The effect of Polymerization from chitosan-g-poly(acrylic acid ...

vainclamInternet and Web Development

Dec 14, 2013 (3 years and 7 months ago)

154 views

E
ffect of cross
-
link
ing agents

on the modification of chitosan
with poly(acrylic acid) as superabsorbent polymer


Agus Haryono, Sri Budi Harmami and Dewi Sondari


Polymer Chemistry Group, Research Center for Chemistry

Indonesian Institute of Sciences

(LIP
I)

Kawasan Puspiptek Serpong, Tangerang 15314


Indonesia

Phone: +62
-
21
-
7560929, fax: +62
-
21
-
7560549

e
-
mail:
haryonolipi@yahoo.com



ABSTRAK

Sintesis
superabsorben

k
itosan
-
g
-
poli
(asam
akrilat
)
dilakukan
melalui
proses kopolimerisasi
cangkok

men
ggunakan cerium amonium nitrat

(CAN)
s
ebagai inisiator dan
N
,
N
-
methylenebisacrylamide
(MBA)
sebagai
pengikat silang
.
Penambahan

MBA

pada

proses
polimerisasi mempengaruhi
kinerja
superabsorben
.
Sifat absorbsi

superabsorben d
iuji
dalam
aquades

dan

dalam
larutan 0,9 wt% NaCl.

Kitosan

dilarutkan dalam larutan asam asetat (1%)
dengan
aliran
gas
nitrogen
pada suhu

60
o
C
, dan

di
tambah
kan

dengan
CAN
.

Ke dalam campuran

dit
ambahkan asam akrilat dengan variasi

penambahan
MBA
. Hasil
reak
si

dipindahkan ke dalam
larutan
1 M
natrium hidroksida
,
dicuci dengan etanol
dan
disimpan dalam oven vakum s
emalam
pada suhu kamar.
Superabsorben kitosan
-
g
-
poli
(asam akrilat
)
dikarakterisasi

dengan
spektroskopi
FTIR dan
scanning electron microscope

(SEM).
Daya serap air semakin
meningkat dengan bertambahnya jumlah
pengikat silang

MBA

yang ditambahkan
.
Polimer
kitosan
-
g
-
poli
(asam akrilat
)
yang dihasilkan
menyerap
air
218 kali berat,
dan menyerap

larutan
garam 0,9%,
sebanyak

145 kali beratnya.


Kata kunci
: p
olimeris
asi,
pengikat silang
, superabsorben
,
poli(asam akrilat),

kitosan.



ABSTRACT

A chitosan
-
g
-
poly(acrylic acid) superabsorbent was prepared by graft co
-
polymerization using
cerium ammonium nitrate (CAN) as an initiator and
N,N
-
methylenebisa
crylamide
(MBA) as a
crosslink
ing agent
.
Addition of

MBA

during the polymerization influenced the swelling
capacity of the superabsorbent. The swelling rate
of superabsorbent
was
determined

both
in
distilled water and in 0.9 wt%
solution
of
NaCl. Appropriate amount
of chitosan was dissolved
in acetic acid solution (1%) in
a nitrogen line
,

and

heated to 60
o
C
.

T
he

mixture was

added
by
CAN
and
followed
addition of
vari
ed ammount

of
MBA (2
-
4 wt%)
. The
obtain
ed

granular
product was transferred into sodium hydroxide
1 M
aq
ueous solution
,
washed

with ethanol

and

dri
ed in vacuum oven at room temperature. The chitosan
-
g
-
poly(acrylic acid) superabsorbent
was characterized by FTIR and scanning electron microscope
(SEM). The water absorbency
increase
d

with increasing MBA content
from 2, 3 and 4 wt%.
C
hitosan
-
g
-
poly(acrylic acid)
adsorb
ed water

more than 218 times its weight,
and adsorbed

a 0,9 % saline solution 145 times
its weight.


Keywords
: polymerization, crosslink
ing agent
, superabsorbent, poly(acrylic acid), chitosan.



INTR
ODUCTION

Modification

of natural polymers with synthetic polymers is of great
interest because of their application to biomedical and biodegradable materials
[1].
One natural polymer

that ha
s

attracted great attention recently is chitosan

[
2
]
.
C
hitosan can

be used in the fields of wastewater treatment, food processing,
cosmetics, pharmaceuticals,
biomaterials and agriculture [
3
]
. With its fibrous
structure, chitin is hardly soluble in any solvent.
C
hitosan can be dissolved in
a
weak

acid solution and become
s a cationic polymer because of the protonation
of amino groups on the C
-
2 position of pyranose ring

[
4
]
.

Superabsorbent

polymer is
three
-
dimensionally
crosslinked hydrophilic
polymer

which has
the
capability

of swelling and retaining
large

volumes
of
wate
r

in
the
swollen state

[
5
]
.
S
uperabsorbent

polymer

for agricultural
application
has shown
their capability
to help reduc
ing

irrigation water
consumption,
decreasing

the death rate of plant,
and
improv
ing

fertilizer
retention in soil [
6
].

Superabsorbents pr
epared with natural material, such as
cellulose, starch and chitosan,
have attracted great attention
because of their
abundant resources, low produ
ction
-
cost and biodegradability

[
7
-
9
]. Chitosan, a
high molecular weight polysaccharide from chitin, is the s
econd most abundant
natural polymer after cellulose. Chitosan is excellent biodegradable biomass
and can be degraded into nontoxic products
in vivo

[10
]
. It has both reactive

NH
2

and

OH groups, convenient for graft polymerization of hydrophilic vinyl
mo
nomers into it under mild reaction condition, and the acquired
superabsorbent resin can absorb aqueous solution hundreds of times than their
own dry sample and should have antibacterial activities [
11
-
13
].


Graft co
-
polymeriz
ation is considered to be a

pro
mising approach for
designing a wide

v
ariety of natural polymer applications [14]
.

Research

on the
graft co
-
polymers of chitosan

with vi
nyl monomers
were reported previously

[15
-
17]
.

Chitosan

can be

co
-
polymeriz
ed with PMMA
.
There are a few reports
on chit
osan MMA graft

copolymers [18]
. Recently we reported

synthesis of
chitosan
-
HEMA graft copolymer

and its properties in biological environment

[19]
.

Grafting of poly(ethylene glycol) methyl ether methacrylate
macromonomer (methoxy

poly(ethylene glycol) metha
crylate) onto chitosan
backbone was studied under homogeneous

conditions in a 1% acetic aci
d
solution

with

CAN as the initiator

[20]
.

The crosslinking agent, a monomer with

two or more double bonds,
provides the polymer network

structure by connecting the
long, linear chains in
these

polymerizations. Hyd
rogel networks formed from poly
(acrylic acid)
(PAA) have the ability to absorb many times

their weight in water and are the
basis of a class of materials

called super
absorbents. These polymers are used in
ma
ny

applications including diapers and personal hygiene products,

ion
exchange resins, membranes for hemodialysis and

ultrafiltration
, agriculture

and controlled release devices
[21

24
]
.

Superabsorbent polymers have a
network structure and

suitable degree o
f crosslinking

[25
].

In this article, we synthesized a chitosan
-
g
-
poly(acrylic acid)
superabsorbent with investigation of the influence of crosslinking agent on the
capacity for absorbing water. Fourier transform
ed

infrared (FTIR) spectroscopy,
scanning el
ectron microscopy (SEM)

techniques are used to characterize. The
effect of
ratio of
N,N
-
methylenebisacrylamide (MBA) on water absorbency was
discussed.



EXPERIMENTAL METHODS

Materials

Chitosan
with degree of deacetylation 60%
was su
pplied by Brata
co
Che
m
icals

(Indonesia)
. A
crylic acid was purchased from Merck
(Singapore) of
analytical grade
.

N
,
N
-
methylenebis
-
acrylamide
was purchased
from Sigma
-
Aldrich (Unit
ed Kingdom) of analytical grade
.

C
eric ammonium nitrate was
purchased from Sigma
-
Aldrich (Singapore
) of analytical grade
.

A
cetic acid was
reagent technical grade fr
om Brataco Chemi
c
a
ls

(Indonesia)
.

E
thanol
and
a
quadest
w
ere purified by distillation

at

RCChem
-
LIPI
. S
ilicon oil and
sodi
um
hydroxide was purchased from Merck (Singapore) of analytical grade
purity.


Preparation o
f
chitosan
-
g
-
poly(acrylic acid
)
superabsorbent
polym
e
r

Appropriate amount of 1 g
chitosan
was
dissolved in 120 ml acetic acid

1%
aqueous
solution in a 500 ml three
-
neck flask equipped with a mechanical
stirrer, a reflux condenser, a
funnel and a nitrogen line. After purging with
nitrogen for 30 min to remove the oxygen dissolved in the system, the solution
was heated to 60
o
C and 0.4 g

of c
eric ammonium nitrate

was added while
mixing the process vigorously. After 10 min, 13.52 ml of ac
rylic acid
dan
56
.
8
m
g

of
N
,
N
-
methylenebis
-
acrylamide

were added. The
reaction mixture

was kept
at 60
o
C for 3 hours 40 min then cooled at room temperature for one night. In
the next day, the mixture was distilled. The
obtain
ed granular product was
transfer
red into sodium hydroxide
1 M
aqueous solution
,
and

washed with
ethanol. The sample were
then
spread on a petri dish
,

and

stored in vacuum
oven overnight to dry at room temperature. Synthesis of chitosan
-
g
-
poly(acrylic
acid) was
conducted

with vari
ed

amoun
t of
N
,
N
-
methylenebis
-
acrylamide

as
crosslink
ing agent

in the range of 2
-
4 wt%.


Measurement of water absorbency

1
3

Samples were immersed
both
in excess distilled water and in
0.9 wt%
NaCl
aqueous
solution

at room temperature
with
various time interv
als to

observe

the swelling behavior.
The swollen samples were
were then separated
from unabsorbed water by filtering through a 100
-
mesh screen under gravity for
30 min with no blotting of samples. Water absorbency of the superabsorbent
composite in distilled wa
ter

and in 0.9 wt% NaCl solution
, Q
eq
,
were

calculated
using the following equation:

Q
eq
=

where m
1

and m
2,

respectively, are the weight of the dry sample and the swollen
sample. Qeq is calculated as gram of water per gram of sample
.


Characterization

Infrared absorption spectra of
the
samples were taken using a IR Prestige
-
21 Shimadzu Spectrophotometer.
The
SEM micrographs
photographs of
the
samples were
obtained using

a JSM
-
5600LV SEM instrument (J
EO
L, Ltd.)
after coating the samp
le with gold film using an acceleration voltage of 20
kV
.



RESULT AND DISCUSSION

FTIR Spectra

Analysis

Grafting
co
-
polymerization
of
acrylic acid

to
chitosan
polymer backbone
was carried out

in

NH
2

and

OH

functional groups of chitosan
.

The structural
d
ifference

between
unmodified

chitosan and
the obtained
chitosan
-
g
-
poly(acrylic acid)

superabsorbent

was

confirmed by FTIR spectroscopy

and

show
n

in Figure
1
.
The
unmodified

chitosan showed

the absorption band at
1660, 1546, 1375, 1066 and 1031 cm
-
1
, which
are
attribut
ed to
C=O stretching
of amide I

bands
,

NH
2
,

NHCO of amide,
C

OH
and
C

O

C

of chitosan
,
respectively
.
The presence of amide bands in the spectrum of unmodified
chitosan showed the remaining chitin backbone, since the degree of
deactylation of
chitosan used in this work was 60%.

As show
n

in
Figure

1b, the absorption bands at 3460 cm
-
1

ascribed to O
-
H

of chitosan
, absorption bands at 1633
and 1007 cm
-
1

ascribed

to

C=O

and C
-
OH
of acrylic acid

groups into

chitosan

backbone
.

Grafting polymerization

process
was uncomplete in this step, because the absorption band of
-
N
H
2

of chitosan at
1552 cm
-
1

was remained in the spectrum.
Showed in Figure
1
c and d
, the
absorption bands at 34
5
0



3
460

cm
-
1

ascribed to O
-
H, t
he absorption bands of
chitosan,
C=O (16
0
0



1730 cm
-
1
) and absorption bands at
3040
-

3050

cm
-
1

ascribed to C

H stretching vibration

from of acrylic acid to grafted into
chitosan backbone.

The absorption bands of

NH
2

at around 1500 cm
-
1

was
di
sappeared.
This information
confirm

poly(
acrylic aci
d
) was grafted onto

to
chitosan polymer

backbone
.




Figure
1
. FTIR spectra of pure chitosan (a), chitosan
-
g
-
PAA with crosslink
ing
agent

2 wt% of MBA (b), 3 wt% of MBA (c) and 4 wt% of MBA (d)


Effect of
crosslink
ing agent

on water absorbency

Water ab
sorbency of the superabsorbent
polymers

incopor
ated with
different amounts of MBA

in distilled water and in 0.9 wt% NaCl solution
wa
s
shown in
Figure
2
.
The water absorbency
of the obtained chitosan
-
g
-
poly(acrylic acid)
increase
d

until

218 g/g as the amo
un
t of MBA increase
d

until

4 wt%
.
The

water absorbency
increase
d

with increasing
ammount
of
MBA/AA

ratio
.

According to the relation
ship

between the average kinetic ch
ain length
and concentration of crosslink
ing agent

in
the
polymerization, the molecular
weig
ht of grafted monomer on polymer backbone will decrease with increasing
of the concentration of
crosslink
ing agent
and then more polymer branch will
be generated. As mentioned in previous study
of
Liu & Rempel

(
1997), the
polymer chain contribute
d

to water

absorbency of superabsorbent. Thus, further
b

d

c

a

increasing
crosslink
ing agent

ratio to monomer up to
4 wt
%
increase
d

the water
absorbency.



Figure
2
. Variation of Q
eq

in distilled water and 0.9wt% NaCl aqueous solution
with
crosslink
ing agent

for C
hit
osan
-
g
-
PAA.


Effect of
MBA

content on swelling rate

The swelling rate of a superabsorbent
wa
s significantly influenced by
swelling capacity. The swelling rate for C
hitosan
-
g
-
PAA superabsorbent in
disti
lled water was shown in Figure
3
. The curved for C
hito
san
-
g
-
PAA
superabsorbent prepared with
2

wt% of
MBA

exhibited lower swelling rate and
required more time to reach absorption equilibrium comparing with C
hitosan
-
g
-
PAA grafting with
3

wt% and
4

wt% of
MBA
. The initial swelling progress
was primarily to the

water penetrating into polymeric
backbone
through
capillarity and diffusion. Water absorbency of C
hitosan
-
g
-
PAA was increased
with increasing of
MBA
/AA

ratio.

T
his was because of
MBA

accelerated
grafting process of poly(acrylic acid) onto chitosan backb
one. Therefore, the
superabsorbent with more
MBA

showed higher initial swelling rate and needed
more time to reach equilibrium
of
water absorbency.















Figure
3
.
Influence of crosslink
ing agent

to s
weeling rate in distilled water for
C
hit
osan
-
g
-
PAA superabsorbent

(A) and in 0.9wt% NaCl aqueous
solution for C
hitosan
-
g
-
PAA superabsorbent (B).


Morphological analysis

of chitosan
-
g
-
poly(acrylic acid) superabsorbent

SEM micrograph
of superabsorbent chitosan
-
g
-
poly(acrylic acid) with
various amo
unt of
MBA

were observed and shown in Figure
4, 5 and 6
,
respectively. It can be observed that
in
crosslinke
d

PAA (Figure 4), t
he
superabsorbent with
2
% of
MBA

showed a porous and rough surface
comparred to the other
s

(
3
% and
4
% of
MBA
/ AA ratio
). However,

the addition
of
MBA

as
crosslink
ing agent

resulted in superabsorbent forming a fewer
(
A
)

(B)

porous and tight surface. It can be concluded that addition of more
MBA

as a

crosslink
ing agent

produced a complete grafting co
-
polymerization process.
Thus
,

the obtained

polymer has great influence on su
r
face morphology of the
superabsorbent. This change of surface morphology indicated that the
interaction between chitosan and poly(acrylic acid) was effected by
MBA

ratio,
furthermore influenced on swelling ability of corr
esponding superabsorbent.







Figure 4. SEM micrographs of
chitosan
-
g
-
poly(acrylic acid) superabsorbent
incorporated with 2 wt% MBA






Figure 5. SEM micrographs of chitosan
-
g
-
poly(acrylic acid) superabsorbent
incorporated with 3 wt% MBA






Figure 6. SEM micrographs of chitosan
-
g
-
poly(acrylic acid) superabsorbent
incorporated with
4

wt% MBA


CONCLUSIONS

A C
hitosan
-
g
-
PAA

s
uperabsorbent
polymer

was synthesized by graft
co
-
polymer
ization reaction between chitosan and acrylic acid

(AA)
in the presence
of
N
,
N
-
methylenebis
-
acrylamide as a crosslinking
agent
in aqueous solution.
Various amount of
MBA

crosslink
ing agent

showed significant influenc
e on
water absorb
e
ncy of the chitosan
-
g
-
poly(acrylic acid) superabsorbent.
Ratio

of
MBA

co
ntain
to acrylic acid monomer
improved the obtained
water
superabsorbency of the chitosan
-
g
-
poly(acrylic acid).



REFERENCES

[1] Aoi, K., Takasu, A. and Okada, M.,

Macromolecules
,
30,
6134

(1997).

[2]

Stevens, W. F., Rao, M. S., and Chandrkrachang, S.,
Chitin and Chitosan,

Asian Institute of Technology, Bangkok, Thailand (1996).

[3] Chen, R. H., and Chen, H. C.,
Advances in Chitin Science,
National Taiwan
Ocean University, Keelung, Taiwan (1998).

[4] Tsai, M.
-
L., Ph.D. Dissertation, National Taiwan Ocean

University,
Keelang, Taiwan (1997).

[5] Omidian, H., Hashemi, S. A., Sammes, P. G., & Meldrum, I. G.
Polymer
,
39, 3459

3466

(1998)
.

[
6
] Tomaszewska, M., & Jarosiewicz, A.
,

Journals of Agricultural and Food
Chemistry
, 50, 4634
-
4639

(2002).


[
7
] Farag, S.,
& Al
-
Afaleq, E. I.
,

Carbohydrate Polymers
, 48, 1
-
5

(2002)
.

[
8
] Ge, H. C., Pang, W., & Luo, D. K.
Carbohydrate Polymers
, 66, 372
-
378

(2006)
.

[
9
] Kiatkamjornwong, S., Mongkolsawat, K., & Sonsuk, M.
Polymer
, 43,
3915
-
3924

(2002)
.

[
10
]
Dutkiewicz, J. K. Journ
al Biomedical Materials Research, 63, 373

381

(2002)
.

[
11
] Nge, T. T., Hori, N., Takemura, A., & Ono, H.
Journal of Applied Polymer
Science
, 92, 2930
-
2940
,
(2004).
.

[
12
] No, H. K., Park, N. Y., Lee, S. H., Hwang, H. J., & Meyers, S. P.
Journal
of Food Scie
nce
, 67, 1511
-
1514

(2002)
.

[13
]
Junping
Zhang, Qin Wang and Aiqin Wang
,
Carbohydrate Polymers
,

68
367

374
,
(2007)
.

[
1
4]

L. Wei, L. Zhaoyang, F. J. Xin
-
de,
Biomater. Sci. Polym. Ed.,


4(5), 557
(1993).

[
1
5]

C. Peniche, W.A. Monal, N. Davindenko, R. Sastre,
A. Gallardo, J.S.
Roman,

Biomaterials,

20, 1869 (1999).

[16]

K. Kurita, M. Kawata, Y. Koyama, S.I. Nishimura,
J. Appl Polym Sci
., 42,

2885 (1991).

[17]
T. M. Don, C.F. King, W.Y. Chiu,
J.Appl. Polym Sci
., 86, 3057 (2002).

[18] S. C Hsu, T. Don, W. Y. Chiu
,
J Appl. Polym Sci
, 86, 3047 (2002).

[19]
C. Radhakumary, G. Divya, P. D. Nair, S. Mathew, C. P. Reghunathan
Nair,
J. Macromolecular Sci.
, 40(7), 715 (2003).

[20]
Gerasimčik1,

Asta Zubrienė and

Gervydas Dienys.
CHEMIJA
,
18. No. 2.
33

38

(2007)
.

[
21
] Buchh
olz FL, Grahan AT.
Modern superabsorbent polymer technology
.
New York: Wiley;
(
1998
)
.

[22
] Gudeman L, Peppas NA.
J Membr Sci

107:239

(1995)
.

[23
] Peppas NA,
Hydrogels in medicine and pharmacy, vol. 2
. Boca Raton, FL:
CRC Press;
(
1987
)
.

[
24
] AmEnde MT, Pepp
as NA.
J Appl Polym Sci

59(4):673

85

(1996)
.

[25
]

Omidian, H.; Hashemi, S. A.; Sammes, P. G.; Meldrum, I.

Polymer

40,
1753

1761

(1999)
.