DTIC ADA431164: To Investigate the Impact of Tailorable Interface on the Morphology and Performance Characteristics of High Temperature Nanocomposites

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To Investigate the Impact of Tatlorable Interface an the Morphology
and Performance Characteristies of High Temperature Nauocomposites

D, Raghavan (PI)
Howard University
525 College Street, NW
Department of Chemistry
Washington DC. 20059

&

Dr. Chenggang Chen (Collaborator)
University of Dayton Rescarch Insitute
300 College Park
Dayton, OF 45469-0168

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AFOSRINL
[10 Duncan Avenue, Suite BLS
Bowling Air Force Base
‘Washington, DC 20332-8080

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20050525 138
ARSTRACT
Considerable research es beer conducted ia improving the performance

characteristies of nanocampostes, relatively few atempts have been made 10 address the

Thermal stability of nenocimposile, This research is focused on the preparation of the
layered orgunosiicares swith higher thermal stahilty, which can be used & make high
lemperstore polymir menccompnsites, Two approaches to foremulaue layered
nganosilicates nanoeornpesites with higher dhermal stability were sti

In the fis: approach, spophyi, # pure nalnes) ar uammervially-evailable
ly ara the

fiowstional pendent organic grovp containing a C-C bud. The chutacterivarion. from,

layered silicate, was Coated with 7-octenyltichlorosilan in order to chem

Fowiet wansfonm infrared (FTIR) spectroscopy, wide-angle x-ray diffiction (WAXD)
and ther gravimatic analysis (TGA) supports thal the organic pendant group was
sucueystully covalently grafted in the layeredsilicate backbove, and the layered
cxganosiiedté is Dhermally stable ocemposition temperature; ~430°C\. In addition.

apophyllite filled vinyl cster composites were finmulited and mechanical properties
ealuated.

In the second appronch, u pure, natural and commercially. available layered
silicate, ws Goated with synthesisied jecidazolium salts. 111 NMR and matic assisted
laser desorptionfionizetion time-offlight mass spectrameuy (MALDETOFMIS) were
used up chatacteize the imidwotium salts. The nanodispersion of imidazolium treated
ay in an cpoxy malrix was evaluated qualitstively by Xaay difftaction (XIRD)

tnmsenission electtonic microscopy (FFM), confibval laser tmicrosvopy, and laser induced

tuoresoence spectrowopy. We have demoustrited the applicability of confocal laset
ricrusenpy to stndy the dispersion of clay layers, wapged by a fluneescent dye in the
epoxy mateix, XRD and TEM results riveal that the hand snixed nanocomposite has

‘atloid morphology, while ultconicated orgunoclay (without bydreacy] yroup) epoxy

nanocomposile has intercalated morphology, and an ultrisenicated argimoclay (with
Iyilroxyt group) epoxy manceomposile exbibit a mixed mosphology (interculaied

uneturo with extoliaive). Results ftom the four complimentary tecaniques enable che

shecocterization of the clay peels aver sevecad length seates sangiag Ou che
Tengih scales ranging from the merometer to the nanometer seale, Mechanical property
evaluation ofthe monovennpssites are under.
INTRODUCTION

Turing Ue last decade, the aca of nanochuy Giled polymers has received much
ateution ftom both the sciewific and technological commanicics withthe expectation hal
the materials designed will be lighter and more superior than the pristine polsancrs. In
particu, the utractiveness of polymer-elny annacomposiles resides in the potential of

llding sural araonis of clay platelets 1» polyreeric eesin, to dramatically improve

mechanical, thermal, harrier, and flame-retadant properties. without reducing. The
‘ransparenoy of the pristine polymeric malcral (J-8). Because of the potential benefits of
liting inexpensive clay filo fo polymer matrix, the automotive and zerospace industics
view polymer clay hybrid nanocomposites the

oO

frucuoeal materials af the 214 century

Conidetahle rescarch hss boon conducied to study the strcture-propery
relationship of organically muiied clayfepoxy nanocomposites (10-16). Tsai and Sum
(17) modeled the toad transfer eftciency in nanocomposites and noted that significant
entuncernent in seinforcentent can be achieved y having che efay platelets wall dispersed
inthe polyruer matrix. By ion exelimnging Na“, Ca!2, oF Kon the clay surface with @
Jong chain cation, attempts have becn mats to disperse layered particle (organophilic) in
polymer matix (organophohie). Typically saruclays teated with allyl ammoninm ions.
fave been used wo produce uanspareat clay-epoxy mmocomposites, Tho architechare oF

‘he alky] aramonina fon bas boon commonly chosen so as 2

enpnove clay compatibility
‘with a given polymer resin und provide sufficient layer separation for polymer chuins to

infilzate. Receutly, Vaia ot al, (18) invesiy

ted the ability of socondary fnstional
excupe on the alkylammonium cations to remote intra ge'lary pailymeization und clay
cextoliation. ‘The study found thal he presence of hydeoxyl groups inthe bist2-bydroxy~
chy!) methyl lallowe ammonivn cacion facilited clay exfoliation in a diylyeidy] ete:

onstrated

Fisphenol A (DGEBA}poly(ether aroine) epoxy resin, ‘This work clearly
the

ability of using onium salts having a secondary fivetimal hydroey1 group For

‘ay plattet exfoliation ia oposy matrix. Organic modifiers cau participate ir the
teaction{s) with resin componcats and improve the mis

lity of the lay with resin
Conceptually, the organie modifiers oan assist in palymer network formation, inlerfice
reaction ond ultimately distale the linal morphology’ of nanacomposite by providing layer

separation

Anusher approach to aahicving clay platelet dispersion in polymer matrix is to add
corapatbilizers w enhance the compatibility between polymer and an organoclay (19-
21}, A eampatihilizes containing polar groups ean ho interval between the Layers of
the clay via strong hytroyen bonding. The compatabiizer weskcens the ionic 1

betwces clay layers, Txamples of compatebilizers gm maleic

any,
reethacty‘ate, and styrene, The evieta for swelling agenticomaptabilizer selection are
‘based on its misethilily withthe polymer and its ability ta swell she organically modified

‘The clay platelel morphology
preening conditions. While there ate roports that explore the importance of processing

1 polyutce matric cau also be altered based on the

tonditions to make exfoliated nanocomposite with thermoplastic mates, Hited work hut
foeen dons fo investigate dhe importance of processing paiametars on exfoliated
runocompusite sill thermosct mustrix. Mechenical mixing (Gompounding. sonication,

sheas) is necessary ~ and the efficiency of mixing is dependent ou the rmediura viscusiiy

snd renclivty, Ultrasound sonieation is a form of vibration that provides energy for the
nanoclay platelets to escape from the surcounding restsining force. Utttasound’

sonication of premixed sanoelayipolymner samples has shown promise in the dispc

‘or exfliation of the nacpeley plislets im palymer matrix (22). All these apprnaches are
ssimetive, and ey provide 9 Gamework tw manipulate the worpbology of
natosornposites, 30 ws lo achieve ancimal propestics.

Although ficfors influencing Ow marphology of nanccumposite have boon
studied, litle is known about the thermal stobility of nanocomposites. This property
bbecamex purliculasly relevant since most of the composite matcrials used in aerospace
applications are exposed to sir at slovaled fempuruture lor prolonged periods. Te date
tho themal stibility of eposy munocomposites has only heen investicated for model
epoxy resin (DGKBA system), These studies have reported an improvement in thermst
stability of polymeric nsin wich addition of layered silicate (22-24), The mechuniam of
the improveaent of thesuta) stailty in polymer nanocomposites however is not fully
understood, It is widely believed that at high temperature the amine gruflert organic
poiymer layer will dagrade from the eluy particle surfce resulting in more hycrophilic
and less compalihte clay aggregates disporsed in opoxy resin.

Thermo-gravimetric analysis (IGA}MS suulies af organo layered silicate
unwed thatthe onset temperature for decomposiian of organie modifer ean range from
150°C ta 220°C 5), If the orgiically modified clay tilled nanocomposites axe exposes
to temperatures exovading the decomposition temperature of organic modifier, the
amreoaiten ious ate capable of undergoing thenmat dissociation to gecctate primary

amines snd protons, These protons can subsequently participate inthe

thomopelymetization of epoxies (26). The free amines can possibly react with the epoxide
fmetionalitey, present inside the galferics or may diluase mul of clay particles and seaet
swith the epoxide functionalities in the hulk epoxy (27). Bocuse these amines are
primacy amines, the epoxy-primary amine reactions will yield only linear cured epoxy

sins unlike the comventionsl three dimensional ented opoxy’ resin, Furtheranone, the

epoxy primary amine wesefions con erenke & sisichiomettic imbalance to result in the
plastisization of the epoxy networks because of excess primay amine (11). Finally, the
refewse of organic modifir frum layered silicate at elevated tempsrature can have strong
itmplications on the distibuticn of nanoclay platslets, inferfeeial properties, and on the
ultimate mechanical propaitcs of nanocomposite, Thus, the suecess of high performance

‘nanocompasitos depands on the suhility of organic modifior used in the functionabization

of clay ns the organic ercarment isthe intorfuce between layered silicate and polymer, A.

poor inteaface betwen pelyrer nd layered sllicato will often resull in a mierocomposi

‘ora raitional filled system, Ip this research, 160 aspects were focused : One is bs make:
layered organosiliene with higher thermal stability. Another is to make a laycred
oryunonificate With potostial interfacial honding bebween the umosilicale and polyruer

mattis, Two approaches to formulate [ayorad organositicaes nanocomposites with

higher thermal stability were studied and have been discussed below.
1D Synthesiv of Siylated Apophyite Nanocomposite

tn this wesoarch, epophyllite, a pm, natural and commercslly available Irs
silleate, was firs reated with T-ocfonylitichlorosilone in order to chemically graft the
ining a C-€ bond. ‘The double bond of the
silylated chain un he further epoxidized or hydroxylated inthe next step, so as to form a

Functional pendent enganie group ea

strong chemical bonding inforfvor with the epoxy mati
4) Sliylnted Apophylite
“The rexotion of 7-octeuyl trcblorosilane with apophybite bas been

and was
soscesslul. ‘the sultant powder (els soft, which is totally diffrent Rom the erigal
popliyllite silicate erystal particles. WAXD of the apophyllite and octenysiloxy
spophyllite was taken in a Rigale x-ray powder diffcumeter (Ca Ky rian
emealor power of 40 KY und 150 mA) with ¢ 28 scan ramge Irom 2.2° 10 40°, and is
shown in Figure 1. “Tle x-ray ditaction cleaey indicates that the threedimersionsl
crsstal stricture of the original silicate is destroyed, Mowever, the ordered layered
sxracture is yfil preserved with the 2.8 A-inteplanar spacing betwen tho nauoayers
“The origina intcrplanir spacing betwoen the silicate nanotayers in 7.8 A. The gallery is
‘expanded becuute of he presence ofthe uganic pendent group inside the gallery. This
supports the theory Lat the octeuyslony group has been fled onto the

anbluyer backbone,

FAIR speetrascopy of the apophyllis nd actenglsley apophy ive was caken in a
‘Nicolet Magna: LR 560 spectrometer aad is shown in Figure 2. The Si-0-Si sureoch band
J very intense, The spectra from 3160 to 2760 exo were inserred inside the complete
spectral plot lo show this rogion more clearly. ‘The presonce ofthe C-H bund (3080 em)
Trou © CAH andl C11 band (2930, 2860 em) fron the satuiated alkyl chain clearly
domonsirales that the oofenyl yrnup is preseut in the produt afler Ge treatment of
apuplyflits with the T-oetensluicholorosilne, So both xray diffraction and FTIR.
indicate that the 7-octenylksiloxy groug: has becn sucecssful grafved onto the batkhone wf
puphslitesiieate sheet backbone,

‘TGA was used 40 find the thermal stabifity of silylated apophylite povrder.
Thermal analysis was performed on a TA Instruments Lit Res IGA 2950 thermogravity

analyver at 2°Ciinin, with wittagen sweep gas The TGA data are shown in Figure
decomposition isinperatme, whieh is gener defined as the fempoestine when 57%
‘wcight is lost, is ~430°C:. This decomposition temperature is uch higher tam thet of
the genoral organmelays, such ay TAO (270°C). “Tho reason for the nsuch higher
thermal stability for the vetensiloxy-apophplite than the general crganoclays is the
sitfsrot decomposition teutprstore wf the organic pendent group banding tthe Nici

ranvlayers, Lae bonding hetvieen the organic pendent group and the sifcate nanolayer
Tackbone in the cetenytiloxs-aponbyllite is covalenl bonding, while the bonding in the
geustal orgimoclays sucht as L30R. is ionic handing, ‘The covalent boning is mach
stronger than that of the fonie handing. Therefore the octunylsiloxy-apopbyline is utacl

smote stable than the genetal oxgenaclays, Tl musl be noted that goretal organoclays have

ionic imersetins between the orgie pesueat group zed the silicate manstayer hackboce,
‘This reslt is very significa. Tealso opens the door for the high-temperature thermoset
materials, such a5 bismaleimide (BMI) and polyimide, in the application of
mocomposite nateials. while general organoselay cannot stand the high eempecane
1h addition, the introduction of che fmetional bonding (CC
k chemin, makes it possible to transfer the olefinic grip inlo the OU, epoxy group,

group. wich has such &

and other fouctional group, and cventually he involved in foeraing «strong inerlave eth

the polymer matrix.

Bish |—cetenytitaxy-Apepte

3000

Higure 1. Wide-Angle Xaay Diffuclioa of dhe Apophyllite and 7-Ocienybilengy
Apophellite
See vlte
Octal

022 +

one

Leg cur

92
4900 3700 2aN0 3100 2800 2600 2200 1900 1600 1300 1000 700

Weaverumbor fem")
Figure 2, FTIR Spectta of the Apophyllite, 7-Octeayliloxy-Apophyllite, and
Octylsiloxy —Apophyllite

15 |- —_- or
400 oxen cana) ag
aes =

= |—oceny! Aposhyte! | as 2

ge 2 UOC 1 &

= 8 - —— 1°42

2 so oa 2

3 3

Bost oe
nl =
70 2
ost ond
eo = Me

° 200 400 600 00

Temperature (°C)
Figure 3. TGA Spectrum of the Oclenylsilaxy-Aponbylite and 150K (goncral

‘oorumereally-available organoclay) under Nitrogen at 2°CYnin,
1m order to test the role af the Snterfval interaction between the sitcato
ranolayers unt polymer matrix, we alerapted to synthesize a ayered organosieule wth
high thermal stability bol without a fictional group én contra 10 a Tnyered
orgsnosiionte wth a fantional yroup (uch as CC) for potential stronger intacil
bonding, Lhe lnyored sical of apophbite was treated with moeryttchlorosilone in
oder to chemiclly graft the pouden osmnie group containing on inat nets] group
‘The ewvelent bond gevfiing. pwmuntees highce thermal stability, white the inert moctyl
rou mikes the conpatison betwaen ibe svg interfacial bonding or jist van der Walt
Sverfucial interaction, The reaction was successful. The resultant power feels sof.
WAXD ofthe wpophylite aud n-etssoxy apophslite was ton wie shown in Tigute
4, While che theee-dimensionel erystal strato of tho origina silsute is destrove, the
dered layered structure i till preserved with the ~21.0 A-iterplnar spacing between
the natolayer, The original interplanar spacing betwen th silica nanolaers is 7.8 A.
The gallery is expanded because of the presauce ofthe anganie pendent group inside the
auillery. ‘his provides the supporting evidenee that the octysiloxy group vine
succcssflly grated onto the silicate nanslayer backbone.

FTIR spoctrescopy wf the epophylite and x-ctybiloty apophyilite was taken mr
fs shown in Figure 3. Tho 8-0-8 seh band is vory, very intense. So the spect from
3160 10-2760 om ! were inserted inside in oder to show I more clearly, The psec a
4. CH bond (2960, 2936, 2860 en) fom the sotrated aly! ehuin cleat demorstapes
the presence of the m-vety group ia the product afer teaument of apopbyllife with the
cetytnicholorositane, A compurise withthe spectrum of 7actenylslony-apophsilite in
Figure 2, there is ro presence of the C:HT hand (3080 em) ftom O=CH in the
octysiloxyapeptglite, $0 both xxay ditfaction and FTIR indicate the success graft
othe notyl yroup nt te layered seat backhoe.