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Journal of Engineering Science and Technology Special Issue on SOMCHE 2014 & RSCE 2014 Conference, January (2015) 61 - 70 © School of Engineering, Taylor’s University
61
PREPARATION AND CHARACTERIZATION OF HYDRAZINE-MODIFIED POLY(ACRYLONITRILE-CO-ACRYLIC ACID)
NUR S. M. RAPEIA1,*, SITI N. A. M. JAMIL
2, LUQMAN C. ABDULLAH
1,3,
MOHSEN N. MOBAREKEH3,5, THOMAS C. S. YAW
1, SIM J. HUEY
4,
NUR A. M. ZAHRI1
1Department of Chemical and Environmental Engineering, Universiti Putra Malaysia,
43400 UPM Serdang, Selangor D.E. Malaysia 2Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM
Serdang, Selangor D.E. Malaysia 3Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia,
43400 UPM Serdang, Selangor D. E. Malaysia 4Department of Chemical Engineering, Faculty of Engineering and Science, Universiti
Tunku Abdul Rahman, Jalan Genting Kelang 53300 Setapak, Kuala Lumpur, Malaysia 5Department of Environmental Science, Faculty of Agriculture and Nature resource,
Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
*Corresponding Author: [email protected]
Abstract
Copolymerization of acrylonitrile (AN) with acrylic acid (AA) was carried out
in deionized water (DI) at 40 °C by free radical polymerization method using
sodium bisulfite (SBS) and potassium persulfate (KPS) as redox initiators. The
synthesis of poly(AN/AA) was investigated with mole ratio of AN/AA; 100/0,
97/3, 95/5, 93/7 and 90/10. The poly(AN/AA) was then modified with
hydrazine hydrate via nucleophilic addition reaction. The functional groups,
morphology and polymer contents (carbon, hydrogen, nitrogen and sulphur) of
the poly(AN/AA) and hydrazined poly(AN/AA) were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM)
and Elemental analysis respectively. The yield of polyacrylonitrile (PAN) was
73% and decreased as the amount of AA increased. The successful of
polymerization was confirmed by the appearance of C≡N functional group at
2240 cm-1 and the incorporation of acrylic acid in copolymer system was
established by the appearance of C=O at 1730 cm-1 from the IR spectra. The
polymer modification was successfully accomplished by the complete
disappearance of C≡N from IR analysis. The SEM images have shown that the
average spherical diameter of poly(AN/AA) and hydrazined poly(AN/AA) were
~130 nm and ~150 nm respectively.
Keywords: Polyacrylonitrile, Acrylic acid, Copolymer modification, Synthesis,
Hydrazine.
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Nomenclatures
C=N Imine group
C=O Carbonyl group
C≡N Nitrile group
NH2 Amine group
OH Hydroxyl group
Abbreviations
AA Acrylic acid
AN Acrylonitrile
CHNS Carbon Hydrogen Nitrogen Sulphur
DI Deionized water
FTIR Fourier Transform Infrared
H Hydrazine hydrate
IR Infrared spectra
KPS Potassium persulfate
PAN Polyacrylonitrile
SBS Sodium bisulphite
SEM Scanning Electron Microscope
1. Introduction
Polyacrylonitrile (PAN) is well known and has widespread acceptability among
variety of precursors available for making carbon fibers. Carbon supply is an
interesting subject due to high demand from all around the world since the
production of PAN fibers increased up to 26 million lbs per year and currently
reached nearly 6 billion pound sterling per year worldwide effort [1-3].
However, homopolymer (PAN) alone as precursor results poor quality of
carbon fibers [4, 5]. Hence, the suitable acidic comonomers are introduced
during polymerization of PAN to improve its properties. During the heat
treatment process of PAN precursor, acidic group catalyses the cyclization of
nitrile group producing thermally stabilized acrylic fibers and increased the
hydrophilicity of the polymers [4, 5].
Copolymers of acrylonitrile with various comonomer such as acrylic acid,
methacrylic acid, itaconic acid and methyl acrylate have been reported in the previous
study [1, 4-6]. In this present study, AA was selected to copolymerize with AN due to
AA properties that could provide hydrophilicity, reactivity (more reactive than AN)
and ionic effect of carboxylate ions due to the dissociation of AA [7]. The
incorporation of AA monomer could reduce the hydrophobicity of PAN system and
increase the chances of carboxylic group to interact with nitrile group during
cyclization reaction [4, 6, 8]. In addition, the improvement of the polymer properties
by chemical modification is an interesting topic to the researchers.
Modification of polymer was introduced to achieve desirable properties in
sequence that the resulting materials could possibly be used for particular
application [9]. Modification on polymer surfaces either physically or chemically
is needed to improve its adsorption capacity [10]. Hydrazine hydrate (H)
is basically used to improve chemical and heat resistance of the polymer
fibers. Hydrazine has highly alkaline character (pH> 12.5) and only certain type
of polymer can be modified with hydrazine because some polymers
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cannot withstand such highly alkalinity. In addition, hydrazine has strong
hydrolyzing, reducing effects and relatively environmental friendly due to fast
degradation [11]. Therefore, hydrazine hydrate (H) was chosen as modifying
agent for the modification of poly(AN/AA).
In this present work, the copolymerization of acrylonitrile (AN) with acrylic
acid (AA) comonomer was synthesized by free radical polymerization to form
spherical beads of poly(AN/AA). Since the development of the polymer
properties become crucial challenge of the research field for the use in various
industrial application, the modification of known polymer (poly(AN/AA)) is
preferred compared to the synthesis of polymers from the new finding monomers.
In this present work, the selected copolymer with the highest yield was
chemically modified with hydrazine hydrate to form modified poly(AN/AA). The
copolymer of poly(AN/AA) and modified poly(AN/AA) were characterized by
Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscope
(SEM) and Carbon Hydrogen Nitrogen Sulfur (CHNS) elemental analysis.
2. Experimental
2.1. Materials
Acrylonitrile (AN) was purchased from R&M Chemicals. Acrylic acid (AA) and
hydrazine hydrate (H) were obtained from MERCK. AN and AA were purified by
passing over the aluminum oxide to remove an inhibitor. Sodium bisulfite (SBS)
and potassium persulfate (KPS) were supplied from ChemAR and directly used as
received. Hydrazine hydrate, ethanol and methanol were used as received without
further purification. Deionized water (DI) was used throughout this experiment.
2.2. Synthesis of poly(AN/AA)
The acrylonitrile and acrylic acid were copolymerized using free radical
polymerization technique. SBS and KPS were used as initiators to initiate the
polymerization process. The copolymers were synthesized with five different mol
ratios of AN/AA which are 100/0, 97/3, 95/5, 93/7 and 90/10 respectively. The
polymerization was carried out in three necks round bottom flask at 40 °C with
the flow of nitrogen gas. 190 ml of deionized water was added into the flask and
nitrogen gas was purged approximately 30 minutes. After 30 minutes, AN and
AA were added into the reaction medium according to the selected mole ratio
then followed by SBS. After 15 minutes, KPS was added into the reaction flask.
The mixture was continuously stirred with magnetic stirrer and polymerization
process was allowed for 3 hours at 40 °C in nitrogen atmosphere. The product
formed was precipitated, filtered and washed thoroughly with 100 ml of methanol
and 100 ml of deionized water to eliminate the residual of monomers and traces
of initiators. The copolymers was dried in vacuum oven at 45 °C till a constant
weight achieved. Polymerization of PAN was prepared the same way as
poly(AN/AA).
2.3. Modification of poly(AN/AA) with hydrazine hydrate
0.5 g of poly(AN/AA) and 20 ml of hydrazine hydrate were placed together in a
three neck round bottom flask. The mixture was refluxed at 70 °C for 2.5 hours.
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The modified poly(AN/AA) was filtered and washed with the excess water until
the pH was achieved at 6.8-7.5. The modified poly(AN/AA) was washed again
thoroughly and dried overnight in oven at 60 °C until constant weight obtained.
2.4. Characterization
Infrared spectra (IR) of the poly(AN/AA) and modified poly(AN/AA) were
recorded on Fourier Transform Infrared (FT-IR) spectrometer (Perkin Elmer
1750X) using KBr pellets. The functional groups of sample were determined in
the range of 4000-400 cm-1
based on IR spectra. CHNS elemental analysis was
done based on the determination of carbon (C), hydrogen (H), nitrogen (N) and
sulfur (S) contents in the polymer sample of poly(AN/AA). CHNS Elemental
analysis was performed using LECO CHNS-932 spectrometer.
Scanning Electron Microscope (SEM) (Hitachi S-3400N) was operated at 20
kV to examine the morphology of poly(AN/AA) before and after modification.
Samples were coated with a thin layer of Au/Pd. The scanning electron
photographs of the sample were observed at 1000X to 5000X relying on the
nature of sample. The average particle sizes of beads were determined from the
images provided by the SEM.
3. Results and Discussion
3.1. Synthesis of poly(AN/AA)/ yield production
The yield percentage of poly(AN/AA) that was synthesized by redox method is
shown in Fig. 1. PAN achieved the highest yield (73%) as compared to the
copolymers. Possibly, there are no malfunctions or defects exist in polymer chains
since the AA was not incorporated with the AN monomer during the
polymerization of PAN [12, 13]. As anticipated, the yield percentages of
copolymers are lower than the yield of PAN. Amongst all of copolymers
obtained, the 93/7 ratio of AN/AA copolymer achieved the highest yield (72%)
and the 90/10 ratio obtained the lowest yield (63%).
The lower yield of poly(AN/AA) 97/3 (64%) probably caused by the
additional of comonomer during the copolymerization process. This is probably
due to the copolymer radicals with AA units that are considerably more reactive
than the PAN growing radicals. Besides, the additional of AA leads to the
formation of carboxylate ions [8, 14]. The small amount of AA monomer added is
not enough for the carboxylate ions to utilize the polar nitrile group of AN due to
the high degree of dissociation occur in aqueous medium.
As shown in Fig. 1, the yield of polymerization increased as the amount of
AA increased. Probably, higher amount of AA in feed produced more carboxylate
ions that utilized the AN nitrile group during copolymerization and consequently
increased the yield of poly(AN/AA). However, at certain amount of AA, the yield
decreased drastically. Poly(AN/AA) 90/10 resulted the lowest yield percentage as
compared to other copolymers. This is probably due to the incorporation of high
amount of AA monomer as high as 10% reduced the rate of polymerization. Same
observation was reported before by [12].
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Fig. 1. Yield Percentage of Poly(AN/AA).
3.2. Characterization of poly (AN/AA)
3.2.1. Fourier transform infrared spectra (FTIR)
The representative IR spectra of synthesized poly(AN/AA) and modified
poly(AN/AA) are shown in Figs. 2 and 3. Figure 2 shows IR spectra of PAN and
poly(AN/AA). PAN has an absorption band at 2244 cm-1 indicates the existing of
nitrile group (C≡N). The band at 2933 cm-1 is assigned to C-H stretching due to the
vibration of CH2. Similar observation has been reported before [13].
In the case of poly(AN/AA), the band in region 2245 -2244 cm-1
and 2935-2933
cm-1 in the spectra were assigned to C≡N and O-H stretching respectively. The
presence of strong nitrile group (C≡N) band indicate that the existence of the saturated
aliphatic nitriles [12]. The presences of O-H band represent the vibrations of
carboxylic group from AA monomer. The absorption of C=O stretch is at 1732 cm-1
,
1730 cm-1, 1729 cm-1 and 1728 cm-1 for mole ratios of 93/7, 95/5, 97/3 and 90/10
respectively. Similar observations have been reported before [15].
Fig. 2. IR Spectra of Unmodified Poly(AN/AA).
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Journal of Engineering Science and Technology Special Issue 4 1/2015
Figure 3 shows the comparison of IR spectra of the poly(AN/AA) 93/7 and
modified (M) poly(AN/AA) 93/7. The IR spectrum of poly(AN/AA) 93/7-M, (Fig. 3)
has the additional band arising from a newly formed C=N functional group at
range 1628-1620 cm-1 that support the successful of surface modification.
However the band at range 1730-1728 cm-1 which is the characteristic of carbonyl
group (C=O) was disappear. This is probably due to the coupling between C=N and
C=O stretching [16]. New peak arising at range 3400-3100 cm-1
is due to the vibration
of secondary amino group (stretching of N-H). The intensity of nitrile group of
unmodified poly(AN/AA) at range 2245-2244 cm-1
significantly disappear after
modification with the hydrazine. The complete disappearance of C≡N group showed
that hydrazine was chemically attached xto the PAN and poly(AN/AA).
Fig. 3. IR Spectra of Unmodified Poly(AN/AA) 93/7
and Modified Poly(AN/AA) 93/7. M: Modified.
3.2.2. CHNS analysis
The elemental analysis result is tabulated in Fig. 4. All the elements content have
slightly differences between the analyses and calculated. A probable explanation is
that the purity of compounds has high in contents compared with the theoretical
especially for the elements of carbon and sulphur that have very notable differences.
The carbon calculated was shown to be approximately 56% for all ratios but
by analysis, the percentage rose to approximately 63% especially for mole ratio of
100/0 and 93/7. Likewise for sulphur, percentage calculated is 5.9%, but the
analysis result showed that the percentage of sulphur is very low at 0.06% for
93/7 ratio. The low sulphur content indicates that poly(AN/AA) is acceptable to
act as an environmental friendly adsorbent since the chances for sulphur to
interrupt during the adsorption process is low.
In the case of hydrogen content, the difference value between the analyzed
and calculated is ± 3% for the PAN and poly(AN/AA) 97/3. Lower amount of AN
being added into polymerization systems results to the lower amount of nitrogen
content in poly(AN/AA).
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The percentage of carbon, hydrogen, nitrogen and sulphur of poly(AN/AA)
93/7 after modification are shown in Table 1. From the elemental analysis data,
the percentage of carbon after modified had reduced around 10%, meanwhile the
percentage of hydrogen and nitrogen were slightly increased. This is due to the
presence of secondary amino group from the hydrazine during the modification of
poly(AN/AA). The low sulphur content indicates that the poly(AN/AA) is free
from inhibitors.
Fig. 4. CHNS Analysis of Poly(AN/AA).
Table 1. Elemental Analysis of Unmodified and Modified poly(AN/AA) 93/7.
Sample C % H % N % S %
Poly(AN/AA) 63.27 6.85 21.10 0.06
Modified poly(AN/AA) 52.51 7.66 27.02 0.02
3.2.3. Scanning Electron Microscope (SEM)
Figures 5(a) to (e) show the SEM images of unmodified poly(AN/AA). As shown
in Fig. 5(a), the PAN beads have spherical shape that agglomerated with ~216 nm
of particles diameter. As shown in Figs. 5(b) to (e), the morphologies of
poly(AN/AA) are almost similar to the morphology of PAN. The average
particles diameter of poly(AN/AA) 97/3, 95/5, 93/7 and 90/10 are ~178 nm, ~159
nm, ~130 nm and ~89 nm respectively, which are relatively smaller compared to
the particle diameter of PAN (~216 nm).
The size of spherical diameter becomes smaller as the amount of AA
increased. It is expected that smaller spherical diameter of poly(AN/AA) resulted
to the higher complex formation between the poly(AN/AA) and the adsorbate due
to the higher surface area of poly(AN/AA).
Figure 5(f) shows the SEM image of poly(AN/AA) 93/7 after modification with
hydrazine hydrate. The beads agglomeration of the modified poly(AN/AA)
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Journal of Engineering Science and Technology Special Issue 4 1/2015
reduced and the average size of spherical diameter of bead was increased. The
increment of average particle diameter of modified poly(AN/AA) from ~130 nm
to ~150 nm attributed to the surface modification of poly(AN/AA) [17].
a) PAN (100/0)
b) Poly(AN/AA) (97/3)
c) Poly(AN/AA) (95/5)
d) Poly(AN/AA) (95/5)
e) Poly(AN/AA) (90/10)
f) Hydrazine-modified Poly(AN/AA)
(93/7)
Fig. 5. SEM micrograph images of poly(AN/AA) and modified poly(AN/AA).
4. Conclusions
The poly(AN/AA) was successfully synthesized via redox method with the
highest yield percentage of 72%. The poly(AN/AA) was chemically modified
with hydrazine hydrate.
• The successful of chemical modification was confirmed by completely
disappearance of C≡N group in the modified poly(AN/AA) spectra.
• The increment of H and N percentage were shown in elemental analysis after
modification with hydrazine hydrate.
• The SEM micrograph has shown that the average particle size poly(AN/AA)
was increased after chemical modification with hydrazine hydrate.
• The hydrazine modified poly(AN/AA) has potential for use as adsorbent in
wastewater treatment application.
Preparation and Characterization of Hydrazine-Modified Poly . . . . 69
Journal of Engineering Science and Technology Special Issue 4 1/2015
Acknowledgement
The authors would like to acknowledge the Department of Chemical and
Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia
and Department of Chemistry, Faculty of Science, Universiti Putra Malaysia for
providing the facilities.
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