclay nanocomposites [reproduced from 26 with the kind permission of the
authors, Elsevier].
s, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
e inferior da imagem, fundo preto).
sentam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
Table 20. Cone calorimeter data for various polymers and their nanocomposites with organically modified layered-silicates (OMLS) [reproduced from references 243 with permission of the authors and the American Chemical Society, USA].
Sample (structure)
N6
N6/MMT 2% (delaminated)
N6/MMT 5% (delaminated)
PS
PS/silicate mix 3% (immiscible)
PS/MMT 3%
(intercalated/delaminated)
PP-g-MA
PP-g-MA/MMT - 2%
(intercalated/delaminated)
PP-g-MA/MMT 4%
(intercalated/delaminated)
% residue
yield (0.5)
1
3
6
0
3
4
Peak HRR
(kW.m2) (D%)
1010
686 (32)
378 (63)
1120
1080
567 (48)
Mean HRR
(kW.m2) (D%)
603
390 (35)
304 (50)
703
715
444 (38)
Mean Hc
(MJ.kg1)
27
27
27
29
29
27
Mean SEA
Mean CO
(m2.kg1) yield (kg.kg1)
197
0.01
271
0.01
296
0.02
1460
0.09
1840
0.09
1730
0.08
5
6
1525
450 (70)
536
322 (40)
39
44
704
1028
0.02
0.02
12
381 (75)
275 (49)
44
968
0.02
ability with the increasing length of the clay. In other words, the best gas
barrier properties will be obtained by fully exfoliated rather than long
layered silicates. Consequently, the presence of spherical, plate, cylindrical, etc., fillers introduces a tortuous path for a diffusing penetrant.
The reduction of permeability arises from the longer diffusive path that
the penetrants have to travel in the presence of reinforcements.
Nanocomposites systems have also shown to be able to increase
the ionic conductivity of polyethylene oxide (PEO)167. The PEO/
Li-montmorillonite 60 wt. (%) intercalated nanocomposite showed a
significant improvement regarding the stability of ionic conductivity
at lower temperature compared to a conventional PEO/LiBF4 mixture
(Figure 37)167.
This improvement is due to the fact that PEO is not able to
crystallize when intercalated. This eliminates the presence of crystallites, which are non-conductive in nature. The conductivity of PEO/
1.0
Relative permeability coefficient
que representam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
Conventional composites
Hectorite
0.8
Saponite
0.6
Montmorillonite
0.4
0.2
Synthetic mica
0
5000
10000
Length of clay ()
Figure 36. Clay length dependence on the relative permeability coefficient
for poly(imide)/clay nanocomposites [reproduced from reference 255 with
the kind permission of the authors, John Wiley & Sons Inc.].
Temperature (C)
0
4
6
OMSFM wt. (%)
60
40
20
80
50
100
Log (S.cm)
ls.
23
10
Figure 35. Oxygen gas permeability of neat PLA, various PLACNs as a function of OMLS content, measured at 20 C, 90% relative humidity [reproduced
from reference 263 with the kind permission of the authors, the American
Chemical Society, USA].
2.6
2.8
3.0
3.2
1000/ Temperature (1/K)
3.4
24
Camargo et al.
After 32 days
After 60 days
Pure PLA
are almost the same up to 1 month. Other systems which showed large
improvements in their biodegradability are PCL/OMLS and aliphatic
polyester-based nanocomposites18,26,266.
Another way of increasing the biodegradability of resulting materials is by addition of natural fibres. The use of renewable resources
for making biodegradable polymers and reinforcements for nanocomposites may lead not only to the achievement of desirable properties,
but also to the replacement, in the near future, of polymers obtained
from non-renewable sources. This may help minimizing environmental
degradation and waste disposal problems associated with the extensive
use of the synthetic polymers in the world.
It is to be noted that a persistent stress on use of high technology
reinforcements, such as CNTs, in the development of polymer nanocomposites may be a limiting factor in view of their high cost. In this
scenario, the possibility of using large quantities of inexpensive natural
nanofibrous materials may be explored. Such materials include the
natural clay-serpentine group (chrysotile, antigorite, lizardite, amesite),
nanolayers of the kaolin group (kaolinite, dickite, nacrite), ribbons of
the sepiolite-paligorskite group (sepiolite, paligorskite), imogolite of
volcanic origin and other minerals with graftable surfaces176. Further,
synthetic materials made from the double hydroxide or hydroxyl salt
groups with layered or fibrous structures, and even graftable single
hydroxides having low cost and involving very common elements, will
also play an important role in the future. In addition, vegetable fibres
disposed of as agricultural production waste can be also reduced to
nanosize range materials and used as reinforcement agents336. Even in
such non-graftable reinforcement surfaces, one can choose an appropriate chemical treatment and moulding temperature and carefully select
the polymer to arrive at the best chemical compatibilization, leading to
the optimized properties of the resulting materials. It is observed that
these treatments usually improve the surface adhesive characteristics of
the vegetable fibres through the removal of non-crystalline components
such as lignin and hemicelluloses.
150
100
Rw /%
Mw x 10 3 (gm.mol 1)
PLACN4
PLA
ls.
After 50 days
Materials Research
100
80
60
50
40
PLACN4
PLA
20
0
0
10
20
30
40
Time/days
0
50
60
70
Figure 39. Time dependence of the residual weight, Rw, of the matrix
molecular weight, Mw, for PLA, PLA/MMT 4 wt. (%) under compost at
58 2C [reproduced from reference 265 with the kind permission of the
authors, Elsevier].
ls.
4. Applications of Nanocomposites2,16-35,258,305,310,337-378
From the foregoing, it becomes evident that nanocomposites may
provide many benefits such as enhanced properties, reduction of solid
wastes [lower gauge thickness films and lower reinforcement usage]
and improved manufacturing capability, particularly for packaging applications. Tables 21 to 23 present potential applications of ceramic-,
metal- and polymer-based nanocomposites, respectively. As it can be
observed, the promising applications of nanocomposite systems are
numerous, comprising both the generation of new materials and the
performance enhancement of known devices such as fuel cells, sensors
and coatings. Although the use of nanocomposites in industry is not
yet large, their massive switching from research to industry has already
started and is expected to be extensive in the next few years.
For instance, the (Al1-xTixN)/-Si3N4 super hard nanocomposite,
which has been developed by the Czech company SHM Ltd. as a
Nanocomposites
SiO2/Fe
ZnO/Co
Metal oxides/Metal
BaTiO3/SiC, PZT/Ag
SiO2/Co
SiO2/Ni
Al2O3/SiC
Si3N4/SiC
Al2O3/NdAlO3 &
Al2O3/LnAlO3
TiO2/Fe2O3
s.
25
Al2O3/Ni
PbTiO3/PbZrO3
Applications
High performance catalysts, data storage
technology.
Field effect transistor for the optical femtosecond study of interparticle interactions.
Catalysts, sensors, opto-electronic
devices.
Electronic industry, high performance
ferroelectric devices.
Optical fibres.
Chemical sensors.
Structural materials.
Structural materials.
Solid-state laser media, phosphors and
optical amplifiers.
High-density magnetic recording media,
ferrofluids and catalysts.
Engineering parts.
Microelectronic and micro-electromechanical systems.
1 Mm
Figure 40. TEM micrograph of process-induced orientation in nanocomposite
ribbons. The arrow indicates the direction of alignment taken as the principal
direction with a nanotube orientation of 0 [reproduced from reference 230
with the kind permission of the authors, the Institute of Physics Publishing,
USA].
1 Mm
0.1 Mm
Figure 41. SEM micrographs showing the distribution of CNTs through epoxy
resin [reproduced from reference150 with the kind permission of the authors,
the American Institute of Physics, USA].
Nanocomposites
Fe/MgO
Ni/PZT
Ni/TiO2
Al/SiC
Cu/Al2O3
Al/AlN
Ni/TiN, Ni/ZrN,
Cu/ZrN
Nb/Cu
Fe/Fe23C6/Fe3B
Fe/TiN
Al/Al2O3
Au/Ag
Applications
Catalysts, magnetic devices.
Wear resistant coatings and thermally graded
coatings.
Photo-electrochemical applications.
Aerospace, naval and automotive structures.
Electronic packaging.
Microelectronic industry.
High speed machinery, tooling, optical and
magnetic storage materials.
Structural materials for high temperature applications.
Structural materials.
Catalysts.
Microelectronic industry.
Microelectronics, optical devices, light energy
conversion.
26
Camargo et al.
Materials Research
Nanocomposites
Polycaprolactone/SiO2
Polyimide/SiO2
PMMA/SiO2
Polyethylacrylate/SiO2
Poly(p-phenylene vinylene)/SiO2
Poly(amide-imide) / TiO2
poly(3,4-ethylene-dioxythiophene)/V2O5
Polycarbonate/SiO2
Shape memory polymers/SiC
Nylon-6/LS
PEO/LS
PLA/LS
PET/clay
Thermoplastic olefin/clay
Polyimide/clay
Epoxy/MMT
SPEEK/laponite
Applications
Bone-bioerodible for skeletal tissue repair.
Microelectronics.
Dental application, optical devices.
Catalysis support, stationary phase for chromatography.
Non-liner optical material for optical waveguides.
Composite membranes for gas separation applications.
Cathode materials for rechargeable lithium batteries.
Abrasion resistant coating.
Medical devices for gripping or releasing therapeutics within blood vessels.
Automotive timing-belt TOYOTA.
Airplane interiors, fuel tanks, components in electrical and electronic parts, brakes and tires.
Lithium battery development.
Food packaging applications. Specific examples include packaging for processed meats, cheese,
confectionery, cereals and boil-in-the-bag foods, fruit juice and dairy products, beer and carbonated drinks bottles.
Beverage container applications.
Automotive step assists - GM Safari and Astra Vans.
Materials for electronics.
Direct methanol fuel cells.
tribological coating for tools, is suitable for hard and dry cutting operations such as drilling, turning and milling, and is reported to be now
industrialized337,339. In this case, a novel method, which employs vacuum
arc coating with a rotating cathode, is used for commercial production.
This super hard (Al1-xTix)N/-Si3N4 possess high tensile strength, in the
range of 10-110 GPa, and a lifetime 2-4 times higher than that of the
materials currently employed as wear resistant coatings.
Similarly, one of the leading application areas is the automotive sector, with striking impact due to improved functionalities such as ecology,
safety, comfort, etc. Details on the commercial usage of nanocomposites in automotives and future developments in this sector (including
CNT-based nanocomposites) are now available362. For instance, there
are reports on the current use of a number of nanocoatings in different
parts of Audi, Evobus and Diamler Chrysler automobiles, as well as
ongoing trials on fuel cells, porous filters (foams) and energy conversion
components, which include nanoTiO2-containing paints. Additionally,
light weight bodies made of metal- or polymer-based nanocomposites
with suitable reinforcements are reported to exhibit low density and very
high strength (e.g. carbon Bucky fibers, with strength of 150 GPa and
weight 1/5th of steel). Also, two-phase heterogeneous nanodielectrics,
generally termed dielectric nanocomposites, have wide applications in
electric and electronic industries338.
Metal and ceramic nanocomposites are expected to generate a
great impact over a wide variety of industries, including the aerospace,
electronic and military305, while polymer nanocomposites major impacts
will probably appear in battery cathodes6,342, microelectronics343, nonlinear optics344, sensors345, etc. Improved properties include significant
enhancements in fracture strength (about 2 times) and toughness (about
one half time); no time dependent wear transitions even at very low
loads; higher high temperature strength and creep resistance; increased
hardness with increasing heat treatment temperature; hardness values
higher than those of existing commercial steel and alloys; possibility of
synthesis of inexpensive materials; and significant increase in Youngs
modulus [about 105%], shear modulus and fracture strength (almost
3 times compared to microcomposites). These are brought out mainly
by the nanosize reinforcements used, which result in an appropriate
morphology for the products. Tables 21 and 22 summarize the possible
developments associated with these materials in catalysts, sensors,
27
which exhibit better gas barrier properties, can provide a longer shelf
life. Such packaging, with different matrices and reinforcements, as
well as different processing conditions, is being field tested by the US
army since 2002 to arrive at an optimum combination. This is expected
to reduce cost by 10-30% (nearly US$1-3million) compared to the
presently used materials, in addition to better performance.
Various types of polymer-based nanocomposites, containing
insulating, semiconducting or metallic nanoparticles, have been developed to meet the requirements of specific applications. Recently,
some PLS nanocomposites have become commercially available18,
being applied237 as ablatives and as high performance biodegradable
composites265,267,280,343,346, as well as in electronic and food packaging industries346,347. These include Nylon-6 (e.g. Durethan LDPU60
by Bayer Food Packages)18 and polypropylene for packaging and
injection-molded articles, semi-crystalline nylon for ultra-high barrier containers and fuel systems, epoxy electrocoating primers and
high voltage insulation, unsaturated polyester for watercraft lay-ups
and outdoor advertising panels, and polyolefin fire-retardant cables,
electrical enclosures and housings. Table 24 shows some examples
of commercially available polymer nanocomposites. As an example,
Nylon-6/surface-modified montmorillonite 2 wt. (%) nanocomposites
are currently available from two commercial sources, Honeywell Engineered Polymers & Solutions and Bayer AG. Some of the products
made from nanocomposites are shown in Figure 42.
guras - Materials Research
Technological contributions in the areas of gas barrier, reinforce355,356
ment
.
(Roman), tamanho
8. and flame retardancy have also been extensively exploited
For
example,
heat-resistant
polymer
nanocomposites
are
used
to
make
nhas com 0.5 de Stroke.
fire fighter protective clothing and lightweight components suitable to
centes a "Dados grficos" com 0.6 de Stroke.
work in situations of high temperature and stress. This includes hoods
ouver rosa do ventos na imagem original, substituir pela padro da paleta symbols.
of automobiles and skins of jet aircrafts, as opposed to heavier and
o de barras com costlier
10% de preto
50%replace
quando corrosion-prone
no.
metalquando
alloys.houver
They texto
can ealso
metals
ela ou figura devem
estarbuilding
todos emofIngls.
in the
bridges and other large structures with potentially
357, 358
em estar dentro de
caixas
destronger
texto com
2 mm de distncia
nas unsaturated
extremidades.
lighter
and
capabilities
. Also,
polyester (UPE)
nanocomposites
cancase".
be employed in fibre-reinforced products used
ra ou grfico deve
estar em "Sentence
in marine,
transportation and construction industries359-361. Currently,
pas dever ter 1 ponto
de Stroke.
UPE/fibreglass nanocomposites, whose formulations are available
fias, seguir padro correto (respeitando estilo de escala, posio dos dados, caixa
from Polymeric
Supply, Inc., are being used in boat accessories that
arte inferior da imagem,
fundo preto).
are stronger and less prone to colour fading362.
presentam figuras ex: (a), devem estar centralizadas na parte inferior da imagem.
Regarding the variety of applications of polymer nanocomposites,
prominent impacts over the automotive industry can be highlighted,
including their use in tyres, fuel systems, gas separation membranes
in fuel cells and seat textiles, mirror housings on various vehicle
types, door handles, engine covers, intake manifolds and timing belt
covers363,364, with some of these already being exploited. For example,
a thermoplastic nanocomposite containing nanoflake reinforcements
(trade name Basell TPO-Nano) is being employed for the development
of stiff and light exterior parts, like the step-assists by GM348. Also,
porous polymer nanocomposites can be employed for the development of pollution filters365. Other promising technological application
in the horizon is in air bag sensors, where nano-optical platelets are
kept inside the polymer outer layer for transmitting signals at speed of
light gaining milliseconds to bring down the level of possible impact
injuries373. Finally, polymer/inorganic nanocomposites with improved
conductivity, permeability, water management and interfacial resistance
at the electrode are natural candidates for the replacement of traditional
Nafion PEM in fuel cells, and are currently under trial349.
Improvements in the mechanical properties of polymer nanocomposites have also resulted in their many general/industrial applications.
These include impellers and blades for vacuum cleaners, power tool
housings, and mower hoods and covers for portable electronic equipment, such as mobile phones and pagers366. Another example is the use
of polymer nanocomposites in glues for the manufacturing of pressure
moulds in the ceramic industry.
The development of environmentally friendly, non-foil and better
packaging materials can reduce the amount of solid waste, improve
package manufacturing capabilities, and reduce the overall logistics
Center bridge
Sail panel
Box Rail
Foot rest
Food packaging
Figure 42. Nanocomposite-containing products [reproduced from references
347, 351, with the kind permission of US Army Natick Soldier Center, Plastics
Technology, USA, AzoNano.com, PvtLtd., USA].
Table 24. Commercial polymer nanocomposites and their respective target markets (CNT = carbon nanotubes).
Matrix resin
Nylon 6
PP
Nylon 12
PPO/Nylon
Nylon 6 Barrier Nylon
Ube
(Ecobesta)
Antai Haili Ind. & Commerce of China
Nylon 6, 12 Nylon 6, 66
UHMWPE
Nano-filler
Organoclay
Organoclay
CNTs
CNTs
Organoclay
Organoclay
CNTs
Organoclay
Organoclay
Organoclay
Organoclay
Mica
Clay, mica
Organoclay
Organoclay
Organoclay
Target market
Barrier films
Packaging
Electrically conductive
Automotive painted parts
Multi-purpose
Bottles and film
Electrically conductive
Wire & cable
Multi-purpose moulding
PET beer bottles
Flame retardancy Multi-purpose
Multi-purpose
Auto fuel systems
Earthquake-resistant pipes
28
Camargo et al.
5. Perspectives
Outstanding potentials of nanocomposites can be exemplified
by the massive investments from many companies and governments
throughout the world. As a result, nanocomposites are expected to
generate a great impact in world economy and business. This is very
much evident from the publications pouring in, particularly on a variety
of properties suited for different applications350. According to a report
from Principia Partners, which is illustrated in Table 25, a market size
of over than U$ 1,834 billion (USD) is estimated by 2009, considering
only the different applications of polymer/clay nanocomposites350. The
estimative may not be exaggerated, since many of the application areas
already use these composites, with some of them being commercialized
Technology/Application
Polymer-Clay Nanocomposites
Packaging
Automotive
276
115
87
122
Materials Research
29
this regard, critical issues to be looked into include aspects of dispersion, alignment, volume and rate of fabrication and, finally, cost effectiveness. Some light has been thrown on these aspects30. Probably,
processing-structure-properties maps similar to those developed for
metals and alloys by Ashby379 may further enhance the potentials of
nanocomposites. This is because structure, which is dictated by the
processing method, in turn dictates the properties of materials. Added
to this is the engineering aspect of design.
For materials scientists, design could be one of the following380:
i) design of materials having combinations of unique properties or ii)
selection of materials having better characteristics for a specific purpose
or iii) development of a new process for providing one of the above
mentioned materials. Besides, in engineering a term called performance
index (P) is defined, which correlates the properties of materials for
a given product, and helps in their selection for specific applications.
The higher the value of P, the better will be the performance380. Further,
another correlation generally used is between the relative cost and the
performance index, whereby one can arrive at the economical material
selection for a given product. The above concepts should also be applied in the case of nanocomposites, so that one could get the maximum
benefit from them in any application.
Finally, as part of the social implications of this nascent and potential technology, there are some safety aspects to be considered while
dealing with nanosized particles and their composites. For example,
fabrics coated with nanoparticles are available, which can be configured
to imbue the fabric with various attributes. Aerosolised chemical and
biological agents are a clear threat that is likely to grow in the future.
The release of nanoparticles into the environment is a major health
and safety issue. Hence there is an increasing need for research into
emission of nanocomposites and nanoparticles. Potentially harmful
characteristics of nanotechnology products based on their large surface area, crystalline structure and reactivity may facilitate their easy
transport into the environment or interaction with cell constituents,
thus exacerbating many harmful effects related to their composition.
One recent conference was devoted to the study of the safety and risks
of nanoparticles381, while the U.S. Environmental Protection Agency
(EPA), as part of its Science to Achieve Results (STAR) program, is
seeking applications that evaluate the potential impacts of manufactured
nanomaterials on human health and the environment. This is important
as new nanomaterials are constantly being manufactured; there is always
a possibility of human and environmental exposure to waste streams,
or other pathways entering the environment382.
6. Conclusions
In conclusion, new technologies require materials showing novel
properties and/or improved performance compared to conventionally
processed components. In this context, nanocomposites are suitable
materials to meet the emerging demands arising from scientific and
technologic advances. Processing methods for different types of nanocomposites (CMNC, MMNC and PMNC) are available, but some
of these pose challenges thus giving opportunities for researchers to
overcome the problems being encluntered with nanosize materials.
They offer improved performance over monolithic and microcomposite
counterparts and are consequently suitable candidates to overcome the
limitations of many currently existing materials and devices. A number
of applications already exists, while many potentials are possible for
these materials, which open new vistas for the future. In view of their
unique properties such as very high mechanical properties even at low
loading of reinforcements, gas barrier and flame related properties,
many potential applications and hence the market for these materials
have been projected in various sectors. Thus all the three types of nanocomposites provide opportunities and rewards creating new world
wide interest in these new materials.
30
Camargo et al.
Acknowledgements
We are grateful to all authors of the papers, publishers of the journals from where tables and figures have been reproduced [The American
Chemical Society, American Institute of Chemical Engineers, American
Institute of Physics, Elsevier, Institute of Physics, Japan Society of
Powder, Powder Metallurgy, John Wiley & Sons, Materials Research
Society, Plastics Technology Magazine, Springer-Verlag, Wiley-VCH
Verlag Gmbh & Co, web sites], for their courtesy and kind permission.
The authors sincerely express their gratitude to Professor Jaisa F. Soares
of Department of Chemistry, UFPR for her reading of the full manuscript, editing both technical and language aspects as well for her critical
suggestions. We also acknowledge Mr. Gregorio Guadalupe Carbajal
Arizaga, Department of Chemistry, UFPR, Mahesh Kestur Satya, USA,
for their reading of the paper and useful suggestions.
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