Optimization of reaction conditions for preparing carboxymethyl

cellulose from sago waste

V. Pushpamalar a,*, S.J. Langford b, M. Ahmad c, Y.Y. Lim a

a School of Arts and Science, Monash University Malaysia, No. 2, Jalan Kolej, Bandar Sunway, 46150 Petaling Jaya Selangor, Malaysiab School of Chemistry, Monash University, Clayton, Vic. 3800, Australia

c Department of Chemistry, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia

Received 6 May 2005; received in revised form 1 December 2005; accepted 2 December 2005

Available online 18 January 2006

Abstract

Sago pulp (57% w/w) isolated from sago waste was converted to carboxymethyl cellulose (CMC) by etherification using sodium

monochloroacetate and sodium hydroxide. The reaction was optimized against temperature, concentration and reaction time. The optimized

product has a large degree of substitution (DS) of 0.821, which compared favorably to other forms of cellulose. Fourier Transform Infrared spectra

(FTIR) were used to characterize the product and starting sago pulp. Digital photographs of sago waste and sago pulp showed the expected rough

woody structure while that of the CMC generated from the pulp showed a smooth surface morphology.

q 2005 Elsevier Ltd. All rights reserved.

Keywords: Sago waste; Sago pulp; Carboxymethyl cellulose; Carboxymethylation; FTIR

1. Introduction

The conversion of plant waste materials into useful products

would alleviate a variety of socio-economic problems such as

providing a ‘greener’ approach to manufacturing. Plant wastes

comprise more than 90% (w/w) of carbohydrate polymers

(polysaccharides) which are amenable to both chemical and

biochemical modifications. Many polysaccharide derivatives

have been prepared by carboxymethylation reactions using

substances such as cotton linters (Xiquan, Tingzhu, & Shaoqui,

1990), starch (Bhattacharyya, Singhal, & Kulkarni, 1995;

Kooijmann, Ganzeveld, Manurunf, & Heeres, 2003) and

cashew tree gum (Silva et al., 2004).

In Sarawak, Malaysia, sago palms (Metroxylon sago) are

inexpensive and grow well in swampy areas that are in urgent

need of economic development. There exist at present an

estimated two million hectares of wild stands of sago palm

compared to 200,000 ha of cultivated sago palm. A well-

attended farm can produce 175 kg sago starch per palm, giving

a total yield of 25 tons of sago starch/ha. The starch is produced

0144-8617/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.carbpol.2005.12.003

* Corresponding author. Tel.: C60 356360600x3541; fax: C60 356358640.

E-mail address: pushpa.janarthanan@artsci.monash.edu.my (V.

Pushpamalar).

at the rate of about 300 million tones/year and is used as an

ingredient of noodles, vermicelli, biscuits and it has industrial

uses such as processing monosodium glutamate, glucose and

fructose syrups. Sago waste is produced as a by-product from

the production of sago starch (Doelle, 1998). Sago waste

produced from the sago palm is one of the cheapest,

biodegradable and most readily available of all renewable

natural polymers existing in Malaysia. Cellulose is an abundant

naturally occurring macromolecular material in sago waste.

Cellulose usually occurs in the cell wall of plants and is

generally associated with other substances such as lignin and

hemicellulose, which make it difficult to find in pure form.

Fig. 1 shows that cellulose is a linear condensation polymer

consisting of glucose units joined together by b-glycosidicbonds between C(4) of one sugar unit and the anomeric C(1) of

the other. Plants contain on a dry basis between 40–55%

cellulose, 15–35% lignin and 25–40% hemicellulose. The

commercial versatility of cellulose is such that sometimes it is

used in the form of original fibers such as cotton fibers for

textile and sometimes it is used in its derivative form such as

cellulose nitrate and carboxymethyl cellulose (Thomas,

Paquita, & Thomas, 2002).

There are two interconvertable polymorphs of cellulose

known as cellulose I and cellulose II. X-ray crystallography

studies of the different cellulose types have showed that

cellulose I has two chains that lie parallel to one another in the

unit cell. Cellulose II has the direction of the chains in the unit

Carbohydrate Polymers 64 (2006) 312–318

www.elsevier.com/locate/carbpol

O O

HOCH2

OHO

HO

O

HOCH2

HO

HOO

Fig. 1. Fragment of (repeating unit) of a cellulose chain (Jones, 2005).

V. Pushpamalar et al. / Carbohydrate Polymers 64 (2006) 312–318 313

cell in an antiparallel orientation (O’Sullivan, 1997). Carbox-

ymethyl cellulose is produced by etherification of the hydroxyl

groups with sodium monochloroacetate (SMCA) in the

presence of aqueous alkali as shown in Fig. 2. The method is

based onWilliamson’s ether synthesis (Tijsen, Kolk, Stamhuis,

& Beenackers, 2001). The first step in the carboxymethylation

is an equilibrium reaction between NaOH and the hydroxyl

groups of the cellulose. The second step is actual formation of

the carboxymethyl group by the substitution of SMCA. SMCA

can also react by an undesired side reaction with NaOH to form

sodium glycolate.

Carboxymethyl cellulose (CMC) is the most widely used

cellulose ether today, with applications in the detergent, food

exploration, paper, textile, pharmaceutical and paint industries

(Methacanon, Chaikumpollert, Thavorniti, & Suchiva, 2003).

Production of CMC is simpler than that of most other cellulose

ethers because all reactions are operated at atmospheric

pressure using commercially available reagents. The etherify-

ing reagent, sodium monochloroacetate, is easy to handle and

very efficient. For these reasons, CMC has become the largest

industrial cellulose ether. Large quantities are produced in

crude commercial grades without any refining for use in

detergents, oil drilling, and in the paper industry. High-purity

grades are also employed as food additives (Dahlan, Jacobs, &

Sjoberg, 2003).

2. Methods

2.1. Sago pulp purification

The sago waste was dried for 3 h, ground using a blender

and sieved through 0.5 mm2 test sieve. The ground sago waste

was pre-dried in the oven at 60 8C for 1 h. About 5.0 g of sago

waste was added into 500 mL Erlenmeyer flask and suspended

in 160 mL of hot distilled water together with 1 mL of glacial

acetic acid. About 1.5 g of technical grade sodium chlorite was

then added. The conical flask was stoppered and heated in

O

OHO

HOCH2

O

HO

1. aqueous Na2. ClCH2COO

cellulose

Fig. 2. Reaction scheme of the carboxymethyla

the water bath maintained at 70 8C over a period of 3 h. The

final residue should be almost white and retain the woody

structure of the original sample. The mixture was filtered using

a Buchner funnel and washed with cold distilled water until the

pH of the filtrate was 7.0 and the residue was dried in oven at

60 8C to constant weight (Pushpamalar, Langford, Ahmad, &

Lim, 2004).

Precaution. The addition of sodium chlorite and washing

should be carried in well-ventilated hood.

2.2. Preparation of carboxymethyl cellulose from

sago pulp (delignified sago waste)

Sago pulp was used after drying to constant weight. About

5.0 g of sago pulp was weighed and added to 250 mL Schott

bottle and followed by 100 mL of water:solvent in appropriate

ratio. Then, 10 mL of 30% (w/v) sodium hydroxide added

drop-wise and stirred for an hour. The carboxymethylation

reaction was started by adding 6.0 g sodium monochloroace-

tate with reaction mixture placed in thermostated water bath

with horizontal shaker. The reaction mixture was heated up to

reaction temperature of 45 8C and shaken for 3 h of reaction

time. The mixture was then filtered and the residue was

suspended in 300 mL of methanol overnight. The suspended

methanol solution was then neutralized using glacial acetic

acid. The residue was filtered and dried to constant weight.

The procedure used to study the effect of the process

parameters on carboxymethylation was similar to that of

Bhattacharyya et al. (1995) with some modifications. The

parameters to prepare carboxymethyl cellulose from sago pulp

and the initial values used are as follows: different types of

solvents (water, dimethylformamide, methanol, dimethylsulf-

oxide, isopropyl alcohol, ethanol and butanol), water and

solvent ratio (20:80), reaction period (120 min), amount of

sodium monochloroacetic acid (6.0 g), concentration of NaOH

(10 mL of 30%) and reaction temperature (45 8C).

2.3. Determination of degree of substitution

2.3.1. Potentiometric back titration

Absolute values of degree of substitution (DS) were

determined by potentiometric titration. A portion of the

carboxymethylated product was dissolved with 60 mL of

95% ethanol and stirred. Then, 10 mL of 2 M nitric acid was

added and the mixture agitated for 2 min. The mixture was then

OHNa

OCH2COONa

O

ROCH2

ROO

O

sodium carboxymethyl cellulose

R = H or CH2 COONa

according to DSCMC

tion of cellulose (Heinz & Pfeiffer, 1999).

Fig. 3. FTIR spectrum of sago pulp from sago waste.

V. Pushpamalar et al. / Carbohydrate Polymers 64 (2006) 312–318314

heated to boiling for 5 min and agitated further for 15 min and

left to settle. After the solution had settled, the supernatant

liquid was filtered and discarded. The precipitate was washed

with 80 mL 95% ethanol and further washing done by using

80% ethanol which has been heated to 60 8C until the acid and

salts were removed. The precipitate was washed with methanol

and transferred to beaker and heated until the alcohol was

removed. The beaker with the precipitate was dried in the oven

at 105 8C for 3 h.

About 0.5 g of acid carboxylmethyl cellulose was weighed

in 250 mL Erlenmeyer flask and 100 mL distilled water added

and stirred. Twenty-five milliliter 0.5 N sodium hydroxide was

added and boiled for about 15 min. Then the heated solution

was titrated with 0.3 N hydrochloric acid by using phenophtha-

lein as an indicator. The carboxymethyl content and the degree

of substitution were calculated based on the equations below

Carboxymethyl content ð%CMÞ

Z ½ðV0KVnÞ!0:058!100�=M

Degree of substitutionZ 162!%CM=½5800Kð57!%CMÞ�

where V0Zml of HCl used to titrate blank, VnZml HCl used to

titrate sample, NZnormality of HCl used, MZsample amount

(g), and 58Zmolecular weight of carboxylmethyl group

(Elomaa et al., 2004).

2.3.2. Infrared spectroscopy

All measurements were carried out using the KBr method.

The samples were dried in an oven at 60 8C. About 0.2 mg of

sample and 2 mg of KBr were mixed and ground finely and the

mixture was compressed to a form a transparent disk. The

infrared spectra of these samples were recorded with a Perkin–

Elmer Spectrometer (Model spectrum BX) between 400 and

4000 cmK1.

2.4. Surface morphology analysis

Photographs of these samples were taken by using model

Coolpix 950 Nikkor digital camera with a superior perform-

ance of 3! zoom.

Fig. 4. FTIR spectrum of carboxymethylcellulose.

3. Results

3.1. Proof of carboxymethylation

The IR spectra of all the CMC samples synthesized show the

typical absorptions of the cellulose backbone as well as the

presence of the carboxymethyl ether group at 1605 cmK1.

Fig. 3 shows the IR spectrum of sago pulp from sago waste.

It is evident that the broad absorption band at 3432 cmK1, is

due to the stretching frequency of the –OH group as well as

intramolecular and intermolecular hydrogen bonds. The band

at 2920 cmK1 is due to C–H stretching vibration. The bands

around 1420 and 1320 cmK1 are assigned to –CH2 scissoring

and –OH bending vibration, respectively. The band at

1060 cmK1 is due to OCH–O–CH2 stretching (Kondo, 1997).

Fig. 4 shows a representative spectrum of carboxymethyl

cellulose. Clearly, evident is a broad absorption band at

3432 cmK1, due to the stretching frequency of the –OH group

and a band at 2920 cmK1 attributable to C–H stretching

vibration. The presence of a new and strong absorption band at

1605 cmK1 confirms the presence of COOK group. The bands

around 1420 and 1320 cmK1 are assigned to –CH2 scissoring

and –OH bending vibration, respectively. The band at

1060 cmK1 is due to OCH–O–CH2 stretching (Biswal &

Singh, 2004).

3.2. Degree of substitution

The degree of substitution of the carboxyl group in

carboxymethyl cellulose can be determined from both the IR

spectra and potentiometric titration. The values obtained by IR

spectra are the measurements of relative values of the degree of

substitution. Values obtained by potentiometric titration

correspond to the absolute values of the degree of substitution.

It is preferable to obtain the relationship between the absolute

values and the relative values from practical point of view. The

absorption at 1605 cmK1 is assigned to the stretching vibration

of the carboxyl group (COOK) and 2920 cmK1 is assigned to

y= 0.3049x - 0.2618 R2 = 0.9659

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4

Relative I.R absorbance

Deg

ree

of s

ubst

itutio

n

Fig. 5. The relationship between the degrees of substitution determined by

potentiometric titration and IR spectroscopy.

V. Pushpamalar et al. / Carbohydrate Polymers 64 (2006) 312–318 315

the stretching vibration of methine (C–H), respectively. By

taking the ratio of these absorption spectra RrelZA1605/A2920,

we can estimate the relative amount of carboxyl groups in the

samples. Here, the numerical constant is chosen so that the

value of DSrel becomes zero for the original cellulose sample.

DSrel is calculated by the following Eq. (1) (Miyamoto, Tsuji,

Nakamura, Tokita, & Komai, 1996)

DSrel ZRrelK1: (1)

The absolute values of the degree of substitution obtained are

plotted as a function of the relative value of the degree of

substitution in Fig. 5. It is clear from this figure that the

absolute value of the degree substitution is proportional to the

relative value. The least squares analysis of the results shown in

Fig. 5 yields the following relationship as shown in Eq. (2)

DSabs Z 0:305DSrelK0:262: (2)

The optimization of the process of carboxymethylation was

performed by varying the process parameters. Initially spelt

wrong the parameters were selected on the basis of literature

data (Bhattacharyya et al., 1995). During this variation, the DS

of the CMC produced was desirable. Carboxymethylation

reaction parameters were studied by varying a parameter and

fixing other initial parameters value. Once the optimized

parameter condition is obtained, this parameter value is used

for the following parameter study.

3.3. The effects of varying the parameters on carboxymethy-

lation on sago pulp from sago waste

3.3.1. Effect of various solvents

Fig. 6 shows the extent of carboxymethylation, expressed as

degree of substitution when the reaction was carried out in

0.3330.418

0.348

0.531 0.5580.399

0.52

00.10.20.30.40.50.6

H2O

DMF

Meth

anol

DMSO

Isopr

opyl

alcoh

ol

Ethan

ol

Butan

ol

Types of solvent

Deg

ree

of

subs

titut

ion

Fig. 6. Effects of various solvents on degree of substitution of carboxymethyl

cellulose from sago waste.

seven different solvent mediums. A maximum DS of 0.558 was

obtained with isopropyl alcohol as the solvent medium. The

role of the solvent in the carboxymethylation reaction is to

provide miscibility and accessibility of the etherifying reagent

to the reaction centers of the cellulose chain rather than

glycolate formation (Togrul & Arslan, 2003). The differences

in the extent of carboxymethylation can be explained by taking

into consideration their solvent polarities and stereochemistry.

The reaction efficiency increases as the polarity of the solvent

decreases (Barai, Singhal, & Kulkarni, 1997). The results

obtained are in good agreement with the literature but the

solvents, isopropyl alcohol and butanol with same polarity did

not produce the CMC with the same DS value. Isopropyl

alcohol was the best choice, which is in agreement with other

reports as well (Bhattacharyya et al., 1995; Khalil, Hasem, &

Habeish, 1990).

3.3.2. Effect of ratio of water and isopropyl alcohol

As shown in Fig. 7, the carboxymethylation reaction was

carried out in six different water:isopropyl alcohol ratios. A

maximum of 0.585 was obtained with 0:100 water:isopropyl

alcohol. It is observed that the increase in the ratio of organic

solvent increases the DS of the CMC produced. It is observed

that isopropyl alcohol causes pronounced decrystallization of

cellulose and a change of polymorphism from cellulose I to

cellulose II. The change of crystallinity and polymorphismmay

be due to the partition of sodium hydroxide between the

reaction medium and the cellulose chain. This partition occurs

when suspending cellulose in mixtures of an organic solvent,

water and sodium hydroxide. In such a system, the organic

medium plays the role of uniformly distributing NaOH with

water in cellulose and so form an ‘aqueous’ solution of NaOH

in the cellulose phase. The nature and composition of organic

solvents used as reaction media plays an important part in the

structural transformation of cellulose during alkalization.

Isopropyl alcohol having low dielectric constant is a bad

solvent for sodium hydroxide and it favors higher concen-

tration of NaOH in the vicinity of cellulose, giving rise to

substantial change of polymorphism from cellulose I to

cellulose II during alkalization. As Na-cellulose I cannot be

converted to cellulose I, it was deduced that Na-cellulose I

possesses an antiparallel arrangement which has the same

chain polarity as cellulose II. This may explain how cellulose I

can be converted to cellulose II without solubilizing the

cellulose. Cellulose II has more hydrogen bonding which

0.585 0.558

0.3540.288 0.295 0.333

00.10.20.30.40.50.60.7

0:100 20:80 40:60 60:40 80:20 100:0

water:isopropyl alcohol ratio

Deg

ree

of s

ubst

itut

ion

Fig. 7. Effects of various water:isopropyl alcohol ratio on degree of substitution

of carboxymethyl cellulose from sago waste.

0.563 0.592

0.768

0.588 0.5860.705

0.632

0

0.2

0.4

0.6

0.8

1

60 90 120 150 180 210 240

Reaction period/minutes

Deg

ree

of s

ubst

itutio

n

Fig. 8. Effects of various reaction periods on degree of substitution of

carboxymethyl cellulose from sago waste in isopropyl alcohol solvent.

0.3280.479

0.6220.768

0.7

0.515

0

0.2

0.4

0.6

0.8

1

2 3 4 5 6 7

Weight of ClCH2COONa/g

Deg

ree

of s

ubst

itutio

n

Fig. 10. Effects of various amounts of sodium monochloroacetate on degree of

substitution of carboxymethyl cellulose from sago waste in isopropyl alcohol

solvent.

V. Pushpamalar et al. / Carbohydrate Polymers 64 (2006) 312–318316

contribute to the additional stability of the chains and also

thermodynamically more stable compared to cellulose I

(O’Sullivan, 1997).

A further discussion on these transformations takes into

consideration the distribution of the crystallite size and the

crystallite order in cellulose. The smallest and most imperfect

cellulose I crystallites are first attacked until completely

converted to amorphous material. When increasing the

NaOH concentration in the cellulose phase (by increasing the

ratio of isopropyl alcohol in the mixture), the largest and more

perfect crystallites are penetrated and transformed, but even

after this penetration they can remain in a well-ordered state.

After neutralization, these crystals are converted to crystallites

of cellulose II. This effect may be enhanced by the presence of

an organic solvent, which act as swelling restrictive agents to

cellulose and thus do not allow the full hydration of the

cellulose chains. The change of cellulose structure may be

considered as an explanation for the increase of DS of

carboxymethyl cellulose obtained in these reaction media.

The similar finding has been reported by Olaru and Olaru

(2001), where the study using pure isopropyl alcohol as the

reaction media increases the DS of carboxymethyl cellulose

from wood pulp cellulose.

3.3.3. Effect of various reaction periods

As shown in Fig. 8, the carboxymethylation reaction was

carried out in seven different reaction periods. A maximum DS

of 0.768 was obtained with 180 min as the reaction period.

There was an increase in the DS with reaction period up to

180 min and thereafter it decreases. The increase may be due to

the fact that there is better reaction environment created and a

0.578 0.589

0.821

0.633 0.6440.569

0

0.2

0.4

0.6

0.8

1

35 40 45 50 55 60

Temperature/°C

Deg

ree

of s

ubst

itutio

n

Fig. 9. Effects of various reaction temperatures on degree of substitution of

carboxymethyl cellulose from sago waste in isopropyl alcohol solvent.

prolonged time available for carboxymethylation. Prolonging

the duration of the reaction results in the favorable effect of

time on diffusion and absorption of the reactants with the

ultimate effect of inducing better contacts between the

etherifying agent and cellulose (Bhattacharyya et al., 1995).

A possible explanation for the decrease after 180 min may be

due to an increased degradation of the polymer when the time

is prolonged (Heinze & Pfeiffer, 1999).

3.3.4. Effect of reaction temperature

As shown in Fig. 9, the temperature parameter study was

carried out in six different reaction temperatures. A

maximum DS of 0.821 was obtained with 45 8C as the

reaction temperature. There was an increase in the DS with

reaction temperature up to 45 8C thereafter it decreases. The

increase may be due to the fact that there is better reaction

environment created for carboxymethylation. The decrease

of the DS beyond 45 8C may be due to the cellulose

degradation where chemical elimination of water from

cellulose originates primarily from an intramolecular

elimination leading to C2, C3 unsaturation or a ketone

group on C2. Concurrently, there might be intermolecular

elimination between hydroxyl groups of neighboring chains

giving rise to cross-linking by ether linkages, thus

decreasing the sites of –OH groups for carboxymethylation.

It was found that in the temperature region 25–400 8C,

cellulose could have lost 6.1% water (Scheirs, Camino, &

Tumiatti, 2001).

0.513

0.7670.821

0.7680.649

0.723

0

0.2

0.4

0.6

0.8

1

10 20 25 30 35 40

Percentage NaOH/%

Deg

ree

of s

ubst

itutio

n

Fig. 11. Effects of various concentrations of sodium hydroxide on degree of

substitution of carboxymethyl cellulose from sago waste in isopropyl alcohol

solvent.

Fig. 12. (a) Photographs of sago waste, (b) sago pulp and (c) carboxymethyl cellulose from sago waste with the degree of substitution of 0.821 at magnification 10!.

V. Pushpamalar et al. / Carbohydrate Polymers 64 (2006) 312–318 317

3.3.5. Effect of various amounts of sodium monochloroacetate

Fig. 10 shows the effect of concentration of sodium

monochloroacetate on DS. A maximum DS of 0.768 was

obtained with 6.0 g of sodium monochloroacetate. There was

an increase in the DS with amount of sodium monochlor-

oacetate up to 6.0 g and thereafter it decreases. The increase

probably is due to the greater availability of the acetate ions at

higher concentrations in the proximity of cellulose molecules.

At a concentration higher than 6.0 g, glycolate formation seems

to be favored and the reaction efficiency decreases. This finding

is supported by reports in the literature (Bhattacharyya et al.,

1995; Khalil et al., 1990).

3.3.6. Effect of various concentrations of sodium hydroxide

As shown in Fig. 11, the effect of sodium hydroxide

concentration was studied by varying the concentration of the

sodium hydroxide solution. It was observed that the DS of

CMC increased with sodium hydroxide concentration and

attained a maximum DS of 0.821 at an alkali concentration of

10 mL of 25% (w/v). At particular alkali strength, the DS was

maximum after which it started declining. This observation can

be explained by considering the carboxymethylation process,

where two competitive reactions take place simultaneously.

The first involves reaction of the cellulose hydroxyl with

sodium monochloroacetate in the presence of sodium

hydroxide to give CMC as shown in Eq. (3):

Cell � OHCClCH2COONa/Cell � O � CH2COONaCNaClCH2O

Carboxymethylcellulose

(3)

The second reaction is that sodium hydroxide reacts with

sodium monochloroacetate to form sodium glycolate as in Eq.

(4):

NaOHCCl � CH2COONa/HO � CH2COONaCNaCl

Sodium glycolate

(4)

It appears that the first reaction prevails over second up to

alkali concentration of 10 mL 25%. Above this level, glycolate

formation pre-dominates which means inactivation of mono-

chloroacetate and its consumption by this side reaction. Similar

observations have been reported for maize starch (Khalil et al.,

1990).

3.4. Photographic study

The photographs in Fig. 12 shows that sago waste (a) is light

brown in color and has a woody structure, sago pulp (b) is

white in color and maintains the woody structure, and

carboxymethyl cellulose (c) from sago waste with the degree

of substitution 0.821 is light brown in color and has a smooth

surface. Therefore, carboxymethylation reaction has resulted in

the surface morphology changes from a fibrous structure to a

smooth structure.

4. Conclusion

The optimized product has a DS of 0.821 and the optimum

conditions for carboxymethylation cellulose from sago waste

were: pure isopropyl alcohol as the solvent medium, reaction

period of 180 min, 6.0 g of sodium monochloroacetate, NaOH

concentration of 10 mL of 25% and reaction temperature of

45 8C. The sago waste and sago pulp have rough woody

structure but carboxymethyl cellulose has a smooth surface

structure. The optimum conditions for the preparation of

carboxymethyl cellulose from sago pulp isolated from sago

waste can be exploited to prepare industrial products.

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