SYNTHESIS AND CHARACTERIZATION
OF POLYACRYLAMIDE AS A FLOCCULANT
M. Fauz-ul-Azeem, Filza Zafar Khan,
Shafi Ullah Khan, Asrar. A. Kazi
Applied Chemistry Research Center,
Pakistan Council of Scientific & Industrial Research Laboratories Complex,
Ferozepur Road, Lahore-54600, Pakistan
For Correspondence:
Muhammad Fuaz ul Azeem,
e-m@il: mfauzstar@gmail.com
Ph: 0321-4036258
Applied Chemistry Research Centre,
PCSIR Laboratories Complex,
Ferozepur Road,
Lahore-54600.
1
ABSTRACT:
The synthesis of homopolymer of acrylamide was carried by the free radical solution polymerization
technique. Five different grades of hompolymers were synthesized by the variation of initiator
concentrations. These homopolymers were characterized by the infrared red specrtroscopy, transmittance
studies for flocculation performance and viscosity measurements. The flocculation performance was
measured on 5 % w/v china clay suspension using transmittance measurements. Transmittance of clay
suspension increases by increasing the molecular weight of the homopolymers. In the present studies
increasing molecular weight enhances the transmittance to a certain degree beyond which a regular decrease
in the transmittance occurs suggesting an optimum molecular weight suitable for the efficient flocculation
performance. Also the effect of concentration of catalyst on the molecular weight of polymer was observed.
KEY WORDS:
Free radical Polymerization, Flocculant, Polyacrylamide, China clay, Characterization.
2
INTRODUCTION
In wastewater treatment operations, the process of coagulation and flocculation are employed to separate
solids from water. Finely divided solids (colloids) suspended in wastewater are stabilized by repulsive
electric charges on their surfaces, causing them to repel each other. Since this prevents these charge particles
from colliding to form larger masses, called “flocs”, they do not settle. To assist in the removal of colloidal
particles form suspension, chemical coagulation and flocculation are required. Chemicals are mixed with
wastewater to promote the aggregation of the suspended solids into particles large enough to settle and be
removed (Bratby, 1980). Coagulation destabilizes colloids by neutralizing the repulsive forces that keep
them apart. As a result, the particle collides to form “Flocs”. Flocculants form bridges between the flocs and
bind the particles in to large agglomerates or “clumps” which can be removed from the liquid by
sedimentation, media filtration or filtration.
Flocculants are of two types: organic and inorganic. Alum is a typical inorganic flocculent and
polyacrylamide is one of the most widely used organic flocculent. Organic flocculants may be neutral or
synthetic. Starch, alginic acid and guar gum are among the natural polymers used in flocculation.
The synthetic flocculants commonly used are polymers such as polyacrylamide and polyethylene oxide
(non-ionic), polydiallyldimethyl ammonium chloride (cationic) and polystyrenic sulphonic acid (anionic).
The synthetic polymers are highly efficient, used at very low dosages and can be tailored to the needs of a
particular application. They produce no additional solids, reduce waste sludge volume, larger faster settling
floc and, work over wide pH range often eliminating the need for chemicals to adjust pH. However, their
biggest disadvantage is their sheer degradability.
Water-soluble polymers (polyelectrolytes) are well recognized as flocculants in industries for wastewater
treatment, mineral processing and paper making (Subramanian et al., 1999). Synthetic polyelectrolytes have
been developed and used extensively and they have largely replaced the inorganic flocculants such as iron
salts, alum, lime etc. Anionic polyelectrolyte flocculants have been prepared via polymerization of acrylic
acid (Siyam et al., 1994) partial saponification of Polyacrylamide (Whayman and Crees, 1975) and
3
copolymerisation of acrylamide with comonomers bearing acidic groups (Liu et al., 2000). The most widely
used polyelectrolyte is polyacrylamide (Poly-A). Polyacrylamide as such has a variety of applications due to
its ability to flocculate solids in aqueous suspensions (Halverson and Panzer, 1980). Poly-A’s are
inexpensive and easy to process. Acrylamide based polyelectrolytes were found to reduce surface charges
and enable the primary particles to coagulate (Schulz, 1985). The molecular weight and prevailing
flocculation conditions such as pH, mixing and concentration of flocculants used affect largely the
flocculation process (Bajpai and Bajpai, 1996, Chen, 1998). Though a large volume of literature is available
on flocculation studies on TiO2 (Subramanian et al., 1999, Li et al., 1998). The present work describes the
synthesis of different molecular weight Poly-A’s via free radical polymerization and their usage in
flocculation studies of china clay suspension under various conditions. A comparison of flocculation
effectiveness of synthesized Poly-A’s has been made.
MATERIALS AND METHODS
Apparatus and Reagents:
IR Spectrophotometer (Perkin Elmer- 883) and Ostwald's Viscometer were used to evaluate the synthesized
Poly-A's.
Acrylamide monomer (AR Grade) was procured from E.Merck. (Germany). Pottasium persulphate (LR
Grade), sodium metabisulphate (LR Grade) and sodium nitrate (LR Grade) were procured from Aldrich
Chemicals Company, USA. Acetone, Sodium hydroxide and acetic acid (LR Grade) were procured from
BDH. Double distilled water was used throughout the experimental studies.
General Procedure:
All the acrylamide polymers were synthesized by free radical solution polymerization (Suen et al., 1962)
catalyzed by persulphate–bisulphate redox pair (Mishra, 1993). A reaction temperature of 80 ºC and
agitation rate of 80 rpm was maintained throughout the polymerization period. Acrylamide along with the
4
catalyst was introduced in a round bottom flask equipped with rpm controlled mechanical stirrer and
thermometer. The assembly was placed in a water bath with thermostat.
The reaction was allowed to continue for 2 hrs after which it was terminated by the addition of a saturated
solution of hydroquinone. At the end of the reaction, the resulting polymer was placed in 1-liter beaker
where it was made into homogeneous slurry with the addition of double distilled water. The viscous
polymer was then precipitated by the addition of excess acetone and kept for about 5 hrs to remove
unreacted acrylamide (Fig. 1). It was then dried at 70 ºC and ground into fine mesh and sieved.
Polymers with different molecular weight were synthesized by the variation of catalyst concentration. Acetic
acid and sodium hydroxide were used to control the pH of clay suspensions. The synthetic parameters and
results of different polymers are summarized in Table 1. The polymerized products of acrylamide are
referred to as Poly-A’s.
Fig: 1
Flow chart representing the synthesis and purification of Polyacrylamide
Acrylamide
+
Catalyst
Polyacrylamide + Unreacted Acrylamide
Wash with acetone
Solution
5
Precipitates
IR-Spectra
Perkin Elmer-883 IR Spectrophotometer was used following the Potassium bromide (KBr) pellet method for
IR study. The IR spectra of synthesized polyacrylamide and acrylamide monomer are shown in Fig. 2 & Fig.
3 separately.
Fig. 2:
IR Spectra of synthesized Polyacrylamide
Fig. 3:
IR Spectra of acrylamide monomer
Transmittance Studies for Flocculation Characterization
Flocculation performance of the synthesized poly-A’s were tested on china clay suspension at varied dosage
and pH values adjusted at 5, 7 and 9. All tests were performed by measuring the interface b/w slurry and the
clear supernatant as the particles settled in a closed 100 ml graduated cylinder.
6
The clay suspension in the closed cylinder was inverted 15 times to ensure complete mixing then the
specified dosage of poly-A was added. The cylinder was inverted 15 times again. The time of fall of
interface b/w the slurry and the clear supernatant as the particles settled was noted from the initial height.
Final transmittance of supernatant was measured after 20 minutes of settling on a Spectronic-20 Photometer
at 600nm to check the increase in transmittance.
Viscosity Measurements
Viscosity measurements of poly-A solutions were carried out on an Ostwald’s viscometer to determine the
viscosity average molecular weight. The viscosity was measured in 1M sodium nitrate solution and the flow
time was measured for solutions at 5 different concentrations. The intrinsic viscosity was calculated by
plotting ŋsp vs. C and ŋinh vs. C and by taking the common intercept at C=0 of the best fitted straight lines
through the two sets of points (Snell and Hilton , 1967, Kirk and Othmer, 1953). Here C is the polymer
concentration in gm/dl, ŋsp and ŋinh are the specific and inherent viscosities respectively. The intrinsic
viscosities of all the synthesized poly-A’s are also reported in Table 2. The relationship of intrinsic viscosity
to molecular weight is
[ŋ]
=
KMa
Where:
K
=
3.73 x10 -4
a
=
0.66
M
=
Weight average molecular weight
Where M is weight average molecular weight.
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RESULTS AND DISCUSSION
Table 1: Synthetic Parameters of the Polymerized Products
Polymer
Amount of
Monomer
Amount of
Amount of
Potassium
Sodium
persulphate
metabisulphate
Floc-A
15
0.30
0.06
Floc-B
15
0.25
0.06
Floc-C
15
0.20
0.06
Floc-D
15
0.15
0.06
Floc-E
15
0.10
0.06
Table 2: Properties of the Polymerized Products
Viscosity
Yield / %
Intrinsic
Conversion
Viscosity
Floc-A
84.3
1.1
1.8
Floc-B
88.0
2.7
7.0
Floc-C
90.2
3.6
10.9
Floc-D
92.1
4.4
14.8
Floc-E
93.0
4.8
16.8
Polymer
Average Mol.
Wt. x 105
Table-1: Synthetic Parameters of the Polymerized Products and their Properties
Polymer
Amount
Amount of
Amount of
Yield / %
Intrinsic
Viscosity
of
Potassium
Sodium
Conversion
Viscosity
Average
Monomer
persulphate
metabisulphate
Mol. Wt.
x 105
Floc-A
15
0.30
0.06
84.3
1.1
1.8
Floc-B
15
0.25
0.06
88.0
2.7
7.0
Floc-C
15
0.20
0.06
90.2
3.6
10.9
Floc-D
15
0.15
0.06
92.1
4.4
14.8
Floc-E
15
0.10
0.06
93.0
4.8
16.8
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Molecular Weight Variation
From Table 2, it is evident that the molecular weight increased as the concentration of catalyst was
decreased. It can also be seen that the yield for Floc-E was higher than for Floc-A.
Infrared (IR) Spectroscopy
The IR spectrum of Poly-A (Fig. 2 ) showed characteristic absorptions, which agreed very well with those,
reported in the literature (Haas and MacDonald, 1972, McCormick et al., 1982). It can be seen that the
vibrational absorptions within the Poly-A differ from that of the pure monomer (Fig. 3). The typical IR
spectrum of synthesized Poly-A revealed the characteristic absorption frequencies corresponding to C-H
bending at 1452 cm-1, C-H stretching at 2951 cm-1, N-H stretching around 3351 cm-1 and C=O stretching
around 1645 cm-1 . A C=C stretching band around 2000 cm-1 is found in the spectra of pure monomer while
it is absent in the spectra of Poly-A which is the proof that polymerization has occurred.
Flocculation Characterization
Effect of Dosage of Poly-A’s on transmittance at varying pH values
Fig: 4
pH 5
pH 7
pH 9
Floc - A
98
Transmittance (%)
Transmittance (%)
96
94
92
90
88
86
84
82
80
0
5
10
15
20
25
30
Concentration (mg/dl)
35
98
96
94
92
90
96
88
86
84
82
5
10
15
20
25
30
Concentration (mg/dl)
35
40
pH 5
pH 7
pH 9
Floc - D
Transmittance (%)
Transmittance (%)
0
98
94
92
90
88
86
84
82
80
80
0
9
100
98
96
94
92
90
88
86
84
82
80
40
pH 5
pH 7
pH 9
Floc - C
pH 5
pH 7
pH 9
Floc - B
5
10
15
20
25
30
Concentration (mg/dl)
35
40
0
5
10
15
20
25
30
Concentration (mg/dl)
35
40
pH 5
pH 7
pH 9
Floc - E
98
Transmittance (%)
96
94
92
90
88
86
84
82
0
5
10
15
20
25
30
Concentration (mg/dl)
35
40
The efficiency of synthesized flocculants in terms of sedimentation of clay suspensions under different
conditions is summarized in Fig. 4. In some clay samples, it is possible to sediment the suspension without
the addition of polymeric flocculants. But, in the current clay sample, the suspension without polymeric
flocculant was not at all clear even after kept for many hours.
Flocculation efficiency in terms of increase in transmittance of all the synthesized Poly-A’s were measured
at three different pH values i.e. 5, 7 and 9 with different dosages. Transmittance in the range of 91 to 97 %
was observed at all three pH values. In the case of Floc-A at the dosage of 31 mg/dl, the transmittance was
maximum at pH 5.0.
For Floc-B, transmittance in the range of 91 to 98 % at a dosage of 22 to 28 mg/dl at all the three pH values
was obtained with max transmittance at pH 5.0.
In the case of Floc-C, transmittance in the range of 87 to 97 % was observed at the dosages of 22 to 28
mg/dl with three different pH values and the max transmittance at pH 5.0.
In the case of Floc-D, transmittance was found in the range of 89 to 96 % at the dosages of 22 to 25 mg/dl at
all three pH values. Transmittance was max at pH 5.0.
In the case of Floc–E, transmittance in the range of 87.5 to 95.6 % was observed at the dosages of 19 to 25
mg/dl with three different pH values and the max value was obtained at pH 5.0.
The dosage of flocculant was an important factor affecting the treatment program. By increasing the
amount of the flocculant, the transmittancy of the treated water reached the max value rapidly. If excessive
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flocculant was used, the transmittancy decreased, implying that the effect went down. This was because the
excessive polymeric flocculant could re-stabilize the feculence in the water. Only the dosages from 19-28
mg/dl of the complex polymeric flocculant were often effective.
CONCLUSIONS:
In the synthesis of Poly-A’s, the decreasing initiator concentration leads to a higher molecular weight
polymer whereas percentage yield of Poly-A’s increases with the decrease in the catalyst concentration.
Molecular weight is the key factor, which influences flocculation efficiency. Increasing molecular weight
enhances transmittance at certain level beyond which a prominent decrease occurs. Optimum pH plays a
vital role in the flocculation efficiency. Poly-A shows maximum flocculation efficiency at pH 5 whereas
regular decrease in transmittance is prominent at higher pH values. Poly-A’s with higher molecular weight
shows maximum flocculation efficiency at relatively low concentration values. Floc-E has maximum
transmittance at lower concentration as compared to Floc-D and Floc-C.
REFERENCES
Bajpai, A.K., Bajpai, S.K. 1996. Ind. J. Chem. Tech., 3: 219.
Bratby, J. 1980. Coaggulation and Flocculation. Uplands, Croydon, England.
Chen, W.F. 1998. Civil Engineering Handbook, Jaico Publishing House, CRC Press, New York.
Haas, H. C., MacDonald, R. L. 1972. J. Appl. Polym. Sci. 16: 1972-1973.
Halverson, F., Panzer, H.P. 1980. Encyclopedia of Chem. Tech., Vol. 10, M. Grayson, Ed., Wiley, New York.
11
Kirk, R.E., Othmer, D.F. 1953. Encyclopedia of Chem. Tech., Interscience Encyclopedia,Inc., New York.
Li, D., Zhu, S., Pelton, R.H., Spafford, H. 1998. Colloid Polym. Sci., 277: 108.
Liu, Y., Wang, S., Hua, J. 2000. Synthesis of Complex Polymeric Flocculant and its Application in Purifying
Water. J. Appl. Polym. Sci. 76:2093-2097
McCormick, C. L., Chen, G. S., Hutchinson B. H. 1982. J. Appl. Polym. Sci. 27: 3103.
Mishra. 1993. Introductory Polymer Chemistry, Wiley Eastern Ltd., New York.
Schulz, R.C. 1985. Encyclopedia of Polym. Sci. and Tech., Vol.1, J.I. Kroschwitz, Ed., Wiley, New York.
Siyam, T., Ayoub, R., Souka, N. 1994. Floc Formation of Some Water-Soluble Homopolymers. Egypt. J.
Chem. 37: 457-464.
Snell, F.D., Hilton, C.L. 1967. Encyclopedia of Ind. Chem. Anal. Vol. 4, Interscience Publishers, John Wiley
& Sons, Inc., New York.
Subramanian, R., Zhu, S., Pelton, R.H. 1999. Colloid Polym. Sci., 277: 939.
Suen, T.J., Schiller, A.M., Russel, W.H. 1962. Polymerization and Polycondensation Processes, No. 34, Ed.
Platzer, N.A.J. In: Advances In Chemistry Series, American Chemical Society, Washington, D.C.
Whayman, E., Crees, O.L. 1975. Mechanistic Studies of Cane Mud Flocculation. The Sugar J. 20-4.
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