methods for preparation of nano-composites for … · electrical properties of the nano-composite...

173Methods for preparation of nano-composites for outdoor insulation applications

© 2%13 Advanced Study Center C]. Ltd.

Rev. Adv. Mater. Sci. 34 (2013) 173-184

Corresponding author: Muhammad Amin, e-mail: [email protected]

METHODS FOR PREPARATION OF NANO-COMPOSITESFOR OUTDOOR INSULATION APPLICATIONS

Muhammad Amin

COMSATS Institute of Information Technology Wah, Pakistan

Received: October 10, 2012

Abstract. Electrical insulation materials are advancing rapidly due to several advantages includinglight weight, better performance in polluted environment and reduced installation cost. In polymericmicro-composites, enhancing one property of the insulator may affect adversely on the otherdesired properties. This problem can be addressed practically with the invention of nano-composites. This article provides a comprehensive survey of methods and techniques for thedevelopment of nano-composite materials in order to improve its insulation properties as wellas its cost and aging properties. These recently evolved nano-composites provide significantimprovements in combined electrical, thermal and mechanical properties. This article criticallyevaluates the methods, their issues and related challenges. In the end, conclusion has beendrawn by proposing a set of possible solutions which need to be performed as future work.

1. INTRODUCTION

The Ceramic insulators have been used in the powerindustry for more than a decade. This materialhad dem]nstrated its self-sustaining ability againstharsh environmental effects. These are stablestructures due to their atoms seal pack configurationand strong ionic bonding between them which helpto resist against environmental stresses. Therefore,ceramic housing should not be affected by stresseslike Ultra Violet rays, surface electrical activity andhumidity etc. Their mechanical strength is due t]the stiff nature of material. The housing used forbushing on high voltage equipments provide self-sustaining capability and d] n]t re_uire ]thermaterials for strength. The main raw materials ofthese insulators are clays, feldspar and quartz whichare inexpensive and readily accessible.

The seismic acceleration stresses up to 0.5 gcan be withstand by these insulators.

Since 197%’s, the use ]f p]lymeric insulat]rsfor outdoor high voltage insulation has increased sodramatically that ceramic insulators are nearly

becoming obsolete in power industry. Electricalcompanies started using polymeric insulatorsat distributi]n v]ltages, and then gradually, at l]wvoltage transmission, now at 765 kV ac and 500 kVdc [1].

The polymeric insulators have demonstrated bestc]ntaminati]n flash]ver capabilities and theref]re areroutinely deployed in diverse environments. Thereas]n f]r the p]pularity ]f P]lymeric insulati]nmaterials are their numerous advantages, like: thedensity of polymeric materials is lesser thanp]rcelain materials, which makes c]nstructi]n anderection of insulators simpler and quicker. The lighterweight all]ws the use ]f less c]stly structures andfixing arrangements and also results in lowertransportation cost.

Creepage distance per unit length is usuallyhigher in polymeric insulators than porcelaininsulators. AC wet flashover is avoided by providingalternating diameter weather sheds to polymericinsulators which made their structure morecomplex.

174 M. Amin

The composite insulators revealed abetter electrical perf]rmance in p]lluted envir]nmentdue to their hydrophobic properties. The conductivecontamination suspended within the water beads isdiscontinuous due to formation of water beads onthe polymeric surface. This results in lower leakagecurrent and the probability of dry band arcing.

The physical properties of the polymer materialdictate that these materials will n]t smash likeporcelain materials. With the instigation of aninternal fault, the expected failure meth]d is rupturingleading t] an exteri]r flash]ver and dissipati]n ]fthe energy outside of the housing.

The seismic accelerati]n stresses up t] ]ne gramcan be withstand without damage by polymericinsulators due to their lighter weight, high dampingfact]r and high strength design uni_ueness.

Various studies have shown that micro fillershave improved the performance of compositematerials for high voltage insulator performance. Themicro fillers have shown significant improvement inthe thermal properties of composite material usedfor outdoor insulators. This feature is very importantfor protecting insulator against the dry band arcphenomenon. However, further improvement in themicro filled composite material is not possible withthe available processing technology. The nano-composite materials were initially developed forcommercial application using intercalation method.Since the mechanical properties of these materialswere significantly improved, hence the researcherswere attracted to consider the resultant materialsfor outdoor high voltage applications. Later on,significant research was carried out to improve theelectrical properties of the nano-composite materials.Large specific surface area of the nano fillers wasthe focus of researchers to explore its electricalproperties for high voltage insulator applications.Nano-particles have diameter of less than 100 nm.They have been made from different sources andinclude the following types [2]: Aluminum, Gold,Silver, etc. Zinc Oxide, Alumina, CalciumCarbonate, Titania, etc. Silica, Silicon Carbide,Acetylene Black, Polyhedral OligomericSilsesquioxanes (POSS).

2. COMPOSITE MATERIALS

For outdoor insulation, two materials are commonlyused for the housing: ethylene propylene dienemonome rubber and silicone rubber. SiR is preferreddue to its characteristic hydrophobicity and its goodperformance in polluted environments.

3. NANO-COMPOSITES MATERIALS

The conventional polymeric composites can altercertain desired pr]perties ]f the c]mp]site materials(e.g. mechanical and thermal properties); it oftenc]mes with the c]mpr]mise ]f ]ther pr]perties beingnegatively affected (e.g. electricalpr]perties . Interestingly, the newly emergingpolymer nano-composites providesignificant impr]vements in c]mbined electrical,thermal and mechanical properties [3].These pr]f]und impacts create great benefitsspecif ically to the high voltage insulatingindustry, especially in electrical pr]pertiesenhancement. Recently these ‘hi-tech’materials with excellent pr]perties have begun t]attract researchers in the field ]f dielectrics andelectrical insulation. Since new properties arebr]ught ab]ut fr]m the interacti]ns ]f nan]fillers withpolymer matrices, macroscopic properties areexpected to come out, which would be interestingto both scientists and engineers. Improvedcharacteristics are expected as dielectrics andelectrical insulation.

The resistance to arcing is enhanced by addingup of nanofillers and microfillers in ahigh temperature vulcanizing silic]ne rubber. S.Rätzke and J. Kindersberger, in their w]rk, f]undthat the best dispersion was obtained for nanosilica;]n the ]ther hand, large aggl]merates were f]und t]be formed by nanoalumina [4]. The results of thearcing test sh]ws l]nger time durati]n with increasedfiller percentages of Sio

2 and Al

2O

3. Results are

shown in Fig.1.The auth]rs f]und that the thermal c]nductivity

rose in an approximately linear fashion with the fillerc]ncentrati]n and that the higher thermal c]nductivity

Fig. 1. Synthesis and structure of nanosilica.


improved the resistance to erosion. According toDengke et al. [5,6], the addition of a small amount(2 t] 5 wt.% ]f in]rganic nan]fillers t] p]lymersshould be sufficient for mechanical and thermalstability and perf]rmance impr]vement. Theyselected nanosilica because it is ac]mmercial nan]scale material. In ]ther research,Meyer et al. [7] showed that RTV SiR filled withnan]silica, when c]mpared with RTV SiR filled withmicro silica, demonstrated a higher tracking ander]si]n resistance, l]wer r]ughness, and slightlyl]wer hydr]ph]bicity. The c]ncentrati]ns used in thiswork were 5% and 10% wt for nano and micro silica,respectively, and nan]silica had higher tracking anderosion resistance than micro silica. Polyamide filmstested by Irwin et al. [8] displayed significantimpr]vements t] el]ngati]n, scratch hardness, andstrength. Fuse et al. [9] studied polyamide withlayered silicate nan]fillers fr]m 1 t] 5 wt.%.

They found that the conduction current decreasedwith the additi]n ]f nan]particles. M]re]ver, thedielectric strength was independent ofthe nan]particles f]r impulse, direct current, andalternating current voltages. These researchers didn]t see an impr]vement with the use ]f nan]fillers,as they perf]rmed these tests.

The epoxy resin with the mixing of nano, micro,and the c]mbinati]n ]f b]th nan] and micr] fillersis demonstrated by Imai et al. [10]. It was evidentthat micr]filled ep]xy and NMMC maintained a farsmaller erosion depth than the base epoxy resin.Imai et al. [10] assumed that an increase in particlec]ncentrati]n in nan] and micr] filler mixturesprevented treeing from propagating efficiently. Fromthese results, it was evident that the nan] and micr]composites mixture displayed better electricalinsulati]n pr]perties; hence, the f]rmulati]n with thecombination of micro and nano-particles is a goodchoice. According to Roy et al. [11], the voltageendurance behaviour of cross-linkedp]lyethylene (XLPE was significantly impr]ved withthe inclusion of treated nano-particles(amin]silanetreated nan]silica, vinylsilane-treatednanosilica). This difference was attributed tothe chemical treatment ]f the nan]silica. All thenanoscale fillers were characterized bya significantly impr]ved breakd]wn strength andendurance over the base resin. In thisw]rk, nan]fillers sh]wed an impr]vement.

4. POLYMER NANO-COMPOSITES

The specific properties of polymers are typicallyimproved by adding fillers. And the polymer nano-

composites based on silicon rubber have attractedresearchers due to their capability to enhancemechanical, thermal and electrical properties.Polymer nano-composites have been demonstratedat lesser [12] or equal concentrations to haveproperties that are same or enhanced than those ofpolymer micro-composites [13-14].

The nan]-particle’s size and high relative surfacearea to volume ratio causes unusual properties. Dueto its larger specific surface area than micro-particles, it interacts additional with its surrounds[15]. The large interfacial interaction between thematrix and the nano-particles yields the physicaland thermodynamic stability of the polymer nano-composites [12].

A polymer nano-composite can be defined as asystem in which at least one dimension of filler ison a nanometric scale. In the polymer matrix,uniform filler distribution is always desired. Thecreation of a favorable interaction between thepolymer and the nanofiller is mandatory to avoidphase separation and agglomeration. Two potentialsolutions for improving compatibility of theingredients are: chemically transform one or moreof the components or launch an appropriatecompatibilizer [10].

5. NANO-PARTICLES

Nano-particles exist in spherical, tube and plateletsand have at least one dimension in nanometers.Like the micro-particles, nano-particles can bemanufactured by breaking up a big particle. It isimportant to avoid agglomeration of the nano-particles and ensure good bond to the matrixirrespective of the preparation methodology. Surface-treatment of the nanosize particles is also possible.A broad range of polar agents, such as silanes andpolyalcohols, and non-polar agents, such as stearicacid and fatty acids, are commercially available assurface treatment agents for fillers [9].

5.1 Layered silicates

LS/clay minerals are part of the class of silicateminerals, phyll]silicates. They include natural andsynthetic clays such as mica, bentonite, magadiite,lap]nite, flu]r]hect]rite and s] ]n. LS are the m]stwidely used 2-D nanofillers in various fields. Thestructure ]f LS c]nsists ]f a 2-D layer ]f tw] fusedsilicate tetrahedral sheet with an edge-shared]ctahedral sheet ]f metal at]ms, such as Al ]r Mg.The model crystal structure of LS was proposed byHoffmann et al. Fig. 2 [16].

176 M. Amin

These sheet-like nanofillers are ~1 nm thick and1%% s t] 1%%% s ]f nan]meters l]ng; as a resultthey possess a high aspect ratio. Therefore,polymer/silicate nano-composites providean attractive meth]d t] impr]ve the p]lymerproperties such as stiffness, strength andbarrier pr]perties with]ut any change in pr]cessingtechnique.

5.2. Nanotubes

Among different types of nanotubes, carbonnan]tubes are the m]st widely used and accepted inpolymer research field and industry. Carbonnan]tubes are all]tr]pes ]f carb]n and bel]ng t] thefullerene structural family. In nanotubes thediameters are in the order of a few nanometers;h]wever, they are millimeters ]r even centimeterslong. Therefore, these nanotubes possess a highaspect rati], thereby imparting high strength t] thepolymer with a small weight percent. Theexcellent pr]perties ]f carb]n nan]tubes are ac]nse_uence ]f its b]nding nature. Carb]nnanotube-reinforced composites are of particularinterest in the field ]f material science t] devel]psignificantly lightweight strong materials. A majorpr]blem in this field is the failure t] attain ahomogeneous dispersion of nanotubes in thep]lymer matrix due t] the aggregati]n ]f these

Fig. 2. Schematic structure of Layered Silicate.

tubes. Researchers have employed different tech-ni_ues t] attain ]ptimum dispersi]n ]f nan]tubesin the polymer matrix, including: (i) solution mixing[17,18], (ii) sonication [19], (iii) coagulation [20], (iv)melt compounding [21], (v) in situemulsi]n p]lymerisati]n [22], (vi the use ]f surfac-tants [23] and (vii) chemical functionalization]f nan]tubes [24]. Chemical m]dificati]n ]f carb]nnan]tubes is the best techni_ue t] get m]rehomogeneous dispersion. This is done throughcovalent and noncovalent attachments offuncti]nal gr]ups in nan]tubes with the matrix.

5.3. Spherical particles

Nanofillers with three dimensions in the nanometerregime are the spherical nan]fillers generallyobtained by a sol-gel process [25]. In sol-gelpr]cesses, the ]rganic/in]rganic hybrid materialscan be formed by the condensation reaction betweenthe functi]nalized prep]lymers and the metalalkoxides, leading to the formation of achemical b]nd between the p]lymer and theinorganic filler. Therefore, the incorporation offiller particles in p]lymers thr]ugh the s]l-gel pr]cessavoids the aggregation of filler.

Silica, TiO2, ZnO, CaSO

4, CaCO

3, ZnFe

2O

4, and

so on, are the widely used spherical inorganicnan]fillers in the p]lymer field.


6. FUNCTIONALIZED POLYMER WITHNANOPARTICLES

The application area of polymers is generally basedon their end properties. The behavior of polymer maydrastically affects by a change in its structure. Thestructure of a polymer can be changed by addingfunctional groups to the polymer backbone or to theside chains in assorted ways such as grafting [26,27]and using monomers in the polymerization process[28]. However, in these processes unwanted cross-linking and polymer degradation reactions must beavoided by using different techniques. If theinteraction between the components is insufficientor chemical treatment of the fillers to be avoided or,a new component named as polymer compatibilizer[29] can be added. The interfacial bonding betweenthe compatibilizer and the nano-particles aredependent on several factors. These factors are thefunctionality, concentration, and the molecularweight, the molecular weight distribution of thecompatibilizer and the mass ratio of thecompatibilizer to the nano-particles [30].

7. PREPARATION OFNANO-COMPOSITES

Preparation of polymer Nano-composites can bedone by various methods, e.g. they can be preparedby blending or by in situ polymerization. Theblending can be done either in two ways either bymelting if the ingredients bear the blendingtemperature above the melting temperature of thepolymer [31,32], or by solution, if an appropriatesolvent is available [33,34]. A good compatibilitybetween the ingredients is mandatory in order tomake a homogenous polymer nano-compositeirrespective of preparation method [35].

Compatibility can be enhanced by choosingappropriate blending conditions, e.g. by adjustingthe temperature profile and the mixing speed, [36]

Fig. 3. Block diagram for in-situ polymerization.

or by chemical treatment of the filler or the polymer.Researchers used different methods for preparationof Nano-composites which are briefly described withtheir inherent advantages and disadvantages.

7.1. In-situ polymerization method

In this meth]d, nan]filler are sw]llen within the li_uidmonomer solution so the formation of polymer can]ccur between and ar]und the intercalated layers.The polymerization can be initiated either bythe inc]rp]rati]n ]f curing agent, initiat]r ]r byincreasing the temperature, if it is sufficientlyreactive. The in-situ polymerization is shown inFig. 3.

7.2. Solution blending method

This method is based on a solvent system inwhich the p]lymer is s]luble and the nan]filler layersare swellable. The nan]filler are first sw]llen in asolvent. When the polymer and nanofiller solutionsare mixed, the p]lymer chains intercalate anddisplace the solvent within the interlayer of thenan]filler. Up]n s]lvent rem]val, the intercalatedstructure remains, resulting in nano-c]mp]site. Using this meth]d, intercalati]n ]nlyoccurs for certain polymer/solvent pairs.The disadvantages ]f this meth]d are the use ]fenvir]nmentally unfriendly and ec]n]micallyprohibitive organic solvents. The solution blendingmethod is shown in Fig. 4.

7.3. Melt intercalation method

The melt intercalation technique has becomethe standard f]r s]me p]lymer/nan]filler nan]-c]mp]sites and is als] _uite c]mpatible with theindustrial techniques. In this method, polymer andm]dified nan]filler mixture are blended in the m]ltenstate under shear. The polymer chains reptate formthe m]lten mass int] the filler galleries t] f]rm either

178 M. Amin

intercalated ]r delaminated nan]-c]mp]sites. Themelt intercalation method is shown in Fig. 5.

8. DIFFICULTIES IN NANO-COMPOSITES PREPARATION

Researchers faced mainly following problems innano-composites preparation.

8.1. Dispersion

The physical dispersion methods generally includeultras]nicati]n, ball milling, grinding, and high-speedshearing. The main re_uirements f]r effectivereinforcement are as under [37]:(a) Aspect ratio(b) Uniform dispersion(c) Placement(d Interfacial stress

F]r maximum l]ad transfer t] the nan]tubes, theaspect ratio must be large enough. This ismandat]ry f]r the c]mp]site’s strength andstiffness.

Dispersion is perhaps a basic issue. Dispersion]f fillers in a p]lymer matrix ]utc]me fr]m:YThe use of electrochemical and mechanical forces

to make de-agglomeration.YC]mplete rem]val ]f air bubbles and water,YF]rmati]n ]f a real uninterrupted in]rganic–]rganic c]mp]siti]n [38].

Fig. 4. Bock diagram for solution blending method.

Fig. 5. Block diagram for melt intercalation method.

When the nan]-sized fillers are unif]rmly dis-persed in the p]lymer matrix ]nly then the ]ptimalperformance of polymer composites canbe achieved. Manufacturing such h]m]gene]usmixtures creates c]nsiderable challenges.

The kinetic and thermodynamic aspects ofthe penetrati]n ]f p]lymer int] the gap between theclay sheets must be considered in order tounderstand the exf]liati]n pr]cess in p]lymer–clay nan]-c]mp]sites [39]. Theref]re, the efficientdispersion of nano-sized fillers in a polymer matrixis an art than a science.

-. 69W 7204.850.6 PR9P2RT52S

The mechanical pr]perties ]f Nan]-c]mp]sites canbe significantly affected by the interface behavior.The degree of reinforcement is proportional to thefiller’s interacti]ns and is crucial in ]ptimizing theproperties of polymer composites [40].

The ]ther fact]rs c]ntributing t] the l]wmechanical properties include weak interfacialb]nding, bad dispersi]n, and degradati]n ]f thenanofiller [41].

10. PROBABLE SOLUTIONS

In the light of thorough survey on the latest research,following solutions address the problems facedduring nano-composites preparation:


10.1. Surface modification ofnanofillers

Improved dispersion can be achieved throughphysical ]r chemical interacti]ns between the fillerand the modifier. When nanoparticles are modifiedby ]ne ]f these meth]ds, either the character ]fthe surface is changed from hydrophilic tohydr]ph]bic (and vice-versa , ]r specific gr]ups arechemically bonded on their surface (change infuncti]nality . Fillers are typically hydr]philic and d]not disperse easily within most polymeric materials,which are usually hydr]ph]bic. Such m]dificati]nnot only contributes to reinforcement, butals] increases the interacti]ns ]f the particles t]impact rheological properties,prevents sedimentati]n, aids dispersi]n, ]r preventsaggl]merati]n. In additi]n, impr]ved dispersi]n ]fthe nanoparticles can also be achieved with solvents.

10.2. Physical methods

Surface modification by physical methods isachieved using a l]w m]lecular weight surfactantwhich introduces secondary forces between thenanoparticles and the modifier. A surfactant isa m]lecule that, when added t] a li_uid at l]wc]ncentrati]n, changes the pr]perties ]f that li_uidat a surface or interface [42]. The principle ofsurfactant treatment is the preferential ads]rpti]n,or tendency for a surfactant molecule to collect atthe interface, due t] p]lar gr]ups ]n the surfactantmolecules interacting favorably with the high energysurface ]f the filler. All surfactants c]nsist ]f at leasttwo parts, one which is soluble in a specific fluid,kn]wn as the ly]philic part (]r hydr]philic part, inaqueous systems), and one which isins]luble, kn]wn as the ly]ph]bic (]r hydr]ph]bic part. Thus, when a surfactant adsorbs froman a_ue]us s]luti]n ]n a hydr]ph]bic surface, itshydr]ph]bic gr]up usually ]rients t] the surfacewhile its polar group is exposed to water. Since thesurface bec]mes m]re hydr]philic, the interfacialtension between the surface and water is reduced.Different types of surfactants are in use in theindustry [43].

10.3.0IFMiDBL MFSIOER

A variety of coupling agents including silanes, titan-ates, and zirc]nates have been used t] enhancethe bonding between fillers and polymer matrices.As an example, the hydrophilic properties of silicacan be modified by use of silanes. However, uniformsurface c]verage by c]upling agents is hard t] attain

with nanoparticles by simple physical andmechanical means. Stearic acid has thus been usedwith nano CaCO

3, with the result of virtually

n] aggl]merates ]f nan]particles remaining withpr]per d]sage ]f the dispersing agent [44]. An]thernon-reactive modifier used by Seon et al. [45] tomake the filler surface hydr]ph]bic is stearic acid.The presence of adsorbed stearic acid on thesurface ]f the silica nan]particles reduced theinteractions between the silica nanoparticles withinaggl]merates, which c]uld be br]ken d]wn m]reeasily.

11. THERMAL TREATMENT OFNANOPARTICLES (CALCINATION)

Storage of Nanofillers under ordinary conditionspartially blocked their surface by adsorbed speciesin the form of moisture. This condition causes areduced effectiveness of fillers in dispersion. Thesolution to activate the filler surfaces andt] disintegrate the fillers’s aggregates during st]rageis the calcinati]ns [46]. Many ]f the pr]perties ]fsilica such as adsorption, adhesion, chemical, andcatalytic pr]perties depend ]n the chemistry andge]metry ]f their surface. Dehydrati]n ]f the silicasurface, i.e. the removal of physisorbed (adsorbed)water ]ccurs at temperatures bel]w 473K. Theconcentration of silanol groups on the surfaceals] dr]p ]ff m]n]t]nically with rising temperaturewhen silica is heated under vacuum [47].

12. MODIFICATION/ENHANCEMENTIN PROPERTIES OFNANOPARTICLES

12.1. Mechanical properties

One of the primary reasons for adding inorganic fillersto polymers is to improve their mechanicalperformance [48]. The major requirement of polymernano-composites is to optimize the balance betweenthe strength and the toughness as much as possible[49]. The mechanical properties include tensilestrength, elongation at break, tear strength, modulusand hardness etc.

According to Dengke et al. [50, 51] the addition]f a small am]unt (2 t] 5 wt.% ]f in]rganicnanofillers to polymers should be sufficient formechanical stability and perf]rmance impr]vement.Polyamide films tested by Irwin et al. [52] displayedsignificant improvements to elongation, scratchhardness, and strength. Silica nanoparticle-filledPEN composites were melt blended to improve themechanical properties of PEN [53]. Fig. 6 shows

180 M. Amin

Fig. 6. Mechanical properties of nano-composite samples.

mechanical properties such as tensile strength, andelongation at break of the PA 6/modified silica nano-composites also show a tendency to increase andthen decrease with increasing silica content andhave maximum values at 5% silica content [54].

12.2. Thermal properties

Thermal properties are the properties of materialsthat change with temperature.

Thermo-gravimetric analysis (TGA) devices areoften used to investigate nano-composite thermalstability by monitoring the change in sample weightat high temperatures. It has been found that theaddition of nanofillers shifted the thermaldecomposition temperature of polymer to highervalues, which indicated the enhancement of thenanocomposite thermal stability as compared withthe unfilled polymer. The improvement in the thermalstability is probably due to the high surface area ofsuch nano-composites, which prevents the volatiledecomposition products from diffusing out during thehigh temperature degradation process. PI/SiO

2 nano-

composite exhibit higher thermal stability than theirmicr]c]mp]site c]nterpart. The reinf]rcement ]f asilicon rubber composite with nanofiller resulted inan impr]ved c]mp]site with better thermalproperties [55]. Motori1 et al. [56] found that thetemperature index impr]ves c]nsiderably with

respect t] the base p]lypr]pylene, with ]nly 6 wt.%of nanofiller.

13. ELECTRICAL PROPERTIES

13.1. Dielectric breakdown

One of the most important electrical propertychanges of nano-composites is the enhancementin dielectric breakdown strength which is widelydocumented in many literatures [57-66].

13.2. Tracking & erosion resistance

Piah et al. [67] investigated the effect of aluminatrihydrate fillers on the surface tracking and erosionresistance of natural rubber and found improvedsurface tracking and erosion resistance of thecompounds.

El-Hag et al. [68] studied the tracking and erosionresistance of nanosilicafilled silicone rubber andconfirmed that the composites depict significantresistance to erosion as compared with micro-filledsilicone rubber composites.

13.3. PD resistance

Researchers have shown that nano materialsperform better in term of partial discharge resistancewhen compared with that of their base materials.

Polymer composites Corosion Commentslevel meter

Polyamide 14 6kV (AC), 60 Cycles/Sec, 48 hrsPolyamide /LS Nano Material 2.5 Electrode; IEC (b)Epoxy 110 60 Hz equivalent TimekV (AC),Epoxy/ LS Nano Material 50 720 Cycles/Sec,Epoxy/ Titanate (15nm) Nano Material 32 60 hours/120 hoursEpoxy/ Silica (40 nm) Nano Material 27 Rod-gap-plane ElectrodeEpoxy/ Silica (15 nm) Nano Material 19

Table 1. Results of corrosion level in polymeric nano materials due to partial discharge.


Fig. 7. The graph of permittivity verus filler concentration.

Tanaka et al. investigated the partial discharge re-sistance of epoxy/layered silicate nano materialsand found significant improvement [69]. Kozako etal. also confirmed that only 2 wt.% of nanofiller issufficient to improve the partial discharge resistanceof polyamide/layered silicate nano-composites [70].

Lorenzo et al. conducted internal discharge testupon layered nanosilicates filled epoxy resins andthe increment of lifetime was found on those materials[71]. Intensity of erosion in polymer nano-compositesproduced by partial discharges is shown in Table 1.

13.4. Space charge behavior

The addition of nanofillers also results in spacecharge reduction as found in epoxy nano-composites[72-74]. There are also claims that charge transportis of utmost importance in improving the dielectricstrength and electrical erosion of nano-composites[75,76].

13.5. Permittivity & dissipation factor

The permittivity usually increases with inorganicmicro-fillers and tends to decrease with nanofillers,as found in [77,78]. Dissipation factor is also foundto be favorable when polymer nano-composites areintroduced [79]. The graph of permittivity verus fillerconcentration is shown in Fig. 7.

13.6 Tangent loss angle

Certain microfillers have high relative permittivity;hence composite materials prepared using suchmicrofillers show higher relative permittivity, becausethe frequency is increased. However, the behaviorof nano-composite material is surprisingly differentdue to intercalation process. A reduction in tangentloss angle is also observed for epoxy-nanocompositematerials under low frequency and high temperatureconditions [80].

14. CONCLUSION

The microfillers technology had reached at its peakas far as the latest instrumentation for theirmanufacturing is concerned. In polymeric micro-composites, combined properties cannot beenhanced simultaneously. In fact, one propertyenhancement is achieved at the cost of other. Thisproblem can be addressed practically with theinvention of nano-composites. These recentlyevolved nano-composites provide significantimprovements in combined electrical, thermal andmechanical properties.In polluted environments such as industrial andcostal areas, polymeric insulators are prone tosurface degradation, which lead to their breakdown.Micro-fillers are used widely in polymeric insulationmaterials for outdoor high voltage insulators.Awaiting, only micro-sized fillers have been usedas commercial materials. On the other hand, theapplications of nano-fillers have unmitigated over theprevious few years in research fields and someinsulating materials have been manufactured.Considerable endeavor has been exhausted byresearchers to discover a successful technique toadd in nanofillers into outdoor insulation applications.In this research, SEM analysis technique is usedto analyze the quality of prepared nanocomposite.The results suggest that surfactant drasticallyimprove dispersion and hence quality ofnanocomposite.

Breakdown voltage is one of the main factors.The samples were tested in two different conditions,without any moisture and with moisture content,acc]rding t] ASTM D 57% – 95. The samples withmoisture content did show a reduction in thebreakdown voltage as compared to those of withmoisture content.

182 M. Amin

REFERENCES

[1] E. Manias, A. Touny, L. Wu, K. Strawhecker,B. Lu and T.C. Chung // Chem. Mater. 13(2001) 3516.

[2] Y. Cao, P. C. Irwin, K. and Younsi // IEEETransactions on Dielectrics and ElectricalInsulation 11 (5) (2%%4 797.

[3] G.H. Vaillancourt, S. Carignan and C. Jean //IEEE Transactions on Power Delivery 13(1998 661.

[4] S. Rätzke and J. Kindersberger, In: XI:thInternational Symposium on High VoltageEngineering (Tsinghua University, Beijing,China, 2%%5 , p. C-%9 1.

[5] C. Dengke, Y.J. Hui, W. Xishan and L. Lei, In:International Conference on Solid Dielectrics(Toulouse, France, 2004), Vol. 2, p. 796.

[6] C. Dengke, W. Xishan, L. Lei and Y.J. Hui, In;International Conference on Solid Dielectrics(T]ul]use, France, 2%%4 , v]l. 2, p. 8%%.

[7] L.H. Meyer, S.H.L. Cabral, E. Araúj],G. Cardoso and N. Liesenfeld, In:IEEE International Symposium on ElectricalInsulation (ISEI, 2%%6 , p. 474.

[8] P.C. Irwin, Y. Cao, A. Bansal and L.S.Schadle, In: IEEE Conference on ElectricalInsulation and Dielectric Phenomena (CEIDP,2%%3 , p. 12%.

[9] N. Fuse, M. Kozako, T. Tanaka and Y. Ohki,In: IEEE Conference on ElectricalInsulati]n and Dielectric Phen]mena (CEIDP,2%%5 , p. 148.

[10] T. Imai, F. Sawa, T. Nakano, T. Ozaki,T. Shimizu, M. Kozako and T. Tanaka //IEEE Trans. Dielectrics and ElectricalInsulation 13 (2%%6 319.

[11] M. Roy, J.K. Nelson, L.S. Schadler, C. Zouand J.C. Fothergill, In: IEEE Conference onElectrical Insulation and DielectricPhenomena (CEIDP, 2005), p. 183.

[12] W.-G. Hwang, K.-H. Wei and C.-M. Wu //Polym. Eng. Sci. 44 (2004) 2117.

[13] A. Nabok, Organic and InorganicNanostructures, Nanotechnology series(Artch House, New York, 2005).

[14] J.M. Garces, D.J. Moll, J. Bicerano,R. Fibiger and D.G. McLeod, // AdvancedMater. 12 (2000) 1835.

[15] G. Wypych, Handbook of Fillers, 2nd ed(Toronto: ChemTec Publishing, 1999).

[16] U. Hoffmann, K. Endell and D. Wilm,Kristallstruktur und Quellung vonMontmorillonit. (Das Tonmineral der

Bentonittone) (Zeitschrift fur KristallografieMineral Petrografie Abteilung A, 1933).

[17] P.J.F. Harris // Journal of Microscopy 186(1997) 88.

[18] J.Q. Pham, C.A. Mitchell, J.L. Bahr, J.M.Tour, R. Krishanamoorti and P.F. Green //J. Polym. Sci. B Polym. Phys. 41 (2003)3339.

[19] H. Xie, B. Liu, Z. Yuan, J. Shen and R. Cheng// J. Polym. Sci. B Polym. Phys. 42 (2004)3701.

[20] F. Du, J.E. Fischer and K.I. Winey //J. Polym. Sci. B Polym. Phys. 41 (2003)3333.

[21] W.E. Dondero and R.E. Gorga // J. Polym.Sci. B Polym. Phys. 44 (2006) 864.

[22] Y. Yu, C. Ouyang, Y. Gao, Z. Si, W. Chen,Z. Wang and G. Xue // J. Polym. Sci. APolym. Chem. 43 (2005) 6105.

[23] Xiaoyi Gong, Jun Liu, Suresh Baskaran,Roger D. Voise and and James S. Young //Chemistry of Materials 12 (2000) 1049.

[24] T. Ramanathan, H. Liu and L. C. Brinson //Journal of Polymer Science Part B: PolymerPhysics 43 (2005) 2269.

[25] J.E. Mark // Polym Eng Sci 36 (1996) 2905.[26] C.-C. Peng, A. Göpfert, M. Drechsler and

V. Abetz // Polym. Adv. Technol. 16 (2005)770.

[27] L.-F. Zhang, B.-H. Guo and Z.-M. Zhang //J. Appl. Polym. Sci 84 (2002) 929.

[28] M. A. Villar and M.L. Ferreira // J. Polym.Sci.: Part A: Polym Chem. 39 (2001) 1136.

[29] I.S. Suh, S.H. Ruy, J.H., Bae and Y.W.Chang // J. Appl. Polym. Sci. 94 (2004)1057.

[30] Y.W. Chang, Y. Yang, S. Ryu and C. Nah //Polym. Int. 51 (2002) 319.

[31] J.-Z. Liang // Polym. Int. 51 (2002) 1473.[32] M.-T. Ton-That, E. Perrin-Sarazin, K.C. Cole,

M.N. Bureau and J. Denault // Polym. Eng.Sci. 44 (2004) 1212.

[33] B. Pourabas and V. Raeesi // Polymer 46(2005) 5533.

[34] J.-M. Yeh, S.-J. Liou, M.-C. Lai, Y.-W. Chang,C.-Y. Huang, C.-P. Chen, J.-H. Jaw, T.-Y. Tsaiand Y.-H. Yu // J. Appl Polym. Sci. 94 (2004)1936.

[35] U.W. Gedde, Polymer Physics (London,Chapman Hall, 1995).

[36] R. Seymor and C.E. Carraher, Structure-Property Relationships in Polymer (PlentumPress, New York, 1984).


[37] Ig]r N]vák and Ig]r Krupa // EuropeanPolymer Journal 40 (2004) 1417.

[38] J. N. C]leman, U. Khan and Y.K. Gun’k] //Adv. Mater. 18 (2006) 689.

[39] S.J. Monte, In: Functional Fillers for Plastics,ed. by M. Xanthos (Wiley-VCH VerlagGmbH, 2005).

[40] W. Dale Schaefer and S. Ryan Justice //Macromoleculres 40 (2007) 8501.

[41] A.R. Payne // J. Appl. Polym. Sci 9 (1965)2273.

[42] M. J. Rosen, Surfactants and InterfacialPhenomena, Third Edition (Wiley- Interscience, 2%%4 .

[43] E. W. Flick, Industrial Surfactants (NoyesPublicati]ns, Sec]nd Editi]n, 1993 .

[44] A. Lazzeri, S. M. Zebarjad, M. Pracella,K. Cavalier and R. Rosa // Polymer 46 (2005)827.

[45] S.H. Ahn, S.H. Kim and S.G. Lee // Journalof Applied Polymer Science 94 (2%%4 812.

[46] W.W. Kubiak and E. Niewiara,Electroanalysis, 17 (Wiley-VCH, 2%%2 .

[47] L.T. Zhuravlev // Colloids and Surfaces A:Physico chemical and Engineering Aspects173 (2%%% 1.

[48] L.S. Schadler, Nanocomposite Science andTechnology (Wiley- VCH: Weinheim,Germany, 2003).

[49] R. Lach, G.M. Kim, G.H. Michler,W. Grellmann and K. Albrecht // Macromol.Mater. Eng. 291 (2006) 263.

[50] C. Dengke, W. Xishan, L. Lei and Y.J. Hui, In:Proc. International Conference on SolidDielectrics, Vol. 2 (Toulouse, France,2004),p. 800.

[51] A.H. El-Hag, L.C. Simon, S.H. Jayaram andE.A. Cherney// IEEE Transactions onDielectrics and Electrical Insulation 13 (2006)122.

[52] P.C. Irwin, Y. Cao, A. Bansal and L.S.Schadle, In: IEEE Conference on ElectricalInsulation and Dielectric Phenomena (CEIDP,2003), p. 120.

[53] Kim, S.H.; Ahn, S.H.; Hirai, T. Polymer 2003,44, 5625.

[54] F. Yang, Y.C. Ou and Z.Z. Yu // J. Appl.Polym. Sci. 69 (1998) 355.

[55] Isaias Ramirez, Shesha Jayaram and EdwardA. Cherney, Thermal Conductivity of SiliconeRubber Nanocomposites (IEEE CEIDP,2009).

[56] L.H. Meyer, S. Jayaram and E.A. Cherney //IEEE Transactions on Dielectrics andElectrical Insulation 11 (2004) 620.

[57] M. Roy, J.K. Nelson, R.K. MacCrone, L.S.Schadler, C.W. Reed, R. Keefe andW. Zenger // IEEE Transactions onDielectrics and Electrical Insulation 12 (2005)629.

[58] J.C. Fothergill, In: IEEE InternationalConference on Solid Dielectrics (Winchester,2007), p. 1.

[59] C.D. Green, A.S. Vaughan, G.R. Mitchell andT. Liu // IEEE Transactions on Dielectricsand Electrical Insulation 15 (2008) 134.

[60] J.K. Nelson, In: Conference Record of theIEEE International Symposium on ElectricalInsulation (Toronto, 2006), p. 452.

[61] Gao Junguo, Zhang Jinmei, Ji Quanquan, LiuJiayin, Zhang Mingyan and Zhang Xiaohong,In: International Symposium on ElectricalInsulating Materials (Mie,2008), p. 597.

[62] G.C. Montanari, D. Fabiani, F. Palmieri,D. Kaempfer, R. Thomann and R. Mulhaupt //IEEE Transactions on Dielectrics andElectrical Insulation 11 (2004) 754.

[63] Y. Murata, Y. Murakami, M. Nemoto,Y. Sekiguchi, Y. Inoue, M. Kanaoka,N. Hozumi and M. Nagao In: Annual ReportConference on Electrical Insulation andDielectric Phenomena (Nashville, 2005),p. 158.

[64] S.S. Bamji, M. Abou-Dakka, A.T. Bulinski,L. Utracki and K. Cole, In: Annual ReportConference on Electrical Insulation andDielectric Phenomena (Nashville, 2005),p. 170.

[65] M. Roy, J.K. Nelson, L.S. Schadler, C. Zouand J.C. Fothergill, In: Annual ReportConference on Electrical Insulation andDielectric Phenomena (Nashville, 2005),p. 183

[66] F. Guastavino, A. Dardano, A. Ratto,E. Torello, P. Tiemblo, M. Hoyos and J.M.Gomez-Elvira, In: Annual Report Conferenceon Electrical Insulation and DielectricPhenomena (Nashville, 2005), p. 175.

[67] T. Tanaka, In: Annual Report Conference onElectrical Insulation and DielectricPhenomena (Nashville, 2005), p. 713.

[68] M.A.M. Piah, A. Darus and A.Hassan //Journal of Industrial Technology 13 (2004)27.

184 M. Amin

[69] A.H. El-Hag, L.C. Simon, S.H. Jayaram andE.A. Cherney // IEEE Transactions onDielectrics and Electrical Insulation 13 (2006)122.

[70] M. Kozako, N. Fuse, Y. Ohki, T. Okamotoand T. Tanaka // IEEE Transactions onDielectrics and Electrical Insulation 11 (2004)833.

[71] M. Di Lorenzo Del Casale, R. Schifani,L. Testa, G.C. Montanari, A. Motori,F. Patuelli, F. Guastavino and F. Deorsola, In:IEEE International Conference on SolidDielectrics (Winchester, 2007), p. 341.

[72] J.K. Nelson, J.C. Fothergill, L.A. Dissado andW. Peasgood, In: 2002 Annual Report CEIDP(2002), p. 295.

[73] J.K. Nelson and Y. Hu // Annu. Rept. IEEE-CEIDP 8-2 (2003) 719.

[74] J.K. Nelson and Y. Hu // Proc. IEEE-ICSD 70(2004) 832.

[75] Y. Cao and P.C. Irwin // Annu. Rept.IEEE-CEIDP2003 2B-13 (2003) 116.

[76] Y. Cao, P.C. Irwin and K. Younsi // IEEETrans. Dielectr. Electr. Insul. 11 (2004) 797.

[77] T. Imai, Y. Hirano, H. Hirai, S. Kojima andT. Shimizu, In: Conf. Rec. IEEE ISEI (2002),p. 379.

[78] J.K. Nelson, L.A. Utracki, R.K. MacCroneand C.W. Reed // Annu. Rept. IEEE-CEIDP4-2 (2004) 314.

[79] J.K. Nelson, In: Electrical InsulationConference and Electrical ManufacturingExpo (Nashville, 2007) 235.

[80] J.C. Fothergill, J.K. Nelson and M. Fu //Annu. Rept. IEEE-CEIDP 5A.17 (2004) 406.

methods for preparation of nano-composites for … · electrical properties of the nano-composite...

Documents