Metal ion sorption and swelling studies of psyllium

and acrylic acid based hydrogels

Baljit Singh *, G.S. Chauhan, S.S. Bhatt, Kiran Kumar

Department of Chemistry, Himachal Pradesh University, Summer Hill, Shimla 171005, India

Received 15 February 2005; received in revised form 25 August 2005; accepted 27 October 2005

Available online 29 November 2005

Abstract

In order to utilize the psyllium husk a natural polysaccharide for developing new green polymeric materials for specialty applications, we have

prepared psyllium and acrylic acid based polymeric networks by using N,N 0-methylenebisacrylamide (N,N-MBAAm) as crosslinker. The

polymeric networks thus formed have been characterized with scanning electron micrography (SEM), FTIR and Thermogravimetric Analysis

(TGA) techniques to study various structural aspects of the networks. This paper discusses the swelling response of the polymeric networks as a

function of time, temperature, pH and [NaCl]. Equilibrium swelling has been observed to depend on both structural aspects of the polymers and

environmental factors. The swelling response indicates that these materials are potential candidates for use in colon specific drug delivery. Metal

ion sorption shows that these polymeric networks can be used for removal, separation, and enrichment of hazardous metal ions from aqueous

solutions and can play an important role for environmental remediation of municipal and industrial wastewater.

q 2006 Elsevier Ltd. All rights reserved.

Keywords: Psyllium; Hydrogels; Metal ion sorption; Swelling behavior

1. Introduction

Psyllium is the common name used for several members of

the plant genus Plantago whose seeds are used commercially

for the production of mucilage. The mucilage obtained from

the seed coat by mechanical milling/grinding of the outer layer

of the seed and yield amounts to approximately 25% of the

total seed yield. Mucilage is a white fibrous material that is of

hydrophilic nature and forms the clear colorless mucilaginous

gel by absorbing water. Gel-forming fraction of the alkali-

extractable polysaccharides is composed of arabinose, xylose

and traces of other sugars (Fischer et al., 2004).

Modification of carbohydrates is reported by graft copolymer-

ization. The graft copolymerization of reactive pre-gelled starch

with methacrylonitrile has been reported. The resultant copoly-

mers when applied to cotton textile imparted it higher tensile

strength and abrasion resistance than that was sized with original

pre-gelled starch (Mostafa & Morsy, 2004). Flow behavior of

sago starch-g-poly(AAc) prepared by the UV irradiation has been

reported to be dependent on the extent of the UV treatment,

0144-8617/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.carbpol.2005.10.022

* Corresponding author. Tel.: C91 177 2830944; fax: C91 177 2633014.

E-mail address: baljitsinghhpu@yahoo.com (B. Singh).

degree of grafting and type of gelatinizing solvent, whereby the

volume fraction of the granules varies in accordance with the

swelling capacities (Lee, Kumar, Rozman, & Lee et al., 2004).

Crosslinking has been the common practice to improve the

functional properties of the biopolymers to obtain functional

three-dimensional polymeric networks those have different

property profile than the native backbone. A novel biopolymer-

based semi interpenetrating polymer network (IPN) of

carboxymethyl cellulose (Bajpai et al., 2004) and kappa-

carrageenan (Pourjavadi et al., 2004) with crosslinked poly-

acrylic acid [poly(AAc)] has been prepared and its water-

sorption capacity has been evaluated as a function of chemical

architecture of the IPN, pH, and temperature of the swelling

medium. The water uptake potential of the IPNs has also been

investigated in inorganic salt containing aqueous solutions.

Maximum water absorbency of the IPN was found to be 789 g/g

and overall activation energy of the graft polymerization

reaction was found to be 293 kJ/mol (Bajpai & Mishra, 2004;

Pourjavadi, Harzandi, & Hosseinzadeh, 2004).

Modified polymers of renewable origin are environment

friendly and offer highly cost effective technologies to enrich

or separate metal ions from water system by binding, through

adsorption, chelation and ion-exchange processes. Chemical

modification of crosslinked starch with various reactive

monomers yield ionomers those have been used to remove

heavy metal ions from wastewater. The metal-ion

Carbohydrate Polymers 64 (2006) 50–56

www.elsevier.com/locate/carbpol

Table 1

Optimum reaction parameters for the synthesis of Psy-cl-poly(AAc)

Sr. No. APS

(mol/L)!102

Amt of

water (ml)

Time

(min)

Temperature

(8C)

Max. Ps

(after 24 h)

1 0.0 15 120 65 X

2 1.46 15 120 65 1518.0

3 2.92 15 120 65 1502.0

4 4.38 15 120 65 X

5 5.84 15 120 65 X

6 7.30 15 120 65 X

7 2.19 10 120 65 345.0

8 1.46 15 120 65 605.0

9 1.09 20 120 65 976.0

10 0.876 25 120 65 979.0

11 0.625 35 120 65 X

12 0.486 45 120 65 X

13 0.876 25 30 65 510.0

14 0.876 25 60 65 780.0

15 0.876 25 90 65 810.0

16 0.876 25 120 65 950.0

17 0.876 25 150 65 920.0

18 0.876 25 180 65 610.0

19 0.876 25 120 25 X

20 0.876 25 120 35 X

21 0.876 25 120 45 X

22 0.876 25 120 55 883.0

23 0.876 25 120 65 976.0

24 0.876 25 120 75 936.0

PsylliumZ1 g, where X indicates uncrosslinked polymer.

B. Singh et al. / Carbohydrate Polymers 64 (2006) 50–56 51

complexation behavior and catalytic activity of 4 mol% (N,N-

MBAAm) crosslinked poly(AAc) were investigated. The

polymeric ligand was prepared by solution polymerization.

The metal-ion complexation was studied with Cr3C, Mn2C,

Fe3C, Co2C, Ni2C, Cu2C, and Zn2C ions. The metal uptake

followed the order: CuC2OCrC3OMnC2OCoC2OFeC3OZnC2ONiC2. The catalytic activity of the metal complexes

was investigated toward the hydrolysis of p-nitrophenyl

acetate. The CoC2 complexes exhibited high catalytic activity.

The kinetics of catalysis was first order (John, Jose, & Mathew,

2004). Adsorption behavior of Zn2C and Cu2C on crosslinked

amphoteric starches with quaternary ammonium and carbox-

ymethyl groups in aqueous solutions was investigated. It was

observed that adsorption capacity increase with the increase in

the degree of substitution of the carboxymethyl groups. The

adsorption followed a Freundlich adsorption isotherm (Cao

et al., 2004; Xu et al., 2004). Two chemically modified starch

derivatives; crosslinked amino starch and dithiocarbamates

modified starch, were prepared and used for the removal of

Cu2C from aqueous solutions. Crosslinked amino starch was

found to be effective for the adsorption of Cu2C, which tended

to form a stable amine complex (Li et al., 2004).

The chemical modification of mucilage of Plantago

psyllium (Psy), a polysaccharide, is not much reported. Some

work on the use of Psy grafted with polyacrylamide

[poly(AAm)] (Agarwal et al., 2002) and polyacrylonitrile

[poly(AN)] (Mishra et al., 2003) on Psy has been reported for

use as flocculent. The flocculation efficiency of Psy-g-

poly(AN) was tested against tannery effluents. The maximum

extent of the suspended solid (SS) and total dissolved solids

(TDS) removal was, respectively, reported to be 89% (pH 7.0)

and 27% (pH 9.2), when treated with polymer dose of 1.2 mg/L

for 3 h. Whereas water-soluble Psy-g-Poly(AAm) was reported

to be more effective flocculant, capable of removing more than

93% of SS (in alkaline pH after 5 h) and 72% of TDS and

15.24% of color (in neutral pH treated after 3 h) from the

textile wastewater using 1.6 mg/L of polymer (Agarwal,

Srinivasan, & Mishra, 2002; Mishra et al., 2002; Mishra et

al., 2004Mishra et al., 2004; Mishra, Yadav, Agarwal, &

Rajani, 2004).

The present paper discusses the synthesis of Psy and AAc

based hydrogels by using N,N-MBAAm as crosslinker and

ammonium persulfate (APS) as initiator. The polymeric

networks [Psy-cl-poly(AAc)], thus formed were characterized

by SEM, FTIR, TGA, and swelling response of the hydrogels

as a function of time, temperature, pH and [NaCl]. The

hydrogels, thus prepared and well characterized have been used

as metal ion sorbents.

2. Experimental

2.1. Materials and method

Plantago psyllium mucilage (Sidpur Sat Isabgol Factory,

Gujarat, India), acrylic acid (Merck-Schuchardt, Germany),

ammonium persulphate and N,N 0-methylenebisacrylamide

(S.D. Fine Mumbai, India) were used as received.

2.2. Synthesis of Psy-cl-poly(AAc)

The optimum reaction parameters were evaluated for the

synthesis of Psy-cl-poly(AAc) by variation of ammonium

persulfate (APS), reaction time, reaction temperature and

amount of the solvent from the morphology and swelling

behavior of the polymeric networks (Table 1). Reaction was

carried out with 1 g of psyllium husk, 1.095!10K2 moles/L

of APS, known concentration of monomer and crosslinker in

the aqueous reaction system at 65 8C temperature for 2 h.

Polymer thus former was stirred for 2 h in distilled water and

for 2 h in ethanol to remove the soluble fraction and then

was dried in air oven at 40 8C. Different polymeric networks

were synthesized by varying [AAc] (from 1.45!10K1 to

7.25!10K1 moles/L) and by varying [MBAAm] (from

6.45!10K3 to 32.40!10K3 moles/L) to study the effect of

monomer and crosslinker variation on the structure of three

dimensional network and thereafter on the percent swelling

of these polymeric networks.

2.3. Characterization

Psyllium and Psy-cl-poly(AAc) polymer were characterized

by the following techniques.

2.3.1. Scanning electron micrography (SEM)

To investigate and compare surface morphology of psyllium

and Psy-cl-poly(AAc), SEMs of these polymer were taken on

Jeol Steroscan 150 Microscope.

B. Singh et al. / Carbohydrate Polymers 64 (2006) 50–5652

2.3.2. Fourier transform infrared spectroscopy (FTIR)

FTIR spectra of psyllium and Psy-cl-poly(AAc) were

recorded in KBr pellets on Perkin Elmer to study the modified

nature of psyllium.

2.3.3. Thermogravimetric analysis (TGA)

Thermogravimetric analysis of psyllium and Psy-cl-poly

(AAc) was carried out on a Schimatdzu Simultaneous Thermal

Analyzer in air at a heating rate of 20 8C/min to examine the

thermal properties of the polymers.

2.4. Swelling behavior

Swelling studies of the polymeric networks were carried out in

aqueous medium by gravimetric method. Known weight of

polymers were taken and immersed in excess of solvent for 24 h

at a fixed temperature to attain equilibrium swelling and then they

were removed, wiped with tissue paper to remove excess of

solvent, and weighed immediately. The equilibrium percent

swelling (Ps) of the polymeric network was calculated as:

Percent swelling ðPsÞZ ðWsKWdÞ=Wd!100

whereWs are weights of swollen polymers andWd weight of dried

polymers.

Swelling behavior of the polymeric networks prepared with

different monomer and crosslinker concentration was studied

as function of time, temperature, pH and [NaCl].

Fig. 1. (a) Scanning electron micrograph of psyllium. (b) Scanning electron

micrograph of psyllium-cl-poly(AAc).

2.5. Metal ion sorption

Psyllium and Psy-cl-poly(AAc) samples were immersed for

16 h in 50.00 mL solutions of FeC2 ions of known strength.

After 16 h, the polymer was removed from ionic solution.

Filtrates of the solutions (residual solutions) were analyzed for

concentration of rejected ions on DR 2010 Spectrophotometer

(Hach Co., USA) by using its standard pillow reagents. Ion

uptake capacity was reported in each case according to

following expression (Rivas et al., 1998):

Percent metal ion uptake ðPuÞ

ZAmount of metal ion sorbed

Amount of metal ion in feed!100

Partition coefficient ðKdÞ

ZAmount of metal ion in polymer

Amount of metal ion left in solution

!Volume of solution ðmlÞ

Wt: of dry polymer ðgÞ

Retention capacity ðRcÞ

ZAmount of metal ion in polymer ðmequiv:Þ

Wt: of dry polymer ðgÞ

3. Results and discussion

Polymeric networks were synthesized by chemically

induced polymerization through free radical mechanism.

APS generates reactive sites, both in the psyllium and

monomer, leading to the propagation of the reaction. In the

presence of crosslinker N,N-MBAAm (CH2aCHCONHCH2

NHCOCHaCH2), because of its poly-functionality, a new

macroradical get formed that has four reactive sites and these

sites can be linked both with the radical on the psyllium and

the monomer. This will lead to the formation of three-

dimensional networks. In order to study the effect of

monomer and crosslinker concentration on the structure of

three-dimensional networks and thereafter on percent

swelling, polymeric networks of different [AAc] and [N,N-

MBAAm] were prepared.

3.1. Characterization

Psyllium and Psy-cl-poly(AAc) were characterized by

SEM, FTIR and TGA studies.

3.1.1. Scanning electron micrography

The morphology of psyllium and Psy-cl-poly(AAc) were

examined by SEM and presented in Fig. 1a and b, respectively.

It was observed that psyllium has smooth and homogeneous

morphology, whereas Psy-cl-poly(AAc) has structural

heterogeneity.

B. Singh et al. / Carbohydrate Polymers 64 (2006) 50–56 53

3.1.2. Fourier transform infrared spectroscopy

FTIR spectra of polymeric networks synthesized were

studied to investigate incorporation of poly(AAc) in the

network. The broad absorption bands at 3405.0 cmK1 due to

–OH stretching indicate association in the polymer. IR

absorption bands due to CaO stretching has been prominently

witnessed at 1728.2 cmK1 in Psy-cl-poly(AAc), and –CH2 in

plane bending at 1402.7 cmK1, –CH out of plane bending at

788.5 cmK1, –COC stretching at 1079.6 cmK1 were observed

apart from usual peaks in the psyllium. Decrease in the

absorbance was observed in all the peaks of the modified

psyllium. FTIR of psyllium and Psy-cl-poly(AAc) shown in

Fig. 2a and b, respectively.

Fig. 3. (a) Primary thermogram of psyllium. (b) Primary thermogram of

psyllium-cl-poly(AAc).

3.1.3. Thermogravimetric analysis (TGA)

TGA of psyllium and Psy-cl-poly(AAc) showed that the

mechanism of decomposition are different in both the cases

(Fig. 3a and b). The initial decomposition temperature (IDT) of

the psyllium and Psy-cl-poly(AAc) were observed at 245.7 and

174.0 8C, respectively. Final decomposition temperature

(FDT) of the Psy-cl-poly(AAc) (647.43 8C) was observed

higher than the psyllium (539.28 8C). It was observed that the

difference in decomposition temperature (DT) for the

crosslinked polymeric networks was more as compared to

psyllium; hence the rate of decomposition was slower in these

polymeric networks. It is thus understandable that thermal

degradation starts earlier in case of Psy-cl-poly(AAc), but it

becomes stable at the higher temperatures. This observation

was further supported by the decomposition temperature

corresponding to the 10% weight loss (Table 2). Further,

Fig. 2. (a) FTIR spectra of psyllium. (b) FTIR spectra of psyllium-cl-

poly(AAc).

from the data of different degradation stages, it was evident that

maximum loss in weight in most the polymers were in the

second stage of decomposition where the temperature range

was usually corresponded to the depolymerization process.

Further differential thermal analysis (DTA) peaks were

observed at 316.4 and 463.0 8C in case of psyllium and 456.6

and 566.6 8C in the crosslinked polymer. These all results of

thermal properties of the modified psyllium indicate that the

changes have occurred in the backbone polymers.

3.2. Swelling behavior of Psy-cl-poly(AAc)

Swelling behavior of Psy-cl-poly(AAc) prepared with

different [AAc] and [N,N-MBAAm] was studied as a function

of time temperature pH and [NaCl].

3.2.1. Ps as a function of time

The swelling behaviors of the polymeric networks were

studied at different time interval of 10 min, 30 min, 1 h, 2 h,

and 24 h. The effect of different monomer concentration

(Fig. 4a) and different crosslinker concentration (Fig. 4b) on

the Ps was studied. It was observed from Fig. 4a that Ps

increased till the equilibrium attained and for each polymeric

network it decreases with increase in the [AAc] and [N,N-

MBAAm] in the networks.

3.2.2. Ps as a function of temperature

To study the effect of temperature on swelling equilibrium, Ps

was studied at different temperature, i.e. 25, 30, 35, 40 and 45 8C.

As the [AAc] varied from 1.45!10K1 to 7.25!10K1 moles/L,

Ps of Psy-cl-poly(AAc), decreased at each fixed temperature

Table 2

Thermogravimetric analysis of psyllium and Psy-cl-poly(AAc)

Sample IDT (8C) FDT (8C) DT (8C) at every 10% weight loss

10 20 30 40 50 60 70 80 90 100

Psyllium 245.7 539.28 155.7 284.2 305.72 310.0 316.2 320.7 410.6 464.28 494.28 539.28

Psy-cl-poly(AAc) 174.0 647.4 209.26 241.36 264.90 290.58 339.80 402.10 479.14 550.0 590.66 647.4

B. Singh et al. / Carbohydrate Polymers 64 (2006) 50–5654

(Fig. 5a). This observation was supported by the fact that

incorporation of higher amount of monomer leads to self-

crosslinking, hence, prevents accessibility of more solvent in

the matrix. But at each fixed concentration of the monomer in the

polymer networks the increase in swelling observed as the

temperature rose in the swelling medium. Maximum Ps 1900

was observed at 7.14!10K1 moles/L of [AAc] at 45 8C

temperature.

1 2 3 4 5 6 7 80

200

400

600

800

1000

1200

1400

1600

1800

2000(a)

(b)

Ps

Ps

[AAc]X101 mol/L

10 min. 30 min. 1 h 2 h 24 h

–5 0 5 10 15 20 25 30 3550

100

150

200

250

300

350

400

450

500

550

600

650

700

[N,N-MBAAm]X103 mol/L

10 min. 30 min. 1 h 2 h 24 h

Fig. 4. (a) Effect of time on Ps of Psy-cl-poly(AAc) prepared with different

[AAc] (swelling temperatureZ40 8C); (reaction timeZ2 h; temperatureZ65 8C; [APS]Z1.095!10K2 mol/L; [N,N-MBAAm]Z1.62!10K2 mol/L and

psylliumZ1 g). (b) Effect of time on Ps of Psy-cl-poly(AAc) prepared with

different [N,N-MBAAm] (swelling temperatureZ40 8C); (reaction timeZ2 h;

temperatureZ65 8C; [APS]Z1.095!10K2 mol/L; [AAc]Z7.25!10K

1 mol/L and psylliumZ1 g).

Ps decreases with increase in [N,N-MBAAm] from 6.45!10K3 to 32.4!10K3 moles/L at each temperature and

maximum Ps 557 was obtained at 6.45!10K3 moles/L [N,N-

MBAAm]. Only a very small concentration of crosslinker

brings abrupt transition from liquid to gel state during synthesis

of hydrogel. The crosslinking density increases with the

increase of crosslinker concentration and consequently

the pore size of the crosslinked network decreased, that was

1 2 3 4 5 6 7 8

200

400

600

800

1000

1200

1400

1600

1800

2000P

s

[AAc]X101 mol/L

25°C 30°C 35°C 40°C 45°C

Ps

–5 0 5 10 15 20 25 30 35

200

300

400

500

600

700

[N,N-MBAAm]X103 mol/L

25°C 30°C 35°C 40°C 45°C

(a)

(b)

Fig. 5. (a) Effect of temperature on Ps of Psy-cl-poly(AAc) prepared with

different [AAc] at 24 h (reaction timeZ2 h; temperatureZ65 8C; [APS]Z1.095!10K2 mol/L; [N,N-MBAAm]Z1.62!10K2 mol/L and psylliumZ1 g). (b) Effect of temperature on Ps of Psy-cl-poly(AAc) prepared with

different [N,N-MBAAm] at 24 h (reaction timeZ2 h; temperatureZ65 8C;

[APS]Z1.095!10K2 mol/L; [AAc]Z7.25!10K1 mol/L and psylliumZ1 g).

B. Singh et al. / Carbohydrate Polymers 64 (2006) 50–56 55

the reason for decrease in Ps. Ps of the uncrosslinked polymer

was observed lesser than that of the crosslinked one. Ps

increased with the increase in temperature of the swelling

medium (Fig. 5b).

3.2.3. Ps as a function of pH

Ps drastically changed by changing the swelling media.

It has been observed from Fig. 6a that Ps of Psy-cl-

poly(AAc) at higher pH (i.e. in 0.5 M NaOH) was higher

than in the distilled water and at lower pH of the swelling

media. Poly(AAc) is an ionizable hydrophilic network. Its

swelling behavior was observed as pH-dependent due to the

ionization/deionization of the carboxylic acid groups. At

lower pH values, the –COOH groups do not ionize and keep

the network at its collapsed state. At higher pH values, the

–COOH groups ionize and the charged COOK groups repel

each other, resulting in the swelling of the polymer. It was

also observed that polymeric networks with lower monomer

concentration were dissolved at 0.5 M NaOH and 0.5 M HCl.

1 2 3 4 5 6 7 8200

400

600

800

1000

1200

1400

1600

1800

2000

Ps

Ps

[AAc]X101 mol/L

Distilled Water 0.5N NaOH 0.5N HCl

–5 0 5 10 15 20 25 30 3550

100150200250300350400450500550600650700750800

[N,N-MBAAm]X103 mol/L

Distilled water 0.5N NaOH 0.5N HCl

(a)

(b)

Fig. 6. (a) Effect of pH on Ps of Psy-cl-poly(AAc) prepared with different

[AAc] at 24 h (swelling temperatureZ40 8C); (reaction timeZ2 h; tempera-

tureZ65 8C; [APS]Z1.095!10K2 mol/L; [N,N-MBAAm]Z1.62!10K2

mol/L and psylliumZ1 g). (b) Effect of pH on Ps of Psy-cl-poly(AAc)

prepared with different [N,N-MBAAm] at 24 h (reaction timeZ2 h; tempera-

tureZ65 8C; [APS]Z1.095!10K2 mol/L; [AAc]Z7.25!10K1 mol/L and

psylliumZ1 g).

Further it was observed from Fig. 6b that polymer without

crosslinker are soluble in the 0.5 M NaOH solution. Ps

decreases with the increase in [N,N-MBAAm] in the

polymeric networks. The maximum Ps 920 was observed at

6.4!10K3 moles/L of [N,N-MBAAm].

3.2.4. Ps of as a function of [NaCl]

In order to evaluate the super-absorbent nature of Psy-cl-

poly(AAc), the swelling behavior was studied in different

[NaCl] solutions. Ps of polymer prepared with different [AAc]

and different [N,N-MBAAm] is presented in Fig. 7a and b,

respectively. Percent solvent uptake decreases with the

increase in monomer and crosslinker concentration for each

brine solution with the increase in brine concentration.

3.3. Metal ion sorption

The sorption capacity depends on the extent of crosslinking

and decreases with the increase in the extent of crosslinking. It

1 2 3 4 5 6 7 8

100150200250300350400450500550600650700750800850(a)

(b)

Ps

[AAc]X101 mol/L

1% NaCl 5% NaCl 10% NaCl 15% NaCl

–5 0 5 10 15 20 25 30 35100

150

200

250

300

350

400

450

500

550

Ps

[N,N-MBAAm]X103 mol/L

1% NaCl 5% NaCl 10% NaCl 15% NaCl

Fig. 7. (a) Effect of [NaCl] on Ps of Psy-cl-poly(AAc) prepared with different

[AAc] at 24 h (swelling temperatureZ40 8C); (reaction timeZ2 h; tempera-

tureZ65 8C; [APS]Z1.095!10K2 mol/L; [N,N-MBAAm]Z1.62!10K2

mol/L and psylliumZ1 g). (b) Effect of [NaCl] on Ps of Psy-cl-poly(AAc)

prepared with different [N,N-MBAAm] at 24 h (swelling temperatureZ40 8C);

(reaction timeZ2 h; temperatureZ65 8C; [APS]Z1.095!10K2 mol/L;

[AAc]Z7.25!10K1 mol/L and psylliumZ1 g).

Table 3

FeC2 sorption studies of psyllium and Psy-cl-poly(AAc) prepared with

different [N,N-MBAAm]

Sr. No. [N,N-MBA]

(mol/L) !103

% FeC2

uptake

Partition

coefficient (Kd)

Retention

capacity (Rc)

1 0 35.75 278.22 0.247

2 6.45 50.78 515.78 0.351

3 12.9 46.63 436.89 0.322

4 19.45 31.09 225.56 0.214

5 25.45 33.68 253.90 0.232

6 32.4 22.80 147.65 0.157

7 Psyllium 40.30 346.4 0.282

B. Singh et al. / Carbohydrate Polymers 64 (2006) 50–5656

was observed from Table 3 that percent FeC2 uptake of Psy-cl-

poly(AAc) decreases from 50.63 to 22.80% as the [N,N-

MBAAm] increases from 6.45!10K3 to 32.40!10K3 mol/L

in the polymeric networks. This is because of the restricted

diffusion of the ions through the polymer networks and reduced

chain flexibility. Metal ion uptake of the modified psyllium was

more than psyllium. Partitioning of ions between polymeric

matrices and liquid phase is reflected with high values of

partition coefficients (Kd). Structure of polymeric networks has

significant effect on ion-uptake, which is reflected in low

retention capacities (Qr) of the hydrogels.

4. Conclusion

Swelling of the polymeric networks was affected by

synthetic conditions such as [AAc] and [MBAAm] and also

by the environmental factors such as pH of the medium, ionic

strength of the solution and swelling temperature. Further,

from the observation of water uptake in the different swelling

media, it can be concluded that these polymeric networks are

pH sensitive and are able to respond to the environmental

changes. Therefore, it can be used as suitable material for the

colon specific drug delivery. Further, from metal ion sorption

study, it is evident that these polymeric networks can be used

for the removal, separation, and enrichment of hazardous metal

ions in aqueous solutions and can play an important role for

environmental remediation of municipal and industrial

wastewater.

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