Advanced Materials Research Vols. 550-553 (2012) pp 904-907
Online available since 2012/Jul/26 at www.scientific.net
© (2012) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.550-553.904
Preparation and hygroscopic property of the Polyacrylamide/MgCl2
hybrid hydrogel
Ying Wang1,a, Liren Fan1,b
1
Engineering Research Center of Nano-Geomaterials of Ministry of Education, China
University of Geosciences, Wuhan, China.
a
[email protected], [email protected]
Keywords: magnesium chloride, polyacrylamide, hybrid hydrogel, hygroscopic property, swelling.
Abstract: Polyacrylamide/MgCl2 hybrid hydrogel desiccant was prepared from magnesium
chloride and polyacrylamide by aqueous solution polymerization. The hybrid hydrogel was
synthesized and characterized by X-ray diffraction. The effect of the experimental factors such as
content of magnesium chloride, concentration of cross-linking agent, initiator content on
hygroscopic performance of the hybrid hydrogel were investigated, furthermore, the hygroscopic
swelling kinetic process of the hybrid hydrogel was studied. The results indicate that hybrid
hydrogel possessed preferable hygroscopic property under the optimum conditions, the hygroscopic
swelling degree achieving 172%. The hygroscopic swelling process of the hybrid hydrogel follows
the kinetic pseudo-second-order model, in addition, the swelling rate decreases with the increase of
relative humidity.
Introduction
Desiccant is a hygroscopic and hydrophilic material that can absorb moisture from its surroundings.
The solid desiccant such as calcium chloride, silica gel, molecular sieve, are used in many areas
frequently, still having some deficiencies: calcium chloride owns better hygroscopic capability, but
also are corrosive to the things needed to dry [1]; zeolite has poor hydrophilic; silica gel performs
good in moisture absorption, but is easy to rupture after absorbing a large amount of water,
moreover, it is hard to reuse silica gel for its high regeneration temperature [2]. Therefore, it is
significantly important to research and develop a new type of desiccant with the integrated
performance.
Halogen salt is a common solid desiccant. The smaller cationic halide radius, the better
hygroscopicity of halide is [3]. Cationic radius of lithium chloride is smallest of the halogen salt, so
it has the best moisture absorption property, but its application is limited because of its high cost.
The radius of the magnesium ion is less than other cations except lithium ion, hence, magnesium
chloride also has excellent hygroscopic property [4], but it quite deliquesces easily. Magnesium
chloride is abundant in salt lakes in China, nevertheless, it has bad influence on the environment
and production. Thus, the utilization of magnesium chloride becomes an urgent issue to be resolved.
A most promising way of achieving the certain performance of inorganic materials is to
compound with organic compounds, in particular polymers, for making use of the extraordinary
capacity of them. Polyacrylamide (PAM) is a new functional polymer material. Owing to its
attached hydrophilic groups (-CO-NH-) and cross-linked network structure, PAM has remarkable
water absorption and conservation ability. In order to promote the aqueous solutions of magnesium
chloride, in this paper, we aimed to synthesize hybrid hydrogel of magnesium chloride and
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Advanced Materials Research Vols. 550-553
905
polyacrylamide, by which the hybrid hydrogel would combine preferable hygroscopic ability of
magnesium chloride with the good water-binding of polycrylamide. The hygroscopic property and
kinetics for hybrid hydrogel were also investigated.
Experimental
Hybrid hydrogel preparation. Hybrid hydrogel was synthesized by aqueous solution
polymerization. The main monomer, cross-linker, initiator and additive are acrylic amine (AM,
analytic reagent), N,N’ –methylenebisacrylamide (NMBA, analytic reagent), ammonium persulfate
(APS, analytic reagent) and magnesium chloride (analytic reagent), respectively.
Measurements of hygroscopic property. The hygroscopic swelling degree of the hybrid
hydrogel was measured in a constant temperature and humidity incubator (SPX-150C) at 30°C. 0.5g
test sample with thickness 2mm were placed into the constant temperature and humidity incubator
and periodically weighed on an electronic balance. The measurements were terminated after the
equilibrium weight of the specimens was reached.
The hygroscopic swelling degree is calculated using the equation (1):
Ht =
m t − m1
× 100%
m1
.
(1)
Where mt, and m1 are the weight [g] of the hygroscopic sample at time t and the dried sample,
respectively. When achieving hygroscopic saturation, the hygroscopic swelling degree of the hybrid
hydrogel is described as Hmax[%].
Results and discussion
b.PAM/MgCl2(70%MgCl2)
2.9786
2.8818
2.7262
2.6417
175
4.0859
3.9336
2.9723
2.8749
2.7210
2.6365
b
170
165
160
c
10
180
c.PAM
Hmax [%]
3.9499
5.7667
185
a.MgCl2
a
5.7373
Intensity [k cps]
4.0999
The characterization for structural property. The structural properties of the synthesized
material (PAM/MgCl2) were analyzed and compared to the PAM and magnesium chloride by XRD
(Fig.1). There are no sharp diffraction peaks of PAM as its structure is amorphous. The main
diffraction peaks of MgCl2 particles at 2θ =15.5°, 21.7°, 28.6°, 33.5°and 34.2°correspond to (110),
(111), (310), (220), (112) Brrag reflection, respectively, and are similar to the main peaks of that
PAM/MgCl2 particles , but PAM/MgCl2 peaks intensity decreases due to the amorphous structure of
PAM.
155
20
30
40
50
60
degree [2θ]
o
Fig. 1 X-ray diffraction patterns of MgCl2,
PAM/MgCl2 and PAM
70
150
0.7
0.8
0.9
1.0
1.1
1.2
cross-linking content [wt%]
o
Fig. 2 Effect of content of cross linking
agent on hygroscopic swelling degree
1.3
906
Advances in Chemical Engineering II
Table 1 Effect of magnesium chloride mass on hygroscopic swelling degree
MgCl2
0
60
70
80
85
90
[mass%]
Hmax
35
124
136
156
172 The aqueous solution after
[%]
absorbing moisture
100
82
Effect of magnesium chloride mass on hygroscopic swelling degree. Table1 shows the
relationship between magnesium chloride mass and the equilibrium hygroscopic swelling degree at
30°C/90%R.H. condition. Polyacrylamide gel exhibited low hygroscopic swelling degree from
Table1. It can also observed that the hygroscopic swelling degree of hybrid hydrogel is significantly
higher than that of the pure polyacrylamide gel and magnesium chloride, the more addition of
magnesium chloride mass, the higher hygroscopic swelling degree of hybrid hydrogel was, besides,
the hygroscopic swelling degree can reach 172% with 85% MgCl2 mass. The phenomenon was
attributed to synergistic effect of magnesium ions and acylamino in polyacrylamide However, as the
MgCl2 mass surpass 85%, the surface of hybrid hydrogel appeared the extravasation phenomena.
According to the results, the proper additive mass of magnesium chloride is 85%, with which the
PAM/MgCl2 hybrid hydrogel possesses the potential application as high hygroscopic performance
desiccant.
Effect of content of cross-linking agent on hygroscopic swelling degree. Figure 2 indicates
effect of content of cross-linking agent (NMBA) on hygroscopic swelling degree at 30°C/90%R.H.
condition. It can be seen in the Figure 2 that the maximum of the Hmax value for the hybrid hydrogel
attained 184% with 0.9% NMBA content. The results illustrated the appropriate content of
cross-linking agent was 0.9% for the preparation.
Effect of content of initiator on hygroscopic swelling degree. Figure 3 exhibits effect of
content of initiator on hygroscopic swelling degree at 30°C/90%R.H. condition. Considering the
fact that polymerization determines the performance of hybrid hydrogel, in terms of the preparation,
the polymerization depends on the dosage of initiator. It can be speculated clearly from Figure 3
that the optimum amount of initiator is 1.0%.
0.60
175
70%RH
0.55
170
80%RH
0.50
0.45
165
t/Ht
Hmax [%]
0.40
160
0.35
90%RH
0.30
155
0.25
0.20
150
0.15
145
0.10
0.05
140
0.00
0.6
0.7
0.8
0.9
1.0
1.1
content of initiator [wt%]
Fig. 3 Effect of content of initiator
on hygroscopic swelling degree
o
1.2
0
10
20
30
40
50
t/h
o
Fig. 4 t/H t-t curves of adsorption vapor
onto hybrid hydrogel
The hygroscopic swelling kinetic of hybrid hydrogel. In order to develop a model for the
hygroscopic swelling behavior of the hybrid hydrogel, in this paper, pseudo-second-order model [5]
was applied to the experimental swelling data. This equation has the form of the following equation
(2):
Advanced Materials Research Vols. 550-553
907
d (qe − qt )
= − kdt .
(qe − qt ) 2
(2)
Where k [min-1] is used to quantify the swelling rate, qe [%] is the equilibrium hygroscopic
swelling degree, qt [%] is the hygroscopic swelling degree at time t. In this paper, Hmax substitutes
for qe, Ht substitutes for qt. Integrating equation (3) for the boundary conditions: t = 0 to t = t, Ht = 0
to Ht = Ht, gives:
t
1
t
= 2 +
Ht kH max Hmax .
(3)
Table 2 Parameters of Pseudo-second-order model
Relative humidity[%]
Hmax[%]
K[min-1]
Hmax [Experimental data, %]
70
80
90
88.0
95.5
155.0
0.0135
0.0097
0.0024
86.1
92.3
145.6
The fitting curves of t/Ht-t were shown in Figure 4. The value of Hmax and k determined by the
linear curve fitting were summarized in Table 2. As can be seen clearly that t/Ht was linear with
regard to t in Figure 4. In Table 2, it can be speculated from the figures that the swelling model fit
the experimental data quite well for most of the cases. The trend shown in Table 2 was that the
hygroscopic swelling degree of hybrid hydrogel increased as the relative humidity increasing,
therefore, PAM/MgCl2 hybrid hydrogel can play a role in a high humidity environment. On the
contrary, the rate constant k decreased with the increase of the relative humidity, which
demonstrated that it took more time for hybrid hydrogel to reach equilibrium swelling degree at
higher relative humidity.
Conclusion
In this paper, PAM/MgCl2 hybrid hydrogel was prepared by aqueous solution polymerization. The
measurement results reveals that under the optimum preparation conditions, with the content of
magnesium chloride, concentration of cross-linking agent, initiator content were 85%, 0.9% and
1.0%, respectively, the hybrid hydrogel displays great hygroscopic property (172%). In addition,
hygroscopic swelling process of hybrid hydrogel follows the pseudo-second-order model,
furthermore, the lower relative humidity, the greater hygroscopic swelling rate of hybrid hydrogel.
References
[1] Li Xin, Li Zhong, Wei Lifei. CHEMICAL INDUSTRY AND ENGINEERING PROGRESS,
2004. In Chinese.
[2] Surajitr Pramuang, R.H.B. Exell. Renewable Energy, 2007.
[3] Li xin, Li Huiling, Huo Siqi. Kinetics And Catalysis, 2010. In Chinese.
[4] Zhu Peiyi. Ocean University of China, Shan Dong, 2009. In Chinese.
[5] Ho. YS, McKay. G, Process Biochemistry, 1999.
Advances in Chemical Engineering II
10.4028/www.scientific.net/AMR.550-553
Preparation and Hygroscopic Property of the Polyacrylamide/MgCl2 Hybrid Hydrogel
10.4028/www.scientific.net/AMR.550-553.904