Synthesis and flocculation characteristics of cationic modified corncob: A novel polymeric flocculant

doi:10.4236/as.2013.49B004

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Vol.4, No.9B, 23-28 (2013) Agricultural Sciences

http://dx.doi.org/10.4236/as.2013.49B004

Synthesis and flocculation characteristics of cationic

modified corncob: A novel polymeric flocculant

Yanhua Pang1*, Yongsheng Din g 2, Jie Chen3, Weimin Gong3

1Center of Food Inspection, Liaoning Entry-Exit Inspection and Quarantine Bureau, Dalian, China;

*Corresponding Author: cindy_gl@eyou.com

2College of Ocean Environment and Engineering, Shanghai Maritime University, Shanghai, China

3College of Environ ment al Science and Engineerin g, D alian Maritime Univer sity, Dalian, China

Received Ju l y 2013

AB STRACT

A novel organic polymeric flocculant was syn-

thesized by grafting cationic etherifying mono-

mer (3-chloro-2-hydroxypropyl) trimethyl ammo-

nium chloride (CHPTAC) onto the backbone of

corncob powder (CP, Φ ≤ 30 µm). The synthetic

reaction between CP and CHPTAC was initiated

by hydroxyl radical made from Fenton reagent

(H2O2-FeSO4). The alkalization process and syn-

thetic reaction conditions were optimized by va-

rying several parameters affecting grafting effi-

ciency, such as NaOH dose, monomer concen-

tration, reaction temperature and time and dis-

tilled water dose. The synthesized cationic flo c-

culant was characterized by elemental analysis,

Fourier-transform infrared spectrometer and

scanning electron microscope techniques. It was

concluded that the backbone of CP have been

grafted cationic etherifying monomer. The floc-

culation characteristics in 0.25% (w/v) kaolin

suspensions was compared with some of the

comm ercial f loccul ants a vailab le in markets , and

the results demonstrated the synthesized catio-

nic flocculation has superiority as a novel floc-

culant.

Keywords: Flocculation; Corncob; Polymeric

Flocculant; CHPTAC

1. INTRODUCTION

Flocculation [1-3] is a process of bringing together

smaller particles to form larger particles, and settling of

colloidal particles from stable suspensions caused by the

addition of chemicals known as flocculants in minute

quantities. It is well known that the use of organic and

inorganic flocculants can improve the efficiency of sol-

id/liquid separation in a wide range of papermaking,

wastewater treatment and mineral processing industries

[4-7]. The inorganic flocculants, which are mainly based

on hydrolyzable salts of aluminum, cannot be removed

easily during treatment, and the residue in water can cause

some health problems [8]. Natural and synthetic poly-

meric flocculants, which are able to destabilize colloidal

suspensions, have been found wide application as floc-

culating agents in the past dec ade. Water-soluble syn thetic

polymers [9-11] have a disadvantage of non-biodegra-

dability and cost-effective. Thus, the demand for effec-

tive, cheap and environmentally friendly natural floccu-

lants for wast ewater treatment is increasing.

With the characteristics of nontoxic and biodegradable,

the so-called “green flocculants” such as starch [12,13],

amylopectin [14], alginic acid [15], guar gum [16], and

so for th, ha ve bee n paid mu ch att entio n. The chemical and

physical properties of the natural polymers can be mod-

ified by grafting a synthetic polymer onto the backbone of

natural polymers. For highly negatively charged colloidal

particles, cationic polymers are more used as flocculating

agents to remove finely divided solids from aqueous

suspension [17].

The natural corncob powder (CP), mainly composed

of cellulose, lignose and pentosan, has abundant output

in China. Composed of much hydroxyl radicals, CP may

be grafting by cationic polymers and perform efficient

flocculation characteristics. In view of several authors’

earlier findings, CP was chosen as the base pol ymer graft-

ing by a quaternary ammonium compo und [18]. Howev-

er, it has not been much s tudied as floccul ating agent for

wastewater treatment.

Highly charged cationic polymers such as polyamines

and polyimines are costly. Therefore, it has been at-

tempted to synthesize a cationic quaternary ammonium

salt (3 -chloro-2-hydroxypropyl) trimethyl ammonium chlo-

ride (CHPTAC). The present work aims to explore the

feasibility of grafting flocculation (DXSL-I) of CP and

CHPTAC, illustrate it s characteristics b y using elemental

analysis, Fourier-transform infrared (FTIR) and scan-

Y. H. Pang et al. / Agricultural Sciences 4 (2013) 23-28

ning electron microscope (SEM) and evaluate its floccu-

lation performance. The reaction parameters affecting

grafting efficiency, such as NaOH dose, monomer con-

centration, reaction temperature and time and distilled

water dose were also investigated.

2. EXPERIMENTAL

2.1. Materials

Corncob powder (CP, (Ф ≤ 30 mm), obtained from

Dalian Farm Product Processing Plant, was dried at

100˚C for 4 h before use. Triethylamine, Epoxy chloro-

propane, all purchased from Shanghai Reagent Company,

China, were of analytical reagent grade. Aluminum chlo-

rate and Polyacrylamide are used as commercial floccu-

lants for comparison test. All the reagents were used

without further purification. Kaolin clay (Ф ≤ 2 mm) was

purchased from Zhonglong Kaolin Ltd., Chi na.

2.2. Preparation of Cationic Monomer

The reaction conditions were established according to

our previous experience [18]. Epoxy chloropropane (20

ml) was mixed with excessive triethylamine in a sealed

flask with constant stirring. The reaction was allowed to

continue for 3 h at a reaction temperature of 0˚C - 5˚C,

after which the sample was settled at ice bath for 2 h.

The content of upper solution, in which was the cationic

monomer (3-chloro-2-hydroxypropyl) trimethyl ammo-

nium chloride (CHPTAC), can be determined by using

Ag+ solution. The quaternary ammonium monomer was

decomposed easily under daylight or high temperature.

Therefore, the use of instant prepared monomer was

suggested. The reaction of quaternary ammonium group

preparation was shown as followed:

ClCH

CH CH

N(C

)

Fenton reagent

T< 5℃

(1)

2.3. Synthesis of Cationic Flocculant DXSL-I

Corncob powder can be modified by incorporating a

cationic monomer (3-chloro-2-hydroxypropyl) trimethyl

ammonium chloride onto the backbone of the polysac-

charide. The details of the synthesis and the reaction

conditions are as follows.

Corncob powder (2.0 g) was dissolved in distilled wa-

ter (8.0 ml) at room temperature. As alkaline medium is

essential to carry out the reaction, 0.002 g NaCl and 0.6

g NaOH were added to it. The reaction solution was al-

kalized for 60 min at 40˚C - 50˚C, followed by adding

Fenton reagent (H2O2 and Fe2+ were 0.8% - 1.2% and

0.005% of CP mass, respectively) into the solution to

initiate the reactio n for 30 - 90 s. Re actio n was then c on-

tinued for 3 h with excessive CHPTAC at 50˚C. The so-

lution was thereafter cooled to room temperature, and the

copolymer was precipitated by centrifugation. The resi-

due was washed with distilled water several times until

its pH reached 7 - 8 and there was not CHPTAC in the

filtrate checked with Ag+ solution. After washing, it was

dried in a vacuum oven.

2.4. Characterization of Cationic Flocculant

DXSL-I

2.4.1. Elemental Analysis

Elemental analysis of the cationic flocculant DXSL-I,

CP and CHPTAC was undertaken with a LiquiTOC ele-

mental analyzer (Elementar Analysensysteme GmbH,

German). The estimation of only three elements, that is

car bon, hydrogen and nitrogen, was undertaken.

2.4.2. FTIR Spectroscopy

A 500 FTIR Spectrophotometer (Nicolet, USA) was

used and the potassium bromide (KBr) pellet method

was used for FTIR study. The FTIR spectrum of cationic

flocculation DXSL-I, alkalized CP and CP were collected

separately.

2.4.3. Scanning Electron Microscopy (SEM)

The small granules left after the pulverized graft co-

polymers and CP were sieved, and were subjected to

SEM study. The samples were gold-coated, and a magni-

fication of 2000 times was obtained. A Philips XL-30

Scanning Electro-Microscope (Holland) was used for

SEM study.

2.5. Flocculation Test

Flocculation capacity of DXSL-I and other commer-

cial flocculants were evaluated using 0.25% (w/v) of

kaoli n suspe nsio ns. After add ition of flocculants solutio n

(80 - 100 ml), mixtures were mechanically stirred at a

constant speed of 200 rpm for 2 min, followed by a slow

stirring at 40 rpm for 10 min. Thereafter, the sample was

left to settle for 5 min. At the end of the settling, 10 ml of

the supernatant fluid was taken from the beaker surface,

and its transmittance was measured at a wavelength of

610 nm by using JASCO V-500 Spectrometer (Japan).

3. RESULTS AND DISCUSSION

3.1. Synthesis Mechanism

Corncob, mainly consisted of polysaccharide, was a

natural polymer. There were many -OH groups on its

microparticle’s surface [19]. Cationic modification was

based on these radicals. The synthetic reactions were

etherifying processes as shown in Eq s.2 and 3.

Matrix OH

OH n

CH2CH

CH2N+

CH2CH

CH2N+

Matrix O

OH n

(C2H5)3(C2H5)3

-1

(2)

Y. H. Pang et al. / Agricultural Sciences 4 (2013) 23-28

CH2CH

CH2N+

(C2H5)3

CH2CH

CH2N+

Matrix O

(C2H5)3

Matrix OH n

+(n)

(3)

Reactions were theoretically divided into several steps,

including the free radical chain reaction and ion reaction

[20,21]. The formation of free OH groups could be ex-

pressed as followed equations:

Fe2+ H2O2Fe3+ OH OH

+++

(4)

Matrix OH Matrix O

OH OH

(5)

The synthetic reaction was actually an electr o -nuc-

leophilic process as shown below:

Matrix O

)

(6)

Some possible unwished negative reactions may hap-

pen as indicated from Eq s.7 to 10, where included free

radical transfers and exterminations, as well as the spli-

tup of etherified monomer by hydrolyzation.

OH H

OHOO

(7)

OHOO O

++ +

(8)

OH Fe

(9)

CH CH

Matrix OCH

CH CH

(R)

(10)

3.2. Synthesis Conditions and Influence

Factors

3.2.1. NaOH Dosage, A lkalizing Temperature and

Time

In order to evaluate the effect of NaOH dose on the

grafting of CHPTAC onto CP, a set of experiments were

carried out, in which the dose was changed from 0.10 g

to 6.00 g, while all the other parameters were kept un-

changed. The results showed an increase in the grafting

percentage with the increase in NaOH dose. However,

beyond a value of 0.6 g, a significant decrease in grafting

percentage was observed. According to synthesis reac-

tion (Eq.2 ) , the low dose OH- was he lpful to chan ge OH

group into ionic oxygen, of which the nucleophilic ca-

pacity was strengthened consumedly. However, overdose

of NaOH could make the epoxy ring broken up and ac-

celerate the quaternary ammonium radical decomposed,

resulting in grafting efficiency reduced. The similar re-

sults were found after a series of experiments about alka-

lization conditions. There is also an increase in the graft-

ing percentage with the alkalizing temperature and time,

but a reduction occurred with the alkalizing temperature

raised and time prolonged. The density of free radicals

was l ess, r esulti ng in re duct ion of grafti ng efficie ncy with

the alkalizing temperature and time increased. After the

opti mization experiments, it was obtained the NaOH do-

sage is 0.6 g, alkalizing temperature is 40˚C - 50˚C and

alkalizatio n time is 60 min.

3.2.2. Monomer Concentration

As sho wn in Fi gu re 1 , the gr afting p ercenta ge sig nifi-

cantly increased with incr easing mono mer concentration.

The presence of a hi gh concentration of CHPTAC in the

medium provided a greater availability of CHPTAC mo-

lecules to react with the CP macroradicals, leading to a

higher synthesis percentage. However, overdose of mo-

nome r co sts hi gh l y and unbeneficial.

3.2.3. Orthogonal Experi m en t

In addition to monomer concentration, distilled water

medium, synthesis temperature and time were also the

infl uence factor s gove rnin g the gra fting e fficie ncy. There -

fore, a series of experiments were carried out by ortho-

gonal method to optimize the reaction conditions affect-

ing flocculation efficiency. Taking CP (2.0 g), we ex-

amined the influence factors including the reaction tem-

perature (30˚C - 60˚C), reaction time (2 - 5 h) and dis-

tilled water (4 - 16 ml), respectively. T he final optimized

condition was obtained as follo ws: synthesis temperature

50˚C, synthesis time 3.0 h, and distilled water 8.0 ml.

The orthogonal experimental parameters were shown in

Table 1.

0.02 0.04 0.06 0.08 0.10

100

Grafting percentage/%

M onom er Concentration /M

Figure 1. Effect of monomer concentration on grafting percen-

tage (C P dos a ge : 2.0 g).

Table 1. The orthogonal experimen tal parameters.

No. Reaction temperature (˚C) React io n tim e (h) Water (ml)

1 30 2 4

2 40 3 8

3 50 4 12

4 60 5 16

Y. H. Pang et al. / Agricultural Sciences 4 (2013) 23-28

3.3. Caracterization of DXSL-I

3.3.1. Elemental Analysis

The results of element analysis of CP, CHPTAC and

cationic modified flocculants DXSL-I are shown in Ta-

ble 2. It has been found that corncob does not show any

significant presence of nitrogen. And the negligible amount

of nitrogen was 0.2% in CP is because of the presence of

trace quantities of proteins in the corncob powder. It is

shown in Table 1 that there is a considerable percentage

of nitrogen in the flocculants DXSL-I, which can be ac-

counted for the presence of CHPTAC chain onto the

backbone of corncob. Evaluation of the synthesis reaction

efficie ncy is ba sed on t he dete rminatio n of nit rogen co n-

tent in the modified flocculants according to elemental

analysis. From the element analysis table, it appears that

CHPTAC monomer are incorporated in greater extent

with increase in its concentration, possibly through par-

ticipation of larger number of OH groups of corncob in

cova lent li nkages .

3.3.2. FTIR Analysis

The FTIR spectra of cationic flocculation DXSL-I, al-

kalized CP and CP were shown in F i g ure s 2a-c, respec-

tively.

The broad band (Figure 2a) at 3404 cm−1 is due to the

stretching vibration of the OH groups. The band at 1635

cm−1 is for OH b end ing vib rat io n. T he b ands a t 125 2 and

2925 cm−1 are assigned to C=O stretching and CH stret-

ching, respectively. The bands at 1431 cm−1 are due to

CH bending vibration. The two bands at 1051 cm−1 and

1512 cm−1 are attribu ted to CH2-O-CH2 and epoxy groups

stretching vibrations. Figure 2b shows the FTIR spectra

of alkalized CP. The broad peak at 3397 cm−1 is due to

the OH stretching vibration. The intensive band at 2915

cm−1 is due to CH stretching vibration. Two bands at

1051 and 1512 cm−1 are for CH2-O-CH2 and epoxy groups

stretching vibrations, respectively. It is found that the

band at 1251 cm−1 was not present in Figure 2b, which

indicate synthesis reactions in Eqs.2 and 3 have hap-

pened. The broad band (Figure 2c) at 3409 cm−1 is due

to the stretching vibration of the OH groups. The pres-

ence of an additional band at 1395 cm−1 in Fig u re 2c due

to the CN stretching vibration is a clear proof of incor-

poration of cationic monomer onto the backbone of CP.

3.3.3. SEM Analysis

Fig u re s 3-5 show the scanning electron micrographs

Table 2. Results of Elemental Analysis.

Po l ym er %C %H %N

CP 36.5 6.4 0.2

CH PT AC 37.8 7.8 7.2

DXSL-I 37.2 6.1 3.5

602

1 049

1 376

1 512

1 635

2 925

3 409

Absorbance

1000

2000

3000

4000

Wavenumbers

/cm

-1

Figur e 2. IR spectra of (a) CP, (b) alkalized CP and (c) DXSL-I.

Figure 3. SEM micrograph of CP.

Figure 4. SEM micro graph of alkalized CP.

of CP, alkalized CP and DXSL-I, respectively. A careful

examination of the micrographs reveals a difference in

the morphological appearance of the polymers. CP has a

granular structure, which changed drastically when it was

Y. H. Pang et al. / Agricultural Sciences 4 (2013) 23-28

Figure 5. SEM micrograph of DXSL-I.

alkalized and grafted with cationic etherifying monomer

CHPTAC. The appearance of Alkalized CP seems in-

compact, which is helpful for OH groups exposed and

grafting reaction. However, DXSL-I appeared embedded

structure. It can be explained that the alkalized CP com-

bined with etherifying monomers formed a kind of struc-

ture mingling soft and rigid property. This observation

also supported the grafting of CHPTAC onto the back-

bone of CP.

3.4. Flocculation Characteristic

An attempt has been made to compare the flocculation

characteristics of DXSL-I with some of the commercially

available flocculants in 0.25 % (w/v) kaolin suspensions

(Figure 6). The characteristics made it appropriate for

treating wastewater with a high efficiency in a wide pH

range without pH adjustment. It can be concluded that

DXSL-I has the similar capacity to polyacrylamide, but

superior to aluminum chloride. Its performance is better

than that of other commercial flocculants because the

kaolin particles have high negative charges and in this

case, it appears that the cationic along with easy approa-

chability of branched structure of CHPTAC dominates

the performance.

4. CONCLUSI O N

From the above results, it can be concluded that catio-

nic monomer CHPTAC is grafted onto the backbone of

CP. Variation in the synthetic parameters results in dif-

ferent flocculation efficiency. Investigation of elemental

analysis, FTIR spectra and SEM provide a strong proof

of cationization. In comparison with the commercial

flocculants, the best performing of the cationic modified

flocculants DXSL-I having long CHPTAC chains show

better flocculatio n characteristics.

2 4 6 810 12 14

100

bl ank

DXSL -I

Aluminum chlorate

Polyac ryla

Transm ittance /%

Time /min

Figure 6. Flocculation performance in Kaolin suspensions.

5. ACKNOWLEDG E ME NTS

The authors thank the Dalian Maritime University Research Fund for

its support of this research.

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