Accepted Manuscript Title: Mechanical and barrier properties of guar gum based nano-composite films Author: Chaturbhuj K. Saurabh Sumit Gupta Jitendra Bahadur S. Mazumder Prasad S. Variyar Arun Sharma PII: DOI: Reference:
S0144-8617(15)00104-6 http://dx.doi.org/doi:10.1016/j.carbpol.2015.02.004 CARP 9661
To appear in: Received date: Revised date: Accepted date:
10-1-2014 18-11-2014 3-2-2015
Please cite this article as: Saurabh, C. K., Gupta, S., Bahadur, J., Mazumder, S., Variyar, P. S., and Sharma, A.,Mechanical and barrier properties of guar gum based nano-composite films, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.02.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights (for review)
Research Highlights for review Guar gum nanocomposite films made from organically modified and unmodified nanoclay.
ip t
Nanoclay at 2.5 % w/w lead to improved mechanical and barrier properties of films. Improved physical properties were due to intercalation of guar gum in nanoclays.
cr
FEG-SEM images showed better compatibility between guar gum and unmodified
Ac ce p
te
d
M
an
us
nanoclay.
Page 1 of 28
*Manuscript
1 2 3 4 5 6
Mechanical and barrier properties of guar gum based nano-composite films Chaturbhuj K. Saurabha#, Sumit Guptaa#, Jitendra Bahadurb,S Mazumderb, Prasad S. Variyara* and Arun Sharmaa a
Food Technology Division, bSolid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
7
Abstract:
9
Guar gum based nano-composite films were prepared using organically modified (cloisite 20A)
10
and unmodified (nanofil 116) nanoclays. Effect of nanoclay incorporation on mechanical
11
strength, water vapor barrier property, chromatic characteristics and opacity of films was
12
evaluated. Nano-composites were characterized using X-ray scattering, FTIR and scanning
13
electron microscopy. A nanoclay concentration dependent increase in mechanical strength and
14
reduction in water vapor transmission rate was observed. Films containing nanofil 116 (2.5%
15
w/w guar gum) and closite 20A (10% w/w guar gum) demonstrated a 102% and 41% higher
16
tensile strength, respectively, as compared to the control. Lower tensile strength of cloisite 20A
17
films as compared to nanofil 116 films was due to its incompatibility with guar gum. X-ray
18
scattering analysis revealed that interstitial spacing between nanofil 116 and cloisite 20A sheets
19
increased due to intercalation by guar gum polymer. This resulted in improved mechanical and
20
barrier properties of nano-composites compared to control.
22
cr
us
an
M
d
te
Ac ce p
21
ip t
8
Keywords: Guar gum, Nanoclay, Biodegradable film, Irradiation, X-ray scattering.
23
# These authors contributed equally *Corresponding author: E-mail:[email protected]. Food flavor and aroma chemistry section. Food Technology Division, BARC, Mumbai-85, India. Ph: +91-22-25590560, Fax: +91-2225505151. 1 Page 2 of 28
1. Introduction
25
Conventional packaging materials are derived from non-renewable petroleum resources and their
26
disposal is of prime concern because of non-biodegradability and non-economical recycling
27
procedures (Garcia, Rubio, & Lagaron, 2010). Therefore, it is of interest to overcome the
28
disadvantage of petrochemical based plastics by developing biodegradable packaging material
29
from natural sources such as polysaccharides, proteins and lipids. However, relatively poor
30
mechanical and barrier properties of biopolymers as compared to petroleum based packaging
31
materials limit their commercialization. One possible approach for the improving mechanical and
32
barrier characteristics of biopolymer films is to make nano-hybrid composite films by mixing
33
with inorganic nano size clays (Avella et al., 2005; Rhim, Hong, Park, & Perry, 2006; Rhim,
34
Hong, & Ha, 2009).
M
an
us
cr
ip t
24
Among the inorganic nano size clays, Montmorillonite (MMT) has been extensively used for
36
preparation of polymer nano-composites. MMT consists of inorganic layered silicates several
37
hundred nanometers long having layer spacing of few nanometers. Hundreds of such layered
38
platelets are stacked into particles or tactoids (Arora & Padua, 2010). These layered silicates
39
significantly affect the properties of nano-composite films. The size range of nanoclay is around
40
100 nm in one or more dimensions (Bradley, Castle, & Chaudhry, 2011). Due to its nano scale
41
size it interacts with matter at the atomic, molecular, or macromolecular level (Almasi,
42
Ghanbarzadeh, & Entezami, 2010). Intercalation and exfoliation are two approaches that are
43
widely used for the dispersion of nanoclay in polymeric matrices. Intercalation results in
44
moderate penetration of polymeric chain into nanoclay basal spacing resulting in slight
45
expansion of interlayer spaces without disturbing the shape of layered stack. In exfoliation the
46
layered structure loses its shape and forms single sheet that behaves likes a homogenous mixture
47
within the polymeric solution (Uhl, Davuluri, Wong, & Webster, 2004; Arora et al., 2010).
Ac ce p
te
d
35
2
Page 3 of 28
For development of renewable source based biodegradable packaging material guar gum
49
(GG) can be a potential candidate because of its long polymeric chain, high molecular weight
50
and wide availability as compared to other biopolymers. India accounts for 80 percent of world
51
production of GG. It is a galactomannan with mannose to galactose ratio of 1.6 and is derived
52
from endosperm of an annual legume plant Cyamopsis tetragonoloba (Cunha, Castro, Rocha,
53
Paula, & Feitosa, 2005). It consists of mannose backbone linked by (1-4) β-D-mannopyranose
54
with galactose as a side group linked by (1-6) α-D-galactopyranose (Fernandes, Goncalves, &
55
Doublier, 1993). Very few reports exist on GG based biodegradable packaging film. Das et al.,
56
(2011) developed a water resistance biocide film by intrinsically modifying GG into GG
57
benzamide. Enzymatic depolymerization was also previously reported to improve mechanical
58
properties of GG based films (Mikkonen et al., 2007).
an
us
cr
ip t
48
Gamma irradiation has proved to be a convenient tool for inducing cross-links between
60
polymer and nanoclay of the nano-composite films resulting in improved functional properties of
61
biobased films (Xu et al., 2012). Gamma radiation after interacting with biopolymers leads to the
62
formation of very reactive intermediates such as excited states, ions, and free radicals (Khan et
63
al., 2010). The presence of clay stimulated the formation of such radicals from biopolymer and
64
also sustained the life of radicals longer which resulted in high efficiency of cross-linking in the
65
nanocomposite (Ibrahim, 2011). We had earlier demonstrated that low doses of gamma radiation
66
(≥500 Gy) resulted in improved mechanical properties of GG films due to the ordering of
67
polymer structures as confirmed by small angle X-ray scattering analysis (Saurabh et al., 2013).
68
Other reports suggest that gamma radiation improved films characteristics by inducing cross
69
linking of polymeric chains (Kang, Jo, Lee, Kwon & Byun, 2005; Kim, Jo, Park & Byun, 2008).
70
However, to the best of our knowledge no reports exists till date on the combined effect of
71
gamma irradiation and incorporation of nanoclays on the mechanical and barrier properties of
Ac ce p
te
d
M
59
3
Page 4 of 28
GG based biodegradable films. In the present work two types of commonly used nanoclays i.e.
73
nanofil 116 and cloisite 20A were incorporated into GG films and its mechanical and barrier
74
properties were subsequently analyzed. The effect of gamma irradiation on the physical
75
properties of the films thus prepared was also evaluated.
76
2. Materials and Methods
77
2.1. Purification of GG.
78
Purification of GG was carried out as per procedure described earlier by Jumel et al., (1996). In
79
brief, 2.5 g of GG (Merck India ltd.) was dissolved in 250 mL of distilled water by using shear
80
mixer (Omni mixer, Sorvall, USA) at speed 2 for 2 min. Solution obtained was kept overnight at
81
room temperature (25 ± 2°C) on magnetic stirrer. Resulting solution was centrifuged for 30 min
82
at 9000 rpm for removal of insoluble impurities. Ethanol in the proportion of 2:1 was added to
83
the supernatant and resulting mixture was kept overnight for precipitation of GG.
84
precipitate obtained was freeze dried to obtain dry purified GG powder. A 60% yield was
85
obtained by above purification procedure.
86
2.2. Dispersion of nanoclay.
87
Cloisite 20A is a natural MMT modified with a quaternary ammonium salt while nanofil 116 is
88
an inorganic nano-dispersible layered silicate based on a refined natural bentonite. Both the clays
89
were obtained as a gift sample from Southern Clay Products, Inc., US. Rockwood Additives Ltd.,
90
UK. Different dilutions of aqueous nanoclay suspensions (0.01, 0.025, 0.05, 0.075, 0.1 and 0.2%
91
w/v of distilled water) were prepared and then separately kept on magnetic stirrer for 7 days at
92
low temperature (5 ± 0.5 ºC) to avoid microbial contamination. After 7 days of mixing, obtained
93
nanoclay suspension was centrifuged at 4000 rpm for 10 min at 10 ºC to pellet out nanoclay
94
tactoids.
95
2.3. Preparation of nano-composite films.
The
Ac ce p
te
d
M
an
us
cr
ip t
72
4
Page 5 of 28
Purified GG was added to different dilutions of dispersed nanoclays suspension (150 mL)
97
prepared as detailed above to make 1% w/v aqueous solution. Thus the amount of nanoclay on
98
w/w basis with respect to GG was 1, 2.5, 5, 7.5, 10 and 20%. Glycerol (0.6 g i.e. 40% w/w of
99
GG) was added as plasticizer and mixture obtained was kept overnight at room temperature (25
100
± 2°C) on magnetic stirrer for intercalation of polymer in nanoclay sheets. Solution thus obtained
101
was centrifuged at 3000 rpm for 15 min for the removal of air bubbles. 150 mL of solution was
102
poured and spread evenly onto surface of glass plate (21 cm × 21 cm), having removable
103
boundary of insulating tape. For drying, plates were then kept in oven for 8 hrs at 80 °C. Dried
104
nano-composite films were conditioned at 50% relative humidity at room temperature (25 ± 2°C)
105
for 7 days. After conditioning films were peeled and subjected to physical and mechanical
106
analysis.
107
2.4. Irradiation of nano-composite film.
108
GG based films incorporated with 2.5% nanofil 116 or 10% cloisite 20A were subjected to
109
gamma irradiation (1, 5, 10, 25, 50 and 100 kGy) at room temperature in 60Co gamma irradiator
110
(GC-5000, BRIT, India, dose rate 3.6 kGy/hr). The treated films were conditioned as mentioned
111
above (section 2.3) prior to analysis of their physical and barrier properties.
112
2.5. Physical and mechanical properties of nano-composite films.
113
Films were cut into strips of dimension 2 cm × 15 cm. Film thickness was determined by using
114
micrometer (103-131, Mitutoyo, Japan). Measurements were randomly taken at three different
115
locations on each film strip. The lowest value of thickness of each strip was used in calculations
116
for the tensile strength and Young’s modulus of the same strip. Mechanical properties i.e. tensile
117
strength, Young’s modulus, puncture strength and percent elongation of films were analyzed
118
using a texture analyzer (TA. HD. Plus, Stable Micro Systems). The American Society of
119
Testing and Materials (ASTM) standard method D882-10 was used to measure the tensile
Ac ce p
te
d
M
an
us
cr
ip t
96
5
Page 6 of 28
strength, Young’s modulus and percent elongation at break (% E) of films. Puncture strength of
121
films (5 cm × 2 cm) were determined by 2 mm needle probe having pre test speed of 10 mm/sec
122
and test speed of 0.5 mm/sec. Water vapor transmission rate (WVTR) of films were determined
123
by using round cups having 100 mL volume capacity and 120 cm2 mouth area. The cup was
124
filled with 60 mL of distilled water and sealed with films prepared using adhesive tapes. This
125
assembly was kept in desiccators at 25 ± 2°C and 87% relative humidity. The mass of water lost
126
from the cup was monitored as a function of time, and the WVTR was calculated when steady-
127
state was achieved. Color of films were determined using a colorimeter (CM-3600d Konica
128
Minolta sensing Inc., Japan) by measuring L*, a* and b* values. Instrument was calibrated using
129
a white tile supplied along with the equipment. Source used was D65 with observer set at 10
130
degrees. Opacity of films was determined using Hunter lab method, as the relationship between
131
reflectance of each sample on black standard and the reflectance on white standard using Eq. (1)
132
as given below.
133
Opacity = (Yb/Yw)× 100
134
All measurements were carried out in triplicates at room temperature 25 ± 2 °C and 50% relative
135
humidity.
136
2.6. X-rays scattering measurements.
137
SAXS (Small angle X-rays scattering) measurements were performed on the cloisite 20A
138
composite films (films were 4 times folded) and powder cloisite 20A at a lab based SAXS setup
139
using CuKα source. The size of incident photon beam on the sample was 0.4 mm diameter. The
140
SAXS detector was mounted at a sample to detector distance of 1.07 m, corresponding to a q-
141
range of 0.1–2.5 nm-1. The magnitude of the scattering wave vector, q equals:
142
q =2sinθ/λ =q/2π
143
where 2θ is the scattering angle and λ = 0.154 nm the used wavelength of X-ray beam.
M
an
us
cr
ip t
120
Ac ce p
te
d
(1)
(2)
6
Page 7 of 28
144
Interlayer distance (d or d-spacing) between clay layers can be estimated from:
145
d = 2π/q
146
X-ray powder diffraction (XRD) measurements were performed on nanofil 116 powder and
147
nanofil 116 composite films (films were 4 times folded). XRD patterns were obtained on a
148
Philips PW-1820 powder diffractometer using CuKα radiation. The X-ray tube rating was
149
maintained at 30 kV and 20 mA. The goniometer was calibrated for correct zero position using
150
silicon standard. Interlayer distance between clay layers can be estimated from Bragg’s equation
151
(Kasai & Kakudo, 2005):
152
d =λ / (2sin (θ))
153
2.7. Field Emission Gun-Scanning Electron Microscopes (FEG-SEM).
154
The surface morphology of films was analyzed by FEG-SEM. The scanning electron
155
micrographs were taken with a JSM-7600F instrument (Joel, Japan). A sputter coater was used to
156
pre coat conductive gold onto the films surface before observing the microstructure at 25 kV.
157
2.8. FTIR analysis of nano-composite films.
158
Spectra of films were scanned in the range of 4000–600 cm−1 on a FTIR (FT/IR 4100, Jasco)
159
spectrometer. ATR assembly was used for obtaining FTIR spectra. Films were directly pressed
160
on ATR assembly and spectra were recorded. 40 scans were taken for each film sample.
161
2.9. Statistical analysis.
162
DSAASTAT ver. 1.101 by Andrea Onofri was used for statistical analysis of data. Three samples
163
were taken for every treatment and each sample was further analyzed in triplicate. Data was
164
analyzed by Analysis of variance (ANOVA) and multiple comparisons of means were carried
165
out using Duncan’s multiple range test.
166
3. Results and discussion
us
cr
ip t
(3)
Ac ce p
te
d
M
an
(4)
7
Page 8 of 28
3.1. Effect of type and concentration of nanoclay on tensile strength and Young’s modulus of
168
nano-composites.
169
Thickness of native GG films was found to be 15.2 ± 2.3 µm. No significant (p
S0144-8617(15)00104-6 http://dx.doi.org/doi:10.1016/j.carbpol.2015.02.004 CARP 9661
To appear in: Received date: Revised date: Accepted date:
10-1-2014 18-11-2014 3-2-2015
Please cite this article as: Saurabh, C. K., Gupta, S., Bahadur, J., Mazumder, S., Variyar, P. S., and Sharma, A.,Mechanical and barrier properties of guar gum based nano-composite films, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.02.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights (for review)
Research Highlights for review Guar gum nanocomposite films made from organically modified and unmodified nanoclay.
ip t
Nanoclay at 2.5 % w/w lead to improved mechanical and barrier properties of films. Improved physical properties were due to intercalation of guar gum in nanoclays.
cr
FEG-SEM images showed better compatibility between guar gum and unmodified
Ac ce p
te
d
M
an
us
nanoclay.
Page 1 of 28
*Manuscript
1 2 3 4 5 6
Mechanical and barrier properties of guar gum based nano-composite films Chaturbhuj K. Saurabha#, Sumit Guptaa#, Jitendra Bahadurb,S Mazumderb, Prasad S. Variyara* and Arun Sharmaa a
Food Technology Division, bSolid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
7
Abstract:
9
Guar gum based nano-composite films were prepared using organically modified (cloisite 20A)
10
and unmodified (nanofil 116) nanoclays. Effect of nanoclay incorporation on mechanical
11
strength, water vapor barrier property, chromatic characteristics and opacity of films was
12
evaluated. Nano-composites were characterized using X-ray scattering, FTIR and scanning
13
electron microscopy. A nanoclay concentration dependent increase in mechanical strength and
14
reduction in water vapor transmission rate was observed. Films containing nanofil 116 (2.5%
15
w/w guar gum) and closite 20A (10% w/w guar gum) demonstrated a 102% and 41% higher
16
tensile strength, respectively, as compared to the control. Lower tensile strength of cloisite 20A
17
films as compared to nanofil 116 films was due to its incompatibility with guar gum. X-ray
18
scattering analysis revealed that interstitial spacing between nanofil 116 and cloisite 20A sheets
19
increased due to intercalation by guar gum polymer. This resulted in improved mechanical and
20
barrier properties of nano-composites compared to control.
22
cr
us
an
M
d
te
Ac ce p
21
ip t
8
Keywords: Guar gum, Nanoclay, Biodegradable film, Irradiation, X-ray scattering.
23
# These authors contributed equally *Corresponding author: E-mail:[email protected]. Food flavor and aroma chemistry section. Food Technology Division, BARC, Mumbai-85, India. Ph: +91-22-25590560, Fax: +91-2225505151. 1 Page 2 of 28
1. Introduction
25
Conventional packaging materials are derived from non-renewable petroleum resources and their
26
disposal is of prime concern because of non-biodegradability and non-economical recycling
27
procedures (Garcia, Rubio, & Lagaron, 2010). Therefore, it is of interest to overcome the
28
disadvantage of petrochemical based plastics by developing biodegradable packaging material
29
from natural sources such as polysaccharides, proteins and lipids. However, relatively poor
30
mechanical and barrier properties of biopolymers as compared to petroleum based packaging
31
materials limit their commercialization. One possible approach for the improving mechanical and
32
barrier characteristics of biopolymer films is to make nano-hybrid composite films by mixing
33
with inorganic nano size clays (Avella et al., 2005; Rhim, Hong, Park, & Perry, 2006; Rhim,
34
Hong, & Ha, 2009).
M
an
us
cr
ip t
24
Among the inorganic nano size clays, Montmorillonite (MMT) has been extensively used for
36
preparation of polymer nano-composites. MMT consists of inorganic layered silicates several
37
hundred nanometers long having layer spacing of few nanometers. Hundreds of such layered
38
platelets are stacked into particles or tactoids (Arora & Padua, 2010). These layered silicates
39
significantly affect the properties of nano-composite films. The size range of nanoclay is around
40
100 nm in one or more dimensions (Bradley, Castle, & Chaudhry, 2011). Due to its nano scale
41
size it interacts with matter at the atomic, molecular, or macromolecular level (Almasi,
42
Ghanbarzadeh, & Entezami, 2010). Intercalation and exfoliation are two approaches that are
43
widely used for the dispersion of nanoclay in polymeric matrices. Intercalation results in
44
moderate penetration of polymeric chain into nanoclay basal spacing resulting in slight
45
expansion of interlayer spaces without disturbing the shape of layered stack. In exfoliation the
46
layered structure loses its shape and forms single sheet that behaves likes a homogenous mixture
47
within the polymeric solution (Uhl, Davuluri, Wong, & Webster, 2004; Arora et al., 2010).
Ac ce p
te
d
35
2
Page 3 of 28
For development of renewable source based biodegradable packaging material guar gum
49
(GG) can be a potential candidate because of its long polymeric chain, high molecular weight
50
and wide availability as compared to other biopolymers. India accounts for 80 percent of world
51
production of GG. It is a galactomannan with mannose to galactose ratio of 1.6 and is derived
52
from endosperm of an annual legume plant Cyamopsis tetragonoloba (Cunha, Castro, Rocha,
53
Paula, & Feitosa, 2005). It consists of mannose backbone linked by (1-4) β-D-mannopyranose
54
with galactose as a side group linked by (1-6) α-D-galactopyranose (Fernandes, Goncalves, &
55
Doublier, 1993). Very few reports exist on GG based biodegradable packaging film. Das et al.,
56
(2011) developed a water resistance biocide film by intrinsically modifying GG into GG
57
benzamide. Enzymatic depolymerization was also previously reported to improve mechanical
58
properties of GG based films (Mikkonen et al., 2007).
an
us
cr
ip t
48
Gamma irradiation has proved to be a convenient tool for inducing cross-links between
60
polymer and nanoclay of the nano-composite films resulting in improved functional properties of
61
biobased films (Xu et al., 2012). Gamma radiation after interacting with biopolymers leads to the
62
formation of very reactive intermediates such as excited states, ions, and free radicals (Khan et
63
al., 2010). The presence of clay stimulated the formation of such radicals from biopolymer and
64
also sustained the life of radicals longer which resulted in high efficiency of cross-linking in the
65
nanocomposite (Ibrahim, 2011). We had earlier demonstrated that low doses of gamma radiation
66
(≥500 Gy) resulted in improved mechanical properties of GG films due to the ordering of
67
polymer structures as confirmed by small angle X-ray scattering analysis (Saurabh et al., 2013).
68
Other reports suggest that gamma radiation improved films characteristics by inducing cross
69
linking of polymeric chains (Kang, Jo, Lee, Kwon & Byun, 2005; Kim, Jo, Park & Byun, 2008).
70
However, to the best of our knowledge no reports exists till date on the combined effect of
71
gamma irradiation and incorporation of nanoclays on the mechanical and barrier properties of
Ac ce p
te
d
M
59
3
Page 4 of 28
GG based biodegradable films. In the present work two types of commonly used nanoclays i.e.
73
nanofil 116 and cloisite 20A were incorporated into GG films and its mechanical and barrier
74
properties were subsequently analyzed. The effect of gamma irradiation on the physical
75
properties of the films thus prepared was also evaluated.
76
2. Materials and Methods
77
2.1. Purification of GG.
78
Purification of GG was carried out as per procedure described earlier by Jumel et al., (1996). In
79
brief, 2.5 g of GG (Merck India ltd.) was dissolved in 250 mL of distilled water by using shear
80
mixer (Omni mixer, Sorvall, USA) at speed 2 for 2 min. Solution obtained was kept overnight at
81
room temperature (25 ± 2°C) on magnetic stirrer. Resulting solution was centrifuged for 30 min
82
at 9000 rpm for removal of insoluble impurities. Ethanol in the proportion of 2:1 was added to
83
the supernatant and resulting mixture was kept overnight for precipitation of GG.
84
precipitate obtained was freeze dried to obtain dry purified GG powder. A 60% yield was
85
obtained by above purification procedure.
86
2.2. Dispersion of nanoclay.
87
Cloisite 20A is a natural MMT modified with a quaternary ammonium salt while nanofil 116 is
88
an inorganic nano-dispersible layered silicate based on a refined natural bentonite. Both the clays
89
were obtained as a gift sample from Southern Clay Products, Inc., US. Rockwood Additives Ltd.,
90
UK. Different dilutions of aqueous nanoclay suspensions (0.01, 0.025, 0.05, 0.075, 0.1 and 0.2%
91
w/v of distilled water) were prepared and then separately kept on magnetic stirrer for 7 days at
92
low temperature (5 ± 0.5 ºC) to avoid microbial contamination. After 7 days of mixing, obtained
93
nanoclay suspension was centrifuged at 4000 rpm for 10 min at 10 ºC to pellet out nanoclay
94
tactoids.
95
2.3. Preparation of nano-composite films.
The
Ac ce p
te
d
M
an
us
cr
ip t
72
4
Page 5 of 28
Purified GG was added to different dilutions of dispersed nanoclays suspension (150 mL)
97
prepared as detailed above to make 1% w/v aqueous solution. Thus the amount of nanoclay on
98
w/w basis with respect to GG was 1, 2.5, 5, 7.5, 10 and 20%. Glycerol (0.6 g i.e. 40% w/w of
99
GG) was added as plasticizer and mixture obtained was kept overnight at room temperature (25
100
± 2°C) on magnetic stirrer for intercalation of polymer in nanoclay sheets. Solution thus obtained
101
was centrifuged at 3000 rpm for 15 min for the removal of air bubbles. 150 mL of solution was
102
poured and spread evenly onto surface of glass plate (21 cm × 21 cm), having removable
103
boundary of insulating tape. For drying, plates were then kept in oven for 8 hrs at 80 °C. Dried
104
nano-composite films were conditioned at 50% relative humidity at room temperature (25 ± 2°C)
105
for 7 days. After conditioning films were peeled and subjected to physical and mechanical
106
analysis.
107
2.4. Irradiation of nano-composite film.
108
GG based films incorporated with 2.5% nanofil 116 or 10% cloisite 20A were subjected to
109
gamma irradiation (1, 5, 10, 25, 50 and 100 kGy) at room temperature in 60Co gamma irradiator
110
(GC-5000, BRIT, India, dose rate 3.6 kGy/hr). The treated films were conditioned as mentioned
111
above (section 2.3) prior to analysis of their physical and barrier properties.
112
2.5. Physical and mechanical properties of nano-composite films.
113
Films were cut into strips of dimension 2 cm × 15 cm. Film thickness was determined by using
114
micrometer (103-131, Mitutoyo, Japan). Measurements were randomly taken at three different
115
locations on each film strip. The lowest value of thickness of each strip was used in calculations
116
for the tensile strength and Young’s modulus of the same strip. Mechanical properties i.e. tensile
117
strength, Young’s modulus, puncture strength and percent elongation of films were analyzed
118
using a texture analyzer (TA. HD. Plus, Stable Micro Systems). The American Society of
119
Testing and Materials (ASTM) standard method D882-10 was used to measure the tensile
Ac ce p
te
d
M
an
us
cr
ip t
96
5
Page 6 of 28
strength, Young’s modulus and percent elongation at break (% E) of films. Puncture strength of
121
films (5 cm × 2 cm) were determined by 2 mm needle probe having pre test speed of 10 mm/sec
122
and test speed of 0.5 mm/sec. Water vapor transmission rate (WVTR) of films were determined
123
by using round cups having 100 mL volume capacity and 120 cm2 mouth area. The cup was
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filled with 60 mL of distilled water and sealed with films prepared using adhesive tapes. This
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assembly was kept in desiccators at 25 ± 2°C and 87% relative humidity. The mass of water lost
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from the cup was monitored as a function of time, and the WVTR was calculated when steady-
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state was achieved. Color of films were determined using a colorimeter (CM-3600d Konica
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Minolta sensing Inc., Japan) by measuring L*, a* and b* values. Instrument was calibrated using
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a white tile supplied along with the equipment. Source used was D65 with observer set at 10
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degrees. Opacity of films was determined using Hunter lab method, as the relationship between
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reflectance of each sample on black standard and the reflectance on white standard using Eq. (1)
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as given below.
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Opacity = (Yb/Yw)× 100
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All measurements were carried out in triplicates at room temperature 25 ± 2 °C and 50% relative
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humidity.
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2.6. X-rays scattering measurements.
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SAXS (Small angle X-rays scattering) measurements were performed on the cloisite 20A
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composite films (films were 4 times folded) and powder cloisite 20A at a lab based SAXS setup
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using CuKα source. The size of incident photon beam on the sample was 0.4 mm diameter. The
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SAXS detector was mounted at a sample to detector distance of 1.07 m, corresponding to a q-
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range of 0.1–2.5 nm-1. The magnitude of the scattering wave vector, q equals:
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q =2sinθ/λ =q/2π
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where 2θ is the scattering angle and λ = 0.154 nm the used wavelength of X-ray beam.
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Interlayer distance (d or d-spacing) between clay layers can be estimated from:
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d = 2π/q
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X-ray powder diffraction (XRD) measurements were performed on nanofil 116 powder and
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nanofil 116 composite films (films were 4 times folded). XRD patterns were obtained on a
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Philips PW-1820 powder diffractometer using CuKα radiation. The X-ray tube rating was
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maintained at 30 kV and 20 mA. The goniometer was calibrated for correct zero position using
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silicon standard. Interlayer distance between clay layers can be estimated from Bragg’s equation
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(Kasai & Kakudo, 2005):
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d =λ / (2sin (θ))
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2.7. Field Emission Gun-Scanning Electron Microscopes (FEG-SEM).
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The surface morphology of films was analyzed by FEG-SEM. The scanning electron
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micrographs were taken with a JSM-7600F instrument (Joel, Japan). A sputter coater was used to
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pre coat conductive gold onto the films surface before observing the microstructure at 25 kV.
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2.8. FTIR analysis of nano-composite films.
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Spectra of films were scanned in the range of 4000–600 cm−1 on a FTIR (FT/IR 4100, Jasco)
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spectrometer. ATR assembly was used for obtaining FTIR spectra. Films were directly pressed
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on ATR assembly and spectra were recorded. 40 scans were taken for each film sample.
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2.9. Statistical analysis.
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DSAASTAT ver. 1.101 by Andrea Onofri was used for statistical analysis of data. Three samples
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were taken for every treatment and each sample was further analyzed in triplicate. Data was
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analyzed by Analysis of variance (ANOVA) and multiple comparisons of means were carried
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out using Duncan’s multiple range test.
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3. Results and discussion
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3.1. Effect of type and concentration of nanoclay on tensile strength and Young’s modulus of
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nano-composites.
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Thickness of native GG films was found to be 15.2 ± 2.3 µm. No significant (p
