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Construction and Building Materials 22 (2008) 14–20

and Building

MATERIALS

Mechanical properties of nano-MMT reinforced polymercomposite and polymer concrete

Byung-Wan Jo a,1, Seung-Kook Park b,*, Do-Keun Kim a

a Department of Civil Engineering, 2303 Structural Engineering Laboratory, Hanyang University, 17 Haengdang-dong,

Seongdong-gu, Seoul 133-791, South Koreab Korea Research Institute for Construction Policy, Specialty Construction B/D, 14F, 395-70 Sindaebang-dong, Dongjak-gu,

Seoul 156-714, Republic of Korea

Received 15 December 2006; received in revised form 12 February 2007; accepted 23 February 2007Available online 19 April 2007

Abstract

Unsaturated polyester (UP) resin is widely used for the matrix of composites such as fiber reinforced plastic (FRP) and polymer con-crete. Consequently, inexpensive and high performance resins are important for the future of polymer composites. One recent method forenhancing the performance of polymer composites is the manufacture of MMT (montmorillonite)-UP nanocomposite synthesized byintercalating the UP resin into the silicate layers of MMT. This study investigates the mechanical and thermal properties of MMT-UP nanocomposites, and those of polymer concretes using these nanocomposites. Test results indicate that the mechanical propertiesand thermal stability of MMT-UP nanocomposites are better than those of pure UP. The glass transition and main chain decompositiontemperatures of the MMT-UP nanocomposite exceed those of pure UP. The compressive strength, elastic modulus, and splitting tensilestrength of the polymer concrete using MMT-UP nanocomposites exceeded those of polymer concrete using pure UP. Also, the polymerconcrete made with MMT-UP nanocomposite has better thermal performance than that of pure UP. The improved performance of UP isvery important for the future of polymer concrete.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Polymer concrete; Unsaturated polyester resin; MMT-UP nanocomposites; Mechanical properties

1. Introduction

Polymer composites are increasingly considered asstructural components for use in civil engineering due totheir excellent strength-to-weight ratios. Due to its excel-lent adhesion properties, unsaturated polyester (UP) resinis widely used for the matrix of composites such as FRPand polymer composites. However, compared to other res-ins, unsaturated polyester (UP) resin has relatively poormechanical properties, thermal stability, and fire retardantproperties, which limits its use in advanced composites.The modification of polymers is of considerable signifi-cance from a material science and engineering point of

0950-0618/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2007.02.009

* Corresponding author. Tel.: +82 2 2220 0327; fax: +82 2 2292 0321.E-mail address: plus_skpark@yahoo.com (S.-K. Park).

1 Tel.: +82 2 2220 0327; fax: +82 2 2292 0321.

view. The performance of unsaturated polyester (UP) resinmay be enhanced by the addition of inorganic fillers [5,7].Conventional particulate polymer composites, often calledfilled polymers, are of significant commercial importance asmaterials in industrial applications. Polymer nanocompos-ites are a new class of composites derived from nano-scaleinorganic particles. Their dimensions typically range from1 to 1000 nm and they are homogeneously dispersed inthe polymer matrix. Owing to the high aspect ratio of thefillers, the mechanical, thermal, flame retardant and barrierproperties of polymers may be enhanced without a signifi-cant loss of clarity, toughness or impact strength. The lay-ered silicate is generally made organophilic by exchangingthe inorganic cation, which is located between the layers(d-spacing), with an organic ammonium cation. Clay–poly-mer composites can be classified into three types: conven-tional composite, intercalated nanocomposites and

- 1nm

Sorbed cations, H2O

Fig. 1. The oxygen framework (solid circles) of smectite clay nanolayers.

B.-W. Jo et al. / Construction and Building Materials 22 (2008) 14–20 15

exfoliated nanocomposites (Fig. 1). In a conventional com-posite the registry of the clay nanolayers is retained whenmixed with the polymer, but there is no intercalation ofthe polymer into the clay structure (see Fig. 2a). Conse-quently, the clay fraction in conventional clay compositesplays little or no functional role and acts mainly as a fillingagent for economic considerations. An improvement inmodulus is normally achieved in a conventional clay com-posite, but this reinforcement benefit is usually accompa-nied by a sacrifice in other properties, such as strength orelasticity. Two types of clay–polymer nanocomposites arepossible [1,3,6]. Intercalated nanocomposites (Fig. 2b) areformed when one or a few molecular layers of polymerare inserted into the clay galleries with fixed interlayerspacings. Exfoliated nanocomposites (Fig. 2c) are formedwhen the silicate nanolayers are individually dispersed inthe polymer matrix, where the average distance between

monomer

Layered clay mineral

poly

polymerization

Fig. 2. Schematic illustrat

segregated layers is dependent on the clay loading. The sep-aration between the exfoliated nanolayers may be uniform(regular) or variable (disordered). Exfoliated nanocompos-ites show greater phase homogeneity than intercalatednanocomposites. More importantly, each nanolayer in anexfoliated nanocomposite contributes fully to interfacialinteractions with the matrix. This structural distinction isthe primary reason why the exfoliated clay state isespecially effective in improving the reinforcement andother performance properties of clay composite materi-als. The key to the extraordinary performance of polymer–clay nanocomposites is dependent on the completedispersal (exfoliation) of the clay nanolayers in the polymermatrix.

The structure of the montmorillonite clay used as the fil-ler comprises an octahedral alumina sheet sandwichedbetween two tetrahedral silica sheets. Alkylammonium ionslower the surface energy of the clay so that monomers andpolymers with different polarities can enter the spacebetween the layers and cause further separation of the sili-cate layers to form the nanocomposite [2,4].

The objective of this study is to enhance the performanceof polymer composites using unsaturated polyester (UP)resin based recycled PET (poly ethylene terephthalate) [8].Therefore, this work investigates the mechanical propertiesand thermal stability of MMT-UP nanocomposites andpolymer concrete using the MMT-UP nanocomposite.

The results are supported by mechanical testing, X-raydiffraction (XRD), transmission electron microscopy(TEM), differential scanning calorimetry (DSC), andthermo gravimetric analysis (TGA).

2. Research significance

This study contributes to the understanding of the prop-erties of MMT-UP nanocomposite and polymer concreteusing MMT-UP nanocomposite as follows.

Conventional Composite

mer

IntercalatedNanocomposite

ExfoliatedNanoomposite

a)

b)

c)

ions of the structures.

16 B.-W. Jo et al. / Construction and Building Materials 22 (2008) 14–20

1. It proves possible the manufacture of a higher gradepolymer concrete using nano-MMT.

2. It posits methods for enhancing the performance ofpolymer concrete with the addition of nano-MMT.

3. It suggests that polymer concrete made with recycledPET and nano-MMT may be useful materials for pro-ducing polymer concrete products.

3. Experiments

3.1. Materials

Three different kinds of MMT were used. Southern ClayProducts Inc., USA, supplied non-treated Na+-MMT andorganophilic treated MMT under the trade names of Cloi-site 30B and 25A. Cloisite 30B is a montmorillonite modi-fied with methyl, tallow, bis-2-hydroxyethyl, quaternaryammonium chloride; Cloisite 25A is a montmorillonitemodified with dimethyl, dehydrogenated tallow, 2-ethyl-hexyl, quaternary ammonium chloride. Table 1 showssome of the manufacturer’s data on these MMTs.

The unsaturated polyester resin based on recycled plas-tic (PET) was used as the matrix [8]. A styrene content of40% in unsaturated polyester was chosen for its low viscos-ity (1300 mPa s at 25 �C) and to achieve improved resin dif-fusion into the galleries of the MMT. To start the curingprocess, 1% (by weight of resin) of 10.7% active oxygenmethylethy ketone peroxide initiator and 0.1% (by weightof resin) of 8% solution cobalt octoato promoter (used asan accelerator) were added to the resin.

The following coarse and fine inorganic aggregates wereused in the experimental study of polymer concrete: 8 mmpea gravel; siliceous river sand with a fineness modulus of2.48, and CaCO3 (calcium carbonate). The aggregate wasoven-dried for a minimum of 24 h at 200 �C to reduce itsmoisture content to less than 0.3% by weight, thus ensuringa perfect bond between the polymer matrix and the inor-ganic aggregates. The use of calcium carbonate greatlyimproved the workability of the fresh mix. The fine andspherical calcium carbonate particle provided the freshmix with better lubricating properties, thus improving its

Table 1Properties of modified montmorillonite

Properties Na+ Cloisite 30B Cloisite 25A

Organic modifier None MT2EtOH 2MHTL8Specific gravity (g/cc) 2.86 1.87 1.98% Weight loss on ignition (%) 7 34 30X-ray results (d001) (A) 11.7 18.5 18.6

MT2EtOH (methyl, tallow, bis-S-hydroxyethyl, quaternaryammonium), 2MHTL8 (dimethyl hydrogenated tallow 2-ethylhexylammonium).

Table 2Properties of the aggregates

Type Size Specific

Coarse aggregate Maximum size 8 mm 2.63Fine aggregate 0.1–0.6 mm 2.60

plasticity and cohesiveness. The better gradation obtainedwith calcium carbonate also resulted in a hardened mate-rial with improved strength properties and surface appear-ance. The properties of the aggregate and resin are shownin Tables 2 and 3, respectively.

3.2. UP-MMT Nanocomposites

There are two steps for manufacturing the UP-MMTnanocompostite. First, in the mixing process, the UP linearchains are mixed with styrene monomers and layered sili-cate. Second, in the curing process, the crosslinking reac-tion is started by decomposing the initiators. Theunsaturated polyester chains, styrene monomers andnano-MMTs were mixed for 3 h at 60 �C. The weight per-centages of MMT in UP-MMT nanocomposite used were2%, 5%, 8% and 10%, respectively. The mixture was thencooled to room temperature. 1% by weight of initiator(MKPO) was added and the mixture was stirred for2 min. The mixture was poured into molds, cured at roomtemperature for 12 h and post-cured at 120 �C for 4 h.

X-ray diffraction (XRD) patterns were obtained using aRigaku X-ray diffractometer equipped with CuKa radia-tion and a curved graphite crystal monochromator. Sam-ples were prepared by applying the pre-intercalatedmixture and nanocomposite of UP-MMT in sheet formon a slide. All XRD data were collected with an X-ray gen-erator (k = 1.5406A). Bragg’s law (k = 2d/sinh) was usedto compute the crystallographic d-spacing.

In order to evaluate the change in the glass transitiontemperature, Tg, associated with increases in the MMTcontent, a differential scanning calorimeter (DSC) analysiswas carried out using a General V4.1C DuPont 2000. Themeasurement was carried out from 30 �C to 300 �C using aheating rate of 10 �C/min in a nitrogen atmosphere. Thethermal behavior was determined with a thermogravimetricanalyzer (TGA). Microscopic investigation was performedwith a transmission electron microscope (TEM) with anacceleration voltage of 100 kV.

3.3. Polymer concrete using UP-MMT Nanocomposites

Tensile tests were performed according to ASTMD638M-91a at a crosshead speed of 5 mm/min. The poly-mer concrete cylinders used for compression and splittingtensile tests were 76 mm in diameter and 152 mm in length.Specimens were tested in a hydraulic load machine at aconstant loading rate of 44,500 N/min. The mix design ofpolymer concrete, proportioned by weight, was as follows:11% resin (MMT-UP), 45% oven-dried coarse aggregate,33% oven-dried sand, and 11% CaCO3. The compressive

gravity Fineness modulus Absorption (%)

6.42 0.082.48 0.05

Table 3Unsaturated polyester resin formulation

Components Recycled PET Propylene glycol, diethylene glycol,dipropylene glycol

Terephthalic acid, maleicanhydride

Styrene monomer (SM)

Percentage by weight (%) 29.1 16.0 14.9 40.0

2 4 6 8 10 12

Degrees (2Θ)

Rel

ativ

e In

tens

ity

(a) Na +

17.0(b) Na + - UP

(f) 30B - UP

(d) 25A - UP

(e) 30B

(c) 25A

11.7

18.5

34.6

18.6

Fig. 3. XRD data for MMT-UP nanocomposites with MMT contents of5%: (a) Na+, (b) Na+-UP composite; (c) Cloisite 25A-UP composite, (d)Cloisite 25A-UP composite; (e) Closite 30B, (f) Cloisite 30B-UPcomposite.

B.-W. Jo et al. / Construction and Building Materials 22 (2008) 14–20 17

modulus of elasticity was first obtained using a compress-ometer with a 76-mm gauge length using two diametricallyopposite sides. The compression elastic modulus was calcu-lated where the stress was 40% of the maximum strain on thestress–strain (load–deflection) graph. Flexural specimenswere mixed and compacted in a steel mold with dimensionsof 50 · 50 · 305-mm. The beams were loaded in third-pointloading at a uniform rate of 2225 N/min. The specimenswere cast, cured, and tested at room temperature. Testingof the specimens was performed at 7 days. Tests were per-formed to determine the effect of temperature on the PCcompressive strength, splitting tensile strength, modulus ofelasticity, and flexural strength. After curing, specimenswere put in an environmental chamber at the desired tem-perature for a period of 2 days prior to testing. Selected tem-peratures were�15 �C, 25 �C, and 65 �C. Actual testing wasperformed at room temperature immediately after removingthe specimens from the environmental chamber.

4. Results and discussion

4.1. UP-MMT Nanocomposite

Silicate layer dispersion in the MMT-UP nanocompositewas analyzed by XRD. As shown in Fig. 3, the XRDs ofMMTs and MMT-UP composites investigated differentpeak with the types of MMTs. The peaks for Na+, Cloisite25A, Na+-UP and Cloisite 25A-UP nanocomposite areshown at 7.5�, 3.5�, 5.2� and 2.6�, respectively. These 2h val-ues correspond to interlayer spacings of 11.7, 18.6, 17.0 and34.6 A, respectively. A new peak was observed in the Na+-UP composite. This indicates that UP by polymerization isintercalated between the MMT layers. However, for the

Fig. 4. Transmission electron micrographs (TEM) of MMT

Cloisite 30B-UP composite, the peak at the lower angle dis-appeared, suggesting that either the silicate layer plateletswere exfoliated in the polymer matrix or they disappearedbecause the spacing between the layers was too large. It isimportant to note that polymerization of Na+-UP and Cloi-site 25A-UP composite led only to an intercalated structure,while Cloisite 30B promoted the delamination process oflayered silicates to achieve exfoliation.

More direct evidence for the formation of a nanocom-posite is provided by the TEM. The dark lines in theTEM image in Fig. 4b are individual silicate layers. In thecase of the MMT (Cloisite 30B) layers, some irregular dis-persions exist in the silicate layer. Also, the relatively exfo-liated and well-dispersed portion of the nanocomposite was

-UP nanocomposite: (a) Na+-UP, (b) Cloisite 30B-UP.

1500

2000

2500

3000

3500

4000

4500

0% 2% 4% 6% 8% 10% 12%

MMT contents (%)

Ten

sile

mod

ulus

(M

pa)

UP

Na+ -UP25A-UP

30B-UP

UP

Na+ -UP25A-UP

30B-UP

Fig. 5. Tensile modulus of nanocomposites with MMT contents.

77

78

79

80

81

82

83

84

85

86

87

88

-1 1 3 5 7 9 11

MMT contents (%)

Tg

(ºC

)

Fig. 7. Glass transition temperature of Cloisite 30B-UP nanocomposite.

18 B.-W. Jo et al. / Construction and Building Materials 22 (2008) 14–20

made with Closite 30B, as shown in Fig. 4b. However, theMMT (Na+) layers shown in Fig. 4a are more regular andsome of the silicate layers maintained their original order.

With the addition of the MMT, the tensile modulus ofthe composites shown in Fig. 5 increases up to 5% loadingsince MMT is more rigid than the matrix resin. The modu-lus of the Cloisite 30B and Cloisite 25A composites exceedthat of the Cloisite Na+ composite owing to their higherdegree of exfoliation and better adhesion at the MMT-UPinterface. Above 5% MMT content, the tensile modulusstarts to decrease with MMT content in both types of com-posites, due to a lower degree of exfoliation and a lowerdegree of polymer–MMT surface interactions at higherMMT content. For the Cloisite Na+ composite, the increasein the tensile modulus is not significant compared to the ten-sile modulus of pure unsaturated polyester. This is becausethere is little or no intercalation/exfoliation between the sil-icate layers of the Cloisite Na+ composite, so these materi-als act as conventional composites, especially at high MMTcontents. Also, the cross-link density might be lower with ahigher MMT content, leading to a lower modulus. Theincrease in tensile strength associated with increases inMMT content is demonstrated in Fig. 6. The variation intensile strength of the composite with MMT contents is sim-

20

30

40

50

60

70

80

90

100

0% 2% 4% 6% 8% 10% 12%

MMT contents (%)

Ten

sile

str

engt

h (M

Pa)

UPNa+ -UP25A-UP30B-UP

Fig. 6. Tensile strength of nanocomposites with MMT contents.

ilar to that of the tensile modulus. The maximum tensilestrength emerged at 5% MMT content.

Work done on the thermal properties of polymers hasshown that the glass transition of polymer–MMT nano-composites increases with increasing MMT content. Theeffect of nano-MMT (Closite 30B) content on the Tg isshown in Fig. 7. The Tg increases with increasing ofMMT (Closite 30B) content. This implies improved adhe-sion between the UP and MMT surfaces. Also, the nano-MMT prevents segmental motions of the polymer chains.It is known that the primary factor affecting the Tg of curedUP is the crosslinked density in the same UP resin. There-fore, it can be concluded that the UP-MMT nanocompositehas a high crosslinking density. However, beyond a certainMMT content (approximately in the range of 5–7%), Tg

decreases with increasing MMT content. Thus, the cross-linking density might decrease at a high MMT content.

TGA curves of the pure UP and the Closite 30B-UPnanocomposite are shown in Fig. 8. The onset of degrada-tion is slightly but progressively hastened in the pure UPcompared to the Closite 30B-UP nanocomposite. Thermaldegradation of pure UP and MMT-UP has three distinct

-20

0

20

40

60

80

100

120

0 200 400 600 800 1000

Temperature (ºC)

resi

dual

wei

ght (

%)

pure UP

30B-UP

Fig. 8. TGA thermal degradation profiles for Cloisite 30B-UP nanocom-posites and pure UP Samples were heated from 23 �C to 1000 �C innitrogen.

0

10

20

30

40

50

-15 ºC 25 ºC 65 ºC

Temperature

Mod

ulus

of

elas

ticity

(G

Pa)

0

20

40

60

80

100

Com

pres

sive

str

engt

h (M

Pa)

Modulus of elasticity of PC using pure UPModulus of elasticity of PC using MMT-UP nanocompositeCompressive strength of PC using pure UPCompressive strength of PC using MMT-UP nanocomposite

Fig. 9. Compressive strength and elastic modulus of polymer concreteusing UP- MMT (Closite 30B) nanocomposite.

5

15

25

35

45

-15 ºC 25 ºC 65 ºCTemperature

Stre

ngth

(M

Pa)

Splitting tensile strength of PC using pure UPSplitting tensile strength of PC using MMT-UP nanocompositeFlexur al st re ngth of PC us ing pure UPFlexural strength of PC using MMT-UP nanocomposite

Fig. 10. Splitting tensile and flexural strength of polymer concrete usingUP-MMT (Closite 30B) nanocomposite.

B.-W. Jo et al. / Construction and Building Materials 22 (2008) 14–20 19

steps. The first is the decompostition of relatively weakhead-to-head linkages, impurities, and styrene monomersin the UP. The second is the decomposition of the UPchain-end, and the third is the decomposition of the UPmain chains. The three degradation steps occurred at161 �C, 272 �C, and 321 �C in the pure UP and at 224 �C,326 �C, and 408 �C in the MMT-UP nanocomposite. Thetemperature of the main chain decomposition of the Cloi-site 30B-UP nanocomposite exceeds that of the pure UPby about 80 �C. Pure UP is completely decomposed at400 �C. The nanocomposites show slower degradationabove 400 �C since only inorganic MMT is left in the sys-tem at that stage. This demonstrates that the MMT-UPnanocomposite has better thermal stability than pure UP.

4.2. Effect of UP-MMT (Closite 30B) nanocomposite on

polymer concrete

4.2.1. Testing temperature �25 �C

The strength of polymer concrete specimens cast withCloisite 30B-UP nanocomposite containing 5% MMT con-tent was estimated. The compressive strength, elastic mod-ulus, and splitting tensile strength of polymer concreteusing Cloisite 30B-UP nanocomposite exceeded the corre-sponding properties of polymer concrete using pure UP,suggesting that the use of exfoliated MMT-UP nanocom-posite enhances polymer concrete strength. The flexuralstrength of the polymer concrete does not significantlyincrease with the use of the Cloisite 30B-UP nanocompos-ite. The compressive strength, elastic modulus, and split-ting tensile strength of polymer concrete were found tobe correlated with the tensile strength and tensile modulusof the MMT-UP nanocomposite. However, the flexuralstrength of the polymer concrete was not significantly cor-related with the tensile strength and tensile modulus of theMMT-UP nanocomposite.

4.2.2. The effect of temperature on strength and modulus ofelasticity

The effects of temperature on the compressive strength,modulus of elasticity, and splitting tensile and flexuralstrength of the polymer concrete using UP-MMT nano-composite are shown in Figs. 9 and 10.

The modes of failure of polymer concrete differeddepending on the temperature at which the materials weretested. Compression cylinders had a sudden, brittle failurewhen tested at �15 �C and 25 �C. Conversely, cylinderstested at 65 �C had a slow, ductile failure resulting in anexcessive bulging of the specimens. This behavior arisesfrom decreases in the modulus of the resin binder in thepolymer concrete specimens under increasing temperature.That is, the modulus of the polymer concrete specimendecreases with increases in temperature, as shown in Fig. 9.

Increase in temperature effected a loss in strength andmodulus of elasticity in the polymer concrete specimensbecause the resin binder decreased in strength with anincrease in temperature. In the case of the polymer concrete

specimens using pure UP, an increase in temperature from25 �C to 65 �C decreased the compressive strength by about33%, modulus of elasticity by about 36%, splitting tensilestrength by about 31%, and flexural strength by about38%. In the case of the polymer concrete specimens usingUP-MMT nanocomposite, an increase in temperature from25 �C to 65 �C decreased the compressive strength by about18%, modulus of elasticity by about 22%, splitting tensilestrength by about 18%, and flexural strength by about 22%.

This result demonstrates that the polymer concretemade with MMT-UP nanocomposite has mechanical prop-erties that are better than those of pure UP. The improvedperformance of UP is very important for the future of poly-mer concrete. Therefore, the enhancement of the mechani-cal and thermal performance of polymer concrete affordedby the use of nano-MMT is remarkable.

5. Conclusions

The main objective of this study was to enhance the per-formance of polymer concrete using unsaturated polyesterresin. This work investigated whether MMT-UP nanocom-posite can be used to produce polymer concrete that exhibits

20 B.-W. Jo et al. / Construction and Building Materials 22 (2008) 14–20

excellent mechanical and thermal performance. The follow-ing conclusions can be drawn from the results of this study:

1. The mechanical and thermal properties of the compos-ites, which have their maximum tensile strength, tensilemodulus, and Tg with 5% nano-MMT, were dramati-cally improved by the addition of nano-MMT dispersedin the polymer matrix. Also, the elastic modulus ofMMT-UP nanocomposite was enhanced by the additionof nano-MMT. However, beyond a certain MMT con-tent (approximately in the range of 5–7%), the mechan-ical and thermal performance of the compositesdecreased with increasing nano-MMT content.

2. In composites with Na+, the mechanical and thermalproperties did not show a significant change becausethe degree of exfoliation is less than that of Cloisite30B-UP nanocompostites.

3. The strength and elastic modulus of the polymer con-crete was enhanced by the use of exfoliated MMT-UPnanocomposite. It is important to note that the exfoli-ated MMT-UP nanocomposite greatly affects the per-formance of the polymer concrete. Also, the strengthand elastic modulus of polymer concrete was found tobe positively correlated with the tensile strength and ten-sile modulus of the MMT-UP nanocomposite.

4. Unsaturated polyester resins made with recycled PETand nano-MMT may be used to greatly enhance the per-formance of polymer composites at a relatively low cost.

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