SYNTHESIS AND CHARACTERIZATION OF SUPER ABSORBENT HYDROGELS BASED ON POLYACRYLAMIDE WITH SAGO AGRICULTURAL APPLICATIONS

SYNTHESIS AND CHARACTERIZATION OF SUPER-ABSORBENT

HYDROGELS BASED ON POLYACRYLAMIDE WITH SAGO

AGRICULTURAL APPLICATIONS

Jeevitha Vedaiyan1 and Lynda Merlin*2

1

Research Scholar, 2Assistant Professor (Supervisor)

University College of Engineering, (UCEK), Anna University, Kanchipuram-631552.

ABSTRACT

A kind of novel sago starch-based super absorbent polymer (SBSAP)

with excellent water absorbency capacity (WAC) was synthesized by

the graft polymerization of acrylamide (AAM), cross linker (N, N’ -methylene-bisacrylamide, or N, N’-MBA, with sago starch. Sago starch (SG) based graft copolymers are becoming increasingly important due

to its remarkable adhesion, high water absorbency and

biodegradability. The various factors that influenced the water

absorbency of the modified sago starch were studied, including AAM

content, sago starch content, and weight ratio (to monomer)2% and

5%, cross-linker and initiator. The optimal conditions were found as

follows: (N, N’-MBA) 1%: m (AM) 1g: m (sago starch) 2%, and also the swelling studies of PAAMS-2 and PAAMS-5 was 1784 %and

1616% respectively. The comparative study of hydrolytic stability of all the hydrogels shows

5% starch incorporated polyacrylamide hydrogels has better hydrolytic stability when

compared to PAAM and PAAMS-2 hydrogels. The characteristics of the hydrogels were also

investigated by Fourier Transform Infrared (FT-IR), scanning electron microscope (SEM),

Thermo gravimetric analysis and Differential Scanning Calorimetric. The results indicated

that the undulant surface and broad network structure offer the hydrogels excellent water

absorbency. Therefore, the developed hydrogel may be widely applicable in agriculture and

could provide a minimum wastage of water, utilization of fertilizer nutrients, as soil

conditioners, water retainers, and bio-remediating agents.

KEYWORDS: Water absorbency capacity; starch; superabsorbent polymer; gel strength.

Volume 7, Issue 7, 103-119. Conference Article ISSN 2277– 7105

Article Received on 13 Feb. 2018,

Revised on 05 March 2018, Accepted on 26 March 2018,

DOI: 10.20959/wjpr20187-11594

*Corresponding Author

Lynda Merlin Assistant Professor

(Supervisor)

University College of

Engineering, (UCEK),

Anna University,

ABBREVIATIONS

SAP, superabsorbent polymer; SBSAP, starch-based superabsorbent polymer; SG,sago

starch, N,N’-MBA, N,N’-methylene-bisacrylamide; AAM, acrylamide; PAAM, polyacrylamide; FTIR, Fourier-transform infrared; TGA, thermo gravimetric analysis; SEM,

scanning electron microscopy; DSC, differential scanning calorimetry; WAC, water

absorptioncapacity;PAAM, polyacrylamidemonomer;PAAMS, polyacrylamidemonomersago

starch.

INTRODUCTION

Hydrogels are water-swellable, three dimensional polymeric networks. The capacity of

hydrogels to absorb water is enormous and can be as much as 1000 times the mass of

polymer (Huglin and Zakaria (1986); Peppas and Mikos (1986); given and Sen (1991);

Kulicke and Noltelman (1989). Hydrogels find application in food industry (as thickening

agents, etc.), in pharmaceuticals (as controlled release preparations etc.), agriculture and

related fields (in controlled release of moisture, fertilizers, pesticides, etc.). Hydrogels are

three-dimensional cross-linked polymeric network having substantial affinity for water.

Classes of hydrogels which are derived from biopolymers have been widely used in number

of industries because of their biocompatibility and environmental safety. Sago starch (SG)

based graft copolymers are becoming increasingly important due to its remarkable adhesion,

high water absorbency and biodegradability. There are many reports on the physico-chemical

characteristics, pharmaceutical, agricultural applications and several other chemical

modifications (esterification, etherification, oxidation of–OH groups etc.)[1-5]

A superabsorbent polymer (SAP) can absorb and retain significant amounts of water, forming

a superabsorbent hydrogel which is a three-dimensional matrix constituted by hydrophilic

polymers that are chemically or physically cross linked, and which slowly release the water

and associated Ingredients in a dry circumstance. SAPs have already been widely used in

agriculture and many other areas.[6-10]

In agricultural sector, they are extensively used as soil conditioners, water retainers, and

bio-remediating agents. Acrylamide based hydrogel are the most common hydrogel. These

hydrogel undergo large volume transition on swelling but they lack hydrolytic stability. Their

hydrolytic stability can be increased if substituted acrylamides have alkyl or hydroxyl alkyl

Polyacrylamide hydrogel is an atoxic, stable, non resorbable sterile watery gel consisting of

approximately 2.5% cross-linked polyacrylamide and no pyrogenic water. Hydrogels based

on polyacrylamide have wide potential for used as superabsorbent, sanitary materials as

specific sorbents separation and enrichment technologies. Comparing with traditional SAPs,

the starch-based SAP (SBSAP) is superior regarding its biodegradability, renewability,

abundance, and low cost.[23] These advantages of Starch are in alignment with the current

regulations addressing the environmental concerns. Increasing attention has been focused on

innovative technologies for the cost-effective production of SBSAPs with improved

performance. This work has established a synthesis of PAA (polyacrylamide) with), cross

linker (N, N’-methylene-bisacrylamide, or N, N’-MBA, and monomer Acrylamide. For the chemical modification, the starch was grafted with acrylamide and then cross-linked by N,

N’-MBA to produce a starch-based hydrogel. Specifically,2 and 5% of sago starch, 1g of

AM 2ml of deionised water and 2ml of 1% potassium per sulphate solution with 1% of N,N’ -MBA were added. The solution was flushed with nitrogen for 15 minutes to remove

dissolved oxygen. Polymerization was carried out in a constant temperature bath at 55°C for

30 minutes. The cross-linked starch grafted polyacrylamide gel obtained was washed with

distilled water to remove unreacted monomer and the residual initiator by immersing the gel

in deionized water for 24 hrs. The yield of the cross-linked gel was found to be 97%.

Grafting sago starch into acrylamide hydrogel is one of the effective ways to improve the

water retention properties of superabsorbent polymers. The prepared hydrogels PAA,

PAAMS-2, PAAMS-5 was used for Fourier-transform infrared spectroscopy (FTIR), thermo

gravimetric analysis, swelling properties, mechanical behaviour and hydrolytic stability.

2. MATERIALS AND METHODS

2.1 Materials

Sodium chloride, sodium hydroxide, ethyleneglycoldimethacrylate (EGDMA),

N,N’-methylenebisacrylamide (MBAAM), potassium per sulphate, Acrylamide (AAM), Sago

starch, 2-bromophenol B, hydrochloric acid, sulphuric acid(MERCK) etc., employed in the

present study were all analytical grade and used as such without further purification.

Benzoyl peroxide (BPO) was recrystallized from a 1:1 mixture of methanol and chloroform

and used. Acrylamide (AAM) was purified by recrystallization from benzene m.pt 84-85°C.

Acrylamide monomer (AAM) (1g) and N, N’methylenebisacrylamide (MBAAM) (1%) were

dissolved in 2ml of deionised water. A 1% solution of potassium per sulphate (2ml) was

added and the solution was flushed with nitrogen for 15 minutes to remove dissolved oxygen.

Polymerization was carried out in a constant temperature bath at 55°C for 30 minutes. The

cross linked polyacrylamide gel obtained was washed with distilled water to remove

unreacted monomer and the residual initiator by immersing the gel in deionised water for 24

hrs. The yield of the cross linked gel was found to be 96%.

2.2.1 Preparation of starch incorporated polyacrylamide based hydrogels (PAAMS)

Acrylamide monomer (AAM) (1g) and N, N’methylenebisacrylamide (MBAAM) (1%) and

different weight percent of starch (2% and 5%) with respect to acrylamide monomer were

dissolved in 2ml of deionized water and 2ml of 1% potassium per sulphate solution was

added. The solution was flushed with nitrogen for 15 minutes to remove dissolved oxygen.

Polymerization was carried out in a constant temperature bath at 55°C for 30 minutes. The

cross-linked starch grafted polyacrylamide gel obtained was washed with distilled water to

remove unreacted monomer and the residual initiator by immersing the gel in deionized water

for 24 hrs. The yield of the cross-linked gel was found to be 97%.

2.3. CHARACTERIZATIONS

2.3.1. Infrared spectra

Fourier transform infrared (FTIR) spectra were recorded by using a KBr pellet on a Spectrum

one FTIR (Perkin-Elmer instruments, USA) in the wave number range 4000-400cm-1.

2.3.2. Differential scanning calorimetry (DSC)

Differential scanning calorimetry (DSC) thermograms were recorded using a DSC 200PC

NETZSCH-Geratebau Gmbh thermal analyzer. The heating rate was 20°C min-1 in the

temperature range of -150°C to 300°C.

2.3.3. Thermo gravimetric analysis (TGA)

Thermo gravimetric analysis (TGA) was performed on a STA 409PC NETZSCH-Geratebau

Gmbh thermal analyser in nitrogen atmosphere at a heating rate of 20°C min-1.

2.3.4. Water absorption

The water absorption was determined by immersing the cut membranes in a beaker of water

diameter by using a sharp-edged stainless steel knife. The drained samples were weighed

every 10 min until they attained the maximum water content. The water absorption (WS) was

calculated by using the formula

100 x W W W . S . W 1 1 2        

Where, W1 and W2 are the weights of the sample before and after the test.

2.3.5. Swelling behaviour

The dried samples were immersed in an excess of deionised water until swelling equilibrium

was attained. The weight of swollen sample (Ws) was determined after removing the surface

water by blotting with filter paper. Dry weight (Wd) was determined after drying the gel in a

vacuum oven for 1 day at room temperature. The equilibrium water content was calculated

using the formula

EWC (%) = [Ws-Wd / Wd] x100

Were, Ws and Wd are the weights of the water absorbed and the dry samples respectively.

2.3.6. Swelling behaviour at different pH values

Equilibrium water contents were measured at pH 4.2, pH 7 and pH 9.2 using appropriate

buffer solution. Preweighed, dry samples were immersed in pH 4.2, 7 or 9.2 buffer solutions

until they swelled to equilibrium. It was confirmed that 24 hr equilibration was enough to

reach the equilibrium swelling of disks. After excessive surface water was removed by filter

paper, the weights of swollen sample were measured. The equilibrium water content was

calculated from the formula mentioned in section 2.3.5.

2.3.7. Hydrolytic stability measurement

The hydrolytic stability was determined as follows: 12 preweighed dry films were saturated

with phosphate buffer solution (pH 7.4) and stored in sealed glass vials and kept in an oven at

80°C. Three samples were removed after 3rd day, similarly each three samples were removed

after 5day, 7day and 14 day respectively. They were washed with distilled water and dried at

80°C for 16 hrs. The percent weight loss of sample after different periods of testing were

obtained by comparing the weight of dry sample before and after testing.

2.3.8. Tensile strength

The tensile strength and elongation of the polymer samples were tested using a Universal

standard. For test specimens, the standard dumbbell shaped test specimens were used so that

the geometry ensures that only tensile stresses occur which act parallel to the surface and

perpendicular to the cross sectional area. Moreover, rupture of the test specimen through

stress concentration in the grip area was avoided. Both dried and swollen samples were

measured; the tensile specimen, 1mm thick and 6mm wide were cut from the sheet. The

elongation at break (ultimate elongation) and the corresponding stress (breaking stress) were

used as characteristic values of a material. The tensile strength was determined using the

formula,

Breaking load in kgs Tensile strength (kg/cm2) =

Thickness in cm x width in cm

2.3.9. Compressive strength

The compressive strength of the swollen polymer samples were tested using a Universal

Testing Machine (Hounsfield, UK) at a crosshead speed of 5mm/min as per ASTM

D695-02A standard. The hydrogel samples were prepared as per the ASTM standard measurement

and tested. The hydrogel samples were cut into certain lengths of cylindrical shape and

swollen in distilled water to equilibrium. The swollen samples were used for testing by

mounting on the UTM instrument.

2.3.10. Scanning Electron Microscopy (SEM)

SEM observations were made with Leo Stereoscan 440 Scanning electron microscope. The

cryogenically fractured film in liquid nitrogen was mounted vertically on the SEM stub by

silver adhesive paste. The specimens were sputter coated with gold to avoid electrostatic

charges and to improve image resolution before being examined by the electron microscopy.

3. RESULTS AND DISCUSSIONS

3.1. Chemical structure Analysis (Infrared spectra)

The FTIR spectrum of polyacrylamide (PAAM) network is shown in Figure3.1.1. In the

polyacrylamide (PAAM) network spectrum the strong absorption at 3435 cm-1and the merged

peak at around 3200 cm-1 are attributed to the N-H stretching vibrations of the primary amide.

The cross linked polyacrylamide exhibit the characteristic absorption peaks 1655-1665cm

-1

(strong), 1618 cm-1(weak) and 1352 cm-1(weak), indicating the C=O, N-H bending and C-N

The FTIR spectrum of pure starch and starch grafted polyacrylamide (PAAMS) network are

shown in Figure3.1.2. a and b indicated that both have a broad absorption band characteristic

of glucosidic ring of starch between 3700 cm-1 and 3200 cm-1,1160 cm-1 and 1030 cm-1.

Moreover, there is a difference in the intensity of this band in the case of starch grafted

acrylamide sample, owing to the utilized hydroxyl groups of the starch. The strong absorption

peak at 1675 cm-1 corresponds to the presence of CONH groups.

Figure 3.1.1: FT-IR spectrum of Polyacrylamide (PAAM) network.

Figure 3.1.2: FT-IR spectra of (a) pure sago starch (b) FT-IR spectra of 2% starch

incorporated polyacrylamide

3.2. Thermal Stability

TG thermogram of PAAM network (Figure 3.2.1.) showed three stages of decomposition

degradation of PAAM network that is due to the loss of ammonia with the formation of imide

group via cyclisation (Nayak and Singh 2001). The degradation of volatile products such as

water and ammonia was observed below 320°C. Decomposition of cyclised product was

observed starting from 381°C.

TGA thermogram of pure sago starch (Figure 3.2.2.) showed two stages of decomposition

with maximum weight loss at 316°C. The initial weight loss is due to the moisture present.

The second stage decomposition temperature of starch was found to be around 278-318°C.

This may be due to the degradation of the glucosidic linkages. The TGA thermogram data of

pure sago starch, PAAMS-2 and PAAMS-5hydrogels were given in (Table 3.2.a.).

TG thermogram of PAAMS-2 network (Figure 3.2.3a.) showed three stages of decomposition

with a maximum weight loss at 381°C. The weight loss above 210°C was due to the

degradation of PAAM network that is due to the loss of ammonia with the formation of imide

group via cyclisation. The degradation of volatile products such as water and ammonia was

observed below 320°C. Decomposition of the glucosidic linkages of starch was observed

starting from 381°C.

TGA thermogram of PAAMS-5 network (Figure 3.2.3b.). 5% starch incorporated

polyacrylamide hydrogels showed three stages of decomposition with a maximum weight

loss at 395°C. The degradation of glucosidic linkages of starch was observed above 365°C. A

slight increase in thermal stability was observed with the increase in the starch content. The

5% starch incorporated polyacrylamide hydrogels showed higher thermal stability when

compared to polyacrylamide and 2% starch incorporated polyacrylamide hydrogels. This may

be due to the increased crosslink density as the starch content increased in the network.

Figure 3.2.1: TGA thermo gram of Polyacrylamide (PAAM) network.

Figure 3.2.2. TGA thermogram of pure sago starch.

Figure 3.2.3. (a) TGA thermogram of 2% starch incorporated polyacrylamide based

hydrogel (b) TGA thermogram of 5% starch incorporated polyacrylamide based

hydrogel.

Table 3.2.a TGA thermogram data for Pure starch, PAAM, PAAMS-2, PAAMS-5.

Sample code

Stages of decomposition

I II III

Pure starch 105°C 278-318°C -

PAAM 180-210°C 284-314°C 381- 425°C

PAAMS-2 110-180°C 210-310°C 360- 440°C

PAAMS-5 115-195°C 240-380°C 390- 450°C

The DSC thermogram of PAAM network (Figure 3.3.1.) showed a single glass transition

temperature (Tg) in the range of 75-80°C and an endothermic peak at 110°C is due to the

melting of the PAAM network.

The DSC thermogram of pure sago starch, PAAMS-2 and PAAMS-5 hydrogels (Figure 3.3.2

- 3.3.4) showed a single glass transition temperature. In the DSC theromograms of pure sago

starch, PAAMS-2 and PAAMS-5 the glass transistion temperatures (Tg) (Table 3.3.a.) were

observed as 60-80°C, 92-93°C and 107-108°C respectively. The Tg of PAAMS-5 is higher

than PAAMS-2. This is due to the increased crosslink density caused decreased chain

mobility as a result the Tg of PAAMS-5 shifted to higher temperature when compared to

PAAMS-2 Tg value (Koenig and Huang 1995). The Tg value of PAAMS-2 and PAMMS-5

was found to be higher than PAAM hydrogel confirmed the grafting of starch onto

acrylamide monomer via crosslinking.

Figure 3.3.2. DSC thermogram of pure sago starch.

Figure 3.3.3: DSC thermogram of 2% starch incorporated polyacrylamide.

Table 3.3.a:DSC thermogram data for PAAM, Pure starch, PAAMS-2, PAAMS-5.

Sample code Tg

PAAM 75-80°C

Pure starch 60-80°C

PAAMS-2 92-93°C

PAAMS-5 107-108°C

3.4.Swelling Studies

The PAAM network prepared from 1% of the crosslinking agent (MBAAM) showed an

equilibrium swelling ratio of 406% as shown in (Table 3.4.a.). Swelling studies in both acidic

pH 4 and basic pH 9 were carried out and the results are shown in the Table 3.4. It was found

that the equilibrium swelling increases in pH 9 but decreases in pH 4 this is due to the fact

that at increased pH the acrylamide undergo partial hydrolysis and produce anionic charged

centers along the co-polymeric chains and cause repulsions between the macromolecular

chains and free volume widen in the network resulting in enhanced water absorption.

The equilibrium swelling ratio of all the hydrogels (Table 3.4.a.) PAAM, PAAMS-2, and

PAAMS-5 hydrogels were found to increase to about 60%. The equilibrium swelling ratio of

PAAMS-2 and PAAMS-5 hydrogels was found to be higher than PAAM hydrogel. This may

be due to the increased hydrophilicity in the network caused by the incorporation of starch

into the acrylamide hydrogel. The equilibrium swelling ratio of PAAMS-2 is higher

compared to PAAMS-5. The decrease in swelling ratio of PAAMS-5 is due to the increased

crosslink density. The equilibrium swelling increases in pH 9 but decreases in pH 4 for

PAAM, PAAMS-2, and PAAMS-5 hydrogels. This is due to the fact that at increased pH the

acrylamide undergo partial hydrolysis and produce anionic charged centers along the

co-polymeric chains and cause repulsions between the macromolecular chains and free volume

widen in the network resulting in enhanced water absorption.

Table 3.4.a. Swelling and Hydrolytic stability data for PAAM, PAAMS-2, PAAMS-5.

Sample code Equilibrium Swelling Ratio (%) Equilibrium Swelling ratio at

different pH

(a) % weight loss (b) % water content

4 9

Days

3 5 7 14

a b a b a b a b

PAAM 406 352 412 0.41 404.2 0.64 403.5 0.73 403.0 0.82 402.7

PAAMS-2 1784 937 1092 0.59 1773.5 0.61 1773.1 0.64 1772.6 0.71 1771.4

3.5. Hydrolytic stability

The presence of amide group in the PAAM network is susceptible to hydrolysis in acidic and

basic medium. In PAAM network the presence of the network structure through crosslinking

enhanced the hydrolytic stability. The hydrolytic stability was demonstrated by the weight

loss of the dry sample as well as the change in water content. Weight loss of 5% or lower

over a 14-day period was considered stable. Table 3.4.a. shows the hydrolytic stability data

for PAAM network. The results showed a weight loss of less than 5% over a period of 14

days indicated the stability of PAAM network.

The hydrolytic stability of all the hydrogels (Table 3.4.a.) PAAM, PAAMS-2, and PAAMS-5

hydrogels showed a weight loss of less than 5% over a period of 14 days indicated the

reduced leaching of the hydrogels. The stability of the network is due to the crosslinking

density. From the percentage weight loss data it was found that the 5% starch incorporated

polyacrylamide hydrogels showed a decrease in percentage weight loss when compared to

2% starch incorporated polyacrylamide hydrogels. This may be due to the increased

crosslinking density in PAAMS-5 due to the increased amount of starch content. Hence it is

clear that the 5% starch incorporated polyacrylamide hydrogels has better hydrolytic stability

when compared to PAAM and PAAMS-2 hydrogels.

3.6. Mechanical properties

The compressive strength data of PAAM and starch incorporated polyacrylamide hydrogels

were given in the Table 3.6.a. The starch incorporated polyacrylamide hydrogels (PAAMS-2

and PAAMS-5) showed higher resistance to compression even under higher water content

compared to PAAM hydrogel. This suggests that the mechanical performances are more

related to the structure of the hydrogels. The higher mechanical strengths of PAAMS-2 and

PAAMS-5 are due to the increased cross linked density and the amount of starch present.

The PAAMS-5 showed higher strength than PAAMS-2 hydrogel. This due to the fact that as

the starch content in the gel increases the compressive strength of the gel also increased

(Yong Qiu and Park 2003).

Table 3.6.a: Mechanical studies data for PAAM, PAAMS-2and PAAMS-5 hydrogels.

S.No Sample code Compressive strength (Kg/cm2)

1. PAAM 3.32 ± 0.2

2. PAAMS-2 5.92 ± 0.2

3.7. Morphology

The scanning electron micrographs of PAAM network is shown in Figure 3.7.1. The SEM

picture of PAAM network showed a cross linked structure with a fractured surface. The

surface appears to be more continuous without much broken ends. The structure since it is

cross linked and possess hydrophilic group barring pendants it is expected to have high water

absorption property.

Figure 3.7.1: Scanning electron micrograph of PAAM network.

The scanning electron micrographs of pure sago starch, PAAMS-2 and PAAMS-5 were

shown in Figure 3.7.2a - 3.7.2c. The morphology of all the hydrogels PAAM, PAAMS-2, and

PAAMS-5 was found to be different from each other. The surface morphology of all the

hydrogels showed a porous structure with void spaces in between. The SEM image of pure

starch showed a globule like structure. The SEM images of PAAMS-2, and PAAMS-5

showed a fractured surface of starch mixed with acrylamide monomer. The significant

morphological differences among the different hydrogels confirmed the grafting of starch

into the PAAM network hydrogel. These studies indicate that the increase of starch

concentration results in a tougher material due to chain interpenetration.

(b) (c)

Figure 3.7.2. Scanning electron micrograph of (a) pure sago starch (b) PAAMS-2

hydrogel (c) PAAMS-5 hydrogel.

4. CONCLUSION

The starch incorporated polyacrylamide based hydrogels showed an enhancement in

properties such as swelling and hydrolytic stability by the incorporation of 2% & 5% starch

into the polyacrylamide network may be due to the increased hydrophilicity in the network

caused by the structure of starch. The SEM image of starch incorporated polyacrylamide

hydrogel showed a different morphology compared to that of pure sago starch and that of

polyacrylamide hydrogel confirming the grafting of starch with the acrylamide monomer.

Starch incorporated polyacrylamide are widely used as superabsorbent. The present research.

Provides a effective water absorbency capacity in starch based superabsorbent polymer

(SBSAP) which was promising in agriculture applications. Future studies to implement these

superabsorbent hydrogels to the growth of different grains.

REFERENCE

1. Lele, V. V, Kumari, S. and Niju, H., Syntheses, Characterization and Applications of

Graft Copolymers of Sago Starch - A Review. Starch - Stärke, 1700133. Accepted Author

Manuscript. doi:10.1002/star.201700133

2. X. Xiao, L. Yu, F. Xie, X. Bao, H. Liu, Z. Ji, L. Chen, One-step method to prepare starch

3. P.-Q. Gao, Y. Zhang, L. Zhao, and Y.-Z. Chen. Swelling Properties and Environmental

Responsiveness of a Superabsorbent Composite Microsphere Based on Starch-g-Poly

(acrylic acid)/Organo-Mordenite. International Polymer Processing, 2017; 32(2):

150-158.

4. N. Che Ani et al., "Effect of Cross-Linker Concentration on the Synthesis and Swelling

Behaviour of Superabsorbent Polymers (SAP) Using Graft Polymerization Techniques",

Key Engineering Materials, 2017; 719: 62-66.

5. Liu, T. G., Wang, Y. T., Guo, J., Liu, T. B., Wang, X. and Li, B., One-step synthesis of

corn starch urea based acrylate superabsorbents. J. Appl. Polym. Sci., 2017; 134: 45175.

doi: 10.1002/app.45175

6. Pourjavadi, A.M. Harzandi, H. Hosseinzadeh, Modified carrageenan 3. Synthesis of a

novel polysaccharide-based superabsorbent hydrogel via graft copolymerization of acrylic

acid onto kappa-carrageenan in air, European Polymer Journal, 2004; 40: 1363-1370.

7. M.R. Guilherme, F.A. Aouada, A.R. Fajardo, A.F. Martins, A.T. Paulino, M.F.T. Davi,

A.F.Rubira, E.C. Muniz, Superabsorbent hydrogels based on polysaccharides for

application in agriculture as soil conditioner and nutrient carrier: A review, European

Polymer Journal, 2015; 72: 365-385.

8. Chang, B. Duan, J. Cai, L. Zhang, Superabsorbent hydrogels based on cellulose for smart

swelling and controllable delivery, European Polymer Journal, 2010; 46: 92-100.

9. Rashidzadeh, A. Olad, D. Salari, A. Reyhanitabar, On the preparation and swelling

properties of hydrogel nanocomposite based on Sodium alginate-g-Poly (acrylic

acid-co-acrylamide)/Clinoptilolite and its application as slow release fertilizer, Journal of Polymer

Research, 2014; 21.

10.L. Sartore, G. Vox, E. Schettini, Preparation and Performance of Novel Biodegradable

Polymeric Materials Based on Hydrolyzed Proteins for Agricultural Application, Journal

of Polymers and the Environment, 2013; 21: 718-725.

11.M. Avella, M.E. Errico, R. Rimedio, P. Sadocco, Preparation of

biodegradablepolyesters/high-amylose-starch composites by reactive blending and their

characterization, J. Appl.Polym. Sci., 2002; 83: 1432-1442.

12.Nakason, T. Wohmang, A. Kaesaman, S. Kiatkamjornwong, Preparation of cassava

starch-graft-polyacrylamide superabsorbents and associated composites by reactive

13.Qiao, H. Liu, L. Yu, X. Bao, G.P. Simon, E. Petinakis, L. Chen, Preparation and

Characterization of slow-release fertilizer encapsulated by starch-based superabsorbent

polymer,Carbohydr. Polym, 2016; 147: 146-154.

14.Jyothi, A. N., Starch graft copolymers: Novel applications in industry. Compos. Interfaces, 2010; 17: 165–174.

15.Huglin BM and Zakaria BM. J App Poly Sci., 1986; 31: 457-475.

16.Ghanshyam S Chauha., Singha AS and Guleria Lalit K. Orint J Chem., 2000; 16(2): 331.

17.Rodriguez-Gonzalez, P. J., Ramsay, B. A., Favis, B. D., Rheological and thermal

properties of thermoplastic starch with high glycerol content. Carbohydr. Polym, 2004; 58: 139–147.

18.Yong Qiu, Kinam Park Super porous IPN hydrogels having enhanced mechanical

properties AAPS Pharm Sci Tech, December 2003; 4(4): 406–412

19.B R NAYAK, D R BISWAL, and N C KARMAKAR† and R P SINGH* Grafted

hydroxypropyl guargum: Development, characterization and application as flocculating

agent Bull. Mater. Sci., November 2002; 25(6): 537–540. © Indian Academy of Sciences.

20.S.J. Lu, M.L. Duan, S.B. Lin, Synthesis of superabsorbent starch graft-poly (potassium

acrylate-co-acrylamide) and its properties, Journal of Applied Polymer Science, 2003; 88:

1536-1542.

21.K. Kabiri, H. Omidian, S.A. Hashemi, M.J. Zohuriaan-Mehr, Synthesis of fast-swelling

superabsorbent hydrogels: effect of crosslinker type and concentration on porosity and

absorption rate, European Polymer Journal, 2003; 39: 1341-134.

22.M.F. Koenig, S.J. Huang Biodegradable blends and composites of polycaprolactone and

starch derivatives Polymer, 1995; 36: 9: 1731-192.

23.K. Zhong, Z.T. Lin, X.L. Zheng, G.B. Jiang, Y.S. Fang, X.Y. Mao, Z.W. Liao, Starch

Derivative-based superabsorbent with integration of water-retaining and

controlled-release fertilizers, Carbohydrate Polymers, 2013; 92: 1367-1376.

24.NA Peppas. Advanced materials 21 (32‐33), 3307-3329, 2009. 1464, 2009. Preparation

methods and structure of hydrogels, Peppas NA, Hydrogels in Medicine and Pharmacy,

1986; I. NA Peppas, AG Mikos.

25.Kulicke. W. M., Noltelman, H., Polymers in Aqueous. Media, Performance Through