The Effects of Initiator Content on Sago (Metroxylon Rottb.) Starch-G-PAN Hydrogel

Nurizan Omar1,a and Zuraida Ahmad 2,b

1, 2 Department of Manufacturing and Materials Engineering, Kulliyyah of Engineering,

International Islamic University Malaysia, 50728 Gombak, Kuala Lumpur, Malaysia.

Email: anurizanomar86@gmail.com, bzuraidaa@iium.edu.my Keywords: polysaccharide, biodegradable, hydrogels, sago starch, water absorbency, morphology

Abstract. This paper explores the effects of ammonium persulphate (S-PANHs) content (1wt % - 5

wt %) to the properties of sago starch-graft-polyacrylonitrile hydrogels (S-PANH). S-PANHs were

prepared via graft copolymerization of polyacrylonitrile (PAN) onto sago starch in the presence of

ammonium persulphate (APS) as initiator and N, N-methylenebisacrylamide (MBA) as crosslinker.

The percentage of water absorbency is observed to increase with increasing initiator content from

1wt% until reaching optimum point of 3 wt% APS. 48.78 % water absorbency was recorded at 3

wt% APS sample. The morphology of the hydrogels from the micrographs captured via scanning

electron microscope (SEM) revealed the existence of pores and matching with the results of

percentage water absorbency. Fourier transform infrared (FTIR) spectroscopy proved that the

grafting process had occurred in S-PANH.

Introduction

The hydrophilic polymers which have the ability to absorb and retain huge amount of water within

their structures and swell without dissolving in water are termed as superabsorbent polymer

hydrogels (SAPH) [1]. The hydrophilicity of gel arises due to the presence of polar groups, which

can be non-ionic (––OH, ––O––, ––NH2, ––CONH––, ––CHO) or ionic––SO3H, ––COOH, ––

COONa, ––COONH4, ––NR2HX, etc.). SAPH are widely used as an absorbent in diapers, adult

incontinence products and feminine napkins. It is also applicable in agriculture and horticulture as

plant growth medium in enhancing water absorbing property of sandy soil. Synthetic polymer

hydrogels from polyacrylates, polymethacrylates and polyacrylamides exhibit excellent water

absorbency properties as reported by previous researchers [2-4].These kinds of SAPH however,

exhibit toxicity and carcinogenicity as well as poor degradability which will result in increasing

amount of landfill. This problem merits further investigation. Due to this issue, many researchers

have diverted their attention in producing ‘greener’ SAPH products by incorporation of

biodegradable polysaccharides such as cellulose, starch, chitin and chitosan.

Polysaccharides such as starches were often used since it can enter reaction with initiator by

either neighboring OHs on the saccharide units and initiator reacts to produce redox pair-based

complexes or another way is by disruption of hydrogen radicals from the OHs of polysaccharide by

persulphate to initiate the radicals on the polysaccharide backbone [5].

Recently, the S-PANHs were prepared by synthesizing of PAN onto sago starch in the

normal atmosphere by using APS as initiator and MBA as crosslinker via graft copolymerization.

This research is aimed at developing superabsorbent polymer hydrogel which posses the

advantages of low cost and environmental friendly. This paper encompasses the effect of initiator

content to the functional group, morphology and water absorbency of sago starch-graft-PAN

hydrogel (S-PANH).

Advanced Materials Research Vol. 683 (2013) pp 218-221Online available since 2013/Apr/24 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.683.218

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Materials and Methods

Materials. The commercial sago starch (Metroxylon Rottb.) powder (25% amylose) was

purchased from Nee Seng Ngeng and Sons Sago Industries Sdn. Bhd. Polyacrylonitrile (PAN), N,

N-methylene-bisacrylamide (N-MBA) and Ammonium Persulphate (APS) were supplied by Sigma

Adrich Sdn. Bhd. and used without any further purification. Sodium hydroxide (NaOH) used for

neutralization was supplied by Merck (M) Sdn. Bhd.

Graft Copolymerization of Polyacrylonitrile (PAN) onto sago starch. S-PANHs were

produced via graft copolymerization of polyacrylonitrile (PAN) onto sago starch. Ammonium

persulphate (APS) and N, N-methylenebisacrylamide (MBA) were used as initiator and crosslinker

respectively. The reaction was carried out in the three-neck flask equipped by condenser and

mechanical stirrer. The equipment was placed in thermo stated water bath at temperature of 80±2

°C in vacuum hood. The process involved gelatinization of sago starch (2 g) with 60 ml distilled

water for 30 minutes. The gelatinized starch was cooled to room temperature before APS (1 wt%-5

wt %) was added. Stirring process was continued for another ten minutes before certain amount of

PAN and MBA were added for further grafting process. NaOH (40% concentration) was used to

neutralize the hydrogels produced. The whole polymerization process was kept for 3 hours. The

washed samples were oven dried for 24 hours and subjected to grinding process to obtain powder

particles. The S-PANHs were put in desiccators to keep away from moisture before the

characterization was executed. The amount of sago starch, PAN, MBA, distilled water and NaOH

used in this research were kept constant in order to determine the effects of APS on S-PANHs

properties.

Characterization. FTIR analysis of the samples were performed through Perkin Elmer FT-IR,

Spectrum 100 Series using ATR sampling technique by recording 45 scan in %T mode in the range

of 4000-600cm-1

Water Absorbency. Prior to water absorbency measurement, the S-PANHs were immersed in

distilled water and sodium chloride solution (NaCl) by using tea bag method. S-PANH (0.5g) was

put into sealed tea bag. The weights of dried samples were measured. The dried samples were then

immersed in distilled water and NaCl solution at room temperature. The swollen samples were

weighed after the excess water was removed with filter paper. The percentage water absorbency

was calculated according to the formula:

(1)

Where Wa is the weight of swollen samples and Wb is the weight of dried samples.

SEM Analysis. SEM analysis of the samples was performed by JEOL 5400 with 1000x and

3000x magnification operating at 7kV. The dried hydrogels were gold sputter-coated before

observing under SEM.

Results and Discussions

FTIR Analysis. Figure 1 shows the FTIR spectra of sago starch, S-PANHs with 1, 3 and 5 wt%

APS. Infrared spectrum of sago starch indicates the characteristics absorption bands of starch at

3267 due to hydroxyl (OH) stretching and bending modes [7]. While, the broad absorption bands

were observed for S-PANH1 at 3361 cm-1

, S-PANH3 at 3420 cm-1

and S-PANH5 3412 cm-1

which

attributed to the stretching of hydroxyl groups on the starch backbone due to the effect of grafting

process with different initiator content [8].

After the copolymerization reaction, the absorption peaks of OH groups has altered due to the

reaction which lead the formation of water absorbed group as reported in the research done by W.

Jihuai et al., using other type of starch [9]. The appearance of the bands at 2251 cm-1

for S-PANH 1

, 2247cm-1

for S-PANH 3 and 2243cm-1

for S-PANH 5 attributed to the stretching of the –CN group

of PAN. The peaks of 1585 cm-1

in S-PANH 1, 1575 cm-1

in S-PANH 3 and 1576 cm-1

in S-PANH

5 attributed to C=O stretching in carboxamide functional groups and symmetric and asymmetric

Advanced Materials Research Vol. 683 219

stretching modes of carboxylate groups since the S-PANHs comprised a starch backbone which

carry these functional groups. The wave number of 1013 cm-1

for S-PANH 1 and S-PANH 3 and

1014 cm-1

for S-PANH 5 assigned for the C-O-C stretching which is probably due to change in

crystallinity after grafting process taken place.

Figure 1: FTIR spectrums of sago starch and S-PANHs

The Effect of Initiator Addition on Water Absorbency. The effect of initiator content on water

absorbency of the hydrogels was studied and results are illustrated in Figure 2. According to the

figure, the absorbency is increased considerably with an increase in the amount of initiator with the

same concentration up to 3 wt%. The highest percentage of water absorbency was recorded at

48.78% in distilled water and 40.1% in saline solution (NaCl).

Figure 2: The effects of initiator content on water absorbency

Increase in amount of initiator to the hydrogels, results in the formation of large number of free

radicals on the starch backbone at which the monomer molecules can be grafted and led to more

cross linking density to the network [10]. The declination of water absorbency after the optimum

value as shown in Figure 2 is rationalized as non-availability of sites of starch molecules at which

APS can react to generate more free radicals and the initiation of homopolymerisation by unutilise

APS.

SEM Analysis. Figures 3a to 3c show the micrographs of S-PANH with 1 wt% APS, 3 wt% APS

and 5 wt% APS respectively. These figures proved that the S-PANHs produced in this research

have porous microstructure. The porosity proved the three-dimensional structure of S-PANHs was

formed as reported by A.Pourjavadi et al., [11]. Obviously, the surface morphology of S-PANH

with 3 wt% APS is different from S-PANH with 1 wt% and 5 wt% APS. S-PANH with 1 wt% APS

in Figures 3a shows the smooth surface .The smooth surface however, has been destroyed with

increasing amount of initiator of 3 wt%. Relating the micrographs to the water absorbency result,

the coarse porous structure of S-PANH with 3 wt% APS in Figures 3b gave the higher water

absorption compared to the less porous structure of S-PANH with 5 wt% APS in Figure 3c.

220 Advanced Materials and Engineering Materials II

(a) (b) (c)

Figure 3: The micrographs of S-PANH with (a) 1 wt% APS in 3000x magnification (b) 3 wt%

APS in 3000x magnification (c) 5 wt% APS in 3000x magnification

Conclusions

In conclusion, the effects of APS content on functional group, water absorbency and morphology of

sago-g-PAN hydrogels (S-PANH) was described in this paper. The S-PANHs were characterized

using FTIR, SEM as well as water absorbency. The grafting process was proved to occur since

FTIR analysis shows the alteration of OH groups absorption peaks in grafted starch as compared to

pure starch. Water absorbency result shows the increment in percentage water absorbency with

increasing amount of APS up to 3 wt%. The morphologies of S-PANH obtained by SEM revealed

the increment of porosity that plays an important role in water absorption capacity and is correlated

with water absorbency result.

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Advanced Materials and Engineering Materials II 10.4028/www.scientific.net/AMR.683 The Effects of Initiator Content on Sago (Metroxylon rottb.) Starch-G-PAN Hydrogel 10.4028/www.scientific.net/AMR.683.218