Study on Morphology and Mechanical Properties of

V ol. 18

No. 3

CH INES E JO U RN A L O F AER ON A U TICS

A ugust 2005

Study on Morphology and Mechanical Properties of High functional Epoxy Based Clay Nanocomposites 1

1

2

1

DAI Feng , XU Ya hong , ZHENG Ya ping , YI Xiao Su ( 1 . Nat ional K ey L aborat ory of A dvanced Comp osites , Beij i ng Inst it ut e of A er onautical Mat erial s, Beij ing

100095 , Chi na)

( 2 . Dep ar tm ent of A pp li ed Chemistry , College of Science, Nor thw ester n Poly technic University , X i an Abstract:

710072 , Chi na)

M orphology and mechanical properties of clay/ high functional epoxy nanocomposites are in

vestig ated. An inter calated morpholog y is always observed for clay loadings

5 wt % . T he glass transi

tion temper ature ( T g ) of the co mposites decr eases wit h the clay loading, and t he impact strength in creases first by 10% at 2 w t% clay loading, and is follo wed by a dramatic decline, w hile the flexur al strength decreases in all cases. Key words:

clay; nano composite; high functional epox y resin; mechanical properties

关于粘土/ 高性能环氧纳米复合材料的形态及力学性 能的研究. 戴峰, 许亚洪, 政亚萍, 益小苏. 中 国航空学报( 英文版) , 2005, 18( 3) : 279- 282. 摘

要: 对粘土片层在纳米粘土/ 高性能 环氧树 脂体系 中的分 散状态及 力学性 能进行 了研 究。通

过加入较 少的粘土( 含量

5wt% ) 得到插层型纳米复合材料。纳米粘土 的存在使环 氧树脂的 玻璃

化转变温度有所降低。粘土质量含量为 2% 时, 复合材 料的冲 击强度约 上升 10% , 但 超过 2% 后, 冲击强度随之下降。材料的弯曲强度则随着粘土含量的升高而逐步降低。 关键词: 有机蒙脱土; 纳米复合材料; 高性能环氧树脂; 力学性能 文章编号: 1000 9361( 2005) 03 0279 04

中图分类号: V258

In t he last decade, many st udies focused on a

文献标识码: A

individual nano sheet s of the layered silicates in t he

new area t hat ut ilizes organoclay to alt er t he prop

polym er mat rix and the interfacial coupling be

erties of polymers. Unlike traditional advanced composit es, clay/ polymer nanocom posit es ex hibit

t w een t he individual sheets and t he polymer m at rix should f acilitate t he st ress transfer to the reinforce

signif icant improvements in mechanical and t her

ment phase so as to improve t he mechanical proper t ies.

mal propert ies just at volume fract ion as low as [ 1, 2]

3 w t% 5 w t% . Clay/ polymer nanocomposite has generally t wo dist inct ive morphologies: ( 1) in t ercalat ed nanocomposit e, in w hich t he m at rix polym er is intercalat ed bet ween t he silicat e layers and t he expanded silicat e layers are st ill in order; ( 2) exfoliat ed nanocomposite, in w hich individual silicat e layers are completely separat ed and dis persed in a cont inuous polymer matrix. In most cases, morphology ( 1) and ( 2) co appears. T he high aspect rat io and high st reng th of t he nano scaled clay play t he key roles in t he improvement of the mechanical propert ies. T he dispersion of t he

Although t here were ext ensive st udies on e pox y/ clay nanocomposites, litt le at tent ion w as paid on the high f unctional epox ies as matrix resin, which w idely used in aerospace due to their higher [ 3]

modulus and g lass transition t emperat ure . T he object ive of t his w ork is to invest ig at e t he morphol ogy and mechanical propert ies of the clay/ hig h funct ionalit y epoxy nanocomposite under various clays loading.

1

Experimentals

T he high funct ional epox y matrix used w as a combination of st andard dig ly cidal et her of bisphe

R eceived dat e: 2004 12 16; R evision received dat e: 2005 04 25 Foundation it em: N at ional K ey Fundament al Research Program ( 973 Program) ( 2003CB615604)

∃ 280 ∃

DAI Feng , XU Ya hong , ZHEN G Ya ping , Y I Xiao Su

nol A epox y ( DGEBA, E 54, Wuxi Resin Fact o r y)

and tetraglcidyl met hylene dianilline epox y

CJA

Specimens for mechanical t est ing had t he di mension according to GB/ T 2570 1995 and GB/

( T GM DA, AG 80, Shanghai Institute of Synt het

T 2571 1995. T he f lexural propert ies were deter

ic Resin) . DDS w as used as curing agent. T hey w ere m ix ed at a rat io of DGEBA!T GM DA!DDS=

m ined according t o GB/ T 2570 1995 on a ZM GI250 universal t ester using a crosshead speed of 2

2!3!2. T he molecular structures of the tw o epox ies

mm/ min. T he im pact t oughness w as measured on

mentioned above are show n in F ig . 1. T his t wo component epox y syst em w as donat ed as 5268 in

a XCJ 40 Impact T ester according to GB/ T 2571 1995. T he loss t angent w as determined on T A

the st udy. T he organoclay used was an ammonium

Q800 Dynamic M echanical T herm al Analyzer.

ion modified montmorillonite layered silicat e pro

Frequency sw eep scans w ere preformed at a scan

vided by Northwestern Polyt echnic Universit y.

ning rate of 3 ∀ / min using frequencies of 3, 5 and 8 Hz.

2 2. 1

Results and Discussion

Morphology

Nanocomposites containing 0, 1, 2, 3, 4 and 5 wt % clays were f abricated. WAXS t races show that t he clay w ith an init ial d spacing of 19 ( Fig. 2) is intercalated by the epox y precursors F ig. 1 T he molecular structures of the two epox ies

T he t wo epox ies were first st irred in a weig ht rat io of DGEBA!T GMDA= 2!3 at 50 ∀ until t hey

( Fig. 3) . T he XRD patt erns in F ig. 3 for the com posites containing 1 ~ 5 w t % clays indicat e that they all are only intercalated . All of them show a

w ere com pletely m ix ed. T hen, an appropriate quantit y of the org anoclay w as added into t he m ix t ure by stirring at 80~ 90 ∀ for 1 h. T he m ix ture w as subsequently heat ed up t o 120 ∀ and evacuat ed at a vacuum of 0. 08~ 0. 09 M Pa for 0. 5 h. Final ly , an account ed amount of DDS w as m ix ed int o the syst em and st irred slig ht ly at 130 ∀ for 10 min. T he mix ture was then cast in a met allic mold aft er the mold w as hold at 80 ∀ for 30 min. Resin

F ig. 2 XRD pattern of the pure organoclay used

curing was carried out first at 130 ∀ f or 1 h, then 160 ∀ for 1 h, and f inally 180 ∀ for 2 h, follow ed by a post t reatment at 200 ∀ for 2 h. T he morphology of the cured samples w as in vestigated using w ide ang le X ray scat tering ( WAXS) . XRD ( X ray Dif fraction) pat terns w ere obtained by a Rigaku D/ m ax 2400 equipped w ith Cu K X ray radiation ( = 1. 54 A) , operat ed at 40 kV and 100 mA. T he diff ract ion patt erns w ere collected betw een angles ( 2 ) of 1. 5#~ 40# at a scanning rat e of 5#/ m in. T EM w ere obtained w ith a H 600 apparatus.

Fig . 3

XRD patterns of epoxy / clay nanocomposites for different clay loadings

A ugust 2005

∃ 281 ∃

St udy on M orphology and M echanical Propert ies of High funct ional Epoxy Based Clay N anocomposit es

dist inct peak corresponding t o a d spacing, w hich is around 37 . T he clay/ polymer nanocomposites can be regarded as disordered intercalat ed and or [ 4]

dered int ercalated, respectively . Intercalat ed in dicates t hat the polymer is located betw een t he clay plat elets but some long range stacking order st ill remained. T he ordered and disordered charact eriza t ions ref er t o the level of order present in the inter calat ed structures. F ig . 4 shows the T EM imag e of the part ially exf oliat ed composit e. It is likely t hat t he init ial cure t emperat ure of 130 ∀ is presumably t oo low t o

F ig. 5 DM T A spectrums of Clay/ EP nanocomposites Table 1

allow suff icient precursors diff using int o the layers

Tg of Clay/ EP composites for different loading levels Clay loading / ( wt % )

0

1

2

3

T g/ ∀

249. 0

248. 5

248. 0

241. 5

[ 5, 6]

before gelat ion and vit rification , because t he v iscosity of high funct ional epox y at 130 ∀ is too

2. 3

Mechanical properties

high for int ergallery diff usion and delam inat ion. In

F ig. 6 summarizes the results of impact and

addit ion, at the low er cure temperatures, react ions

flexural t est s. As t he clay loading increases, t he

at the edges of t he silicate layers and subsequent bridging eff ect s m ay also prevent exfoliat ion[ 5] .

impact st rength increases first by 10% at a loading level of 2 w t % , f ollowed by a dramat ic decline. As reported[ 7] , investigation on correlat ion bet ween morpholog y and impact behavior provides strong experimental evidence that the f orm at ion of anisotropic laminat ed nanopart icles can help t o im prove toughness. It is regarded that the t oughening eff ect result s from t he role of % pin& played by lami nat es, which prevents the ext ending of cracks[ 7] . In addit ion, the ex ist ence of t he laminates induces yielding of t he mat rix, absorbing a lot of energ y ow ing t o t he t ig ht binding betw een the laminates and t he matrix. As the clay loading increases, it is possible that t he inhomogeneous dist ribution of

Fig . 4

T EM image showing the partially exfoliated structur e ( 2 wt% clay)

2. 2

Glass transition temperature

T ypical tan! t races by means of DMT A are shown in F ig . 5 f or the nanocom posit es loaded w ith 0~ 3 w t% clays. T able 1 show s the glass t ransit ion temperatures( T g ) for different clay loadings. T g decreases steadily w ith t he increase of the loading. Giannelis[ 3] report ed that the intercalated polymers showed a reduced glass t ransit ion due to the lack of surrounding entanglem ent s.

Fig . 6

Plots of impact and flex ural streng th ag ainst clay loadings of the clay/ EP nanocomposites

∃ 282 ∃

DAI Feng , XU Ya hong , ZHEN G Ya ping , Y I Xiao Su

cate t hermoset nanocomposit es[ J] . Comp Sci Tech, 2002, 62:

laminates may cause st ress concent rat ion, w hich produces cracks in matrix. In this case, t he clays

1033- 1041. [ 2]

act as f laws or crack init iat ors inst ead of reinforce ment s, and st rength.

leading to reduct ion

CJA

Lee J Y , Lee H K . Charact erizat ion of organobent onite used f or polymer nanocomposit es [ J ] . M at erials Chemist ry and Physics, 2004, 85: 410- 411.

of impact [ 3]

Ole B, R ussell V , G eorge S. M orphology, t hermal relaxat ions and mechanical properties of layered silicate nanocomposites

T he f lexural strengt h decreases in all cases.

based upon h igh funct ionality epoxy resins [ J ] . Polymer,

[ 7]

Lu Jian kun also found t hat t he flex ural st reng th of t he intercalated composite declined w it h the in

2002, 43: 4365- 4373. [ 4]

creasing of t he clay loading . It is presumed t hat t he intercalat ed morphology may not be beneficial t o

[5 ]

T ech, 2002, 62: 1249- 1258. D errick D. Ef fect of nanopart icles on morphology develop ment , rheology and properties of epoxy/ layered silicate

the st rength of t he composite.

3

John F T . N anoclay reinf orcement ef fects on t he cryogenic m i crocracking of carbon f iber/ epoxy composit es [ J ] . Comp Sci

nanocomposit es[ A ] . Th e 48t h Internat ional SA M PE Sympo

Conclusions

sium and Exhibit ion [ C ] . Long Beach, U SA: SA M PE, 2003. 1663- 1671.

( 1) XRD patt erns indicates that t he clays are

[ 6]

vanced composit es [ A ] . The 48t h Int ernat ional SA M PE S ym

only int ercalated by t he high funct ional epoxy resin syst em at the processing condit ions described. ( 2) T g of t he clay/ EP nanocomposit es decreas es st eadily w it h the increase of clay loadings. ( 3) As the clay loading increases, t he impact st rength increases about by 10% at a loading level

W ei P L. Organoclay modified high performance epoxy for ad posium and Exhibit ion [ C ] . Long Beach, U SA : SA M PE, 2003. 142- 154.

[ 7]

吕建坤. 环氧树脂及高性能热塑性树脂与粘土插层 复合的 研究[ D] . 杭州: 浙江大学, 2001. Lu J K. St udy on int ercalated nanocomposit es of st ructural resins and organoclay [ D ] . Hangzhou: Zhejiang U n iversit y, 2001.

of 2 w t % , f ollowed by a dramatic decline, w hereas

Biographies:

the flexural st reng th decreases at all. References

DAI Feng Bor n in 1979, she is a M . S. candidate at Bei jing Institute o f A ero nautics M aterials. She received B. S. fro m Beijing U niversity of Aeronautics and Astronautics.

[ 1]

T ia B T, David P A . M orphology development in layered sil i