Research Article Effects of Surface Treatments of ...downloads.hindawi.com/journals/jns/2013/864141.pdfa DGEBA epoxy system with low shrinkage and relatively high thermal stability,

Hindawi Publishing CorporationJournal of NanoscienceVolume 2013 Article ID 864141 12 pageshttpdxdoiorg1011552013864141

Research ArticleEffects of Surface Treatments of Montmorillonite Nanoclay onCure Behavior of Diglycidyl Ether of Bisphenol A Epoxy Resin

Alfred Tcherbi-Narteh Mahesh V Hosur Eldon Triggs and Shaik Jelaani

Department of Material Science Engineering Tuskegee University Tuskegee AL 36088 USA

Correspondence should be addressed to Mahesh V Hosur hosurmytutuskegeeedu

Received 1 May 2013 Revised 15 October 2013 Accepted 27 October 2013

Academic Editor Yeong Suk Choi

Copyright copy 2013 Alfred Tcherbi-Narteh et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Diglycidyl ether of Bisphenol A (DGEBA) based SC-15 epoxy resin was modified with three different commercially availablemontmorillonite (MMT) nanoclay Nanomer I28E and Cloisite 10A and 30B Cure behavior of nanocomposites was studied usinga variety of techniques Primary focus of this study was to investigate influence of different surface modifications of MMT nanoclayon rheological properties and cure behavior of SC-15 epoxy resin By adding MMT to SC-15 epoxy resin chemistry of the epoxy isaltered leading to changes in rheological properties andultimately enthalpy and activation energy of reactions Addition ofNanomerI28E delayed gelation while Cloisite 10A and 30B accelerated gelation regardless of the curing temperature Activation energy ofreaction was lower with the addition of Nanomer I28E and Cloisite 10A and higher for Cloisite 30B compared to neat SC-15 epoxycomposite

1 Introduction

Thermosetting epoxy resins are widely used across manyindustries in a variety of applications such as in paint andcoating industries adhesives and as matrices for compositelaminates due to exceptional properties [1ndash4] These prop-erties are further enhanced by modifying resins with smallamounts of fillers such as nanoparticles In this processchemistry of the polymer systems is altered and consequentlyaffects their processing Properties of most polymeric com-posites depend on processing parameters including curingtemperature and time to a great extent leading to forma-tion of network of polymer chains However in reinforcedpolymer composites properties are mostly dictated by theinterfacial chemistry and subsequent interaction betweenfiller materials and polymers molecules along with the afore-mentioned factors Among many commercially availablenanoparticles used as fillers in epoxy resins nanoclay standsout as the onewith an ability to improvemechanical and ther-mal properties [4ndash6] MMT also exhibits good barrier prop-erties against moisture and volatiles during decompositionbased on their unique morphology [7 8] One such nanoclay

is naturally occurring 2 1 phyllosilicate montmorillonite claywhich in the natural form is hydrophilic and incompatiblewith most polymers Hence surface of most commerciallyavailable nanoclay used as fillers is modified using organicmodifiers to overcome these challenges leading to the for-mation of miscible solutions [9 10] Surface modificationsalso help to reduce tendency of clay agglomeration duringdispersion by reducing interlayer attractive forces betweenthe platelets thereby enhancing dispersion [6] Other studies[11 12] have shown that presence of MMT facilitates ringopening polymerization in most epoxy polymers by readilyreacting with epoxide ring affecting the rate of chemicalreaction

Generally nanoclay infusions into polymer result inflocculated intercalated or exfoliated morphologies eachwith diverse potential to influence the polymer chain networkstructure and overall properties [3 13] During processingsilicate layers in an epoxy mixture can orient along withthe mesoscale structure and this ability dictates linear vis-coelastic properties of the mixture [13] In highly exfoliatedsystems nanoclay particles orientation results in the forma-tion of anisotropic solutions increasing viscosity and surface

2 Journal of Nanoscience

Nanomer I28E-quaternary trimethyl

Stearyl ammonium

Cloisite 10A-quaternary benzyl

Hydrogenated tallow ammoniumCloisite 30B-quaternary

Dimethyl dihydrogenated tallow

ammonium

Al Fe Mg LiOH

OLi Na Rb Cs

Tetrahedral

Octahedral

Tetrahedral

Exchangeable cations

minus

Figure 1 Chemical structure of montmorillonite nanoclay [3]

interactions [12ndash15] Interactions between nanoclay particlesand epoxy molecules affect the viscosity and mobility ofreacting species during curing Consequently this influencesrate of cure reaction time enthalpy vitrification activationenergy viscoelastic properties and crosslinking density ofthe final composite [9 12 16 17] Other factors such as typeand amount of clay fillers and organic modifiers and theirinteraction with the intended host polymer molecules andtheir curing agents have all shown to influence properties ofpolymeric composites during processing [12ndash14 17 18]

Cure kinetic parameters including activation energydepend on constituents of polymeric systems thereforemod-ified polymer systems may require different set of processingparameters in order to optimize their properties other thanthat recommended by manufacturers Gelation is critical inthermoset processing as it defines the most distinguishingcharacteristic of liquid epoxy and its use as matrix systemfor the fabrication of laminated composites Beyond gel pointepoxy processing becomes almost impossible due to onsetof crosslinking coupled with rapid increase in the viscosityTherefore understanding influence of surface modificationsin nanoclay fillers on rheological properties of polymersis critical as it directly relates to consistency in flow dur-ing processing and development of material properties innanocomposites

In the current study influence of three different organ-ically modified montmorillonite nanoclays on rheologicalproperties and cure behavior of DGEBA epoxy resin SC-15 was investigated Nanomer I28E and Cloisite 10A and30B with different surface modifications were used andcure kinetic parameters were evaluated using isothermalrheological studies

2 Experimentation

21 Materials Commercially available two part (A and B)SC-15 epoxy resin system was used for this study SC-15a DGEBA epoxy system with low shrinkage and relativelyhigh thermal stability was obtained from Applied PoleramicInc The curing agent (part B) is a cycloaliphatic aminehardener The epoxy resin system was modified with threecommercially available montmorillonite nanoclays (MMT)Nanomer I28E from Sigma Aldrich and Cloisite 10A andCloisite 30B from Southern Clay Inc The MMT used isnaturally occurring 2 1 layered smectite clay mineral withtypical chemical structure shown in Figure 1 and chemicalcomposition of A

03(Al13Mg07)[Si4]O10sdot(OH)

2sdotxH2O where

ldquoArdquo is exchangeable cation K+ Na+ or 05Ca2+ Particlesize distribution of clustered MMT clays was between 8and 12 120583m Surface of Nanomer I28E is modified with 25ndash30wt of quaternary trimethyl stearyl ammonium withCEC of 937meq100 g while Cloisite 10A and 30B are mod-ified with quaternary dimethyl benzyl hydrogenated tallowammonium and quaternary dimethyl dihydrogenated tallowammonium with CEC of 125meq100 g and 90meq100 grespectively Specific details about surface modifications areproprietaryTherefore aim of this study is to investigate whatinfluence a particular commercially available nanoclay willhave on the cure behavior of an epoxy resin system withoutgoing into the details of the interactions between polymer andnanoclays

22 Sample Preparation Each MMT used in the study wasdried in a convection oven for 2 hours allowed to cool andthen thoroughly dispersed into measured amount of SC-15

Journal of Nanoscience 3

in a beaker to form 2wt MMT-epoxy composite usingmagnetic stirring technique Twowt was chosen based onour previous studieswherein it gavemost enhancement in theproperties Stoichiometric amount of SC-15 hardener (partB) was then added at a ratio of 100 part A 30 part B byweight and stirred mechanically followed by desiccation toget rid of any bubbles Rheological and cure kinetic studieswere conducted using small amount of uncured neat andmodified SC-15 epoxy resin mixture to determine the curekinetic parameters Part of each mixture was poured intomolds and cured at ambient temperature for 24 h followed by2 h after curing at 100∘C to form epoxy composite samples

23 Characterization

231 Rheological Influence of MMT clay type on rheolog-ical behavior of SC-15 was studied using TA Instruments(Delaware)AR2000 rheology equipmentwith 25mmparallelETC steel plates Shear experiments were performed onunmodified andmodified SC-15 at shear rates varying from 0to 100 radsminus1 and compared Rheological measurements werecarried out in ambient temperature with oscillatory maxi-mum normal force of 050N Nanoclay effects on viscosityand subsequent developments of viscoelastic properties ofSC-15MMT during curing were also studied using isother-mal rheology where the rheological equipment was operatedin oscillation-time-sweep mode at 60 70 80 and 90∘CEvolution of storage modulus (119866

1015840) and loss modulus (119866

10158401015840)

was monitored as function of reaction time Test results wereanalyzed using TA Instruments ldquoData Analysisrdquo software

232 Differential Scanning Calorimetry (DSC) Effect ofdifferent MMT clays on cure behavior of modified epoxyresin was investigated by conventional differential scanningcalorimetry (DSC) using Q1000 equipment from TA Instru-ments Inc The instrument was purged with nitrogen gas ata flow rate of 50mLmin during scanning Cell constant andtemperature sensitivity of theDSC equipmentwere calibratedusing sapphire samples and indium metal respectively Alu-minum hermetic pans were used as reference and samplepans Dynamic scans were performed at scanning rates of 2550 100 and 150∘Cmin from 30 to 240∘C while isothermalscans were carried out at 60 70 80 and 90∘C over a period of320 minutes Sample weights were maintained between 8 and10mg for both dynamic and isothermal scans for consistencyand minimization of heat gradient Heat flux was recordedas a function of temperature for dynamic scanning and timefor isothermal scanning up to a point where there was nonoticeable changes in the heat flow compared to baseline dataResults fromDSC scans were analyzed using TA InstrumentsrsquoSpecialty Library

24 Cure Reaction Chemical reactions involved in curing ofepoxies can be complex based on the composition and maytake various forms however degree of cure can be related toheat released during curing at any given temperature Thusrate of cure (119889120572119889119905) of any given chemical reaction in a DSC

experiment is directly proportional to themeasured heat flowrate (119889119867119889119905) relative to the baseline of the instrument and canbe expressed as

119889120572

119889119905

=

119889119867119889119905

Δ119867

(1)

where Δ119867 is the total heat generated from the reactionto reach full conversion (enthalpy) Furthermore reactionmechanism can be analyzed as function of conversion frac-tion (120572) and temperature (119879) which is expressed as

119889120572

119889119905

= 119870 (119879) 119891 (120572) (2)

where 119891(120572) is a time- and temperature-dependant functionand119870(119879) is a temperature-dependant function and expressedin Arrhenius form as

119870 (119879) = 119860 exp(minus

119864

119886

119877119879

) (3)

where119860 is the preexponential factor119864119886is apparent activation

energy 119877 is the universal gas constant (83144KJmol) and119879 is the absolute temperature (K) Thus maximum reactionrate (119889120572119889119905) occurs at the peak temperature (119879

119901) and can be

expressed as119889120572

119889119905

= 119860119890

(minus119864119886119877119879119901)sdot 119891 (120572)

(4)

Introducing the heating rate 120573 which can be expressed as119889119879119889119905 (3) can further be expressed as

119889120572

119889119879

=

119860

120573

119890

(minus119864119886119877119879119901)sdot 119891 (120572) (5)

Taking logarithm of both sides and rearranging terms acti-vation energy (119864

119886) can be obtained from the slope of plots

of ln(120573) versus 1119879

119901according to ASTM E698 [19] utilizing

Ozawa method and can be expressed in as

119864

119886=

119877

1052

sdot

119889 ln120573

119889 (1119879

119901)

(6)

Cure reaction of unmodified and modified epoxy networkwas characterized using the same technique where heat ofreaction Δ119867 activation energy 119864

119886 preexponential factor

were determined and compared with that of the neat system

25 Morphological Microstructural analyses performed oncured samples using X-ray diffraction techniques (XRD)and transmission electron microscopy (TEM) were used toestablish degree of dispersion in each sample Intergalleryspacing between clay platelets was determined for powderednanoclay and their respective nanocomposites samples forcomparison using Braggrsquos law XRD study was done usingRigaku-DMAX-2000 equipped with Cu K120572 radiation ofwavelength 120582 = 154 nm operating at 40KV and 30Aand samples were scanned at 02∘ from 2120599 values of 2ndash40∘ High resolution TEM studies were performed on eachnanocomposite to further establish MMT dispersion in eachSC-15 nanocomposite TEM samples were microtomed fromeach cured epoxy nanocomposite collected in a water bathand transferred onto 200 Cu mesh and scanned


Table 1 Dependency of viscosity on shear rate

Sampleshear rate 1s Viscosity at various shear rates 120583PasdotsNeat SC-15 SC-15Nanomer I28E SC-15Cloisite 10A SC-15Cloisite 30B

1 51250 plusmn 1413 85573 plusmn 3267 333561 plusmn 34506 108355 plusmn 22345






0 10 20 30 400 10 20 30 402-120579

Nanomer I28E powderCloisite 10A powderCloisite 30B powder

SC-15nanomer I28E compositeSC-15cloisite 10A compositeSC-15cloisite 30B composite

0

5000

10000

15000

20000

Inte

nsity

Figure 2 XRDdiffraction peaks ofNanomer I28E Cloisite 10A and30B clay samples and their respective composites

3 Results and Discussion

31Morphological Studies Property enhancements involvingnanoclays have been attributed to degree of dispersion abilityof host polymer molecules to percolate and expose largesurface area of nanoclay to enhance interactions Interactionsof these high aspect ratio particles with epoxymolecules gov-ern most chemical reactions and subsequent enrichments inproperties Prominent diffraction peaks indicative of highlyorganized clay platelets in each clay sample were observedat 2120579 values of 360 488 and 480∘ for Nanomer I28Eand Cloisite 10A and 30B respectively (Figure 2) Subse-quent diffraction peaks from their respective nanocompositesshowed broader peaks with lower intensities and at higher2120579 values between 1750 and 1850∘ Variation in diffractionpeaks can be attributed to different surfactant used in theirrespective surface modifications and interaction with SC-15epoxy molecules Intergallery 119889-spacing determined usingBraggrsquos law for each type of nanoclay was 791 1193 and1140 A for Nanomer I28E and Cloisite 10A and 30B respec-tively while that of their corresponding nanocomposites was132 272 and 244 AThe results showed an increase of about67 127 and 114 in 119889-spacing between powdered clay andtheir respective composites Increasing lattice space between

the clay platelets suggests intercalation of epoxy moleculesinto the intergallery of the clay particles by percolating intoclay platelets and moveing them apart This phenomenondepends on factors such as clay surface morphology disper-sion time curing agents and curing temperature [11 14 1619 20] These results also illustrate chemical compatibilitybetween quaternary benzyl hydrogenated tallow ammoniumsurfactant used in Cloisite 10Amodification and SC-15 epoxymolecules This was demonstrated by the ability of theCloisite 10A clay to allow epoxy molecules to percolate intothe intergallery and move them farthest apart compared toother nanocomposites as can be seen from increased 119889-spacingThis study revealed thatmore epoxymolecules inter-calated into Cloisite 10A followed by Cloisite 30B and finallyNanomer I28E based on the intensities of XRD observed intheir respective nanocomposites

Further morphological studies were done to qualita-tively establish degree of clay dispersion in their respec-tive nanocomposites using transmission electronmicroscope(TEM) TEM micrographs obtained at different locationsfrom various nanocomposite surfaces are shown in Figure 3Intercalated morphologies were prevalent in all samples asseen from micrographs obtained from samples used in thecurrent study possibly due to ambient curing condition andinsufficient dispersion time Microstructural analyses indi-cated that due to different surface modifications percolationand interaction of clay particles and epoxy molecules werediverse as shown by different 119889-spacing values in theirrespective nanocomposites

32 Rheological Studies

321 Viscosity Dependency on Shear Rate Experimentalplots of viscosity of uncured neat and MMT modified SC-15 epoxy systems in ambient temperature are presentedin Figure 4 and average values presented in Table 1 forcomparison At low shear rate influence of different surfacemodifications in montmorillonite clay became apparent asviscosity varied for various MMT infused samples Initialresponse in viscosity to applied shear stress significantlyvaried from one system to the othermainly due to interactionbetween clay and epoxy molecules These interactions inconjunction with that between the nanoclay particles withinthe epoxy in response to applied stress led to higher viscositymeasurements at low shear rate (0ndash5 sminus1) compared to neatSC-15 system [14 21] Low shear rate further allowed epoxy


(a) (b)

(c)

Figure 3 TEMmicrographs of SC-15 nanocomposites infused with (a) Nanomer I28E and (b) Cloisite 10A and (c) Cloisite 30B

0

2

4

6

0 20 40 60 80 1000 20 40 60 80 10

SC-15 epoxySC-15Nanomer I28E

SC-15Cloisite 10ASC-15Cloisite 30B

Shear rate (1s)

Vis

cosit

y (P

amiddots)

(a)

0

2

4

2 5 8 11 14 17 20Shear rate (1s)

Vis

cosit

y (P

amiddots)

2 5 8 11 14 17 2Shear rate (1s)



(b)

Figure 4 Influence of different MMTs on rheological properties at room temperature at (a) shear rates from 0 to 100 sminus1 and (b) from 0 to20 sminus1 heating rate 10∘Cmin


Table 2 Summary of isothermal rheology

Sample Cure temperature ∘C Gel time s Storage modulus at gel point Pa Viscosity at gel point Pasdots

SC-15 composite

60 3451 43810 984470 1801 30380 688280 1001 8884 297790 391 4606 1027

SC-15Nanomer I28E

60 5851 98170 2257070 3131 28260 610980 1491 12010 213890 841 4767 1073

SC-15Cloisite 10A

60 3007 92680 2082070 1616 27690 619780 646 10400 235290 474 7761 1743

SC-15Cloisite 30B

60 3275 58920 1328070 1597 28650 645180 566 7166 166390 326 6374 1378

molecules to percolate between layers of clay platelets causingswelling and increase of intergallery spacing This processis controlled among other things by temperature interfa-cial chemistry of clay surface particle-particle interactionspH of the system and host polymer molecules leading tochanges in rheological behavior [22 23]

As shear rate increased from 8 to 20 sminus1 percolationtime and orientation of clay platelets in each mixture inresponse to applied shear stress varied due to the presence ofdifferent organic modifiers in each composition [9 12 14 15]This effect can be seen in viscosity measurements of eachsample shown in Figure 4(b) However behavior of all MMTmodified SC-15 systems in response to increasing shear stressbeyond 20 sminus1 was identical to that of neat systemThis behav-ior was possibly due to inadequate time for epoxy moleculesto move further into the clay layers forming a mesoscopicmixture in response to increasing shear rate Hence allsystems behaved indistinguishably regardless of clay surfacemodifications Identical rheological behavior with varyingviscosities demonstrates dependence of viscosity on particle-particle and particle-host interactions as studies have shown[9ndash13] Also behavior of all systems at shear rates of 5 8 and20 sminus1 can be characteristic of SC-15 epoxy system in responseto applied stress [12 21] Overall viscosity of samples withCloisite 10A showed higher values throughout the studycompared to other nanocomposites including neat system asshown in Figure 4(b) Higher values of viscosity observedin SC-15Cloisite 10A samples are indicative of anisotropicmicrostructural behavior where epoxymolecules moved intothe intergallery spacing and cause the clay layers to swelland move further apart [12ndash15] It also demonstrates betterinteraction between epoxy molecules and quaternary benzylhydrogenated tallow ammonium salt between clay layersallowing percolation and causing swellingThis phenomenoncan lead to complete separation of clay platelets to form

anisotropic solution leading to higher viscosity [14 15]It is therefore safe to assume that among various MMTcompositions used in this study SC-15Cloisite 10A mixtureshowed relatively better dispersionThis assertion can be cor-roborated by results fromXRD studies showing relative lowerintensity and broader diffraction peaks and highest percentchange in 119889-spacing between clay platelets in SC-15Cloisite10A samples (Figure 2) Furthermore with extended disper-sion time we speculate that SC-15Cloisite 10A clay plateletsmaymove even farther apart enhancing dispersion and affectviscosity and final properties of composites as suggestedby several studies [11 24 25] In this work at the end ofthe study viscosity of Cloisite 10A and Cloisite 30B infusedSC-15 resin increased by about 173 and 76 respectivelywhile Nanomer I28E decreased by nearly 5 This showsthat although identical behavior was observed beyond 20 sminus1clearly organic modifiers significantly influenced viscosity ofthe host polymer which may affect processability and curingleading to different property development

322 Isothermal Rheological Studies Generally curing ofepoxy resin with amino curing agents involves reactions ofprimary and secondary amine with epoxide molecules and areaction between hydroxyl by-product and epoxide to formether molecules (etherification) resulting in branching andcrosslinking [26ndash28] Kinetic model for these reactions caneither be 119899th order or autocatalytic However studies haveshown that most epoxy resin cure reactions are autocatalyticin nature [16 17 27 29] During curing low viscosity SC-15 epoxy resin system undergoes physical changes such asgelation and vitrification before complete solidification [1524 27] Gel time is very critical in polymer processing anddepends on numerous factors which include constituents ofreactants cure temperature cure rate and pH of the mixture[13 23] In the current study gel point for each composition


was determined as the crossover point between storage andloss moduli and the results are summarized in Table 2 Atonset of experiment viscosity of each composition was lowwith higher values of loss moduli due to the dominanceof viscous properties of SC-15 epoxy resins However withprogression of chemical reaction viscosity increased rapidlypassing gel point at different times based on stoichiometriccomposition and curing temperature Various gelation timereported in each system was not only indicative of influenceof surface modifications but also manifests comparative cat-alytic behavior among nanoclay-infused samples during cur-ing For example gelation occurred sooner in Cloisite modi-fied SC-15 samples compared to Nanomer modified samplesat all temperatures considered in this studyThis behavior wasattributed to better interactions between organic modifiersused in Cloisite nanoclays and SC-15 molecules leading toincreased nanoclay participating in the chemical reactionduring curing It also leads to increased rate of chemicalreaction and demonstrates an active interaction betweenexposed surface of nanoclay particles and epoxy moleculeswithin the percolated pseudosolid-like structure during cur-ing [14 21 24] On the other hand Nanomer infused sampleshad longer gel time indicating a relatively less interactionbetween SC-15 epoxy molecules and quaternary trimethylstearyl ammonium salts used in modification of clay Fornanoclay based systems there was an enhanced reactionwhen compared to neat samples at the same temperatureTemperature has also been shown to influence viscosityvitrification and degree of intergallery expansion of clayplatelets thereby affecting chemical reaction during curing[16ndash18]

Viscoelastic properties at various curing temperatureswere observed to decrease with increasing temperature Forexample gelation time and corresponding storagemodulus atgel points decreased across the board as curing temperatureincreased Maximum storage modulus at gel point wasattained at 60∘C for all samples and the values were higherin all nanophased samples Among the nanocompositesNanomer I28E infused samples yielded the highest value ofstorage modulus For samples cured at 70∘C neat system hadthe highest modulus at gel point and among the nanoclayinfused SC-15 samples with Cloisite 30B had the highestvalues However at curing temperature of 80∘C sampleswith Cloisite 10A showed the highest values in storagemodulus at gel point This behavior leads to the speculationthat optimization of material properties in nanoclay infusedcomposites can be achieved when cured at temperatureslower than 70∘CThus a significant drop in storage modulusand viscosity at gel point observed among nanocompositessamples cured at 60 and 70∘C attests to this conclusion

According to Floryrsquos (1953) gelation theory degree ofcure at gel time (120572gel) of any polymer system depends onthe chemical structure and functionalities of that systemand considered constant regardless of the cure temperatureTherefore integrating (4) with limits from of 0 to gel time(119905gel) and taking natural logarithm of both sides a relationcan be established from the plots of ln(119905gel) versus absolutetemperature (T) where the slope of curve gives the apparent

5

6

7

8

9

27 28 29 30 31

1T (10minus3Kminus1)

ln(t

gel)

7 28 29 30 3


SC-15 compositeSC-15Nanomer I28E


Figure 5 Plots of ln(119905gel) versus inverse absolute temperature (119879)

during isothermal rheological studies

activation energy of cure reaction The relationship can beexpressed as

119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860

0is preexponential factor at 119905 = 0 and 120572gel is the

conversion at gel pointFigure 5 shows experimental data plots of ln(119905gel) versus

absolute temperature (119879) where apparent activation energydetermined from the linear fit curve was 6959 6593 6503and 8006KJmol for neat SC-15 Nanomer I28E andCloisite10A and 30B infused SC-15 epoxy system respectively

33 DSC Characterization

331 Dynamic DSC Studies Representative DSC thermo-grams obtained from dynamic scans of unmodified andmodified SC-15 at heating rates of 25 and 10∘Cmin are shownin Figure 6 Results fromDSC scans showed a single exother-mic peak throughout the curing process for all samples anindication that presence of differentMMTdid not affect reac-tion mechanism At lower heating rates onset of chemicalreactions and reaction rates were slow due to lower viscosityand less molecularmobility of reactants while higher heatingrates offered less time and increased reaction rate for eachsystem As a result exothermic peak temperature (119879

119901) shifted

to higher temperatures with increasing ramp rate to com-pensate for insufficient reaction time Also higher heatingrates provided enough momentum to the system therebyincreasing mobility and collisions between epoxy moleculesresulting in higher enthalpy at the end of each scan Summary


0

01

02

03

0 50 100 150 200 250

Exo

Heating rate 25∘Cmin

Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo

HeaHHHH ting rate 25∘Cmin

Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo

Heating rate 25∘Cminnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn

Temperature (∘C)



(b)

Figure 6 DSC thermograms of neat SC15 and SC15 modified with Nanomer I28E and Cloisite 10A and Cloisite 30B at (a) 25 and (b) heatingrate 10∘Cmin

Table 3 Results of dynamic DSC scan

Epoxy system Scanning rate Cmin Kinetic parameter119879

119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907

31580 plusmn 2086 4910 plusmn 589 612 plusmn 085

50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182

of dynamic scans for all samples are presented in Table 3where influence of clay surface modifications on kineticparameters can be observed There were slight changes inonset of reaction temperature (119879

119894) between neat and the vari-

ousMMT infused samples as can be seen in Table 3Howeverfinal reaction temperature (119879

119891) significantly increased with

the addition of MMT at various heating rates along withenthalpy (Δ119867) and activation energy of reaction Apparentactivation energy of reaction for each system (Table 3) wascalculated using TA Instrumentsrsquo Specialty Library basedon ASTM E698 utilizing Ozawa (1964) method [19] Thisapproach required at least three or more scans at different

heating rates hence different heating rates were employed inthe current study

Overall heat of reaction (Δ119867) and activation energy (119864119886)

of reaction for all nanocomposites were higher comparedto neat Nanomer I28E infused samples showed the highestvalues with about 13 and 26 increase when comparedto neat respectively Observed high enthalpy for NanomerI28E infused samples may be due to lower viscosity andrelatively less percolation of epoxy molecules into clay layershence more heat was required to initiate polymerization andcrosslinking leading to higher enthalpy of reaction On theother hand samples with Cloisite 10A showed lower enthalpy


Table 4 Summary of isothermal DSC scans

Samples Isothermal temperature ∘C Kinetic parameters119899 119898 (times10minus2) 119870 (times10minus3) 119879

119901 min Δ119867 Jg

SC-15 epoxy composite

60 115 plusmn 0053 311 plusmn 29 240 plusmn 20 3253 3011070 166 plusmn 0096 260 plusmn 52 330 plusmn 40 1993 4440480 172 plusmn 0065 298 plusmn 35 730 plusmn 60 1337 3513690 244 plusmn 012 308 plusmn 68 940 plusmn 140 1270 42927

SC-15Nanomer I28Eepoxy nanocomposite


SC-15Cloisite 10A epoxynanocomposite


SC-15Cloisite 30B epoxynanocomposite


and activation energy of reactions among MMT infusedsamples

From these results it can also be seen that each infusedMMT system required different amount of energy to over-come energy barrier to fuse reacting species together com-pared to neat It also establishes the influence of differentsurfactants used in clay modification on overall reactionkinetics including activation energy Among MMT infusedsamples Cloisite 10A had relatively lower activation energywhile Nanomer I28E had the highest value These resultscorroborate results from rheological and XRD studies Thesevalues when compared with neat system constitute anincrease of approximately 17 and 26 for Cloisite 10A andNanomer I28E infused samples respectively

332 IsothermalDSCStudies Advantages of isothermalDSCtechnique include elimination of thermal gradient effectserrors due to nonlinear heating ramps and minimizingdecomposition interferences of sample Curing of epoxyamine system is shown to be autocatalytic in nature [26ndash29] where the cure rate 119889120572119889119905 and degree of cure 120572 can beexpressed according to Kamalrsquos model as follows

119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)

where 119898 and 119899 are the reaction orders 119896

1and 119896

2are the

reaction rate constants where 119896

1is the kinetic rate constant

corresponding to noncatalytic reaction between epoxide andamine groups and 119896

2is the rate constant due to hydroxyl

group formed as a result of catalytic effect of amine curingagent Constant 119896

1can be determined based on the initial

rate 120572 = 0 1198961and 119896

2are assumed to have an Arrhenius

relationship that is

119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)

However TA Instruments ldquoSpecialty Libraryrdquo considers over-all 119896 for each reaction set during analyses and thereforereported rate constant values (119896) are that of overall value foreach composition

Representative isothermal DSC thermograms obtainedfor unmodified and Cloisite 10A infused SC-15 epoxy systemsat 60 70 80 and 90∘C are shown in Figures 7(a) and7(b) with characteristic autocatalytic thermogram Duringisothermal curing rate of chemical reaction increased withtime and each reaction went through a maximum reac-tion peak before retarding due to gelation and vitrificationWith increasing isothermal cure temperature reaction rateincreased and intensity of reaction peaked at a relativelyshorter time regardless of the composition Heat of reaction(Δ119867) from isothermal scans also showed higher values forMMT infused systems compared to neat as shown inTable 4 This corroborates results from dynamic scans for allnanophased compositions compared to neat (Table 3) Theseresults also showed a dependency of kinetic parameter 119899 onreaction temperatures and surface modifications of clay Asreaction temperature increased reaction order 119899 increasedand among various MMT infused samples Cloisite 10Asamples had the least values While no particular trend wasobserved in the values of119898 it however confirms complexitiesinvolved in epoxy curing

Studies [27 28] have shown that for autocatalytic epoxycuring overall reaction order (119899+119898) is assumed to be 2 UsingldquoSpecialty Libraryrdquo software reaction temperatures at various


0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200

SC15Cloisite 10A 60∘C




Hea

t flow

(Wg

)(b)

Figure 7 Representative isothermal heat flow thermogram for (a) neat and (b) Cloisite 10A infused SC-15 epoxy at different curingtemperatures

0

2

4

6

8

10

60 70 80 90

50

7080

90

95SC-15 epoxy composite

Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)

Figure 8 Conversion time-temperature curves of (a) neat SC-15 and (b) SC-15 with Cloisite 10A

conversion times were generated for all samples includingneat and plotted as shown in Figure 8 Using this set of curvesand reaction orders obtained from each scan presented inTable 4 corresponding temperature for the closest reactionorder (119899 + 119898) of approximately 2 is as follows for neatsystem (0wt) reaction temperature would be 80∘C forNanomer I28E it is 70∘C and for Cloisite 10A and 30Bit is 60∘C It follows that required curing temperature foroptimization of epoxy composite properties was influencedby the presence of different constituents Influence of theseconstituents are dictated by their surface chemistry hencethe effect of different clay surface modifications can affectultimate properties of final nanocomposites In our previous

studies [30] it was shown that surface modifications of theseMMT nanoclays influenced viscoelastic properties and acti-vation energy of decomposition of epoxy composites duringthermal stability studies Furthermore the study showed thatdifferent surface modification of MMT influenced the rateof chemical degradation caused by UV radiation exposureThese observations can be attributed to chemical interactionbetween MMT clay particles and epoxy molecules duringcuring as observed in rheological studies Influence of dif-ferent surface modification of montmorillonite nanoclay oncure behavior was also apparent based on results from eachcuring temperature showing different cure times for eachsample


4 Conclusion

Influence of different surface modifications on rheologicaland cure behavior was studied using SC-15 epoxy resinmodified with Nanomer I28E and Cloisite 10A and 30Bmontmorillonite nanoclays Presence of different surfacemodifications of MMT had no effect on the cure reactionmechanism however viscosity and subsequent heat of reac-tion and activation energy of reaction were significantlyaffected Surface modifications of montmorillonite nanoclayalso affected gelation time leading to different cure timeat various cure temperatures These parameters influenceoverall properties hence for any modified epoxy resinsystem with MMT cure kinetic studies are essential in orderto optimize the processing parameters to obtain desirableproperties of final composites Also temperature and timerequired to cure MMT modified SC-15 may differ based onsurface modification of MMT

Acknowledgments

The authors would like to acknowledge Alabama Commis-sion on Higher Education (ACHE) Office of Naval Research(ONR) and National Science Foundation (NSF-EPSCoR) fortheir financial support The authors have no affiliation andno commercial interests with any of the manufacturers of allcommercially available products used in this study

References

[1] F Hussain M Hojjati M Okamoto and R E Gorga ldquoReviewarticle polymer-matrix nanocomposites processing manufac-turing and application an overviewrdquo Journal of CompositeMaterials vol 40 no 17 pp 1511ndash1575 2006

[2] P H C Camargo K G Satyanarayana and F Wypych ldquoNano-composites synthesis structure properties and new applica-tion opportunitiesrdquo Materials Research vol 12 no 1 pp 1ndash392009

[3] M Alexandre and P Dubois ldquoPolymer-layered silicate nano-composites preparation properties and uses of a new class ofmaterialsrdquoMaterials Science and Engineering R vol 28 no 1ndash2pp 1ndash63 2000

[4] X Kornmann M Rees Y Thomann A Necola M Barbezatand R Thomann ldquoEpoxy-layered silicate nanocomposites asmatrix in glass fibre-reinforced compositesrdquoComposites Scienceand Technology vol 65 no 14 pp 2259ndash2268 2005

[5] E Bozkurt M Tanoglu and E Kaya ldquoMechanical and thermalbehavior of non-crimp glass fiber reinforced layered clayepoxynanocompositesrdquo Composites Science and Technology vol 67no 15ndash16 pp 3394ndash3403 2007

[6] P I Xidas and K S Triantafyllidis ldquoEffect of the type of alky-lammonium ion clay modifier on the structure and ther-malmechanical properties of glassy and rubbery epoxy-claynanocompositesrdquo European Polymer Journal vol 46 no 3 pp404ndash417 2010

[7] E Manias G Polizos H Nakajima and M J Heidecker ldquoFun-damentals of polymer nanocomposite technologyrdquo in FlameRetardant Polymer Nanocomposites Wiley Hoboken NJ USA2007

[8] P Kiliaris and C D Papaspyrides ldquoPolymerlayered silicate(clay) nanocomposites an overview of flame retardancyrdquoProgress in Polymer Science vol 35 no 7 pp 902ndash958 2010

[9] L Le Pluart J Duchet H Sautereau P Halley and J-F GerardldquoRheological properties of organoclay suspensions in epoxynetwork precursorsrdquo Applied Clay Science vol 25 no 3ndash4 pp207ndash219 2004

[10] A Yousefi G Lafleur and R Gauvin ldquoKinetic studies of ther-moset cure reactions a reviewrdquo Polymer Composites vol 18 no2 pp 157ndash168 1997

[11] T P Mohan R Velmurugan and M R Kumar ldquoRheology andcuring characteristics of epoxy-clay nanocompositesrdquo PolymerInternational vol 54 no 12 pp 1653ndash1659 2005

[12] D W Litchfield and D G Baird ldquoThe rheology of high aspectratio nanoparticle filled liquidsrdquoThe British Society of Rheologypp 1ndash60 2006

[13] S S Ray andM Okamoto ldquoPolymerlayered silicate nanocom-posites a review from preparation to processingrdquo Progress inPolymer Science vol 28 no 11 pp 1539ndash1641 2003

[14] K Beazley ldquoIndustrial aqueous suspensionsrdquo in RheometryIndustrial Applications Research Studies Press England UK1980

[15] J Ren B F Casanueva C A Mitchell and R KrishnamoortildquoDisorientation kinetics of aligned polymer layered silicatenanocompositesrdquoMacromolecules vol 36 no 11 pp 4188ndash41942003

[16] S Montserrat and J G Martın ldquoNon-isothermal curing of adiepoxide-cycloaliphatic diamine system by temperature mod-ulated differential scanning calorimetryrdquo Thermochimica Actavol 388 no 1ndash2 pp 343ndash354 2002

[17] H Cai P Li G Sui et al ldquoCuring kinetics study of epoxyresinflexible amine toughness systems by dynamic and isother-mal DSCrdquo Thermochimica Acta vol 473 no 1ndash2 pp 101ndash1052008

[18] Z Wang and T J Pinnavaia ldquoIntercalation of poly(pro-pyleneoxide) amines (Jeffamines) in synthetic layered silicasderived from ilerite magadiite and kenyaiterdquo Journal of Mate-rials Chemistry vol 13 pp 2127ndash2131 2003

[19] ASTM E698 Standard Test Method for Arrhenius Kinetic Con-stants for Thermally Unstable Materials American Society ofTesting and Materials West Conshohocken Pa USA 2005

[20] D Dean R Walker M Theodore E Hampton and ENyairo ldquoChemorheology and properties of epoxylayered sil-icate nanocompositesrdquo Polymer vol 46 no 9 pp 3014ndash30212005

[21] T B Tolle and D P Anderson ldquoThe role of preconditioningon morphology development in layered silicate thermosetnanocompositesrdquo Journal of Applied Polymer Science vol 91 no1 pp 89ndash100 2003

[22] R Krishnamoorti J Ren and A S Silva ldquoShear response oflayered silicate nanocompositesrdquo Journal of Chemical Physicsvol 114 no 11 pp 4968ndash4973 2001

[23] Y Jung Y-H Son J-K Lee T X Phuoc Y Soong and MK Chyu ldquoRheological behavior of clay-nanoparticle hybrid-added bentonite suspensions specific role of hybrid additiveson the gelation of clay-based fluidsrdquo ACS Applied Materials andInterfaces vol 3 no 9 pp 3515ndash3522 2011

[24] P Pustkova J M Hutchinson F Roman and S Montser-rat ldquoHomopolymerization effects in polymer layered silicatenanocomposites based upon epoxy resin implications forexfoliationrdquo Journal of Applied Polymer Science vol 114 no 2pp 1040ndash1047 2009


[25] Y-N Chan T-Y Juang Y-L Liao S ADai and J-J Lin ldquoPrep-aration of clayepoxy nanocomposites by layered-double-hydroxide initiated self-polymerizationrdquo Polymer vol 49 no22 pp 4796ndash4801 2008

[26] F Bensadoun N Kchit C Billotte F Trochu and E Ruiz ldquoAcomparative study of dispersion techniques for nanocompositemade with nanoclays and an unsaturated polyester resinrdquoJournal of Nanomaterials vol 2011 Article ID 406087 12 pages2011

[27] K Horie H Hiura M Sawada and H Kambe ldquoCalorimetricinvestigation of polymerization reactions III curing reactionof epoxides with aminesrdquo Journal of Polymer Science A-1 vol 8no 6 pp 1357ndash1372 1970

[28] S Sourour andM R Kamal ldquoDifferential scanning calorimetryof epoxy cure isothermal cure kineticsrdquo Thermochimica Actavol 14 no 1ndash2 pp 41ndash59 1976

[29] T Ozawa ldquoKinetic analysis of derivative curves in thermalanalysisrdquo Journal of Thermal Analysis vol 2 no 3 pp 301ndash3241970

[30] A Tcherbi-NartehMHosur E Triggs and S Jeelani ldquoThermalstability and degradation of diglycidyl ether of bisphenol Aepoxy modified with different nanoclays exposed to UV radia-tionrdquo Polymer Degradation and Stability vol 98 no 3 pp 759ndash770 2013

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Nanomer I28E-quaternary trimethyl

Stearyl ammonium

Cloisite 10A-quaternary benzyl

Hydrogenated tallow ammoniumCloisite 30B-quaternary

Dimethyl dihydrogenated tallow

ammonium

Al Fe Mg LiOH

OLi Na Rb Cs

Tetrahedral

Octahedral

Tetrahedral

Exchangeable cations

minus

Figure 1 Chemical structure of montmorillonite nanoclay [3]

interactions [12ndash15] Interactions between nanoclay particlesand epoxy molecules affect the viscosity and mobility ofreacting species during curing Consequently this influencesrate of cure reaction time enthalpy vitrification activationenergy viscoelastic properties and crosslinking density ofthe final composite [9 12 16 17] Other factors such as typeand amount of clay fillers and organic modifiers and theirinteraction with the intended host polymer molecules andtheir curing agents have all shown to influence properties ofpolymeric composites during processing [12ndash14 17 18]

Cure kinetic parameters including activation energydepend on constituents of polymeric systems thereforemod-ified polymer systems may require different set of processingparameters in order to optimize their properties other thanthat recommended by manufacturers Gelation is critical inthermoset processing as it defines the most distinguishingcharacteristic of liquid epoxy and its use as matrix systemfor the fabrication of laminated composites Beyond gel pointepoxy processing becomes almost impossible due to onsetof crosslinking coupled with rapid increase in the viscosityTherefore understanding influence of surface modificationsin nanoclay fillers on rheological properties of polymersis critical as it directly relates to consistency in flow dur-ing processing and development of material properties innanocomposites

In the current study influence of three different organ-ically modified montmorillonite nanoclays on rheologicalproperties and cure behavior of DGEBA epoxy resin SC-15 was investigated Nanomer I28E and Cloisite 10A and30B with different surface modifications were used andcure kinetic parameters were evaluated using isothermalrheological studies

2 Experimentation

21 Materials Commercially available two part (A and B)SC-15 epoxy resin system was used for this study SC-15a DGEBA epoxy system with low shrinkage and relativelyhigh thermal stability was obtained from Applied PoleramicInc The curing agent (part B) is a cycloaliphatic aminehardener The epoxy resin system was modified with threecommercially available montmorillonite nanoclays (MMT)Nanomer I28E from Sigma Aldrich and Cloisite 10A andCloisite 30B from Southern Clay Inc The MMT used isnaturally occurring 2 1 layered smectite clay mineral withtypical chemical structure shown in Figure 1 and chemicalcomposition of A

03(Al13Mg07)[Si4]O10sdot(OH)

2sdotxH2O where

ldquoArdquo is exchangeable cation K+ Na+ or 05Ca2+ Particlesize distribution of clustered MMT clays was between 8and 12 120583m Surface of Nanomer I28E is modified with 25ndash30wt of quaternary trimethyl stearyl ammonium withCEC of 937meq100 g while Cloisite 10A and 30B are mod-ified with quaternary dimethyl benzyl hydrogenated tallowammonium and quaternary dimethyl dihydrogenated tallowammonium with CEC of 125meq100 g and 90meq100 grespectively Specific details about surface modifications areproprietaryTherefore aim of this study is to investigate whatinfluence a particular commercially available nanoclay willhave on the cure behavior of an epoxy resin system withoutgoing into the details of the interactions between polymer andnanoclays

22 Sample Preparation Each MMT used in the study wasdried in a convection oven for 2 hours allowed to cool andthen thoroughly dispersed into measured amount of SC-15



23 Characterization



10158401015840)





119889120572

119889119905

=

119889119867119889119905

Δ119867

(1)


119889120572

119889119905

= 119870 (119879) 119891 (120572) (2)


119870 (119879) = 119860 exp(minus

119864

119886

119877119879

) (3)



119901) and can be


119889119905

= 119860119890

(minus119864119886119877119879119901)sdot 119891 (120572)

(4)


119889120572

119889119879

=

119860

120573

119890

(minus119864119886119877119879119901)sdot 119891 (120572) (5)



of ln(120573) versus 1119879



119864

119886=

119877

1052

sdot

119889 ln120573

119889 (1119879

119901)

(6)














0 10 20 30 400 10 20 30 402-120579



0

5000

10000

15000

20000

Inte

nsity









(a) (b)

(c)


0

2

4

6

0 20 40 60 80 1000 20 40 60 80 10



Shear rate (1s)

Vis

cosit

y (P

amiddots)

(a)

0

2

4

2 5 8 11 14 17 20Shear rate (1s)

Vis

cosit

y (P

amiddots)

2 5 8 11 14 17 2Shear rate (1s)



(b)





SC-15 composite

60 3451 43810 984470 1801 30380 688280 1001 8884 297790 391 4606 1027

SC-15Nanomer I28E

60 5851 98170 2257070 3131 28260 610980 1491 12010 213890 841 4767 1073

SC-15Cloisite 10A

60 3007 92680 2082070 1616 27690 619780 646 10400 235290 474 7761 1743

SC-15Cloisite 30B

60 3275 58920 1328070 1597 28650 645180 566 7166 166390 326 6374 1378









5

6

7

8

9

27 28 29 30 31


ln(t

gel)

7 28 29 30 3







119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860






119901) shifted



0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





23 Characterization



10158401015840)





119889120572

119889119905

=

119889119867119889119905

Δ119867

(1)


119889120572

119889119905

= 119870 (119879) 119891 (120572) (2)


119870 (119879) = 119860 exp(minus

119864

119886

119877119879

) (3)



119901) and can be


119889119905

= 119860119890

(minus119864119886119877119879119901)sdot 119891 (120572)

(4)


119889120572

119889119879

=

119860

120573

119890

(minus119864119886119877119879119901)sdot 119891 (120572) (5)



of ln(120573) versus 1119879



119864

119886=

119877

1052

sdot

119889 ln120573

119889 (1119879

119901)

(6)














0 10 20 30 400 10 20 30 402-120579



0

5000

10000

15000

20000

Inte

nsity









(a) (b)

(c)


0

2

4

6

0 20 40 60 80 1000 20 40 60 80 10



Shear rate (1s)

Vis

cosit

y (P

amiddots)

(a)

0

2

4

2 5 8 11 14 17 20Shear rate (1s)

Vis

cosit

y (P

amiddots)

2 5 8 11 14 17 2Shear rate (1s)



(b)





SC-15 composite

60 3451 43810 984470 1801 30380 688280 1001 8884 297790 391 4606 1027

SC-15Nanomer I28E

60 5851 98170 2257070 3131 28260 610980 1491 12010 213890 841 4767 1073

SC-15Cloisite 10A

60 3007 92680 2082070 1616 27690 619780 646 10400 235290 474 7761 1743

SC-15Cloisite 30B

60 3275 58920 1328070 1597 28650 645180 566 7166 166390 326 6374 1378









5

6

7

8

9

27 28 29 30 31


ln(t

gel)

7 28 29 30 3







119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860






119901) shifted



0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












0 10 20 30 400 10 20 30 402-120579



0

5000

10000

15000

20000

Inte

nsity









(a) (b)

(c)


0

2

4

6

0 20 40 60 80 1000 20 40 60 80 10



Shear rate (1s)

Vis

cosit

y (P

amiddots)

(a)

0

2

4

2 5 8 11 14 17 20Shear rate (1s)

Vis

cosit

y (P

amiddots)

2 5 8 11 14 17 2Shear rate (1s)



(b)





SC-15 composite

60 3451 43810 984470 1801 30380 688280 1001 8884 297790 391 4606 1027

SC-15Nanomer I28E

60 5851 98170 2257070 3131 28260 610980 1491 12010 213890 841 4767 1073

SC-15Cloisite 10A

60 3007 92680 2082070 1616 27690 619780 646 10400 235290 474 7761 1743

SC-15Cloisite 30B

60 3275 58920 1328070 1597 28650 645180 566 7166 166390 326 6374 1378









5

6

7

8

9

27 28 29 30 31


ln(t

gel)

7 28 29 30 3







119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860






119901) shifted



0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c)


0

2

4

6

0 20 40 60 80 1000 20 40 60 80 10



Shear rate (1s)

Vis

cosit

y (P

amiddots)

(a)

0

2

4

2 5 8 11 14 17 20Shear rate (1s)

Vis

cosit

y (P

amiddots)

2 5 8 11 14 17 2Shear rate (1s)



(b)





SC-15 composite

60 3451 43810 984470 1801 30380 688280 1001 8884 297790 391 4606 1027

SC-15Nanomer I28E

60 5851 98170 2257070 3131 28260 610980 1491 12010 213890 841 4767 1073

SC-15Cloisite 10A

60 3007 92680 2082070 1616 27690 619780 646 10400 235290 474 7761 1743

SC-15Cloisite 30B

60 3275 58920 1328070 1597 28650 645180 566 7166 166390 326 6374 1378









5

6

7

8

9

27 28 29 30 31


ln(t

gel)

7 28 29 30 3







119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860






119901) shifted



0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






SC-15 composite

60 3451 43810 984470 1801 30380 688280 1001 8884 297790 391 4606 1027

SC-15Nanomer I28E

60 5851 98170 2257070 3131 28260 610980 1491 12010 213890 841 4767 1073

SC-15Cloisite 10A

60 3007 92680 2082070 1616 27690 619780 646 10400 235290 474 7761 1743

SC-15Cloisite 30B

60 3275 58920 1328070 1597 28650 645180 566 7166 166390 326 6374 1378









5

6

7

8

9

27 28 29 30 31


ln(t

gel)

7 28 29 30 3







119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860






119901) shifted



0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







5

6

7

8

9

27 28 29 30 31


ln(t

gel)

7 28 29 30 3







119905gel =1

119870 (119879)

sdot int

120572gel

0

1

119891 (120572)

119889120572

ln (119905gel) = ln [

1

119860

0

(int

120572gel

0

1

119891 (120572)

119889120572)] +

119864

119886

119877

sdot

1

119879

(7)

where 119860






119901) shifted



0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

01

02

03

0 50 100 150 200 250

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 50 100 150 200 250

Exo


Temperature (∘C)



(a)

0

02

04

06

08

10

0 100 200 300

Exo


Temperature (∘C)

Hea

t flow

(Wg

)

0 100 200 30

Exo


Temperature (∘C)



(b)




119894 ∘C 119879

119901 ∘C 119879

119891 ∘C Δ119867 Jg 119864

119886 KJmol ln119860 1min

SC-15

25 5516 9347 21907


50 6540 10733 21816100 7898 11967 21657150 9441 13364 21840

SC-15Nanomer I28E

25 6131 9616 24146


50 6699 10643 21819100 7978 12078 26925150 8711 12970 27740

SC-15Cloisite 10A

25 6341 9734 25237


50 7092 11064 26154100 7677 12226 26550150 9203 13429 28280

SC-15Cloisite 30B

25 6140 9449 24294


50 6930 11051 27619100 8227 12385 29192150 9627 13412 29182












119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






119901 min Δ119867 Jg












119889120572

119889119905

= (119896

1+ 119896

2120572

119898) (1 minus 120572)

119899

(8)


1and 119896

2are the







rate 120572 = 0 1198961and 119896



119896

1= 119860

1119890

(1198641198861119877119879)

119896

2= 119860

2119890

(1198641198862119877119879)

(9)





0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

01

02

0 100 200Time (min)

SC-15 60∘C

SC-15 70∘C

SC-15 80∘C

SC-15 90∘C

Hea

t flow

(Wg

)

(a)

0

02

04

06

0 50Time (min)100 150 200





Hea

t flow

(Wg

)(b)


0

2

4

6

8

10

60 70 80 90

50

7080

90


Con

vers

ion

time

(hr)

Temperature (∘C)

(a)

0

1

2

3

4

60 70 80 90

50

70

80

90

95

SC-15Cloisite 10A

Con

vers

ion

time

(hr)

Temperature (∘C)

(b)





4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




4 Conclusion


Acknowledgments


References







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Research Article Effects of Surface Treatments of ...downloads.hindawi.com/journals/jns/2013/864141.pdfa DGEBA epoxy system with low shrinkage and relatively high thermal stability,