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Abstract

Organophilic montmorillonite (OMMT) was synthesized by cationic exchange between Na-MMT and tricetade-

1. Introduction

methylmethacrylate (Blair et al., 1987), acrylamide

crylate (El-Tahlawy and Hudson, 2001), N,N0-dimethy-

nite (MMT), which belongs to the 2:1 layered silicate. Its

ARTICLE IN PRESS(Yazdani-Pedram et al., 2002), 2-hydroxyethlymetha- crystal lattice consists of two silica tetrahedral sheets

fusing into an octahedral sheet. Isomorphous substitu-

tions of Si4+ for Al3+ in the tetrahedral lattice and of

Al3+ for Mg2+ in the octahedral sheet can generate

negative charges that are counterbalanced by cations

*Corresponding author. Tel.: +86-551-3601586; fax: +86-

551-3606763.

E-mail address: fye@ustc.edu.cn (F. Yuee).

0969-806X/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.raChitosan is a high molecular weight polysaccharide

composed mainly of b-(1,4)-linked 2-deoxy-2-amino-d-glucopyranose units and partially of b-(1,4)-linked2-deoxy-2-acetamido-d-glucopyranose. Because of its

biocompatibility, biodegradability and avirulence, chit-

osan has been used in many areas.

Interest in the modication of chitosan through graft

copolymerization has grown signicantly. The combina-

tion of natural and synthetic polymers via grafting yields

hybrid materials which may produce desirable proper-

ties. In previous studies, a number of different mono-

mers have been grafted onto chitosan, these include

laminoethylmethacrylate (Singh and Ray, 1997). As we

know there are no references in the literature to the

incorporation of clay into graft-modied chitosan.

Polymer/clay nanocomposites are of interest because

they combine the structure, physical and chemical

properties of both inorganic and organic materials.

Compared to the pure polymers these nanocomposites

demonstrate excellent properties such as improved

storage modulus (Yao et al., 2002), decreased thermal

expansion coefcients (Sun and Garces, 2002), reduced

gas permeability (Usuki et al., 2002), and enhanced ionic

conductivity (Wu and Lerner, 1993).

The clay that is most generally used is montmorillo-cylmethyl ammonium bromide in an aqueous solution. A new nanocomposite consisting of poly(butyl acrylate)-

modied chitosan and OMMT was prepared by g-ray irradiation polymerization in acetic acid aqueous solution. Thedegree of dispersion and the intercalation spacing of these nanocomposites were investigated using X-ray diffraction.

The enhanced thermal stabilities of nanocomposites were characterized by the thermal gravimetric analysis. The

improved mechanical properties of nanocomposites were characterized by static tensile studies and dynamic mechanical

analysis. The nanocomposites showed improved resistance to water absorption.

r 2003 Elsevier Ltd. All rights reserved.

Keywords: Nanocomposites; Chitosan; Butyl acrylate; g-ray irradiationRadiation Physics and Chem

A new hybrid nanocomcopolymerization of butyl

presence of organop

Li Yu, Liu Li, Zhan

Department of Polymer Science and Engineering, Univers

Peoples Re

Received 22 September 20dphyschem.2003.10.01269 (2004) 467471

site prepared by graftylate onto chitosan in thelic montmorillonite

eian, Fang Yuee*

Science and Technology of China, Hefei, Anhui 230026,

c of China

ccepted 15 October 2003

tion. Tricetadecylmethyl ammonium bromide (TRIAB)

was supplied by Fei Xiang Chemicals Co. Ltd.,

ARTICLE IN PRESSL. Yu et al. / Radiation Physics and Chemistry 69 (2004) 467471468Jiangshu, China.

The samples were irradiated at room temperature,

with the 2.22 1015 Bq 60Co g-ray source. Theirradiation doses were measured by ferrous sulfate

dosimeter.

2.2. Preparation of OMMT

The OMMT was prepared by cationic exchange

between Na+-MMT galleries and TRIAB in an aqueous

solution. The suspension solution containing 12.5 g

of Na+-MMT and 4.6 g TRIAB was mixed in

240ml of distilled water. The suspension solution

was stirred at 75C for 2 h, the exchanged MMT

was ltered and washed with distilled water until no

bromide ions was detected with 0.1MAgNO3 solution.

Then the product was dried in vacuum oven at 60C for

24 h. The OMMT obtained was ground with a mortar

and pestle and sieved through a 280 mesh copper

griddle.such as Ca2+ and Na+. Many cationic surfactants can

be exchanged easily with the hydrated cations between

the layers and render the clay more organophilic than

the weak forces holding them together. As the

surface energy of the organoclay is much lower, many

polymers and monomers can intercalate within the

galleries easier.

In this work, we studied the modication of chitosan

by g-ray irradiation-induced graft copolymerization withbutyl acrylate in acetic acid aqueous solution containing

organophilic montmorillonite (OMMT). Chitosan was

used not only as a reactive component but also as a

cationic, polymeric surfactant (Hsu et al., 2002). Graft

copolymerization and the intercalation of BuA occurred

at the same time. The resulting nanocomposite emulsion

was used directly to prepare the sample with no

coagulation or separation. The purpose of this paper

was to investigate the effects of OMMT on the

structural, thermal, mechanical and water absorption

properties of the nal composites.

2. Experimental

2.1. Materials

Chitosan was obtained from San Huan Ocean

Biochemical Co. Ltd. (China). Its degree of deacetyla-

tion and the apparent viscosity were determined as

91.2% and 30MPa s. Butyl acrylate was chemical grade.

Na+-MMT, with a cation exchange capacity (CEC)

value of 100mmol/100 g, (Ling An Chemicals Co. Ltd.,

Hangzhou, China) was used without further purica-2.3. Preparation of nanocomposites

An exact amount of chitosan was rst dissolved in 1%

acetic acid to prepare 2wt% solution using a 50 cm3

stoppered bottle, followed by the addition of 3.0 g

monomer poly(butyl acrylate) (BuA). Then the required

amount of OMMT was added. After constant stirring

for 30min, the system was deoxygenated by slow

bubbling of nitrogen gas through the solution for

10min. The sample bottles were irradiated for a specied

time in a 60Co g-ray chamber applying continuousstirring (dose: 10 kGy; dose rate: 60Gy/min). After

completion of the reaction, the contents were cooled and

cast on a glass plate, the solvent was then evaporated

under an infrared lamp and sample lms were obtained.

The conversion of BuA was determined by the following

equation:

Conversion %

Sample film g OMMT g Chitosan g

BuA used g100:

2.4. Percentage of grafting

The homopolymer of butyl acrylate was removed

from the sample lms by exhausive Soxhlet extraction

with toluene for 48 h. The grafting percentage are

dened and calculated as follows:

Grafting % Wg W W0

W0 100;

where Wg is weight of grafting copolymer, W0 is weight

of chitosan, W is weight of OMMT.

2.5. Characterization of nanocomposites

X-ray diffraction (XRD) patterns were obtained by

using a Rigaku D/max gA X-ray diffractometer usinggraphite mono-chromatized Cu Ka radiation (l =0.154178 nm). The scanning range was 1.510 with a

scanning rate of 2/min.

The thermal gravimetric analysis (TGA) was con-

ducted on a PerkinElmer TGA 7 Thermal Analyzer

under N2 ow. The heating rate was 10C/min.

Dynamic mechanical analysis (DMTA) was carried

out on Rheometric Scientic DMTA IV at the frequency

of 1Hz and at the heating rate of 2C/min from 70Cto 200C at which the sample lost its dimensional

stability.

The tensile properties of sample lms were measured

using an instron tensile tester (UTM, 1112) under the

following conditions: crosshead speed 10 cm/min, gauge

length 3.0 cm, temperature 25C, and relative humidity

65%.

2.6. Water absorption measurements

The clean, dried sample lms of known weights were

immersed in distilled water at 25C until equilibrium

was reached (almost 24 h). The lms were removed,

blotted quickly with absorbent paper and then weighed.

The absorption percentage of these samples was

calculated using the equation

X % M1 M0

M0;

where M0 and M1 are the weight of dry and swollen

samples, respectively.

3. Results and discussion

3.1. Characterization of the Na+-MMT and OMMT

became organophilic and its basal spacing was

increased.

3.2. XRD of nanocomposites

The X-ray diffraction curves for pure OMMT and

Poly (butyl-acrylate)-modied chitosan (CTS-PBuA)

nanocomposites with different OMMT contents are

shown in Fig. 2. In this gure, the pure CTS-PBuA does

not exhibit any diffraction peak, but when the amount

of the OMMT dispersed in CTS-PBuA is only 3wt%,

there is a diffraction peak is at 2y= 1.8 (d = 4.78 nm),which means that the intercalation has occurred and the

intercalated nanocomposites have been formed. With

the amount of the OMMT increased to 7wt%, there was

no distinct shift, indicating that the distance between the

sheets of nanocomposite was not affected by the amount

ARTICLE IN PRESSL. Yu et al. / Radiation Physics and Chemistry 69 (2004) 467471 469 2 4 6 8

OMMT

Na+-MMT

2 (degrees)

Inte

nsity

Fig. 1. XRD patterns of Na+-MMT and OMMT.The preparation of the OMMT is a critical step in the

synthesis of polymerMMT nanocomposites. Firstly,

aliphatic amines are often used as they are very effective

agents for modifying clays. Secondly, the OMMT opens

the gallery spacing allowing monomers and polymers to

enter more easily. Fig. 1 shows XRD patterns of the

Na+-MMT and the OMMT. The intercalation of

polymer chains usually increases the interlayer spacing

relative to that of the pure MMT, leading to a shift in

the X-ray diffraction peak toward a lower angle. The

parameters were calculated from the observed peaks of

the angular position 2y by the Bragg formula: l =2d sin y. The nite layer expansion associated withintercalated structures resulted in a new reection that

corresponded to the layer gallery height of the inter-

calated nanocomposites. After intercalation, the XRD

data shows that the broad peak centered at 1.32 nm

corresponding to Na+-MMT was shifted to a new peak

at 3.75 nm for the OMMT. This conrms that MMTof the OMMT.

3.3. Influence of OMMT on monomer conversion and

grafting percentage

Fig. 3 shows the relationship between radiation dose

and monomer conversion. It can be seen that below

2 kGy, conversion of BuA dramatically increases with

increasing dose. After the conversion of BuA reaches

about 80%, the increasing viscosity of system and the

lower monomer concentration lead to the decrease of

polymerization rate. Under the same conditions, due to

the restricted movement of BuA and the inhibition of

the propagating chain radicals in the OMMT galleries,

the polymerization rate of BuA was decreased. There-

fore, the conversion of BuA in the OMMT system was

lower than in the pure system.

Under the same conditions (dose: 10 kGy; dose rate:

60Gy/min; BuA conversion: 95%) the inuence of

OMMT on the grafting percentage of PBuA-modied

e

d

cba

a: 0% OMMTb: 3% OMMTc: 5% OMMTd: 7% OMMTe: pure OMMT

3 6 92 (degrees)

Inte

nsity

Fig. 2. XRD patterns of pure OMMT and nanocomposites

with different OMMT contents.

degradation of the whole material. Evidently, at the

second stage, the decomposition onset temperature of

the CTS-PBuA nanocomposites shifted towards higher

temperatures compared to CTS-PBuA, indicating the

enhancement of thermal stability of the nanocomposites.

It may be due to the fact that MMT is inorganic

material with high thermal stability and great barrier

properties and can prevent the heat from transmitting

quickly and can limit the continuous decomposition of

the nanocomposites.

3.5. DMTA and static tensile testing of nanocomposites

Fig. 5 shows the storage modulus, E0 of the CTS-

PBuA and CTS-PBuA nanocomposites with different

OMMT contents. Compared with the CTS-PBuA, the

CTS-PBuA nanocomposite with 3wt% OMMT exhib-

ited an enhanced E0. The CTS-PBuA nanocomposites

ARTICLE IN PRESSL. Yu et al. / Radiation Physics and Chemistry 69 (2004) 4674714700 1 2 3 4 5 6 7 8 9 10 11 12

0

20

40

60

80

100

con

vers

ion

Radiation dose (kGy)

0% OMMT 7% OMMT

Fig. 3. The monomer conversion vs. radiation dose of CTS-

PBuA (m) and CTS-PBuA nanocomposite with 7wt% OMMT

(); dose rate: 60Gy/min.chitosan was also investigated and we found that below

7wt% the percentage of grafting did not change

signicantly with increasing OMMT concentration.

Beyond 7wt% (OMMT conc.) there is a marked

decrease in the grafting percentage. This is attributed

to the fact that the diffusion of BuA and propagating

chain radicals into chitosan matrix was inhibited under a

higher OMMT concentration.

3.4. Thermal properties

The TGA thermograms of CTS-PBuA and CTS-

PBuA nanocomposites with different OMMT contents

are presented in Fig. 4. The thermal degradation prole

of CTS-PBuA exhibit two main decomposition stages

with one starting at around 270C and another starting

at around 350C. The rst stage is attributed to the

degradation of chitosan. The second stage is the

with more than 3wt% OMMT did not show an increase

100 200 300 4000

20

40

60

80

100

Wei

ght l

oss

(%)

Temperature (C)

a: 0% b: 3% c: 5% d: 7%

a

b

dc

Fig. 4. TGA thermograms of CTS-PBuA and CTS-PBuA

nanocomposites with the different OMMT contents.in E0, and in fact the E0 decreased below the glass

transition temperature of PBuA. A similar phenomenon

was also observed in the tensile testing results (Table 1).

This may be explained as follows: the introduction of

OMMT can form many cross-linking points which

strengthen the interaction of the MMT and PBuA;

when the concentration of OMMT is higher, some

MMT forms clusters in the composites and these clusters

may act as stress concentrating points resulting in a

decrease in E0.

The loss tangent tan y for these nanocomposites isshown in Fig. 6. CTS-PBuA shows a narrow peak

around 50C and a broad peak at 100C. The formerpeak corresponds to the glass transition temperature

(Tg) of PBuA. The second peak may be due to some

transition of chitosan. With the increase of OMMT

concentration, two peaks of CTS-PBuA nanocomposites

-50 0 50 100 150 2000

200

400

600

800

1000

E' (m

Pa)

a: 0% b: 3% c: 5% d: 7%

b

ad

c

Temperature (C)Fig. 5. The trend of the storage modulus E0 of CTS-PBuA

and CTS-PBuA nanocomposites with the different OMMT

contents.

ARTICLE IN PRESSL. Yu et al. / Radiation Physics and Chemistry 69 (2004) 467471 471Table 1

Tensile testing of CTS-PBuA nanocomposites

OMMT conc (wt%) 0 3 5 7

Tensile strength (mPa) 3.09 3.91 2.89 2.33

Elongation at break (%) 36 39 33 30

Tensile modulus (25C) (mPa) 103 146 97 80

-50 0 50 100 150 200

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

tan

a: 0% b: 3% c: 5% d: 7%

a

d

c b

b c

d

a

Temperature (C)are shifted to higher temperature, compared to CTS-

PBuA. The Tg of PBuA in the nanocomposite with

7wt% OMMT is about 10C more than that in the pure

CTS-PBuA. It means the interaction between the MMT

and PBuA limits the segmental movement of the PBuA.

We do not at present understand the origin of the second

peak, but according to the result of a previous report

(Ratto et al., 1996), it may be due to the signicant

rearrangement of bond structure taking place within the

acetamide and amine bond regions of chitosan. The

introduction of OMMT may inhibit the rearrangement

of bond structure. Hence, the transition temperature of

chitosan is increased.

3.6. Water absorption studies

Table 2 shows the percentage of water absorption for

the CTS-PBuA nanocomposites. It shows an decreasing

trend of water absorption percentage with the increase

of OMMT concentration. This is probably because that

OMMT can form large numbers of cross-linking points

which results in a crosslinking network structure. As a

consequence the water absorption is reduced.

Chitosan and modied chitosan membranes I. Preparation

ization. J. Appl. Polym. Sci. 86, 30473056.

Fig. 6. The tan y vs. temperature of CTS-PBuA and CTS-PBuA nanocomposites with the different OMMT contents.

Table 2

Water absorption of CTS-PBuA nanocomposites

OMMT conc. (w%) 0 3 5 7

Water absorption (%) 24 h 133.2 82.2 80.5 75.6Ratto, J.A., Chen, C.C., Blumstein, R.B., 1996. Phase behavior

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N,N0-dimethylaminoethylmethacrylate onto chitosan lms.

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Sun, T., Garces, J.M., 2002. High-performance polypropylene-

clay nanocomposites by in situ polymerization with

metallocene/clay catalysts. Adv. Mater. 14, 128130.

Usuki, A., Tukigase, A., Kato, M., 2002. Preparation and

properties of EPDMclay hybrids. Polymer 43, 21852189.

Wu, J.H., Lerner, M.M., 1993. Structural, thermal, and

electrical characterization of layered nanocomposites de-

rived from Na-montmorillonite and polyethers. Chem.

Mater. 5, 835838.

Yao, K.J., Song, M., Hourston, D.J., Luo, D.Z., 2002.

Polymer/layered clay nanocomposites: 2 polyurethane

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Yazdani-Pedram, M., Lagos, A., Retuert, P.J., 2002. Study of

the effect of reaction variables on grafting of polyacryla-

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El-Tahlawy, K., Hudson, S.M., 2001. Graft copolymerization

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Polym. Sci. 82, 683702.

Hsu, S.C., Don, T.M., Chiu, W.Y., 2002. Synthesis of chitosan-

modied poly(methyl methacrylate) by emulsion polymer-4. Conclusion

A new hybrid nanocomposite was prepared by graft

copolymerization of butyl acrylate onto chitosan in

acetic acid aqueous solution containing OMMT and

direct casting of the resulting emulsions into lms. XRD

shows that the layers of MMT are intercalated and

orderly dispersed in this nanocomposite. The nanocom-

posites exhibit an enhancement of the storage

modulus and the glass transmission temperature. Rela-

tively small amounts of OMMT (3wt%) can provide

composites with substantial improvements in mechan-

ical and thermal properties, and resistance to water

absorption. Because synthesis and molding methods are

environmentally benign and simple, these nanocompo-

sites may have many potential applications in industry

and agriculture such as packaging lms and seed

coating.

Acknowledgements

Thanks for the nancial support by the National

Natural Science Foundation of China (20274044).

References

Blair, H.S., Guthrie, J., Law, T., Turkington, P., 1987.

A new hybrid nanocomposite prepared by graft copolymerization of butyl acrylate onto chitosan in the presence of organophilic mIntroductionExperimentalMaterialsPreparation of OMMTPreparation of nanocompositesPercentage of graftingCharacterization of nanocompositesWater absorption measurements

Results and discussionCharacterization of the Na+- MMT and OMMTXRD of nanocompositesInfluence of OMMT on monomer conversion and grafting percentageThermal propertiesDMTA and static tensile testing of nanocompositesWater absorption studies

ConclusionAcknowledgementsReferences