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Carbohydrate Polymers 87 (2012) 19891993

Contents lists available at SciVerse ScienceDirect

Carbohydrate Polymers

journa l homepage: www.e lsev ier .com/locate /carbpol

Biodegradable starch based nanocompositeswith low water vapor permeabilityand high storage modulus

Luca Fam a,b,c,d, PiedadGanan Rojo e, Celina Bernalc,d, Silvia Goyanesa,b,

a LP&MC,Dep. de Fsica, Facultad de Ciencias Exactas y Naturales, Universidad de BuenosAires, Ciudad Universitaria, 1428 Ciudad Autnomade Buenos Aires, Argentinab IFIBA (CONICET), Argentinac Grupo deMateriales Avanzados, INTECIN(UBA-CONICET), Departamento de IngenieraMecnica, Facultad de Ingeniera, Universidad de BuenosAires, Paseo Coln 850, C1063ACV,

CiudadAutnomade BuenosAires, Argentinad Consejo Nacional de Investigaciones Cientficas y Tecnolgicas (CONICET), Argentinae Grupo de Nuevos Materiales, Facultad de Ingeniera Qumica, Escuela de Ingenieras, Universidad Pontificia Bolivariana, Circular 1, No 70-01Medelln, Colombia

a r t i c l e i n f o

Article history:

Received4 August 2011

Received in revised form

16 September 2011

Accepted 3 October 2011

Available online 8 October 2011

Keywords:

Starch-MWCNTsnanocomposites

Starchiodinecomplex

Dynamicmechanicalproperties

Water vapor permeability

a b s t r a c t

Nanocomposite materials based on a starchmatrix reinforced with very small amounts ofmulti-walled

carbon nanotubes (MWCNTs) (from 0.005wt% to 0.055wt%) were developed. The materials dynamic-

mechanical and water vapor permeability properties were investigated. An increasing trend ofstorage

modulus(E) anda decreasing trendofwatervaporpermeability(WVP) with fillercontentwereobserved

at room temperature.For the composite with 0.055wt%offiller,E valuewasabout 100%higherandWVP

valuewasalmost 43%lowerthan thecorrespondingmatrixvalues.MWCNTswerewrappedin anaqueous

solution ofa starchiodine complex before their incorporation into the matrix, obtaining exceptionally

well-dispersed nanotubes and optimizing interfacial adhesion. This excellent filler dispersion leads to

the development ofan important contact surface area with the matrix material, producing remarkable

changes in the starch-rich phase glass transition temperature even in composites with very low filler

contents. This transition is shifted towards higher temperatures with increasing content ofnanotubes.

So at room temperature, some composites are in the rubber zone while others, in the transition zone.

Therefore, this change in the material glass transition temperature can be taken as responsible for the

important improvements obtained in the composites WVP and E values for carbon nanotubes content

as low as 0.05wt%. 2011 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, current industries have shown an increas-

ing interest in replacing non-degradable materials by renewable

source-based environmental-friendly ones, without impairing

their properties. In particular, the Biomedical Industry has beenfocused in the development ofnanocomposites with appropriate

characteristics for their use as sensors or stimulators ofbone cells

(Harrison & Atala, 2007; Tsai et al., 2007; Wu and Liao, 2007).

Starch appears as an excellent alternative to synthetic materi-

als because it is abundant, renewable, low cost and biodegradable

(Bertuzzi, Armada, & Gottifredi, 2007; Gonera & Cornillon, 2002;

Talja, Heln, Roos, & Jouppila, 2007). Its properties allow starch

to behave as an excellent polymer matrix for biodegradable

Corresponding author at: Departamento de Fsica, FCEyN, UBA,Ciudad

Universitaria (1428), Ciudad Autnoma de Buenos Aires, Argentina.

Tel.: +54 11 45763300x255; fax: +5411 45763357.

E-mail address: goyanes@df.uba.ar(S. Goyanes).

films-forming (Fam, Rojas, Goyanes, & Gerschenson, 2005; Fam,

Flores, Gerschenson, & Goyanes, 2006; Fam et al., 2007, 2011;

Flores, Fam, Rojas, Goyanes, & Gerschenson, 2007; Garca, Ribba,

Dufresne, Aranguren, & Goyanes, 2009).

On the other hand, due to the extraordinary mechanical, elec-

trical and thermal properties of carbon nanotubes (De Azeredo,2009; Matayabas & Turner, 2000; Matayabas et al., 2000; Sung

et al., 2005), considerable effort has been focused in their use

as reinforcements or sensors (Harrison & Atala, 2007). The main

advantage of nanotubes over nanoparticles is their high aspect

ratio which allows achieving percolation with very low amounts

offiller. This fact makes their main disadvantage: the price, not a

drawback. From the biomedical point ofview, it has been shown

that nanotubesembedded in a biodegradablematrix canstimulate

bone formation (Harrison & Atala, 2007) and also have the abil-

ity togenerate a structuralreinforcement.Besidesbiomedicine, the

packaging industry is also a tempting industry for the use ofcom-

positesbasedon starch andnanofillers.However, theuse ofcarbon

nanotubes as reinforcement could serve as secondary packagingapplication, not applicable directly to food.

0144-8617/$ seefrontmatter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.carbpol.2011.10.007

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1990 L. Fam et al. / Carbohydrate Polymers 87 (2012) 19891993

The addition ofMWCNTs can modify the mechanical proper-

ties ofthe composite, depending on the adhesion between fillerandmatrix (Ajayan& Zhou, 2001; Suhr, Zhang,Ajayan, & Koratkar,

2006). Furthermore, the incorporation ofcarbon nanotubes to the

polymermatrix alsoaffectsroughnessand consequently, themate-

rial wear properties.

So far, nomajor effects have achieved with the addition oflow

contents ofcarbon nanotubes since they tend to aggregate, being

very difficult to separate them and thus to have a highsurface area

with very low amounts offiller.The effective utilization of composite materials strongly

depends on the homogeneous dispersion ofthe filler throughout

thepolymermatrixandthe adequate interfacial adhesionbetween

phases (Zilli et al., 2007). A few years ago, Star, Steuerman, Heath,

andStoddart (2002) showed thatan effective techniquetodispersecarbon nanotubes in an aqueous system was to wrap their sur-

faces by an aqueous solution ofa starchiodine complex. In this

way, their desirablepropertieswere preserved and their solubility

was improved. This technique is ideal for introducing the filler in

a starch-based matrix since; in addition to ensure a good disper-

sion, it is highly possible to obtain excellent interfacial adhesion

because the samematerial is used as the matrix and for wrapping

the nanotubes.

A few papers about starchcarbon nanotubes composites have

been reported in the literature (Cao, Chen, Chang, & Huneault,

2007; Ma, Jian, Chang,& Yu, 2008; Ma, Yu, &Wang,2008; Zhanjun,

Lei, Minnan, & Jiugao, 2011) but there, the nanotubes were non-

covalent functionalized. Recently, Fam et al. (2011) have shownthat the method proposed by Star et al. (2002) is very effective

to disperse low contents offiller in the matrix, leading to simul-

taneous improvements in tensile strength, elongationat break and

toughness.However,to ourknowledge,therehavenotbeenalready

reported studies about the mechanical relaxations and theperme-

ability ofstarch based composites reinforced with small amounts

ofcarbon nanotubes.

The aimofthis researchwasto determinetheeffectofthe incor-

porationofvery small fractions ofMWCNTs (

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L. Fam et al./ CarbohydratePolymers87 (2012) 19891993 1991

Fig. 1. Typical macroscopic imagines of the composites with 0.005wt% offiller:

pristinenanotubes(a) andcarbonnanotubespreviouslywrappedby a starchiodinecomplex (b).

Fig. 2. FE-SEMmicrographs ofthe cryogenic fracture surface ofthe matrix (a) and

the nanocomposites with0.027wt%(b) and 0.055wt%(c) ofwMWCNTs (5000).

-100 -80 -60 -40 -20 200 40 600.05

0.10

0.15

0.20

0.25

0.30

(e)(d)

(c)

(b)

(a)

f(wt %)

(a) 0(b) 0.005

(c) 0.010

(d) 0.027

(e) 0.055

Tan

Temperature (C)

Fig. 3. Loss tangent, Tan, as a function oftemperature for the different nanocom-

posites investigated.

the glycerolplasticized starch: the glycerol-rich phase at around

60 C and the starch-rich phase between 0 C and 20 C. These

values agree well with those previously reported in the litera-

ture (Averous & Bouquillon, 2004; Cao et al., 2007; Fam et al.,

2005, 2006; Fam, Gerschenson, & Goyanes, 2009; Garca et al.,

2009; Ma, Yu, et al., 2008; Teixeira et al., 2009). The lower tem-perature peak did not change with filler addition suggesting that

carbon nanotubes did not modify the distribution ofthe glycerol

in the matrix. Nevertheless, the width ofthis peak decreasedwith

the incorporation ofa small amount ofwMWCNTs, indicating that

some restriction in the number ofrelaxation mechanisms existed

in our composites. On the other hand, the upper transition peak

broadened and was shifted to higher temperatures (the wrapped

fillerwouldhavebeen interactingwith thestarchbutnotwithglyc-

erol). Besides, the peak intensity diminished with the increase in

wMWCNTs content. The observed behavior can be attributed to

the higher surface area promoted by the incorporation ofthe nan-otubes and the very good adhesion between the matrix and the

wrapped filler. During the glass transition temperature, the long-range polymer chain acquires mobility and therefore dissipates a

great amount ofenergy through viscous movement. This is shown

by the loss tangent peak in a dynamic-mechanical test. Hence, a

depression in loss tangent values indicates the reduction of the

number ofmobile chainsduringthe glass transition(Rao& Pochan,

2007). Inour case, intermolecular interactions between starch and

wMWCNTs, reduce themolecularmobility ofthe starch in contact

with the carbon nanotubes surface (Ma, Jian, et al., 2008; Ma, Yu,

et al., 2008) and therefore, decreased Tan values and increased

relaxationpeak temperature valueswere observed. It is also inter-

esting to note, that even such a low content offiller as 0.055wt%

ofwell-dispersed nanotubes (approximately 1m in length and

35nm in diameter) generates a surface area ofabout 90m2/g. Theobservedchanges in therelaxationtemperaturepeakfrom0 C for

the matrix to40 C for thecompositewith the highest nanotubes

content had important implications in the materials behavior at

room temperature. While at 20 C, the matrix and some compos-

ites were in the rubbery state, other composites were around their

glassyrubbery transition zone.

The addition ofcarbon nanotubes also modified storage mod-

ulus versus temperature curves (Fig. 4). As expected, at the lower

transition range (60 C) there were no significant changes in E

curveswith filler content, whereas the upper transition exhibited

a shift in E curves to higher temperatures with the increase in

carbon nanotubes content. In addition, an increment in E values

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L. Fam et al./ CarbohydratePolymers87 (2012) 19891993 1993

temperature. The matrix material has it glassyrubbery transition

around0 C (below roomtemperature) whereas the Tgofthe com-positewith0.05wt% ofMWCNTs is around 40 C.Then, at 20 C the

matrix is in the rubber state,while the compositewith the highest

fillercontent is in the transitionstate.Theresults ofthis study show

that the addition ofan extremely small amount ofnanotubes can

lead tomajor changes in the material behavior ifthe MWCNTs are

well dispersedandthematrixmaterial has itsmainrelaxationnear

room temperature.

Acknowledgements

The authors want to thank the National Research Council of

Argentina (CONICETPIP 20102012 Project 11220090100699), the

University of Buenos Aires (UBACYT X094 20082011, UBACYT

20102012 Project 20020090300055, UBACYT 20112014 Project

20020100100350), andMINCYT/COLCIENCIA (CO/08/09) forfinan-

cial support ofthis investigation.

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