Characterization of Starchpoly(Vinyl Alcohol)Clay Nanocomposite f

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Original Article

Characterization ofstarch/poly(vinyl alcohol)/clay nanocomposite filmsprepared in twin-screwextruder for foodpackaging application

Amir H Navarchian, Mehdi Jalalian andMajid Pirooz

Abstract

Starch/poly(vinyl alcohol)/montmorillonite (MMT) nanocomposites were pre-

pared in a twin-screw extruder for food packaging film application. In order to

obtain a better compatibility between starch and silicate layers, MMT modification

was performed using citric acid. X-ray diffraction (XRD) analysis was used to

characterize the expanded microstructure of citric acid-modified MMT

(CMMT). The effects of some compositional and operational factors including

poly(vinyl alcohol) content, CMMT content, screw speed, and temperature profile

in the extruder, on the tensile strength parameter of resulted films were investi-

gated by using Taguchi experimental design. It was found that PVA content, CMMT

percentage and screw speed were the most important factors, respectively, affect-

ing the tensile strength property; while the temperature profile was insignificant

factor, in the range of examined levels. The best levels of examined factors that

could lead to the maximum tensile strength were obtained. The optimum sample

was further characterized by XRD, transmission electron microscopy (TEM),

Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), water

uptake, biodegradability, oxygen permeability, and overall migration test.

Department of Chemical Engineering, Faculty of Engineering, University of Isfahan, Isfahan, Islamic

Republic of Iran

Corresponding author:

Amir H Navarchian, Department of Chemical Engineering, Faculty of Engineering, University of Isfahan,

P.O. Box 81746-73441 Isfahan, Islamic Republic of Iran.

Email: [email protected]

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Keywords

Nanocomposite, starch, poly(vinyl alcohol), clay, packaging film

Introduction

Synthetic polymers have long been utilized for packaging applications. Their

synthesis involves production of hazardous waste and the products made by

these plastics are not easily degradable, causing environmental problems.1

Therefore, the biodegradable materials, derived from renewable resources,

have been carried into the center of public interest for environmental protec-

tion and sustainable development.2 Biodegradable polymers have become

important materials tailored to new environmental friendly products, espe-

cially in the packaging industry.3

Starch is a natural polymer that is known to be completely biodegradable

in soil and water.4 In the food packaging sector, starch-based material has

received great attention owing to its biodegradability, wide availability, and

low cost.5 It is produced in plants and is mainly a mixture of linear amylose

(poly-a-1,4-D-glucopyranoside) and branched amylopectin (poly-a-1,4-D-glu-copyranoside and a-1,6-D-glucopyranoside). The ratio of amylose to amylo-pectin varies with the starch source. Amylose is the minor component

(approximately 20%) of the starch and forms the amorphous regions,

whereas the short branching chains of the amylopectin are predominantly

responsible for crystalline properties of the starch due to its helical form

that can be packed together.6,7 This crystalline property of amylopectin

leads to its poor process capability, and therefore plasticizers are often intro-

duced to make the starch ow when processed.

Thermoplastic starch (TPS) or plasticized starch is obtained after disrup-

tion and plasticization of native starch macromolecules, by temperature and

in presence of water and/or another plasticizer, such as glycerol. However, the

TPS has some limitations: it is mostly water-soluble and has low mechanical

strength.8 These properties may be improved by adding certain synthetic

polymers, inorganic materials, or lignin (Table 1). Poly(vinyl alcohol)

(PVA), has been used previously in TPS to improve properties such as elong-

ation, reduce brittleness, and facilitate processability.9 On the other hand,

with development of nanotechnology, polymer/layered silicate (PLS) nano-

composites have attracted great attention because of their remarkably

improved mechanical, thermal, and barrier properties compared with the ori-

ginal polymers. Montmorillonite (MMT), as an environmentally-friendly

layered silicate, has been successfully used to prepare TPS/clay composites

by melt intercalation. Experimental results have already revealed that MMT

can be dispersed in the TPS matrix and the TPS/clay composites exhibited

2 Journal of Plastic Film & Sheeting 0(0)



higher tensile strength, thermal stability, and moisture barrier properties than

TPS itself.10 Our previous work proved that citric acid-modied montmoril-

lonite (CMMT) clay represented even better mechanical properties in com-

parison with MMT in the starch. The interactions between citric acid and

starch chains were responsible for this improvement.4

TPS and TPS/clay lms can be made by various techniques such as solu-

tion casting and thermoplastic extrusion processing. Compared with solution

casting, thermoplastic extrusion is a green and facile process.11 Melt extru-

sion is an attractive route for cost eective polymer processing, which

enhances the commercial viability and cost-competitiveness of these mater-

ials.12 Various compositional factors and processing parameters may inu-

ence the nal properties of TPS-based packaging lms. Many authors have

investigated just the eects of material composition including clay and/or

PVA content8,9,1316 on physical and mechanical properties of these lms.

There are also some limited reports available on the eects of processing

conditions such as screw speed and extruder temperature prole.1720

Although there are many papers recently published on the starch-based

nanocomposite lms as shown in Table 1, there are few reports that apply

experimental design to analyze the eects of both material and process par-

ameters on the physical and mechanical properties of starch/clay nanocom-

posites produced in extruder.

In this study, the inuence of clay content, PVA percentage, screw speed,

and temperature prole on the tensile stress of starch/PVA/clay nanocompo-

site lms prepared in a twin-screw extruder (followed by thermo-pressing) has

been statistically investigated by using a Taguchi experimental design

approach. The optimum conditions to attain the maximum tensile stress

have been obtained for above factors and the optimum sample has been

characterized by X-ray diraction (XRD), transmission electron microscopy

(TEM), Fourier transform infrared (FTIR), and thermogravimetric analysis

(TGA). The water absorption, oxygen permeability, biodegradability, and

overall migrated materials of the lms were also examined.

Navarchian et al. 3



Table

1.Summaryofsomerecentworksonstarch-basednanocomposite

films.

Ref.

Secondpolymer

Fillertypeandcontent

Film

preparation

method

Investigatedfactors

13

MMT

Meltextrusionintw

in-

screw

extruder

Watercontent

Claycontent

PVAcontent

Claycontent

21

Beta

Zeolite

Na-Beidellite

(1%,2%,4%)

Solutioncasting

Fillertype

Fillercontent

22

Naturalrubber(0%,10%

and20%)

MMT

(0%,3%,6%)

Meltextrusionintw

in-

screw

extruder

Naturalrubbertype

Fillercontent

Glycerolcontent

Naturalrubbercontent

23

Carboxym

ethylcellulose

(10%)

MMT

(0%,1%,3%,5%,7%)

Solutioncasting

Fillercontent

24

PVA

(0%,40%,50%,60%,

100%)

Nano-TiO

2

(0%,2.5%,5%)

Solutioncasting

PVAcontent

Fillercontent

25

MMT

(0%,2.5%,5%)

Solutioncasting

Fillercontent

26

PVA

(40%)

Nano-TiO

2

(0.5%,1%,2%)

Solutioncasting

Fillercontent

27

Talc

(0%,1.7%,5.2%,8.7%)

Compressionmolding

Fillercontent

(continued)




Table

1.Continued

Ref.

Secondpolymer

Fillertypeandcontent

Film

preparation

method

Investigatedfactors

28

MMT

(0%,1%,3%,5%,7%,10%)

Solutioncasting

Fillercontent

Film

preparation

methodology

29

MMT

OMMT(C

loisite30B)

(3%,5%)

Extrusion/therm

o-

pressing

Fillertype

30

Poly(lacticacid)

(58%)

MMT

(2%,4%,6%,8%)

Extrusion/therm

o-

pressing

Fillercontent

31

PVA

(0%,10%,30%)

MMT

(3%,5%)

Therm

o-pressing

Fillercontent

Glycerolcontent

PVAcontent

32

PVA

(20%,33%,50%,67%,

80%)

MMT

(0,5,10,15,20)

Solutioncasting

PVAcontent

Fillercontent

PVAtype

Navarchian et al. 5



Experimental

Material

Cornstarch with 28% amylose and 10.1% moisture was obtained from

Glucozan Ghazvin Company (Ghazvin, Iran). PVA with molecular weight

of 145,000 g/mol, 98% hydrolyzed and 1.3 g/cm3 density was supplied by

Merck (KGaA, Darmstadt, Germany). Sulfuric acid (98% w/w), citric acid

(C6H8O7) with 1.665 g/cm3 density, and glycerol (about 87% purity) were also

obtained from the same company. Cloisite Na (MMT) as untreated MMTwas purchased from Southern Clay Products (USA).

Design of experiments

The Taguchi experimental design approach was used as an eective technique

to reduce the number of experiments while retaining quality of data collec-

tion. The rst important step in designing an experiment is the proper selec-

tion of factors and their levels. In this study, the following main factors were

considered each at three levels (Table 2):

. clay content

. PVA content

. screw rotation speed

. extruder temperature prole.The factors and their levels have been selected according to our literature

review on previous publications4,9,17,18,20,3336 and some screening experi-

ments in this work. CMMT and PVA percentages were reported based on

a xed weight of starch. Three extruder temperature proles were used in

order to investigate thermal processing conditions on the extruded compos-

ites. Each temperature prole included four temperature zones from the feed

section to the die exit. The three temperature proles were:

. Low: 8090100110 (C)

. Mid: 90100110120 (C)

. High: 100110120130 (C)For a Taguchi-designed experiment with four factors all in three levels, a

standard L9 orthogonal array was employed as shown in Table 3.36 This

saturated design yields the main eects and is suitable for the experiments

for which it is assumed that there is no signicant interaction among the

selected factors. In order to avoid the systematic bias, the sequence in which

these runs were carried out was randomized.37 The statistical analysis of the

results was carried out using Qualitek-4 (Nutek Inc., USA) software. The

signal-to-noise ratio (S/N) is used as a transformed response in the Taguchi

method to indicate the magnitude of changes in response due to variations




of controlled factors respect to that of errors. In this work, the tensile

properties were used as the response in calculations. In order to maximize

the tensile properties, the following S/N formulation was used:37

S=N 10 log 1=y21 1=y22 1=y2n

n

1

Preparation of modified MMT with citric acid

In order to provide more compatibility between silicate layers and starch

macromolecules, MMT was modied by citric acid according to our previous

work.4 About 5.04 g citric acid (26.25mmol) and 2.4ml sulfuric acid (98%)

Table 3. Designed experiments with coded variables based on the Taguchi method.

Trial no.

Factors

CMMT% PVA% Screw speed Temperature

1 1 1 1 1

2 1 2 2 2

3 1 3 3 3

4 2 1 2 3

5 2 2 3 1

6 2 3 1 2

7 3 1 3 2

8 3 2 1 3

9 3 3 2 1

Table 2. Selected factors and their respective levels.

Factor Unit Level 1 Level 2 Level 3

CMMT content wt.% 3 5 7

PVA content wt.% 0 5 10

Screw speed r/min 12 24 36

Extruder temperature profile C Low Mid High

Navarchian et al. 7



were added subsequently to 700 ml water at 80C in a 1000 cm3 beaker. Thissolution was gradually added to clay suspension containing 20 g MMT in

500ml water. The mixture was stirred at 80C for 3 h, and then cooled toroom temperature. The resulted suspension was subsequently ltered, and the

cake was washed with distilled water and centrifuged for 30min. The modied

clays were dried at 60C for 24 h, and nally ground into a ne powder. TheCMMT was obtained after screening.4,14

Preparation of TPS/PVA/clay nanocomposite films

Dried CMMT was dispersed in distilled water (with CMMT/water:1/5 weight

ratio) at room temperature by subsequent mechanical and ultrasonic mixing,

each for 1 h. Specied amount of cornstarch, PVA, and glycerol were com-

pletely premixed and then added to clay dispersion. The mixture was heated

at 80C for 30min with continuous stirring to gelatinize the starch granulesand then was retained in the tightly sealed plastic bags for 24 h to swell the

granular cornstarch molecules. In all experiments, the amount of glycerol was

constant at 30% of starch weight.

In the next step, the swollen mixtures were transferred into a 26:1L/D

counter-rotating twin-screw extruder (BPM, Iran) with screw diameter of

46mm. The screw speed and the extruder temperature prole were set at

specied conditions as given in Table 2. The round cross-section extrudate

was cooled and pelletized. Finally, the lms were prepared by hot press mold-

ing at 200C for 2min. The lms thickness was 0.25 0.02mm.

Characterization

X-ray diffraction. XRD analysis was carried out on a BrukerD8-Advance X-ray

diractometer (Bruker, Germany) using CuKa radiation (40 kV, 40mA and

l 0.154 nm). Samples were scanned at 1/min in the range of 2 210.The basal spacing of the silicate layer, d(001), was calculated using Braggs

equation (nl 2d sin ), where is the diraction angle and l is thewavelength.

Tensile strength measurement. Tensile tests were performed according to ASTM

D882-02 by using H25KS tester (Hounseld, England). The crosshead speed

was 50mm/min. Rectangular specimens were conditioned at 50 5% relativehumidity (RH) and 23 2C for one week before testing. Two samples weretested for tensile strength at each run.

Fourier-transformed infrared. FTIR spectra of nanocomposite lms were mea-

sured by Nicolet 400D Impact spectrometer (Nicolet Instrument




Corporation, USA) in the range of 4504000 cm1 and with a resolution of16 cm1.

Transmission electron microscopy. TEM was used to study the nanocomposite

lm morphology. An EM900 microscope model (Zeiss, Jena, Germany),

operating at an accelerating voltage of 80 kV, was used.

Thermogravimetric analysis. TGA of composites (about 10mg) was carried out

using a TG 50-METTLER model TGA instrument (USA) under nitrogen

atmosphere at a heating rate of 10C/min. The scanning temperature wasbetween 25C and 500C.

Water absorption. The samples were cut into small pieces (60 20 0.25mm),put into oven, and dried at 110C for 24 h. Then, they were taken out,weighted, and stored at 75% RH for a period of time and weighted every

day. The water content (K) was calculated from the following equation:

K w2 w1w1

100 2

where

w1 dried sample weight (g)w2 humidified sample weight (g)

Biodegradation. Biodegradation of nanocomposites was studied by soil burial

test under laboratory conditions (average temperature of 25C). Local soilwas enriched with 20wt.% bovine manure. The soil pH was 7.7. Samples were

cut into pieces with 25 25 0.25mm dimensions, weighted (0.20 0.05 g),and buried in separate plastic containers (10 l) lled with soil, previously

passed through a 2mm sieve. Every seven days for a period of 28 days, sam-

ples were cleaned with a smooth brush and weighted. Periodically, the soil

moisture content was measured; an average value of 7wt. % was maintained

during the test. The weight reduction with time was used to evaluate

degradation.

Permeability test. In this study, the constant-volume method is used to measure

oxygen permeability through starch-based nanocomposite lms. This method

is based on pressure measurement at a constant volume when subjecting pres-

sure dierence on the sides of a thin layer. A NM1391 model apparatus

(designed at University of Isfahan, Iran) was used and the tests were carried

out according to ASTM D1434.

Navarchian et al. 9



Overall migration test. Overall migration test was performed according to

Iranian National Standard Test Number 1-13737. Fourteen nanocomposite

specimens (11mm diameter disks) were threaded onto a stainless steel wire

with alternating glass bead spacers and placed in a 23ml glass vial. Vial was

lled with 22ml of water and then was capped and maintained at 40C for 10days. The blank sample was prepared by water poured in a vial (without

sample) containing the support stand with glass bead spacers. Blank vial

was placed in the same temperature-controlled oven. Test result in milligrams

of migrant (s) per square meter of sample exposed, E, was expressed as

follows:

E W B2R2 CTN 3

where

W total weight of migrant (s) in the liquid (mg)B weight of migrant (s) in the blank (mg)R radius of the disk (m)C circumference of disk (m)T thickness of disk (m)N number of disks per cell

Results and discussions

Microstructure of films

The XRD analysis was used to investigate the silicate layer dispersion in the

starch/PVA matrix. Table 4 shows the XRD results for all nanocomposite

lms prepared in accordance with the designed experiment (Table 3). In this

table, the distance between the silicate layers in nanocomposites (dnc) minus

that of intact clay (d0) is shown by d:

d dnc d0 4

According to Majdzadeh et al.,4 the initial distances between the layers (d0)

in MMT and CMMT used in our lab are 1.11 and 1.48 nm, respectively. As

observed in Figure 1, the XRD peak displacement toward the smaller angles

indicates the intercalation morphology for all nine samples. The d values

can be considered as a quantitative criterion for the degree of intercalation of




polymer chains within the silicate layers. In this work, d variation among

various samples is 0.30 0.02 nm, representing a rather similar expansion ofsilicate layer galleries in the polymer matrix for all nanocomposite lms.

The XRD patterns from trial numbers 2, 5, 6, and 7 (as representatives of

dierent values of d) are illustrated in Figure 1.

Table 4. XRD results and tensile strength of the starch/PVA/CMMT nanocomposite

films.

Trial No. 2 () dnc (nm) d (nm)

Tensile strength (MPa)

Replication 1 Replication 1

1 4.98 1.77 0.29 9.7 10.0

2 4.90 1.80 0.32 17.7 17.3

3 5.02 1.76 0.28 9.0 8.7

4 4.94 1.79 0.31 16.7 15.3

5 4.94 1.79 0.31 14.7 16.3

6 5.02 1.76 0.28 10.7 9.3

7 4.98 1.77 0.29 11.3 10.7

8 4.94 1.79 0.31 14.0 12.0

9 4.98 1.77 0.29 10.0 11.7

Figure 1. XRD patterns of some nanocomposite films as illustrations.

Navarchian et al. 11



Tensile strength property

The replicated tensile strength results are given in last columns of Table 4.

This property is usually selected as representative for tensile properties.37

Figure 2 indicates that the average values of tensile strength for nanocompo-

site lms prepared in dierent experimental runs is essentially proportional to

the silicate layer gallery expansion (d) obtained from XRD analysis.

Increasing the silicate layer spacing in nanocomposite lms linearly increases

the tensile strength. A same behavior was also observed by other authors.4

The relation between silicate layer gallery expansion and tensile property is

ascribed to the better contact area between the polymer chains and the silicate

layers for samples with greater d. This conrms the strong dependency of

the mechanical properties to the nanocomposite morphology.

Analysis of variance for mechanical properties

Analysis of variance (ANOVA) is a powerful technique in Taguchi method

that explores the percent contribution of factors aecting the response. The

strategy of ANOVA is to evaluate the variations that each factor cause rela-

tive to the total variation observed in the results.37

In this work, the target is to maximize the tensile strength (or Bigger is

better for this response in Taguchi terminology), as this is the main mech-

anical property for packaging lms. There are several statistical terms in

Figure 2. Correlation between tensile strength (average value for each run) and cor-

responding gallery spacing expansion (d) of nanocomposites.




ANOVA table, among them the F-ratio is the most meaningful one.

As observed, the F-ratio values of some factors are greater than critical

value (9.00), with 90% condence level, indicating the signicance of these

factors on the response. According to ANOVA table, three factors namely

PVA percentage, screw speed, and clay percentage have the highest eects,

respectively, on the tensile strength of nanocomposite lms. The extruder

temperature prole however has a minor eect on the response. As the inu-

ence contribution of this factor is less than 10% of the most important factor

(PVA wt.%), its eect can be pooled in the error term.37

The last column of the ANOVA table represents the percent contribution

of variability resulted from each factor after pooling the insignicant factor

with error term. The other/error term is therefore consisted of the eects of

three sources of variability:

. the uncontrollable factors,

. the pooled factors and/or those that are not considered in the experi-ments, and

. the experimental error.37

In the following, the eects of each factor on the tensile strength are

investigated as shown in some bar charts. Each data on these main eect

graphs is an average of replicated results obtained at each level of the corres-

ponding factor according to Table 3. Thus, each graph is plotted based on 18

(9 2) experimental data. It should be noted that the interpretation ofANOVA information (Table 5) is valid just in the range of examined levels

for the factors. That is why the level selection is very important in any experi-

mental design approach.

Table 5. ANOVA table for tensile strength after pooling the effect of extruder tem-

perature profile with the error term (confidence level of 90%).

Factors DOF

Sum of

squares Variance F-ratio Pure sum

Percent

contribution

CMMT content 2 3.756 1.878 11.842 3.439 9.520

PVA content 2 21.445 10.722 67.609 21.128 58.491

Screw speed 2 10.603 5.301 33.427 10.286 28.476

Extruder temperature

profile

(2) (0.317) Pooled (CI 90%)

Other/error 2 0.316 0.158 3.513

Total 8 36.122 100.000




Effect of PVA content

Figure 3 shows the main-eect plot of PVA content. Tensile strength of

starch/PVA/clay nanocomposite lms increased with added PVA content

from 0% to 5% by weight. The positive eect of PVA percentage in this

range is probably due to the fact that all components in the nanocomposite

lms including starch, PVA, citric acid, and silicate layers have hydroxyl

groups (OH) in their chemical structure. Thus, all components may tend

to form inter-molecular and intra-molecular hydrogen bonds together

which improve the integrity of the lms.38,39

With increasing PVA from 5% to 10% the tensile strength drops. It is

supposed that at higher PVA content, some of the excess PVA macromol-

ecules probably encapsulate the CMMT particles leading to agglomerates

that reduce tensile strength.9

Effect of screw speed

Mixing intensity as a function of screw speed and screw geometry (length and

shape of mixing elements) aects the stress subjected on clay layers and poly-

meric chains. Screw speed is therefore the most important mixing factor in a

twin-screw extruder for delaminating and dispersing clay layers.18

Figure 3. Effect of PVA content on S/N of tensile strength for nanocomposite samples

(the data label on each point is the corresponding actual tensile strength (MPa)).




ANOVA analysis of the results showed that screw speed at its mid-level

(24 r/min) led to the highest tensile strength for the nanocomposite lms

(Figure 4). When the screw speed is very high (say 36 r/min), the stress applied

to nanocomposite increases, while the residence time for material in the extru-

der decreases. In other words, there is not enough time for macromolecules to

migrate into the silicate layers. On the other hand, if the screw speed is very

low (12 r/min), materials suer lower stress which cannot force polymer into

clay galleries and as result cannot lead to well-intercalated morphology with

increased mechanical strength. Therefore, there will be an optimum point for

screw rotational velocity. The stressstrain behaviors of some nanocomposite

lms are illustrated in Figure 5.

Effect of clay content

Addition of a proper amount of clay to TPS increases the tensile strength of

resulted lms. This could be justied by structural reasons such as:

. the homogeneous dispersion of silicate layers with very high Youngmodulus (170GPa8) in the starch matrix,

Figure 4. Effect of screw speed on S/N of tensile strength for nanocomposite samples

(the data label on each point is the corresponding actual tensile strength (MPa)).




. the strong interactions (typically by hydrogen bonding) between thenanoller and matrix, and

. the high aspect (width-to-thickness) ratio and thus the vast exposedsurface of the nanoller.40

According to main-eect plot of clay content (Figure 6), clay content at its

mid-level (5wt.%) provides the highest tensile strength. In other words, there

is an optimum level for the clay content. A higher CMMT content might

contribute to aggregates and CMMT stacks in a starch matrix and also to

lower starch phase plasticization.11,40,41

Figure 5. Stressstrain curves of some illustrated nanocomposite films.




Optimum conditions

The optimum conditions to attain a starch/PVA/clay nanocomposite with

maximum tensile strength can be determined from maximum points in

main-eect plots (Figures 3, 4, 6). The nanocomposite with optimum proper-

ties is therefore obtained with 5% by weight CMMT, 5% by weight PVA, and

at 24 r/min screw speed for the current extruder. Since the extruder tempera-

ture prole was found to be an insignicant factor, it can be xed arbitrarily

for example on its mid-level. Applying the optimum condition, the contribu-

tion of each factor on improvement of response above the current grand

average of results can be found using Taguchi approach.36

CMMT content: 1.11MPa (0.913 in S/N unit),

PVA content: 1.25MPa (1.936 in S/N unit),

screw rotation speed: 1.19MPa (1.506 in S/N unit), and

extruder temperature prole: 1.02MPa (0.196 in S/N unit).

The expected result (tensile strength) at optimum condition is therefore

predicted to be about 20.02MPa (26.029 in S/N unit). This result is the

Figure 6. Effect of CMMT content on S/N of tensile strength for nanocomposite sam-

ples (the data label on each point is the corresponding actual tensile strength (MPa)).




sum of factor contributions plus the average value, that shows even 24.3%

improvement in tensile strength over the best result (i.e. run #2) in Table 4.

Characterization of nanocomposite film

Chemical structure. Figure 7 shows the FTIR spectra for CMMT, starch, TPS,

and optimum nanocomposite lm. One can see that the characteristic OH

stretching peak for hydroxyl groups in the starch at 3389 cm1 shifts to3328 cm1 for the TPS. Primary hydroxyl inter-molecular and intra-molecularinteractions in starch are weakened due to new strong hydrogen bond forma-

tion between starch and glycerol.13 In other words, glycerol is able to create a

more stable hydrogen bond with hydroxyl groups, which decreases the fre-

quency of stretching in corresponding OH bond in the TPS.4

Formation of nanocomposite shifts the peak of OH group in TPS to lower

wavenumbers even more (3308 cm1) which indicates formation of strongbonds among PVA, silicate layers, and starch. Tensile properties enhance-

ment of samples containing optimum amount of PVA and CMMT can be

ascribed to disruption of the crystallites by breaking inter-molecular hydrogen

bonds in starch molecules themselves and formation of new hydrogen bonds

between PVA, CMMT, and starch molecules.9




Figure 7. FTIR spectra of (a) CMMT, (b) starch, (c) TPS, and (d) optimum nanocompo-

site film.




Morphology. Figure 8 indicates the XRD pattern of nanocomposite lm pre-

pared at optimum condition. The peak position for this sample is slightly

shifted to the left showing a d-spacing of 1.88 nm (d 0.4 nm). Thus, theXRD result represents an intercalated morphology for the optimum sample.

Generally, TEM is combined with XRD to arm the nanocomposite

microstructure. Figure 9 shows the TEM micrographs of optimum starch/

PVA/CMMT nanocomposite lm. As seen, most of the CMMT layers are

dispersed throughout the polymer matrix. It is very interesting that in this

image some exfoliation is also observed. The intercalation morphology is

however more cautioning remark as it corresponds better with XRD results.

The mechanism of this dispersion level can most probably be suggested by

the CMMT compatibility with starch and PVA chains. Citric acid in MMT

gallery space can make desirable hydrogen binding and, accordingly, it can

improve the intercalation of polymer chains within the gallery. This micro-

graph also justies the good mechanical behaviors of optimum nanocompo-

site lms, as the silicate layers can play the role of reinforcing action into the

matrix.4

Figure 8. XRD pattern of optimum sample.




Water absorption. Low water uptake property is an important parameter for a

packaging lm as it aects the food conservation. Figure 10 shows the water

uptake behavior of some nanocomposite lms including the optimum.

Comparing samples made in runs 1, 4, and 7 and looking at their correspond-

ing preparation conditions (Table 3), one can understand that all have no

PVA content, but with dierent clay content (3%, 5% and 10%, respectively)

as well as mixing extent (12, 24 and 36 r/min, respectively). The water uptake

decreases with simultaneous increasing of both CMMT content and screw

speed. Generally, this means that the eect of silicate layers content with

better distribution throughout the matrix (most probably due to the higher

r/min) should be important for reducing water absorption. Increasing the clay

percentage decreases the water absorption as a result of:

. introducing tortuous and thus longer pathways through the matrix forthe diusion of water molecules and

. strong interactions between the polymer matrix and clay silicate layerinterface that decrease the tendency of the polymer chains hydroxyl

groups to interact with water.15,40,42,43

On the other hand, as observed from these curves, in the initial testing

days, the water absorption rate is higher than those in the later days due to

driving force reduction.

Figure 9. TEM micrograph of optimum sample.




A comparison between samples 9 and 7 indicates that PVA content is a

signicant factor also for water uptake. Increasing the PVA percentage

decreases water absorption which is probably due to lower sensitivity of

PVA to humidity than starch and/or better distribution of clay layers in

presence of PVA. Furthermore, hydroxyl groups in PVA react most probably

with starch which decreases free hydroxyl groups in the resulted nanocompo-

site to create hydrogen bonds with water and moisture absorption.42

As mentioned, for a food packaging application, a lower water uptake is

desired for starch-based nanocomposite lms. The water uptake curve of

sample prepared at optimum condition (the best tensile property) is the

lowest one among the examined samples. This sample was prepared at mid-

levels of all factors and so it is implied from the experimental design point of

view, that the factors have probably synergetic and compatible interactions

for water absorption so that their setting at mid-levels results in a compara-

tively lower water uptake.

Thermogravimetric analysis. It is important to investigate the thermal behavior

of food packaging lm, as it is exposed to heat when food is warmed up inside

the package by a microwave or other devices.44

TGA and dynamic task graphs of optimum nanocomposite lm are shown

in Figure 11. Three weight losses are obvious on the thermograph. The rst

one occurs between 50C and 130C, most possibly corresponding to waterloss; the second one is observed between 110C and 210C due to plasticizer(glycerol) volatilization; and the third one around 300C is ascribed to the

Figure 10. Water absorption behavior of some illustrated nanocomposite films and the

optimum one.




starch decomposition. The decomposition mechanism begins with hydroxyl

groups eliminating accompanied by depolymerization, decomposition, and

nally carbon production.45

It should be noted that the maximum temperature used in our extrusion

experiments performed in this study was about 130C. For starch/clay/PVAsystem, the maximum increase in temperature due to the viscous dissipation is

about 46C.46 This means that there is no possibility for degradation ofcomponents during the extrusion process.

Figure 11. Thermo gravimetric curves of nanocomposite prepared at optimum

condition.




Biodegradation. Gradual variation in the color, thickness, surface roughness,

and increasing erosion indicates the progress of degradation.36 Figure 12

shows the biodegradation progress for nanocomposite lm prepared at opti-

mum condition. The photos include the sample at:

. initial state (a),

. after 14 days (b), and

. after one month (c).Figure 13 plots the weight loss (Wt/W0 100) for optimum sample versus

time (in days). Sample decomposition rate is low initially due to adaption of

the microorganism population to the new polymeric environment.36 During

surface erosion, a-amylase molecules agglomerate and scission of a (1-4) glu-cose units occurs, while in the second stage bulk diusion takes place, causing

complete decomposition.47

Figure 12. Photographs for nanocomposite films; before soil burial (a); after soil burial

for 14 days (b), and for 30 days (c).




Permeability test. One of the most important characteristics of a food packa-

ging lm is its barrier property against oxygen. Table 6 illustrates the oxygen

permeability values for sample 6 and for the optimal one. These two samples

contain same amounts of CMMT. The optimum sample however contains

silicate layers with slightly greater gallery distance (1.88 nm vs. 1.76 nm) and

therefore has probably better clay dispersion than sample 6. The optimum

sample has a lower diusivity and better barrier against oxygen molecules,

though the clay content is the same. The dierence can be ascribed to the

more intercalated microstructure that leads to more tortuous and longer dif-

fusion pathways for oxygen molecules.40

Overall migration test. The total amount of migrated species from packaging

lms into the food is vital for preventing any hygienic problem. The migration

test showed that the average overall migration of components in the starch

nanocomposite lm into the water was 6.417mg/dm2. According to Iranian

National Standard Test Number 1-13737, the total migration of a food

packaging lm should not exceed 10mg/dm2. Thus the optimum nanocom-

posite sample has appropriate migration value as a food packaging lm. The

migrant materials most probably contain starch molecules, PVA, glycerol and

clay. The barrier properties of clay layers and the tortuous pathway for

migrant to exit from lm decelerate this migration process. Furthermore,

hydrogen bonds between nanocomposite components prevent them to be

released into the solution and result in a low migration value.42

Figure 13. Weight loss versus time for optimum nanocomposite film.




Conclusions

Plasticized starch/PVA/clay nanocomposites were prepared by melt extrusion

and the inuences of various factors on the microstructure, mechanical, and

physical properties of these nanocomposites were statistically analyzed using

a Taguchi experimental approach. The main conclusions in the range of con-

sidered levels can be listed as follows:

. The tensile strength is strongly inuenced by PVA content, screwspeed, and clay content. The temperature prole (in the range of exam-

ined levels in this study) was found to be an insignicant factor for

tensile property improvement.

. The optimum conditions for prepared starch/PVA/clay nanocompo-sites were obtained as follow: screw speed and temperature prole in

their mid-levels, PVA and clay content were 5wt. % for both.

. The optimum sample indicated an intercalated/exfoliated morphologywith very low water uptake and oxygen permeability, sucient thermal

stability, and excellent biodegradability. The lms also passed the

migration test. This means that the starch/PVA/clay nanocomposites

have potential to be used as food packaging lm.

Conflict of interest

None declared.

Funding

This work was nancially supported by Iranian Nanotechnology Initiative.

References

1. Chung Y-L, Ansari S, Estevez L, et al. Preparation and properties of biodegradable

starchclay nanocomposites. Carbohydr Polym 2010; 79: 391396.

Table 6. Oxygen permeability values for sample 6 and optimum sample.

Sample

d-spacing

(nm)

O2 permeability Preparation condition

cm3(STP)

cm/cm2 S cmHg (Barrer)

Temperature

distribution

Screw

speed

(r/min)

PVA

content

(%)

CMMT

content

(%)

Optimum

sample

1.86 0.11 1010 0.11 Mid 24 5 5

Sample 6 1.76 0.24 1010 0.24 Mid 12 10 5




2. Barikani M and Mohammadi M. Synthesis and characterization of starch-mod-

ified polyurethane. Carbohydr Polym 2007; 68: 773780.

3. Mondragon M, Mancilla JE and Rodrguez-Gonzalez FJ. Nanocomposites from

plasticized high-amylopectin, normal and high-amylose maize starches. Polym

Eng Sci 2008; 48: 12611267.

4. Majdzadeh-Ardakani K, Navarchian AH and Sadeghi F. Optimization of mech-

anical properties of thermoplastic starch/clay nanocomposites. Carbohydr Polym

2010; 79: 547554.

5. Avella M, De Vlieger JJ, Errico ME, et al. Biodegradable starch/clay nanocom-

posite films for food packaging applications. Food Chem 2005; 93: 467474.

6. Dean K, Yu L and Wu DY. Preparation and characterization of melt-extruded

thermoplastic starch/clay nanocomposites. Compos Sci Technol 2007; 67: 413421.

7. Ghanbarzade B, Almasi H and Entezami A. Studying morphological and mois-

ture barrier properties of starch-CMC-nanoclay biodegradable bionanocomposite

film. J Innov Food Sci Technol 2013; 5: Pe83Pe92. (En117).

8. Cyras VP, Manfredi LB, Ton-That M-T, et al. Physical and mechanical properties

of thermoplastic starch/montmorillonite nanocomposite films. Carbohydr Polym

2008; 73: 5563.

9. Dean KM, Do MD, Petinakis E, et al. Key interactions in biodegradable thermo-

plastic starch/poly (vinyl alcohol)/montmorillonite micro- and nanocomposites.

Compos Sci Technol 2008; 68: 14531462.

10. Qiao X, Jiang W and Sun K. Reinforced thermoplastic acetylated starch with

layered silicates. Starch-Starke 2005; 57: 581586.

11. Wang N, Zhang X, Han N, et al. Effect of citric acid and processing on the

performance of thermoplastic starch/montmorillonite nanocomposites.

Carbohydr Polym 2009; 76: 6873.

12. Raquez JM, Narayan R and Dubois P. Recent Advances in reactive extrusion

processing of biodegradable polymer-based compositions. Macromol Mater Eng

2008; 293: 447470.

13. Majdzadeh-Ardakani K and Nazari B. Improving the mechanical properties of

thermoplastic starch/poly (vinyl alcohol)/clay nanocomposites. Compos Sci

Technol 2010; 70: 15571563.

14. Huang M, Yu J and Ma X. High mechanical performance MMT-urea and for-

mamide-plasticized thermoplastic cornstarch biodegradable nanocomposites.

Carbohydr Polym 2006; 63: 393399.

15. Huang M-F, Yu J-G and Ma X-F. Studies on the properties of montmorillonite-

reinforced thermoplastic starch composites. Polymer 2004; 45: 70177023.

16. Wilhelm H-M, Sierakowski M-R, Souza G, et al. Starch films reinforced with

mineral clay. Carbohydr Polym 2003; 52: 101110.

17. Di Y, Iannace S, Di Maio E, et al. Nanocomposites by melt intercalation

based on polycaprolactone and organoclay. J Polym Sci B Polym Phys 2003;

41: 670678.

18. Incarnato L, Scarfato P, Russo G, et al. Preparation and characterization

of new melt compounded copolyamide nanocomposites. Polymer 2003; 44:

46254634.




19. Sauceau M, Fages J, Common A, et al. New challenges in polymer foaming: A

review of extrusion processes assisted by supercritical carbon dioxide. Prog Polym

Sci 2011; 36: 749766.

20. Kumar P, Sandeep K, Alavi S, et al. Preparation and characterization of bio-

nanocomposite films based on soy protein isolate and montmorillonite using melt

extrusion. J Food Eng 2010; 100: 480489.

21. Belibi PC, Daou TJ, Ndjaka J-MB, et al. Tensile and water barrier properties of

cassava starch composite films reinforced by synthetic zeolite and beidellite.

J Food Eng 2013; 115: 339346.

22. Majdzadeh-Ardakani K and Sadeghi-Ardakani S. Experimental investigation of

mechanical properties of Starch/natural rubber/clay nanocomposites. Dig J

Nanometer Biosys 2010; 10: 20.

23. Almasi H, Ghanbarzadeh B and Entezami AA. Physicochemical properties of

starchCMCnanoclay biodegradable films. Int J Biol Macromol 2010; 46: 15.

24. Hejri Z, Ahmadpour A, Seifkordi AA and Zebarjad SM. Role of nano-sized TiO2on mechanical and thermal behavior of starch/Poly(vinyl alcohol) blend films. Int

J Nano Sci Nanotechnol 2012; 8: 215226.

25. Heydari A, Alemzadeh I and Vossoughi M. Functional properties of biodegrad-

able corn starch nanocomposites for food packaging applications. Mater Des

2013; 50: 954961.

26. Sreekumar P, Al-Harthi MA and De S. Reinforcement of starch/poly(vinyl alco-

hol) blend using nano-titanium dioxide. J Compos Mater 2012; 46: 31813187.

27. Castillo L, Lopez O, Lopez C, et al. Thermoplastic starch films reinforced with

talc nanoparticles. Carbohydr Polym 2013; 95: 664674.

28. Slavutsky AM, Bertuzzi MA and Armada M. Water barrier properties of starch-

clay nanocomposite films. Brazilian J Food Technol 2012; 15: 208218.

29. Muller CM, Laurindo JB and Yamashita F. Composites of thermoplastic starch

and nanoclays produced by extrusion and thermopressing. Carbohydr Polym 2012;

89: 504510.

30. Jalalvandi E, Majid R, Ghanbari T, et al. Effects of montmorillonite (MMT) on

morphological, tensile, physical barrier properties and biodegradability of

poly(lactic acid)/starch/MMT nanocomposites. J Thermoplast Compos Mater.

Epub ahead of print 2013. DOI: 10.1177/0892705713486129.

31. Katerinopoulou K, Giannakas A, Grigoriadi K, et al. Preparation and character-

ization of acetylated corn starch(PVA)/clay nanocomposite films. Carbohydr

Polym 2014; 102: 216222.

32. Ali SS, Tang X, Alavi S, et al. Structure and physical properties of starch/poly

vinyl alcohol/sodium montmorillonite nanocomposite films. J Agric Food Chem

2011; 59: 1238412395.

33. Mao L, Imam S, Gordon S, et al. Extruded cornstarch-glycerol-polyvinyl alcohol

blends: Mechanical properties, morphology, and biodegradability. J Polym

Environ 2000; 8: 205211.

34. NurHanani Z, Beatty E, Roos Y, et al. Manufacture and characterization of

gelatin films derived from beef, pork and fish sources using twin screw extrusion.

J Food Eng 2012; 113: 606614.




35. Xie F, Halley PJ and Averous L. Rheology to understand and optimize proces-

sibility, structures and properties of starch polymeric materials. Prog Polym Sci

2012; 37: 595623.

36. Magalhaes N and Andrade C. Thermoplastic corn starch/clay hybrids: Effect of

clay type and content on physical properties. Carbohydr Polym 2009; 75: 712718.

37. Roy RK. Design of experiments using the Taguchi approach: 16 steps to product

and process improvement. New York: John Wiley & Sons, 2001.

38. Tang X, Alavi S and Herald TJ. Effects of plasticizers on the structure and proper-

ties of starchclay nanocomposite films. Carbohydr Polym 2008; 74: 552558.

39. Chen C-H and Lai L-S. Mechanical and water vapor barrier properties of tapioca

starch/decolorized hsian-tsao leaf gum films in the presence of plasticizer. Food

Hydrocoll 2008; 22: 15841595.

40. Xie F, Pollet E, Halley PJ, et al. Starch-based nano-biocomposites. Prog Polym

Sci 2013; 38: 15901628.

41. Kampeerapappun P, Aht-ong D, Pentrakoon D, et al. Preparation of cassava

starch/montmorillonite composite film. Carbohydr Polym 2007; 67: 155163.

42. Chen B and Evans JR. Thermoplastic starchclay nanocomposites and their char-

acteristics. Carbohydr Polym 2005; 61: 455463.

43. Dai H, Chang PR, Geng F, et al. Preparation and properties of thermoplastic

starch/montmorillonite nanocomposite using N-(2-hydroxyethyl) formamide as a

new additive. J Polym Environ 2009; 17: 225232.

44. Tunc S and Duman O. Preparation of active antimicrobial methylcellulose/carva-

crol/montmorillonite nanocomposite films and investigation of carvacrol release.

LWT-Food Sci Technol 2011; 44: 465472.

45. Masclaux C, Gouanve F and Espuche E. Experimental and modelling studies of

transport in starch nanocomposite films as affected by relative humidity. J Membr

Sci 2010; 363: 221231.

46. Martin O, Averous L and Della Valle G. In-line determination of plasticized

wheat starch viscoelastic behavior: Impact of processing. Carbohydr Polym

2003; 53: 169182.

47. Spiridon I, Popescu MC, Bodarlau R, et al. Enzymatic degradation of some

nanocomposites of poly(vinyl alcohol) with starch. Polym Degrad Stab 2008; 93:

18841890.

Biographies

Amir H Navarchian received his PhD in chemical engineering from Tarbiat

Modares University, Tehran, Iran, in 2003. He is currently an associate pro-

fessor of chemical engineering at the University of Isfahan, Isfahan, Iran,

where he is also the Head of Oce for University-Industry Collaborations.

His research interests cover polymer/clay nanocomposites, starch-based

packaging lms, polymer gas sensors, polymer membranes and emulsion

polymerization.




Mehdi Jalalian received his MSc in chemical engineering from the University

of Isfahan, Isfahan, Iran, in 2012. His research was focused on starch/clay

nanocomposites and packaging lms. He is currently a process engineer in

National Iranian Gas Company (NIGC).

Majid Pirooz received his MSc in chemical engineering from the University of

Isfahan, Isfahan, Iran, in 2014. His research is focused on starch/clay nano-

composites and packaging lms.



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Characterization of Starchpoly(Vinyl Alcohol)Clay Nanocomposite f