Characterisation of the Chitosan/layered silicate nanocomposites
Catalina Natalia Cheaburu1, b, Cornelia Vasile 1, a, 2,c Donatella Duraccio,
2,d
Sossio Cimmino
1
Petru Poni Institute of Macromolecular Chemistry of the Romanian Academy, Aleea Grigore Ghica
Voda 41A, Iasi, Romania
2
Instituto di Chimica e Tecnologia dei Polimeri (ICTP), Consiglio Nazionale delle Ricerche (CNR),
Via Campi Flegrei 34, 80078 Pozzuoli (NA). Italia
a
cvasile@icmpp.ro, bduncaty@icmpp.ro, cduraccio@ictp.cnr.it, dcimmino@ictp.cnr.it
Keywords: Chitosan, Montmorillonite, Nanocomposites, Intercalation
Abstract Characterization of chitosan / layered silicate nanocomposites obtained by solutionmixing technique, having different compositions including treated and untreated montmorilonite
(MMT) has been performed. The optimum amount of MMT and also the effect of nanoparticles
type on nanocomposite properties by DSC, X-ray diffraction and TG measurements have been
established. The chitosan chains were inserted into silicate layers to form the intercalated
nanocomposites. The interlayer distance of the silicates in the nanocomposites enlarged as their
amount increased. The stiffness and thermal stability enhanced.
Introduction
Polymer nanocomposites generally consist of nano-scale layered clay dispersed within the polymer
matrix [1]. Due to the nanometer-size particles (obtained mainly by dispersion), nanocomposites at
a certain amount of nanoparticles, nanocomposites exhibit distinctly improved mechanical, thermal,
optical and physico-chemical properties when compared with the pure polymer or conventional
(microscale) composites. Chitosan, a biocompatible, biodegradable, non-toxic linear polymer
available by the deacetylation of chitin (the second abundant polysaccharide extracted from the
shells of shrimps and crabs) was used to obtain nanostructured materials based on montmorillonite.
One function of particular interest of chitosan is its broad antimicrobial activity [2] in conjunction
with the excellent film forming ability [3] becoming in this way a very interesting polymer for
applications like agriculture, medicine [4], environment [5], food [6], etc. In particular, the use of
chitosan as films and edible coatings to extend shelf-life and preserve quality of fruits and
vegetables has received considerable attention. [7, 8] The exfoliated nanocomposite offer more
significant improvements in physical properties and the silicate layers are completely delaminated
from each other and are well dispersed. [1] The thermal stability of the nanocomposites depends
strongly on the compatibility of the components [9]
In our previous paper [10] by the mechanical properties determinations coupled with SEM
examination of the chitosan/montmorilonite nanocomposites it has been established that by the
incorporation of 5 wt% of nanoparticles, the stress of break and Young modulus increase in respect
with those of chitosan, because of a fine dispersion of the MMT in the chitosan matrix.
This study deals with the more detailed characterization of the same chitosan / layered
silicate nanocomposites with different compositions using treated and untreated montmorillonite
(MMT). To establish an optimum amount of MMT and also the effect of nanoparticles on
nanocomposite properties the chitosan / clay nanocomposites were characterized by means of
differential scanning calorimetry (DSC), thermogravimetry (TG) and X-Ray diphractograms.
Experimental
Details on the materials can be found in the previous paper [10]. The characteristics of other
materials used in this study are; Cloisite 15A is a natural montmorillonite modified with a
quaternary ammonium salt 2M2HT -dimethyl, dehydrogenated tallow, quaternary ammonium,
Southern Clay Product Inc from Rockwood Additives Ltd. Cloisite 93A is a natural montmorillonite
modified with a quaternary ammonium salt M2HT-methyl, dehydrogenated tallow ammonium,
Southern Clay Product Inc from Rockwood Additives Ltd.
The thin film of the chitosan/ clay nanocomposites were obtained by casting on Petri dishes
the viscous solutions of chitosan and clay dispersions and air dried by evaporation. Two series of
samples have been investigated namely: (1) the nanocomposites containing variable content of clay
from 1 to 15 wt% and (2) nanocomposites with a constant amount of 5 wt% of diferent types of
nanoparticles.
Investigation methods: DSC measurements were performed by using a Diamond Perkin Elmer
instrument and the thermal program used was from 30°C to 130°C at 20°C/min; 130°C for two
hours from 130 to -10°C at 50°C/min; kept at -10°C for 5 minutes from -10°C to 200°C at
10°C/min in order to remove the traces of solvent and to evidence better the glass transition. The
WAXD measurements were carried out at room temperature with a Philips PW 3710 Wide Angle Xray Diffraction (WAXD) (Cu-Ni radiation, λ= 0.154 Å). The distances between clay layers were
calculated with Bragg’s law: 2d sin θ = nλ; where λ is the wavelength of the X-ray d is the
interspacing distance and θ is the angle of incident radiation. TG/DTG analyses were performed by
a Diamond Perkin Elmer (TGA/DTA) apparatus with a heating rate of 10°C/min in nitrogen
atmosphere from 25 to 500°C.
Results and discussion
DSC results are presented in Fig. 1 and Table 1. Two transition temperatures have been detected in
the temperature range studied (room temperature – 200°C) (Table 1) in 110- 125°C and 168- 173°C
region. The first one is not influenced by the nanocomposite content while the second one increases
with both Na+MMT and C30B content up to 6 oC in respect with that of chitosan film. The data are
in accordance with those obtained by DMTA, but the first temperature region is situate at high
temperature in DSC curves because the heating rate used was higher (2°C/ min in DMTA and
20°C/ min in DSC).
CSflakes
CS film
CS-C30B 5 wt%
CS- C93A 5 wt%
+
CS- Na MMT 5 wt%
CS- C15A 5 wt%
(a)
100
120
140
160
Temperature (oC)
180
200
CS film
First derivative
First Derivative
CS flakes
+
CS-Na MMT 1 wt%
+
CS-Na MMT 3 wt%
+
CS-Na MMT 5 wt%
+
CS-Na MMT 7 wt%
+
CS-Na MMT9 wt%
(b)
100
+
CS-Na MMT 15 wt%
120
140
160
180
200
Temperature (°C)
Fig. 1: DSC thermograms for the nanocomposites based on chitosan with various amounts of clay;
(a) and with a constant amount of clay (5 wt %) with different types (b)
Table 1: The Tg values determined from the first derivative of DSC thermograms
From the first derivative of DSC thermograms
Sample
First peak [°C] Second peak [°C]
CS film
CS-flakes
CS-Na+MMT 1 wt%
CS-Na+MMT 3 wt%
CS-Na+MMT 5 wt%
CS-Na+MMT 7 wt%
CS-Na+MMT 9 wt%
CS-Na+MMT 15 wt%
CS-C30B 3 wt%
CS-C30B 5 wt%
CS-C30B 7 wt%
CS-C93A 5 wt%
CS-C15A 5 wt%
123
125
120
115
113
116
121
124
124
124
124
122
124
From DMTA
T2 [oC]
T1 [oC]
168
171
173
170
168
170
169
174
170
172
172
171
51; 105
156
100
75
170
167
91.8
84
175
168
X-Ray Patterns
4.96
o
o
4.93
3.45
(a)
o
4.85
2.8
+
4.83
o
+
CS- Na MMT 5 wt%
o
4.93
+
CS- Na MMT 3 wt%
o
7.2
4.91
4.87
o
C30B
o
CS-C30B 7%
4.8
o
CS- C30B 5%
o
C93A
4.79
o
CS-C93A 5 wt%
4.87
2.8
o
C30B
o
CS-C30B 5 wt%
2
o
C15A
CS-Na+MMT 1wt%
o
CS
CS
10
 deg)
20
7.2
CS-C30B 3%
+
Na MMT
0
Intensity (u.a.)
Intensity (u.a.)
CS- Na MMT 7 wt%
4.83
Intensity (u.a.)
CS- Na MMT15 wt%
+
(c)
(b)
o
4.83
o
CS-C15A 5 wt%
+
Na MMT
o
+
CS- Na MMT 5 wt%
CS
5
10
2 (deg)
15
2
4
6
8
10
2 (deg)
Fig. 2: X-ray patterns of nanocomposites based on chitosan; nanocomposites with various amounts
of clay, Na+MMT (a) and C30B (b), (c) nanocomposites with different clay type
Because of the hydrophilic and cationic structure of chitosan in acidic medium, this
biopolymer has a good miscibility with montmorillonite (especially with Na+MMT) and can easily
intercalate into the interlayers by means of cationic exchange [11, 12]
Fig. 2a shows the XRD patterns of Na+MMT, neat CS and its CS/Na+MMT nanocomposites with
different Na+MMT amount. The XRD pattern of the MMT shows a reflection peak at about 2θ =
7.2o, corresponding to a basal spacing of 1.23 nm. The XRD pattern of CS shows the characteristic
crystalline peaks at around 2θ~10º, 20ºand 25º- Figure 2a, according to literature data [13-14]. After
montmorillonite incorporation within CS, the basal plane of Na+MMT at 2θ = 7.2º disappears,
substituted by a new peak at around 2θ~ 4- 5º- Fig. 2a. The shift of the basal reflection of Na+MMT
to lower angle indicates the formation of an intercalated nanostructure, while the peak broadening
and intensity decrease most likely indicate the disordered intercalated or exfoliated structure.[9, 11,
15]
In the case of unmodified MMT the interspace distance (d001) was enlarged from 1.23 nm to
1.91 nm with the increasing of the clay amount indicating a good intercalation of chitosan into the
layers of clay.
Fig. 2b shows the influence of the amount of clay content, particularly C30B, modified
montmorillonite, on the interspace distance. In the Table 2 are summarized the obtained values for
the nanocomposites based of chitosan and unmodified and modified clay. It can be observe that in
the case of C30B there is no significant enlargement of the d001 which means that chitosan did not
enter into the interlayers of C30B.
In the case of Cloisite 30B, organically modified Na+ MMT with a quaternary ammonium
salt, the clay became organic and its hydrophobicity increased. It was very difficult to disperse
Cloisite 30B in the chitosan aqueous solution and to occur an intermolecular reaction between clay
and chitosan in spite of the presence of the hydroxyl group in the gallery of Cloisite 30 B.
Table 2: The obtained values of 2θ angles and d-spacing of nanocomposites based chitosan with
various amount of clay and different types of clay.
2θ [deg]
Sample
+
Na MMT
CS- Na+MMT 1 wt%
CS- Na+MMT 3 wt%
CS- Na+MMT 5 wt%
CS- Na+MMT 7 wt%
CS- Na+MMT 15 wt%
C30B
d001 [nm] Sample
7.20
4.93
4.83
4.83
4.93
4.96
4.79
1.23
1.79
1.82
1.82
1.79
1.91
1.84
2θ [deg]
d001 [nm]
4.80
4.87
4.91
3.45
2.80
2.80
2.00
1.84
1.81
1.8
2.56
3.15
3.15
4.41
CS-C30B 3 wt%
CS-C30B 5 wt%
CS-C30B 7wt%
C93A
CS- C93A 5 wt%
C15A
CS-C15A 5 wt%
It is seems that the strong polar interactions, especially hydrogen bonding, critically affected the
formation of intercalation and exfoliated nanocomposites. [16]
A shift of 2θ to smaller angles was also observed in the case of modified mineral clays C93A and
C15A showing an enlargement of the interspace distance d001 from 2.56 to 3.15 nm for C 93A and
from 3.15 to 4.41 nm for C 15A. The peak of nanocomposite CS- C93A in comparison with C93A,
presented in Figure 2c, shows a rather broaden peak indicating a developement of an exfoliated
structure.
TG/DTG results are given in Fig. 3 and Table 3:
100
90
CS-Na MMT 3 wt%
+
CS-Na MMT 5 wt%
+
60
CS-Na MMT 15 wt%
+
CS-Na MMT 9 wt%
50
40
30
(a)
100
CS film
200
300
400
70
CS-Na+MMT 5 wt%
60
CS-C30B 5 wt%
500
60
50
40
40
(b)
100
Temperature (°C)
70
50
30
30
CS film
200
300
400
CS-C30B 3 wt%
80
CS-C93A 5 wt%
W (%)
+
CS-Na MMT 1 wt%
80
W (%)
W (%)
70
CS-C15A 5 wt%
+
CS-Na MMT 7 wt%
CS flakes
90
CS flakes
90
+
80
100
100
CS flakes
CS-C30B 5 wt%
CS-C30B 7 wt %
(c)
100
500
CS film
200
300
500
Temperature (°C)
Temperature (°C)
CS flakes
CS flakes
400
CS flakes
CS film
CS film
+
CS- C30B 5 wt%
CS- C30B 7 wt%
(e)
0
First Derivative
First Derivative
CS- C30B 3 wt%
+
CS-Na MMT 9 wt%
+
CS-Na MMT 7 wt%
+
CS-Na MMT 5 wt%
+
CS-Na MMT 3 wt%
+
CS-Na MMT 1 wt%
(f)
100 200 300 400 500
Temperature (oC)
0
First Derivative
CS-Na MMT 15 wt%
CS film
+
CS- Na MMT 5 wt%
CS- C30B 5 wt%
CS- C93A 5 wt%
CS- C15A 5 wt%
(g)
100 200 300 400 500
Temperature (oC)
0
100 200 300 400 500
Temperature (oC)
Fig. 3: Thermogravimetric (TG) curves (above) and their derivative (DTG) (below) for
nanocomposites based on chitosan with various amounts of clay, Na+MMT (a), (d) and C30B (b),
(e) and nanocomposites with different clay type (c), (f).
Table 3: TG data for nanocomposites based on chitosan with various amounts of clay and different
clay types.
Sample
Ti* [oC]
T*m [oC]
Tf* [oC]
ΔW [%]
CS film
CS-flakes
CS-Na+MMT 1 wt%
CS-Na+MMT 3 wt%
CS-Na+MMT 5 wt%
CS-Na+MMT 7 wt%
CS-Na+MMT 9 wt%
CS-Na+MMT 15 wt%
CS-C30B 3 wt%
CS-C30B 5 wt%
CS-C30B 7 wt%
CS-C93A 5 wt%
CS-C15A 5 wt%
206
197
183
209
205
210
210
214
174
171
168
170
188
276
302
261
265
281
271
277
275
276
277
277
273
260
393
438
409
402
387
388
382
386
391
406
407
407
403
36.77
48
41.42
38.75
36
35.52
32.54
36.45
38.95
37.76
36.76
39.23
37.59
Ti- onset temperature, Tm- temperature corresponding to the maximum rate of weight loss; Tf- final temperature; ΔW- weight loss
*
Ti increases with increasing Na+MMT content, in other cases decreases and ΔW decreases
indicating an enhancement of the thermal stability by Na+MMT incorporation in chitosan.
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