RHEOLOGICAL PROPERTIES OF CHITOSAN ACETATE BLENDS

RHEOLOGICAL PROPERTIES OF CHITOSAN ACETATE BLENDS
WITH VINYL POLYMERS
Katarzyna Lewandowska
Nicolaus Copernicus University, Faculty of Chemistry,
Chair of Chemistry and Photochemistry of Polymers,
ul. Gagarin 7, 87-100 Toruń, Poland
Abstract
In the present paper the rheological properties of solutions of chitosan
acetate (ChA), poly(vinyl alcohol) (PVA), polyacrylamide (PAM) and of ChA/PVA
or ChA/PAM mixtures were studied. The measurements were carried out under
the change of sample properties such as degree of hydrolysis PVA, molecular
weight, and under variable experimental conditions such as temperature, shear
rate, and blend composition. The criterion of miscibility of solution blends, based
on the additivity rule of apparent shear viscosity has been discussed. Moreover,
for the all investigated samples, the mathematical interpretation of relationship
between the apparent viscosity ha and shear rate g, according to the Ostwald
de Waele model was established. Activation energy of viscous flow (Ea) has
also been determined and discussed. The obtained results suggested that the
miscibility of ChA with PVA or PAM depends on the blend composition and on
the molecular weight of ChA.
Key words: chitosan, poly(vinyl alcohol), poly(acrylamide), blends, rheology.
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K. Lewandowska
1. Introduction
Blending is one of the often applied method in modification of high molecular
weight compounds. This method is usually cheaper and less time-consuming for the creation
of polymeric materials with new properties than the development of new monomers and/or
new polymerization routes. An additional advantage of polymer blend is that the properties
of the materials can be tailored by combining component polymers and changing the blend
composition. It is known that specific properties of chitosan (ChA), particularly connected
with its bioactivity, biocompatibility and biodegradability, results in many applications
e.g. in medicine, pharmacy and food and cosmetic industries. Poly(vinyl alcohol) (PVA)
and polyacrylamide (PAM) are synthetic, water-soluble polymers, showing unique shearthickening properties.
Rheological properties of ChA/PVA blend solutions has been studied by Mucha
[1]. The author [1] did not consider the influence of the hydrolysis degree of PVA on the
rheological properties of chitosan with PVA.
The purpose of this study was to evaluate the miscibility of blends of hydrophilic
high molecular weight compounds. The influence of PVA degree of hydrolysis (DH) on the
rheological properties of ChA/PVA blend was investigated.
2. Materials and methods
Flow measurements were carried out using a rotary viscometer Bohlin Visco 88
with concentric cylinder over a range of temperature from 298 K to 318 K and with shear
rates up to 1220 s-1. The investigated blend system contained:
poly(vinyl alcohol): PVA(99) {degree of hydrolysis DH = 99%, Mv = 1.2×105 g/mol},
PVA(88) {DH = 88%, Mv = 1.1×105 g/mol} with chitosan acetate: ChA {degree of
deacetylation DD = 78% Mv = 1.5×106 g/mol},
polyacrylamide: (PAM) {Mv= 3×106 g/mol} with ChA.
Chitosan, PVA and PAM were solubilized separately in 1 M aqueous acetic acid.
Ternary solutions for each system were prepared by mixing the appropriate quantity of
polymer solutions in the weight rations wA : wB of 0.2 : 0.8, 0.5 : 0.5 etc.
3. Results and discussion
The criterion of miscibility of solution blends [1, 2], based on the logarithmic
additivity rule of apparent shear viscosity {ha} has been discussed in the present work.
Moreover, for the all investigated samples, the mathematical interpretation of relationship
between the apparent viscosity ha and shear rate g, according to the Ostwald de Waele model
was carried out [1 - 4]. Activation energy of viscous flow {Ea} was calculated with Arrhenius
equation [1, 4]. The obtained solutions were transparent and stable as the reproducibility of
the flow curves was very high.
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Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009
Rheological Properties of Chitosan Acetate Blends with Vinyl Polymers
ChA/PVA blends
1 0. 00
B.
1. 00
0. 10
a (P a s )
0. 01
C hA/PVA
1 00 :0
8 0:20
5 0:50
2 0:80
0 :100
0. 00
1 0. 00
A.
1. 00
0. 10
0. 01
0. 00
10
1 00
1 00 0
 (s-1 )
Figure 1. Apparent shear viscosity ha versus shear rate g of 2% of ChA and PVA and their
mixtures: ChA/PVA(99), B. ChA/PVA(88); T = 298 K.
400 1/s ChA/PVA(99)
400 1/s ChA/PVA(88)
30
Ea (kJ/m o l)
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
wChA
Figure 2. Activation energy of viscous flow of ChA and PVA and their mixtures versus weight
fraction of ChA (wChA) in the mixture. Dotted line – the values calculated according to the
additivity rule.
Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009
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K. Lewandowska
0.2
A. 320 s-1 ; ChA/PVA(99)
log a
-0.3
-0.8
-1.3
-1.8
-2.3
0
0.2
0.4
wChA
0.6
0.8
1
0.8
1
0.2
B. 320 s-1 ; ChA/PVA(88)
log a
-0.3
-0.8
-1.3
-1.8
-2.3
0
0.2
0.4
wChA
0.6
n
n
Figure 3. Logarithm of apparent shear viscosity (log ha) of ChA and PVA and their mixtures
versus weight fraction of ChA (wChA) in the mixture; T=298K. Solid line – the values calculated
according to the additivity rule.
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
A. ChA/PVA(99)
0
0.2
0.4
w ChA
0.6
0.8
1
B. ChA/PVA(88)
0
0.2
0.4
w ChA
0.6
0.8
1
Figure 4. Rheological parameter n in two shear rate ranges: u 19 s-1 < g < 400 s-1 and
o 400 s-1 < g < 800 s-1 versus weight fraction of ChA (wChA) in the mixture; T = 298 K.
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Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009
Rheological Properties of Chitosan Acetate Blends with Vinyl Polymers
ChA/PAM blends
10.00
ChA/PAM
100:0
80:20
50:50
20:80
0:100
a   Pa
     s
1.00
0.10
0.01
10
100
1000
 s-1
Figure 5. Apparent shear viscosity ha versus shear rate g of 1% of ChA and PAM and their
mixtures: ChA/PAM; T = 298 K.
0.2
400 1/s ChA/PAM
log ha
-0.3
-0.8
-1.3
-1.8
-2.3
0
0.2
0.4
w
0.6
0.8
1
ChA
Figure 6. Logarithm of apparent shear viscosity (log ha) of ChA and PAM and their mixtures
versus weight fraction of ChA (wChA) in the mixture; T = 298 K. Solid line – the values calculated
according to the additivity rule.
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K. Lewandowska
1.6
1.4
1.2
N
1
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
w
0.8
1
ChA
Figure 7. Rheological parameter n in two shear rate ranges:t 200s-1 < g < 800s-1 and
c 800 s-1 < g < 1220 s-1 versus weight fraction of ChA (wChA) in the mixture; T = 298 K.
40
200 1/s
Ea (k J /mol)
35
1130 1/s
30
25
20
15
10
5
0
0
0.2
0.4
0.6
w
0.8
1
ChA
Figure 8. Activation energy of viscous flow of ChA and PAM and their mixtures versus weight
fraction of ChA (wChA) in the mixture. Dotted line – the values calculated according to the
additivity rule.
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Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009
Rheological Properties of Chitosan Acetate Blends with Vinyl Polymers
The experimental results for homopolymers PVA(99), PVA(88), ChA, PAM and their
blends are shown in Figure 1 and Figure 5. The solutions of chitosan, PVA and PAM samples
used in the present investigation, as well as their solution blends behave as non-Newtonian fluids
(Figure 1; Figure 5). Similar behaviour in the case of chitosan solutions has been observed
e.g. by Mucha [1]. The viscosity curves for PVA and PAM solutions may be roughly divided
into to parts: a region below the critical value of shear rate gc {PVA(99): 19 s-1 < g < 700 s-1;
PVA(88): 19 s-1 < g < 400 s-1; PAM: 19 s-1 < g < 1045 s-1}, where a relatively large shearthinning effect is observed, and a second region above the critical value of shear rate, gc , in
which the shear-thickening behaviour occurs [4, 5]. In the case of solution blends, the shearthickening behaviour in the investigated range of shear rate (n < 1) was not observed. The
activation energy of viscous flow EA versus blend composition given in Figure 2 depicted
the positive deviations from the additivity rule in all the investigated systems. In case of
ChA/PAM blend solutions, the negative deviations are observed (Figure 8). Figure 3 and
Figure 6 shows the logarithm of apparent shear viscosity (log ha) investigated blends versus
weight fraction of ChA (wChA). As can be observed, the positive deviation of log ha from
the additivity rule of ChA/PVA solution blends are observed. For ChA/PAM blends, the
log ha values (Fig. 6) fulfilled the linear dependence drawn according to the additivity
rule. Moreover, the value of rheological parameter n both for used chitosan solution as for
solution blends (Figure 4; Figure 7) is lower than one, which indicates a non-Newtonian,
shear-thinning flow pattern of the fluids [6].
4. Conclusions
1. The solutions of homopolymers and their blends used in the present investigation
behave as non-Newtonian fluids.
2. For ChA/PVA blend solutions, the positive deviation of log ha and Ea from the additivity
rule of ChA/PVA solution blends are observed. The positive deviations of Ea mainly
depend on the PVA degree of hydrolysis.
3. In case of ChA/PAM blend solutions, the activation energy of viscous flow (Ea) show
negative deviations from the linearity. This behaviour suggest that ChA with PAM are
poorly miscible.
4. The obtained results may indicate some degree of miscibility of ChA/PVA and ChA/
PAM blends of suitable composition.
5. References
1. Mucha M.; Rheological properties of chitosan blends with poly(ethylene oxide) and poly(vinyl
alcohol) in solution. Reactive& Functional Polymers 38, (1998) pp. 19-25.
2. Lewandowska K., Staszewska D. U., Trzciński S.; Progress on Chemistry and Application of
Chitin and Its Derivatives, Monograph, vol. IV, In: H. Struszczyk (ed), Łódz, (1998) pp. 17-35.
3. Zhang L. M.; Synergistic blends from aqueous solutions of two cellulose derivatives. Colloid
Polym Sci 277, (1999) pp. 886-890.
Progress on Chemistry and Application of Chitin and Its ..., Volume XIV, 2009
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K. Lewandowska
4. Lewandowska K.; Comparative studies of rheological properties of polyacrylamide and
partially hydrolyzed polyacrylamide solutions. J Appl Polym Sci 103, (2007) pp. 2235-2241.
5. Lewandowska K.; Modyfikacja Polimerów, Stan i Perspektywy w Roku 2007, In: Steller R,
Żuchowska D (eds), Wrocław, (2007) pp. 490-495.
6. Skellard A. H. P.; Non-Newtonian Flow and Heat Transfer. Wiley, New York (1967).
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