comparison of the properties of clay polymer nanocomposites prepared by montmorillonite modified by...

Applied Clay Science xxx (2013) xxx–xxx

CLAY-02776; No of Pages 7

Contents lists available at ScienceDirect

Applied Clay Science

j ourna l homepage: www.e lsev ie r .com/ locate /c lay

Research paper

Comparison of the properties of clay polymer nanocomposites preparedby montmorillonite modified by silane and by quaternaryammonium salts

Miroslav Huskić a,b,⁎, Majda Žigon a,b, Marica Ivanković c

a Centre of Excellence PoliMaT, Tehnološki park 24, 1000 Ljubljana, Sloveniab National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Sloveniac University of Zagreb, Faculty of Chemical Engineering and Technology, Marulićev trg 19, POB. 177, HR-10001 Zagreb, Croatia

⁎ Corresponding author at: National Institute of ChemistrSlovenia. Tel.: +386 1 4760 206; fax: +386 1 4760 420.

E-mail addresses: [email protected] (M. Huskić), miva

0169-1317/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.clay.2013.09.004

Please cite this article as: Huskić, M., et al., Coby silane and by quaternary ammonium salt

a b s t r a c t
a r t i c l e i n f o
Article history:Received 3 September 2012Received in revised form 3 September 2013Accepted 5 September 2013Available online xxxx

Keywords:SilaneMontmorilloniteClay polymer nanocomposite (CPN)X-ray diffraction29Si CP MAS NMRThermogravimetric analysis

In this work, the silylation of sodium montmorillonite (Na+-Mt, Nanofil 757®) was performed using (3-aminopropyl)triethoxy silane (APTES). Different reaction conditions were used varying the reaction timeand the amount of the aminosilane. Epoxy-based nanocomposites were prepared with different amountsof silylated Mt or commercial organically modified Mt intercalated with stearylbenzyldimethyl ammoniumchloride (Nanofil 2®) and distearyldimethyl ammonium chloride (Nanofil 8®), respectively. The grafting/intercalation of the aminosilane inside the Mt interlayer spaces was studied by means of Fourier transforminfrared (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and thermogravimetric analy-sis (TGA). After isothermal curing at 90 °C the Mt epoxy nanocomposites were analyzed by means of XRDand dynamic mechanical analysis (DMA). The glass transition temperature of all prepared nanocompositescontaining silylatedMt, is slightly higher than that of the neat epoxy (2 to 5 °C). In the presence of 1 to 5 m%of silylated Mt in epoxy matrix the storage modulus increases from about 5 to 15% at 25 °C, respectively,compared to the pristine epoxy matrix, while only 0–4% increase was observed for epoxy nanocompositeswith commercial modified Mt.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

In the last decades extensive researchhas beendevoted to organicallymodified layered silicates as reinforcements for polymers. Their layeredmorphology, high aspect ratio and the nanoscopic phase distributionlead to improved thermal, mechanical, and gas diffusion barrier proper-ties. One of the most widely used nanofillers is montmorillonite, Mt, acommon clay mineral from the smectite family (Ray and Okamoto,2003). Mt and other clay minerals contain active sites such as silanols,and exchangeable interlayer cations, typically Na+ and/or Ca2+.

Besides the interlayer cations, the interlayer space contains largeamounts ofwatermolecules. To enhance compatibilitywith organophilicpolymers, chemical modification of Mt plays a crucial role inMt polymernanocomposite formation. Introducing organic groups on the layeredsurface increases the interlayer distance, which facilitates the penetra-tion of the polymer chains inside theMt interlayer spaces. Themost com-monly used procedure to prepare organophilic Mt and other clayminerals is the cation exchange reaction with a quaternary ammonium

y, Hajdrihova 19, 1000 Ljubljana,

[email protected] (M. Ivanković).

ghts reserved.

mparison of the properties ofs, Appl. Clay Sci. (2013), http

salt (Bergaya et al., 2011; Kim et al., 2006; Kozak and Domka, 2004;Pavlidou and Papaspyrides, 2008; Vaia et al., 1994; Vazquez et al.,2008). However, this kind of surface modification does not provide anefficient linkage between the clay mineral and polymer matrices. More-over, most of alkyl ammonium surfactants are not stable at temperatureat which the plastics are commonly processed. For these reasons, thesilylation reaction, between the silane coupling agents and reactivesilanol groups, located at the broken edges of the clay mineral layers,at the structural defects of the interlayer and external surfaces, hasattracted great interest. Several organically modified alkoxysilaneshave been used to modify layered silicates such as Mt (Bourlinos et al.,2004; He et al., 2005; Piscitelli et al., 2010, 2012; Shanmugharaj et al.,2006; Shen et al., 2007). Organo-silanes can be represented by the gen-eral formula R′ − Si − (OR)3, where R′ is a short hydrocarbon chainthat is terminated with a reactive organic functional group such as anamine or epoxy and R is an alkyl group.

Epoxy resins are widely used as polymer matrices for composites. Todate, epoxy-layered silicate nanocomposites have gained widespread at-tention regarding synthesis, morphology and properties. Concerning theuse of silylated Mt in epoxy systems only a limited number of studieshave been published (Choi et al., 2009; Di Gianni et al., 2008; Park et al.,2009; Silva et al., 2011; Wang et al., 2005). Wang et al. (2005) prepared(3-aminopropyl) trimethoxysilane modified Mt epoxy nanocomposites

clay polymer nanocomposites prepared bymontmorillonite modified://dx.doi.org/10.1016/j.clay.2013.09.004

http://dx.doi.org/10.1016/j.clay.2013.09.004

mailto:[email protected]

mailto:[email protected]


http://www.sciencedirect.com/science/journal/01691317


2 M. Huskić et al. / Applied Clay Science xxx (2013) xxx–xxx

with a high degree of exfoliation and better thermomechanical propertiesusing a so-called “slurry-compounding” process.

By introduction of the glycidyl-propyltriethoxysylane (GPTS)-modi-fied Mt with a photocurable epoxy matrix Di Gianni et al. (2008)obtained transparent nanocomposite coatings characterized by a mixedintercalated/exfoliated structure and better thermal and scratch resis-tance performances in comparison with the Mt-free coatings.

Using Mt silylated with different organo-silanes containingamino, glycidyl and methacrylate moieties Park et al. (2009) obtainedMt epoxy nanocomposites with enhanced mechanical interfacialproperties. Choi et al. (2009) also observed better mechanical perfor-mance of epoxy networks modified with silylated Mt, when comparedto the epoxy modified with commercial grade ammonium salt substitut-edMt. Tensile stress and elongation ofMt epoxynanocompositewere im-proved significantly by the silane functionalization of Mt. Dynamicmechanical analysis showed that silane functionalization of Mt resultedin active interactions between Mt and epoxy matrix. In the work ofSilva et al. (2011) Mt was functionalized with N-(2-aminoethyl)-3-aminopropyl trimethoxysilane. The high dispersion of silylated Mt inepoxy matrix, cured with triethylenetetramine, was obtained.

In this work, the modification of Na+-Mt using (3-aminopropyl)triethoxy silane (APTES) was performed. The influence of the reactiontime and the aminosilane concentration on the silylation efficiencywas studied by means of XRD, FTIR, NMR and TGA. Epoxy-based nano-composites were prepared with different amounts of silylated Mt. Thenanocomposite mechanical properties were compared with those ofepoxy systemmodifiedwith commercial organicallymodifiedMt, inter-calated with stearylbenzyldimethyl ammonium chloride (Nanofil 2®)and distearyldimethyl ammonium chloride (Nanofil 8®). Such studiescould help to define the best route to achieveMt epoxy nanocompositeswith adequate properties for technological applications.

2. Experimental

2.1. Materials

The nanofillers used were kindly donated by Rockwood Clay Addi-tives GmbH. Nanofil 757® is a highly purified natural Na+-Mt withcation-exchange capacity of 85 meq/100 g. Nanofil 2® and Nanofil 8®are organically modified Mt intercalated with stearylbenzyldimethylammonium chloride and distearyldimethyl ammonium chloride, re-spectively. It is worth noting that they contain 4 and 10 m%of freemod-ifier, respectively (Huskić and Žigon, 2009). (3-Aminopropyl)triethoxysilane (APTES) provided by Aldrich was used as received. Slow curing

Fig. 1. FTIR spectra of the unmodified (Na+-Mt) and the silylatedmontmorillonites (sMt).

Please cite this article as: Huskić, M., et al., Comparison of the properties ofby silane and by quaternary ammonium salts, Appl. Clay Sci. (2013), http

epoxy resin Epikote™ L 1100 and hardener EPH294 were products ofR&GFaserverbundwerkstoffeGmbH,Germany. Epikote™ L 1100 is amix-ture of epoxy resin based on bisphenol A and dodecyl/tetradecyl glycidylethers with an epoxy equivalent weight of 192 ± 5 g/equivalent. Hard-ener EPH 294 is a mixture of alkyletheramine and 3-aminomethyl-3,5,5-trimethylcyclohexylamine with an amine equivalent weight of56 ± 2 g/equivalent.

2.2. Silylation reaction

To perform the silylation of Nanofil 757®byAPTES different reactionconditionswere used, in which the reaction time and the amount of theaminosilane were varied. 1 g of Nanofil 757® was dispersed in 100 g ofdemineralized water and heated to 50 °C. 3-Aminopropyltriethoxy si-lane was added (0.33; 0.53; 1.00 and 1.5 g) and the dispersion wasstirred for 4 or 24 h. The modified Mt was filtered, washed withdemineralized water and dried by lyophilization. Silylated Mt were la-beled according to the amount of aminosilane and the reaction time(sMt0.3_4h (24 h); sMt0.5_4h (24 h); sMt1.0_4h (24 h); sMt1.5_4h(24 h)).

2.3. Mt epoxy nanocomposite preparation

Epoxy-based nanocomposites were preparedwith different amountsof silylated Mt or commercial organically modified Mt (1, 3, and 5 massparts to 100 mass parts of epoxy/curing agent matrix). Epoxy resin/cur-ing agent ratio was maintained at 3/1 in all samples prepared.

ModifiedMt and hardener weremixed for 4 h at room temperature.Then the epoxy resin was added and mixed for another 2 h. Vacuumwas applied to remove trapped air bubbles and the mixture was trans-ferred in a glassmold, coatedwith release agent. Themoldswere heatedto 90 °C and kept at that temperature for 18 h. The curedmaterialswerecooled to room temperature and then characterized on a Netzsch DSC200 differential scanning calorimeter. Reheating of samples from roomtemperature to 250 °C at 10 °C/min showed no residual heat ofreaction.

2.4. Characterization

Thegrafting/intercalation of the aminosilane inside theMt interlayerspaces and the degree of Mt intercalation/exfoliation in epoxy-basednanocompositeswere studied by X-ray diffraction. For all XRDmeasure-ments a PANalytical X'Pert PRO system with CuKα radiation (λ =

Fig. 2. XRD patterns of silylated montmorillonites (sMt) corresponding to differentsilylation times and aminosilane concentrations. The diffraction pattern of the untreatedmontmorillonite (Na+-Mt, Nanofil 757®) is shown as a reference.



Table 1XRD data for silylated montmorillonite and organically modified montmorillonites and epoxy-based nanocomposites.

ModifiedMt-type

2θ(°)

d001(10−9 m)

Δd(10−9 m)

Mt in epoxy(m%)

2θ(°)

d001(10−9 m)

Δd(10−9 m)

sMt0.3 5.9 1.49 0.54 3, 5 6.5 1.36 0.40sMt0.5 5.4 1.63 0.67 3, 5 5.9 1.50 0.54sMt1.0 4.4 2.00 1.04 3, 5 4.6 1.92 0.96sMt1.5 4.2 2.10 1.14 3, 5 4.4 2.0 1.04Nanofil 2®, N2 4.5 1.96 1.00 5 3.0 2.94 1.98Nanofil 8®, N8 2.5 3.52 2.56 5 2.5 3.57 2.61

3M. Huskić et al. / Applied Clay Science xxx (2013) xxx–xxx

0.154 nm) was used. The diffraction scans were collected within therange of 2θ = 1.5–15°, with a 2θ step of 0.33°. The (001) XRD peak pro-files were fitted to Lorentzian and Gaussian functions using Origin 6.0,MicroCal. Peakpositions (in 2θ) obtained by bothfittingswere very sim-ilar. The relative error was smaller than 1%.

29Si CP MAS spectra were recorded with Varian Unity Inova300 MHzNMR spectrometer at 60.19 MHz. Delay timewas 2 s, acquisi-tion time 0.05 ms, spin rate 5000 Hz, and number of scans 2000–13,000.

Mass loss of prepared silylated Mt, weighing approximately15 mg, was measured by thermogravimetric analysis (TGA), usinga Perkin Elmer thermobalance TGS-2. The samples were heatedfrom room temperature to 1000 °C at 10 °C/min in a nitrogen gasflow of 20 cm3/min.

The dynamical mechanical properties of cured specimens weredetermined with a Thermal Analysis Q800 DMA. Dimensions of thespecimens were 60 × 10 × 1.7 mm. Measurements were performedon dual cantilever, in isothermal conditions at 25 °C, with the ampli-tude of 15 μm, at three different frequencies (0.1, 1 and 10 Hz) and ata constant heating rate of 3 °C/min, from 30 °C to 120 °C and fixedfrequency of 1 Hz.

3. Results and discussion

3.1. Silylated montmorillonites

3.1.1. FTIR analysisFig. 1. shows the FTIR spectra of the unmodified and the silylatedMt.

All spectra display typical absorption bands of Mt. The band at ~3625 isresult of the\OH stretching vibration of the structural\OH groups inMt. The broad bands at 3000–3600 cm−1 and ~1630 cm−1 are charac-teristic of the stretching and bending vibrations of adsorbed water. The

Fig. 3. 29Si CP/MAS NMR spectra of the parent (Na+-Mt) and silylated montmorillonites(sMt).


strong absorption band at ~1000 cm−1 is a result of Si\O\Si stretchingvibrations. In comparison to the pristine Na+-Mt (Nanofil 757®) FTIRspectrum the FTIR spectra of silylated Mt show additional bands. Theabsorption bands at ~2933 and ~2890 cm−1 correspond to the asym-metric and symmetric stretching vibrations of \CH2\ groups ofaminoalkylsilane, respectively. The band at ~3370 cm−1 and a shoulderat ~3290 may be assigned to the stretching vibrations of the \NH2

group (Tonle et al., 2003).

3.1.2. XRD analysisIn Fig. 2 the XRD patterns of silylated Mt, corresponding to different

silylation times and aminosilane concentrations, are compared. The dif-fraction pattern of the untreated Mt (Nanofil 757®) is also shown as areference. Diffraction maximum for Mt is located at 2θ = 9.1° whichis equivalent to basal spacing d001 of 0.97 nm (calculated according tothe Bragg equation).

For Mt silylated with higher quantities of APTES the appearance oftwo (sMt1.0) or even three (sMt1.5) reflections, occurring at a seriesof 2θ values that satisfy the Bragg equation, is observed. XRDdiffractograms of Mt silylated with lower concentrations of APTES(samples sMt0.3 and sMt0.5) exhibit only one peak indicating less or-dered structure.

Regarding thedifferent silylation times forMt silylatedwith the low-est quantity of APTES (sMt0.3) no difference in the peak position is ob-served. Mt silylated with the highest quantity of APTES (sMt1.5)showed a shift of the diffraction peaks towards lower angles with reac-tion time, that is larger d-spacings.

For all silylated Mt the (001) reflections shifted to lower angles ascompared to unmodified Mt indicating that aminosilane species hasbeen grafted/intercalated in the interlayer space of Mt. By subtractingthe thickness of the silicate layer of Mt, which equals 0.96 nm(Bergaya and Lagaly, 2013), the layer distance Δd was calculated. InTable 1 thebasal spacing values and the layer distances are summarized.As seen, the silicate basal spacing increases with increasing aminosilaneconcentration in the reaction mixture. Similar findings are reported inthe literature (Piscitelli et al., 2010). In addition to the experimental ev-idence, molecular dynamics simulation performed by Piscitelli et al.(2010) also revealed that, upon increasing the number of aminosilanemolecules within the Mt interlayer spaces larger value of estimatedbasal spacing is obtained. When more aminosilane molecules aregrafted/intercalated into the Mt interlayer space the surface of the Mt

Fig. 4. Schematic representation of possible covalent bond formation between theaminosilane molecules and the Mt surface OH groups resulting in T2 and T3 structures.



Fig. 5. TGA curves of the unmodified (Na+-Mt) and the silylated montmorillonites (sMt).

Table 2Relative mass loss during decomposition of investigated samples (m%).

Sample/temperature range b200 °C 200–700 °C 40–1000 °C

Nanofil 757®, Na+-Mt 6.4 5.9 13.0sMt0.3_4h 6.3 8.4 15.3sMt0.3_24h 5.1 9.0 14.7sMt0.5_4h 5.4 10.5 16.7sMt0.5_24h 4.7 11.0 16.5sMt1.0_4h 4.8 12.5 18.2sMt1.0_24h 4.2 13.3 18.4sMt1.5_4h 4.6 13.7 19.3sMt1.5_24h 4.4 14.5 19.5


layers is better screened by the organic tail of aminosilane moleculesweakening the attraction forces among the layers. Additionally, athigher aminosilane concentration the organic tail of neighboringaminosilane molecules grafted/physically bounded to the same Mtlayer tends to interact more among themselves than with those lyingon the opposite sheet, weakening the attraction between facing sheetsand yielding larger d-spacing. It is worth noting that the d001 values ofsilylatedMt (sMt0.5 and sMt1.5) are comparable to the values obtainedby Piscitelli et al. (2010). The values fit a bi-layer arrangement ofaminosilane molecules in the interlayer space.

3.1.3. Solid state 29Si CP/MAS NMR spectroscopyThe 29Si CP/MAS NMR spectra of the parent and silylated Mt are

given in Fig. 3. The signal at ~−94 ppm in all spectra is characteristicof Si atom in layered silicate corresponding to Q3 units [Si(OSi)3OM](M stands for Al, Mg, etc. in the Mt octahedral layer) (He et al., 2005).For the parent Mt there is no clear evidence of Q4 [Si(OSi)4] structuresat about −110 ppm, related with Si atom in quartz, an impurity in the

Fig. 6. DTG curves of the unmodified (Na+-Mt)


clay minerals (He et al., 2005), because of the reduced signal-to-noiseratio.

After silylation, two additional 29Si signals at ~−110 ppm and ~−67.7 ppm are recorded, indicating the presence of Q4 [Si(OSi)4] and T3

[Si(OSi)3R] (R = CH2CH2CH2NH2) structural units, respectively. For thesample S_1.5 the signal corresponding to T2 structures [Si(OSi)2(OR′)R](R′ = H or CH2CH3) at ~−58 ppm is hardly seen.

These new signals accompanied with a decrease in the intensity ofQ3 signals indicate that the condensation between the interlayer surfacesilanol groups and the aminosilanemolecules occurred as schematicallyshown in Fig. 4 (Kim et al., 2011).

Uchida et al. (2006) reported that APTES is not intercalated in theinterlayers of Mt as “random” polymerized structures, but as fullycondensed octasilsesquioxane cages. To clarify the structures theycompared the intercalated compounds derived from APTES withthose from pre-synthesized octahedral structure. 29Si NMR spectraof both intercalation compounds were very similar and mainlyshowed the peak at −68 ppm of the Si T3 structure. In previous paperof authors (Ivanković et al., 2009) similar results were obtained forthe sol–gel polymerized 3-glycidyloxypropyltrimethoxysilane.

3.1.4. Thermogravimetric analysisThe decomposition behavior of all silane-functionalized Mt was ex-

amined by thermogravimetric analysis as shown in Fig. 5. DTG (the

and the silylated montmorillonites (sMt).



Fig. 7. XRD spectra of the silylated Mt (sMt) and the corresponding Mt epoxy nanocomposites (E_sMt).


first derivative of the TGA) curves are shown in Fig. 6. For the sake ofcomparison TGA and DTG curves of pristine Mt are shown as well.

In Table 2 the mass loss associated with different temperatureranges and events is summarized. The overall mass loss of silane-functionalized Mt is greater than that of pristine Mt. The TGA and DTGcurves of all investigated systems indicate a complex degradation path-way. In fact, at least three to five distinct decomposition stages could beobserved. Similar findings are reported in the literature (He et al., 2005;Piscitelli et al., 2010; Shen et al., 2007). The DTG curve of pristine Mt

Fig. 8. XRD spectra of commercial organically modified Mt: (a) Nanofil 2® (N2); (b) Na


displays peak at 110 °C, assigned to the loss of the physically adsorbedwater, and two broad peaks from 400 to 700 °C assigned to thedehydroxylation of Mt. In comparison to the unmodified Mt, thesilylated Mt are characterized by the water release peak (at 80–86 °C)of lower intensity and corresponding lower mass loss, indicating thatsilylated Mt are less hydrophilic than unmodified Mt. But, the silylatedMt still contain approximately 4–5 m% of water.

Dependingon the aminosilane concentration in the reactionmixturethe silylated Mt display two or three DTG peaks in the temperature

nofil 8® (N8) and the corresponding Mt epoxy nanocomposites (E_N2 and E_N8).



Fig. 9. The ratio of the storage moduli of the nanocomposite and the pure epoxy resin,E′/E′o, measured at 25 °C, as a function of the filler concentration.


range from 200 to 700 °C. In the report on APTES-functionalized Na+-Mt (He et al., 2005) DTG peaks at 330, 426 and 535 °C were obtained.First two peaks were interpreted as degradation of intercalated silanemolecules and the third one as the co-occurrence of the decompositionof the chemically bound silane and the dehydroxylation of the Mt. An-other paper (Piscitelli et al., 2010) reported peaks at 310, 418 and540 °C. The peak at 310 °Cwas attributed to the aminosilane interactingwith the outer surfaces of the claymineral layers. In our case, the peak at321 °C was obtained for Mt silylated with higher quantity of APTES(sMt1.0; sMt1.5). The peaks at 424–427 °C are attributed to the degra-dation of intercalated silane. As seen from Fig. 5 the peak at ca. 628 °Ccorresponding to dehydroxylation of Mt does not occur in the DTGcurves of silylated Mt. Hence, the broad peak/shoulder at 572–576 °Cin the DTG curve of silylated Mt could be also due to the co-occurrenceof the decomposition of the chemically bound silane and thedehydroxylation of the Mt (He et al., 2005). In DTG curve of the sample

Fig. 10. The loss modulus of the investigated systems as a func


sMt0.5 an additional broad peak from 150 to 250 °C is observed, attrib-uted to desorption of aminosilane from the external surfaces. At tem-peratures higher than 850 °C broad low intensity DTG peak of organicresidue is observed.

3.2. Mt epoxy nanocomposites

3.2.1. XRD analysisXRD spectra ofMt epoxy nanocomposites are shown in Figs. 7 and 8.

In comparison to the spectra of Mt silylated for 24 h the basal signals ofsilylated Mt epoxy nanocomposites (E_sMt) are slightly shifted tohigher angles (see Fig. 7 and Table 1), that is smaller d-spacings. The de-crease in interlayer spacing can be explained by further condensation ofethoxy groupswithMt or between neighboring silanemolecules duringthe curing process. To check this, silylatedMtwere kept at 90 °C for 4 h.After this treatment the diffraction peaks of Mt shifted to slightly higherangles as well (compare curves sMt0.3 and sMt1.5 to curves sMt0.3(90 °C_4h) and sMt1.5 (90 °C_4h) in Fig. 7, respectively) and their posi-tion is almost identical to those observed in the nanocomposites.

The above results indicate that silylatedMt keeps the original crystalstructure and exists as primary particles in the epoxymatrix. The resultsare in good agreement with those obtained by Piscitelli et al. (2012). Asreported, themorphological characterization of silylatedMt epoxy com-posites showed only a slight intercalation of silylated Mt by epoxy mol-ecules. The intercalation of epoxy resin in theMt interlayer spaces couldbe prevented by the cross-linking reaction, which probably takes placeduring the dispersion of silylated Mt in the resin.

For Nanofil 2® epoxy nanocomposite (E_N2), Fig. 8(a), the basal sig-nal is shifted to lower angle (from 2θ = 4.5° to 2θ = 3°) accompaniedby the appearance of at 2θ ≅ 6° indicating intercalation of epoxy resinbetween alumosilicate layers that results in their higher ordering.

As seen from Fig. 8(b) Nanofil 8® (N8) exhibits three well-defineddiffraction signals evenly spaced on XRD pattern indicating a high or-dering in the silicate layers. For epoxy nanocomposite with 1 and3 m% of Nanofil 8® (E_N8_1%; E_N8_3%) no obvious diffraction peakswere identified. It could be due to low concentration of the filler thatis hardly detected by XRD. It is a common practice to classify a

tion of temperature at a constant heating rate of 3 °C/min.




nanocomposite as fully exfoliated from the absence of (001) reflection.However, disordered layers (bunched together but not parallel stacked)are not detected by XRD. Thus, a silent XRDmay hide a large number ofdisordered stacks of layers and can be highly misleading whenemployed as a single tool for quantifying nanocomposite structure orfiller dispersion. The diffraction signal (001) of Nanofil 8® in the nano-composite with 5 m% of the filler (E_N8_5%) decreased in intensity butno obvious change in its position is observed indicating no intercalationof epoxy resin in the silicate interlayer space.

3.2.2. Dynamic mechanical analysisThe ratio of the storage moduli of the nanocomposite and the pure

epoxy resin, E′/E′o, measured at 25 °C, as a function of the filler concen-tration is shown in Fig. 9.

As seen,when 1 m%of N2 or N8 is added to epoxy resin themodulusis decreased up to 4%. For both nanocomposites no obvious (001) dif-fraction peaks were observed. This can be due to small concentration,good particle distribution or even exfoliation. In any case one could ex-pect that high interfacial area for filler–matrix interactionswould resultin an enhancement of mechanical properties. As noted in the experi-mental part, the commercial organically modified Mt contain 4 and10% of free modifier and may act as plasticizer, lowering the modulus.

The storage modulus of the nanocomposite containing silylated Mtat 25 °C is higher between 5 and 15% with respect to the pristineepoxy matrix and increases with an increasing filler loading.

The glass transition temperatures, determined from the maximumvalue of the loss modulus, of all prepared nanocomposites are slightlyhigher (2 to 5 °C) than that of the neat epoxy (Tg = 59 °C). No correla-tionbetween Tg and thefiller concentration can be established as shownin Fig. 10. The above experimental observation indicates the complexityof factors that can affect the modulus and Tg of epoxy nanocomposites.The silylation reaction could enhance the interaction between the epoxymatrix and the fillers by means of covalent bonds due to the cross-linking reaction reducing the mobility of polymer segments near thesolid surface. On the other hand the silane modifier could act as plasti-cizer in epoxy resin (Piscitelli et al., 2012). As seen, XRD spectra ofsilylated Mt epoxy nanocomposites indicated no intercalation ofepoxy resin in the silicate interlayer space leading to not nano- butthe micron scale reinforcement.

4. Conclusions

3-Aminopropyltriethoxy silane was used to functionalize Na+-Mt,by following two different routes in terms of reaction time and theaminosilane concentration. For all silylated Mt the XRD (001) reflec-tions shifted to lower angles compared to the unmodifiedMt indicatingthat aminosilane species has been grafted/intercalated in the interlayerspace of Mt. The silicate basal spacing increases with an increasingaminosilane concentration in the reaction mixture. After silylation anew 29Si NMR signal at ~−67.7 ppm is recorded, due to the presenceof T3 structural units, followed by a decrease in the intensity of Q3 signal,indicating that the condensation between the interlayer surface silanolgroups and the aminosilanemolecules occurred. XRD spectra of silylatedMt epoxy nanocomposites indicated no intercalation of epoxy resin inthe silicate interlayer space leading to not nano- but themicron scale re-inforcement. The storage modulus of the nanocomposite containingsilylated Mt at 25 °C is higher between 5 and 15% with respect to thepristine epoxy matrix and increases with an increasing filler loading.Silylated Mt yields higher elastic modulus compared to commercial or-ganically modified Mt (Nanofil 2® and Nanofil 8®). The glass transitiontemperatures, determined from themaximumvalue of the lossmodulus(E″), of all prepared nanocomposites are slightly higher (2 to 5 °C) than


that of the cured epoxy matrix but do not change with increasingsilylated Mt content.

Acknowledgments

The authors acknowledge thefinancial supports from theMinistry ofHigher Education, Science and Technology of the Republic of Sloveniathrough the contract No. 3211-10-000057 (Center of Excellence Poly-merMaterials and Technologies) and theMinistry of Science, Educationand Sports of the Republic of Croatia (project 125-1252970-3005:“Bioceramic, Polymer and Composite Nanostructured Materials”).

References

Bergaya, F., Lagaly, G., 2013. Handbook of Clay Science, second ed. Elsevier.Bergaya, F., Jaber, M., Lambert, J.-F., 2011. Organophilic clay minerals. In: Galimberti, M.

(Ed.), Rubber–Clay Nanocomposites: Science, Technology and Applications. JohnWilley & Sons, pp. 45–86.

Bourlinos, A.B., Jiang, D.D., Giannelis, E.P., 2004. Clay-organosiloxane hybrids: a route tocross-linked clay particles and clay monoliths. Chem. Mater. 16, 2404–2410.

Choi, Y.Y., Lee, S.H., Ryu, S.H., 2009. Effect of silane functionalization of montmorilloniteon epoxy/montmorillonite nanocomposite. Polym. Bull. 63, 47–55.

Di Gianni, A., Amerio, E., Monticelli, O., Bongiovanni, R., 2008. Preparation of polymer/claymineral nanocomposites via dispersion of silylated montmorillonite in a UV curableepoxy matrix. Appl. Clay Sci. 42, 116–124.

He, H.P., Duchet, J., Galy, J., Gerard, J.F., 2005. Grafting of swelling clay materials with 3-aminopropyltriethoxysilane. J. Colloid Interface Sci. 288, 171–176.

Huskić, M., Žigon, M., 2009. The effects of experimental parameters on the extent of inter-calation of PMMA/MMT nanocomposites prepared in solution. J. Appl. Polym. Sci.113, 1182–1187.

Ivanković, M., Brnardić, I., Ivanković, H., Huskić, M., Gajović, A., 2009. Preparation andproperties of organic–inorganic hybrids based on poly(methyl methacrylate) andsol–gel polymerized 3-glycidyloxypropyltrimethoxysilane. Polymer 50, 2544–2550.

Kim, N.H., Malhotra, S.V., Xanthos, M., 2006. Modification of cationic nanoclays with ionicliquids. Microporous Mesoporous Mater. 96, 29–35.

Kim, S.H., Han, O.H., Kim, J.K., Lee, K.H., 2011. Multinuclear solid-state NMR investigationof nanoporous silica prepared by sol–gel polymerization using sodium silicate. Bull.Kor. Chem. Soc. 32, 3644–3649.

Kozak, M., Domka, L., 2004. Adsorption of the quaternary ammonium salts on montmoril-lonite. J. Phys. Chem. Solids 65, 441–445.

Park, S.J., Kim, B.J., Seo, D.I., Rhee, K.Y., Lyu, Y.Y., 2009. Effects of a silane treatment on themechanical interfacial properties of montmorillonite/epoxy nanocomposites. Mater.Sci. Eng., A 526, 74–78.

Pavlidou, S., Papaspyrides, C.D., 2008. A review on polymer-layered silicate nanocompos-ites. Prog. Polym. Sci. 33, 1119–1198.

Piscitelli, F., Posocco, P., Toth, R., Fermeglia, M., Pricl, S., Mensitieri, G., Lavorgna, M., 2010.Sodium montmorillonite silylation: unexpected effect of the aminosilane chainlength. J. Colloid Interface Sci. 351, 108–115.

Piscitelli, F., Scamardella, A.M., Romeo, V., Lavorgna, M., Barra, G., Amendola, E., 2012.Epoxy composites based on amino-silylated MMT: the role of interfaces and claymorphology. J. Appl. Polym. Sci. 124, 616–628.

Ray, S.S., Okamoto, M., 2003. Polymer/layered silicate nanocomposites: a review frompreparation to processing. Prog. Polym. Sci. 28, 1539–1641.

Shanmugharaj, A.M., Rhee, K.Y., Ryu, S.H., 2006. Influence of dispersing medium ongrafting of aminopropyltriethoxysilane in swelling clay materials. J. Colloid InterfaceSci. 298, 854–859.

Shen, W., He, H.P., Zhu, J.X., Yuan, P., Frost, R.L., 2007. Grafting of montmorillonite withdifferent functional silanes via two different reaction systems. J. Colloid InterfaceSci. 313, 268–273.

Silva, A.A., Dahmouche, K., Soares, B.G., 2011. Nanostructure and dynamic mechanicalproperties of silane-functionalized montmorillonite/epoxy nanocomposites. Appl.Clay Sci. 54, 151–158.

Tonle, I.K., Ngameni, E., Njopwouo, D., Carteret, C., Walcarius, A., 2003. Functionalizationof natural smectite-type clays by grafting with organosilanes: physico-chemical char-acterization and application to mercury(II) uptake. Phys. Chem. Chem. Phys. 5,4951–4961.

Uchida, Y., Sugiyama, T., Noguchi, E., Nakamura, K., Nakamura, Y., Matsui, K., 2006. Interca-lation of (3-aminopropyl) triethoxysilane and (3-aminopropyl) diethoxymethylsilaneinto montmorillonite. Clay Sci. 12 (Supplement_2), 71–75.

Vaia, R., Teukolsky, R., Giannelis, E.P., 1994. Interlayer structure and molecular environ-ment of alkylammonium layered silicates. Chem. Mater. 6, 1017–1022.

Vazquez, A., Lopez, M., Kortaberria, G., Martin, L., Mondragon, I., 2008. Modification ofmontmorillonite with cationic surfactants. Thermal and chemical analysis includingCEC determination. Appl. Clay Sci. 41, 24–36.

Wang, K., Wang, L., Wu, J.S., Chen, L., He, C.B., 2005. Preparation of highly exfoliatedepoxy/clay nanocomposites by “slurry compounding”. Process and mechanisms.Langmuir 21, 3613–3618.


http://refhub.elsevier.com/S0169-1317(13)00298-6/rf0010






























































comparison of the properties of clay polymer nanocomposites prepared by montmorillonite modified by...

Documents