PREPARATION AND CHARACTERIZATION OF HYDRAZINE- …jestec.taylors.edu.my/Special Issue 4_SOMCHE_2014/SOMCHE 2014… · Copolymers of acrylonitrile with various comonomer such as acrylic

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.

62 N. S. M. Rapeia et al.

Journal of Engineering Science and Technology Special Issue 4 1/2015

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

Preparation and Characterization of Hydrazine-Modified Poly . . . . 63


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.



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].



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).



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).



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)



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.



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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PREPARATION AND CHARACTERIZATION OF HYDRAZINE- …jestec.taylors.edu.my/Special Issue 4_SOMCHE_2014/SOMCHE 2014… · Copolymers of acrylonitrile with various comonomer such as acrylic