بسم ا الرحمن الرحيمبسم ا الرحمن الرحيم

In the Name of Allah, the Most In the Name of Allah, the Most Beneficent, the Most Merciful.Beneficent, the Most Merciful.

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A New Method for Carboxymethylation of Starch at Mild Conditions

M.A. ElSheikh

National Research Centre, Textile Research Division, El-Tahrir St., Dokki, Cairo, Egypt, postal code 12311.

E-mail: manal_elsheikh@yahoo.com

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Aim of the Work

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The textile industry is one of the most important industries in Egypt.

Unfortunately, the CMS used in the Egyptian textile industry is not a local

product. The need to produce a local CMS with lower costs for use in the textile

industry, as a substitute for imported CMS, was the motive behind the current work.

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What is new?What is new?

Carboxymethyl starch was first synthesized in 1924. Many reports and patents have been published on the preparation and manufacture of CMS.

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In this work, a new method has been adopted and used to produce a high quality CMS

product at mild condition.

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Carboxymethylation took place at room temperature (30oC) Mild reaction conditions were employed.Little concentrations of etherifying agents were applied. All the reactions took place without stirring during the reaction course. Simple apparatus for the carboxymethylation process was used. However: A 100% reaction efficiency and a completely cold water soluble product with a clear and transparent solution were obtained.

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Plan of Work

Optimization Characterization Utilization

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OptimizationFactors affecting the reaction•Reaction time •Catalyst concentration• Sequence of addition •Cooling during the addition•Material : liquor ratio•Ethanol: water ratio •Type of solvent

Characterization•Degree of substitution (DS)•Reaction efficiency (E%)•Reproducibility•Different kinds of starch•Solubility•Apparent viscosity •Rheological properties•Transparency •Sizing and desizing•Tensile strength •Elongation at break

UtilizationAs sizing agent for cotton fibers

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CarboxymethylationA certain amount of maize starch was placed in sealable bottle

and mixed together with a known volume of the solvent. An aqueous solution of sodium hydroxide was added drop wise to the starch-solvent mixture under stirring until the whole amount of sodium hydroxide was added. The sodium salt solution of monochloroacetic acid prepared by the reaction of monochloroacetic acid with sodium carbonate monohydrate was added drop wise to the starch-solvent-sodium hydroxide mixture under continuous stirring until complete addition of the sodium monochloroacetate solution. Stirring was then stopped and the bottle was closed and kept at 30oC for certain reaction time. After carboxymethylation, the CMS samples were washed with ethanol : water solution (80:20) while excess alkali was neutralized using acetic acid. After washing, the CMS samples were filtered, oven dried at 100oC.

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Mechanism of the reaction The carboxymethylation process could be considered by

the following three reactions:

NaOH2ClCH2COOH +Na2CO3.H2O 2ClCH2COONa + CO2+ 2H2O (1)St-OH + ClCH2COONa St-OCH2COONa + NaCl + H2O (2)

NaOH + ClCH2COONa HO-CH2COONa + NaCl (3)

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Chloroacetic acid, sodium carbonate and sodium hydroxide

were used in equivalent molar ratios (0.2 mole/mole starch). An

alkali metal hydroxide catalyst was used to accelerate the

carboxymethylation reaction at room temperature.

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Factors Affecting the Carboxymethylation Reaction Expressed as DS and E%

solvent type

Ethanol : water ratio

M:L ratio

Cooling

Catalyst concentration

Reaction time (seven days)

Reaction time (50 h)

DS

an

d E

%

0.2, 100%

0.1989, 99.36%

0.185, 93%

0.185, 93%

0.172, 86%

0.1375 , 68.75%

0.068, 34.2%

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Rate of Carboxymethylation Reaction (Effect of Reaction Time)

1. DS, reaction efficiency and rate constant after 50 hours (Figure 1 (a and b)). DS= 0.068 and E%=34.2% were obtained after 50 hours. Rate constant = 0.00724.

2. DS, reaction efficiency and rate constant after seven days (Figure 2 (a and b)). DS= 0.1375 , and E%= 68.75% were obtained after 50 hours. Rate constant = 0.00466.

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[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; Temp.: 30oC; Time: 0-50 h; M:L ratio: 1:2.5; EtOH:H2O ratio:70:30; Sequence: I; No cooling.

Figure 1(a): Rate of carboxymethylation reaction within the first fifty hours

0

0.02

0.04

0.06

0.08

0 10 20 30 40 50 60Time (h)

Deg

ree

of s

ubst

itut

ion

-4

1

6

11

16

21

26

31

36

Rea

ctio

n E

ffic

ienc

y (%

)

DS Reaction Efficiency

Figure 1(b): Carboxymethylation rate constant within the first fifty hours

y = -0.0031x - 0.731

-1.5

-1

-0.5

0

0 10 20 30 40 50 60

Time (h)

log

(a-x

)

correlation coefficient = 0.996Slpoe = -0.00314 k1 = 0.00724

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Figure 2(a): Rate of carboxymethylation within seven days

0

0.04

0.08

0.12

0.16

0 24 48 72 96 120 144 168 192

Time (h)

Deg

ree

of s

ubst

itut

ion

-5

5

15

25

35

45

55

65

75

Rea

ctio

n E

ffic

ienc

y (%

)

DS E%

Figure 2 (b): Carboxymethylation rate constant within seven days

y = -0.002x - 0.8569

-1.5

-1

-0.5

0

0 50 100 150 200

Time (h)

log

(a-x

)

correlation coefficient = 0.954Slpoe = -0.00202k = 0.00466

[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; Temp.: 30oC; Time: 0-168 h; M:L ratio: 1:1.5; EtOH:H2O ratio:70:30; Sequence: I; No cooling.

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Effect of catalyst concentration

DS of 0.172 with reaction efficiency of 86% was obtained after 24 hours of carboxymethylation using 0.3 mole/mole St. of catalyst.

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Figure 3: Effect of catalyst concentration on the degree of substitution and the reaction efficiency

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Catalyst (mole/mole St.)

Deg

ree

of S

ubst

itut

ion

0

25

50

75

100

Rea

ctio

n E

ffic

ienc

y (%

)

DS (24 h)DS (48 h)

DS (72 h)DS (96 h)DS (120 h)DS (144 h)DS (168 h)E% (24 h)E% (48 h)

E% (72 h)E% (96 h)E% (120 h)E% (144 h)E% (168 h)

[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; [catalyst]: 0.1-0.6 mole/mole St; Temp.: 30oC; Time: 0-168 h; M:L ratio: 1:1.5; EtOH:H2O ratio:70:30; Sequence: I; No cooling.

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Sequence of Addition and Cooling During Addition

sequence I (solvent then starch then sodium hydroxide then catalyst then ClCH2COONa),

sequence II (solvent then sodium hydroxide then catalyst then starch then ClCH2COONa) and

sequence III (solvent then sodium hydroxide then catalyst then ClCH2COONa then starch).

Regardless of the sequence of addition, the DS and the reaction efficiency were about 0.185 and 93% respectively.

The increase in the DS and the reaction efficiency is certainly due to the cooling effect.

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Figure 4: Effect of cooling and sequence of addition on the degree of substitution and the reaction efficiency

0

0.05

0.1

0.15

0.2

I II III

Sequence of addition

Deg

ree

of s

ubst

itut

ion

0

25

50

75

100

Rea

ctio

n E

ffic

ienc

y (%

)

DS

E%

[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; [catalyst]: 0.3 mole/mole St; Temp.: 30oC; Time: 24 h; M:L ratio: 1:1.5; EtOH:H2O ratio:70:30; Sequence: I, II and III; Cooling.

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Material : Liquor Ratio

1:1.5 constitutes the optimal material : liquor ratio. Maximum DS and reaction efficiency obtained at this point were 0.185 and 93% respectively.

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Figure 5: Effect of material : liquor ratio on the degree of substitution and the reaction efficiency

0

0.05

0.1

0.15

0.2

1:1 1:1.5 1:2 1:2.5 1:3

Material : Liquor ratio

Deg

ree

of s

ubst

itut

ion

0

25

50

75

100

Rea

ctio

n E

ffic

ienc

y (%

)

DS

E%

[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; [catalyst]: 0.3 mole/mole St; Temp.: 30oC; Time: 24 h; M:L ratio: 1:1- 1:3; EtOH:H2O ratio:70:30; Sequence: I; Cooling.

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Ethanol : Water Ratio • Maximum DS and reaction efficiency

were obtained at an ethanol : water ratio of 90:10 (0.1989 and 99.36% respectively).

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Figure 6: Effect of ethanol : water ratio on the degree of substitution and the reaction efficiency

0

0.05

0.1

0.15

0.2

50:50 60:40 70:30 80:20 90:10

Ethanol : Water ratio

Deg

ree

of s

ubst

itut

ion

0

25

50

75

100

Rea

ctio

n E

ffic

ienc

y (%

)

E%

DS

[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; [catalyst]: 0.3 mole/mole St; Temp.: 30oC; Time: 24 h; M:L ratio: 1:1.5; EtOH:H2O ratio:50:50-90:10; Sequence: I; Cooling.

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Type of Solvent • The highest DS and reaction efficiency was achieved

with isopropanol and the lowest with propylene glycol. • The DS and reaction efficiency using the

aforementioned solvents follow the descending order:• Isopropanol > Ethanol > Tertiary butanol > Methanol >

Propylene glycol • A DS of 0.2 and a reaction efficiency of 100% were

finally obtained using isopropanol as the solvent. The use of isopropanol led to a 100% reaction efficiency while the use of ethanol led to a 99.36% which is an excellent results for both. This means that both isopropanol and ethanol can be used efficiently for the carboxymethylation o starch.

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Figure 7: Effect of type of solvent on the degree of substitution and the reaction efficiency

0

0.05

0.1

0.15

0.2

MeOH EtOH Isopropanol Tert. butanol Propyleneglycol

Type of Solvent

Deg

ree

of s

ubst

itut

ion

0

25

50

75

100

Rea

ctio

n E

ffic

ienc

y (%

)

DS

E%

[ClCH2COONa] and [NaOH]: 0.2 mole/mole St.; [catalyst]: 0.3 mole/mole St; Temp.: 30oC; Time: 24 h; M:L ratio: 1:1.5; Solvent:H2O ratio:90:10; Sequence: I; Cooling.

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Optimum Conditions• Optimum conditions for attaining a DS of 0.2 and a

reaction efficiency of 100% were:• Concentration of ClCH2COONa: 0.2 mole/mole St.,

• Concentration of NaOH: 0.2 mole/mole St.,• Concentration of Catalyst: 0.3 mole/mole St,• Carboxymethylation temperature: 30oC, • Carboxymethylation time: 24 hours,• Material : liquor ratio: 1:1.5,• Solvent :H2O ratio: 90:10,

• Sequence of addition: Solvent then sodium hydroxide then catalyst then starch then ClCH2COONa,

• Cooling: Cooling during addition of the reactants.

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The importance of catalyst in the carboxymethylation process

• Maximum DS and reaction efficiency of the CMS produced in the presence and in the absence of catalyst were 0.1923 and 96.14% versus 0.1078 and 53.88% respectively.

• The rate constants of carboxymethylation reactions in presence and in absence of catalyst were 0.0867 and 0.0288 respectively.

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Figure 8 (a): Rate of carboxymethylation in presence and in absence of catalyst

0

0.04

0.08

0.12

0.16

0.2

0 5 10 15 20 25 30

Time (h)

Deg

ree

of S

ubst

itut

ion

0

25

50

75

100

Rea

ctio

n E

ffic

ienc

y (%

)

DS (catalyst) DS (no catalyst)

E% (catalyst) E% (no catalyst)

Figure 8 (b): Carboxymethylation rate constant in presence and in absence of catalyst

y = -0.0376x - 1.3174

y = -0.0125x - 0.7641

-3

-2.5

-2

-1.5

-1

-0.5

0

0 5 10 15 20 25

Time (h)

log

(a-x

) catalyst

no catalyst

correlation coefficient =0.92798Slpoe = -0.03764k =0.0867

correlation coefficient =0.9632Slpoe = -0.0125k =0.0288

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Reproducibility

Experiment No.

Theoretical DS

Practical DS

Reaction Efficiency (%)

1 0.2 0.21 100

2 0.2 0.21 100

3 0.2 0.2 100

The results in Table 1 indicate that the carboxymethylation process is reproducible and consistent under the set of reaction conditions used.

Table 1: Reproducibility of CMS

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Type of starch

The high values of DS and reaction efficiency reveal that the carboxymethylation process is suitable for different kinds of starch under the set of reaction conditions used.

Table 2: Type of Starch

Type of starch

Theoretical DS

Practical DS

Reaction Efficiency (%)

Maize 0.2 0.2100

Rice 0.2 0.193896.9

Potato 0.2 0.198499.2

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Characterization of CMS produced

The results obtained from the tensile strength and elongation at break of the light cotton fabric sized with CMS under test reveals the suitability of this CMS as a sizing agent.

Desizing efficiency of 98% at 30oC (Table 3) is another evidence of the suitability of CMS under test as a sizing agent where the size is removed efficiently using mild conditions.

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Practical DS 0.2Reaction efficiency 100%

Solubility in cold water (pH=7)

soluble

% Transmittance (0.1%) aqueous solution

97%

Viscosity at 516 s-1 (mPa s) (pH=7(

NSCMS

350198.3

Rheological properties non-Newtonian pseudoplastic fluidSizing

• Control• Sized with cooked CMS

Desizing efficiency% of size removal at 30oC

Tensile strength )kg(

30.8 kg42.7 kg

98%

Elongation at break (%)7

5.9

Table 3: Major properties of CMS produced

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CONCLUSIONThe new carboxymethylation method produced

CMS with DS of 0.2 and reaction efficiency of 100% using 0.2 mole of both ClCH2COONa and NaOH /mole St., 0.3 mole catalyst /mole St., M:L ratio: 1:1.5, isopropanol:H2O ratio: 90:10, cooling during addition of the reactants, for 24 hours at 30oC. The new carboxymethylation process was found reproducible and suitable for different types of starch. The CMS produced was cold water soluble giving a transparent solution with viscosity of 198.3 mPa s at shear rate of 516 s-1. The CMS produced was suitable for use as sizing agent.

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Thank You