CONTINUOUS GRAFTING OF VINYL MONOMERS …shodhganga.inflibnet.ac.in/bitstream/10603/13569/12/12...Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing Performance Enhancement

Chapter 4

CONTINUOUS

GRAFTING OF

VINYL MONOMERS

ONTO COTTON VIS

A VIS DYEING

Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing

Performance Enhancement of Fibrous Polymers Page 127

4.1 Introduction The grafting of textile fibres in the fabric form and the continuous grafting by padding

technique has been explored to a limited extent. In order to study the grafting of vinyl

monomers onto cotton fabric using padding technique, the cotton fabrics were padded

with the vinyl monomers and potassium persulphate as a redox initiator, through their

solutions. The various padding techniques like pad-dry, pad-cure and pad-dry-cure were

analyzed in order to get optimum grafting. The synergism of grafting in the case of

grafting with mixture of monomers was also explored. The grafted fabrics were

characterized, tested for textile properties and dyeing behavior towards cationic and acid

dyes.

4.2 Materials and Methods

4.2.1 Materials

Cotton fabric (EPI- 69, PPI- 88, GSM- 122.95) was supplied by Century mills limited

(Mumbai). All chemicals used were of laboratory grade. Cationic dyes used were

supplied by Clariant India Ltd. Acid dyes used were supplied by Amritlal Dyes India Ltd.

4.2.1 Methods

4.2.1.1 Grafting of Vinyl Monomers onto Cotton

Cotton fabric was padded with solution containing the required concentration of

monomer and initiator with 75± 1% expression using two bowl vertical padding mangle,

dried and/or cured. The various processes selected were pad-dry, pad-cure and pad-dry-

cure and the parameters were varied in order to study the optimization of the reaction

parameters. After completion of grafting process by padding, the grafted fabric was

washed with hot water several times, to remove the homopolymers, till the constant

weight was reached. The graft add-on was calculated using the formula

100(%)1

12

WWWonaddGraft

where W1 and W2 were the weight of ungrafted and grafted fabric respectively.



4.2.1.2 Characterization of Grafted Product

Analysis of grafted cotton fabric was done by FTIR analysis, TGA analysis, SEM

analysis as per the procedure mentioned in chapter 3.2.

4.2.1.3 Measurement of Textile Properties

4.2.1.3.1 Moisture regain & yellowness index

The moisture regain was determined by the vacuum dessicator method and yellowness

index as mentioned in Chapter 3.2.

4.2.1.3.2 Crease Recovery Angle (CRA)

To estimate the wrinkle resistance of the finished fabric, its crease recovery angle was

measured using ASTM D-1296 method by Shirley crease recovery tester (ASTM

standards manual).

4.2.1.3.3 Bending length

In order to estimate the stiffness of the fabric, its bending length was measured using

ASTM D-1388 on Shirley stiffness tester (ASTM standards manual).

4.2.1.3.4 Tensile strength

Tensile strength of finished fabric was evaluated using ASTM D-5035, raveled strip test

method (ASTM standards manual).

4.2.1.3.5 Tearing strength

Tearing strength of the finished fabric was measured using ASTM D 1424-09 on

Elmendorf tear strength tester (ASTM standards manual).

4.2.1.4 Dyeing of the Grafted Fabric and Analysis of Dyed Fabrics

The acrylic acid grafted cotton (AA-g-Cotton) fabrics were studied for its enhanced

dyeability towards cationic dyes. Acrylamide grafted cotton fabrics (AAm-g-Cotton)

were checked for its enhanced dyeability towards acid dyes. The cotton fabrics grafted

with the mixture of monomers (AA.AAm-g-BR) were studied for its enhanced dyeability

towards both types of dyes. The dyeing methods were employed as mentioned in Chapter



3.2. The dyed fabrics were evaluated for colour values and fastness properties as

mentioned in Chapter 3.2.

4.3 Results and Discussion

4.3.1 Grafting of Acrylic acid onto Cotton vis a vis Dyeing with Cationic Dyes

4.3.1.1 Evidence of Grafting

The cotton fabric grafted with acrylic acid (AA-g-Cotton) was characterized in order to

validate grafting. The FTIR spectrum of grafted fabric (refer Figure 4.1) when compared

with that of the ungrafted fabric clearly indicated the peak for –COOH group at 1705cm-1

which is due to introduction of polyacrylic acid graft on to bamboo rayon backbone.

Figure 4.1: FTIR spectra of ungrafted cotton and AA-g-cotton

Figure 4.2 shows the thermogram of ungrafted and grafted cotton samples. In the initial

stage weight loss values of both samples were 6.27% and 5.89% at 250 0C, respectively.

Between 250 0C to 400 0C, the drastic decomposition of the samples resulted in to

significant weight loss which was 84.90% for ungrafted and 81.26% for grafted cotton

fabric at 400 0C. However, beyond 400 0C the loss in weight was slowed down and

finally at 500 0C, weight loss values observed were 96.75% for ungrafted and 91.70% for

grafted cotton, respectively. This clearly indicates relatively higher thermal stability of

the grafted sample as compared to that of ungrafted cotton. This could be attributed to the



formation of side chain network as a result of grafting of acrylic acid onto cellulose

backbone increasing molecular weight.

Figure 4.2: TGA of ungrafted cotton and AA-g-Cotton

SEM micrograph (refer Figures 4.3 A and B) grafted cotton clearly show a surface

deposition, which is absent in unmodified substrate. This further confirms the presence of

grafted acrylic acid on cellulose backbone.

A B

Figure 4.3: SEM photograph of ungrafted (A) and grafted cotton (B)

The carboxyl content values (refer Table 4.2) of the representative samples indicated the

increase in carboxyl content values after grafting, which further confirms the grafting of

acrylic acid on to cotton.



4.3.1.2 Optimization of Grafting Parameters

The effect of various parameters on graft add-on of acrylic acid onto cotton has been

summarized in Table 4.1 and presented graphically in Figure 4.4.. The initial attempt was

to select a process for the optimum grafting using padding technique and hence the three

commonly used padding techniques namely pad-dry, pad-cure and pad-dry-cure were

screened and the result of grafting are presented in Table 4.1 and Figure 4.4. The pad-

cure method was found to provide highest level of grafting when compared with that of

other two methods. This may be because the reaction kinetics principle. In the pad-cure

process, the monomer was padded onto cotton and cured at a high temperature where the

probability of grafting was highest due to presence of initiator and monomer in the wetted

fabric. The pad-dry can be considered as the case where fabric is dried at much lower

temperature (80 0C) after padding and the rate of reaction was quite lower than that at

higher temperature in pad-cure processes. In pad-dry-cure process, the grafting occurred

during drying and even though curing was carried out the fabric was not in the wetted

state so the movement of the monomers was restricted not facilitating grafting. The

curing process (after padding) is advantageous in the cases where the crosslinking is

supposed to happen during curing. However in this case of continuous grafting, the

process not seems to be advantageous compared to pad-cure process.

The pad-cure process was varied for its parameters to get optimum grafting. With

increase in curing temperature from 100 0C to 140 0C, graft add-on increased while

beyond 140 0C, further increase in temperature resulted in decrease in graft add-on. The

increase in graft add-on with temperature is because of higher rate of dissociation of

initiator as well as the diffusion and mobility of monomer from aqueous phase to

cellulose phase. With increase in temperature beyond 140 0C, the radical termination

reaction might be accelerated, leading to decrease in graft add-on (%) and also increase in

extent of homopolymerization. This may be, possibly due to recombination of growing

homopolymer chain radicals; a possibility at higher temperatures. Even in case of

continuous grafting, where grafting takes place at elevated temperature in short time, the

effect of temperature of grafting on the graft add-on was found to be much more

pronounced.



The increase in graft add-on was observed with time of curing from 1 min to 5 min. It

may be attributed to increase in number of grafting sites in the initial stages of reaction

due to higher amount of initiator participating in the formation of reactive sites at

cellulose backbone. However after 5 min, there was no significant increase in graft add-

on. The higher curing time however, can result in loss in mechanical properties of cotton

fabric and hence 5 min curing time was taken as optimum.

Results in Table 4.1 and Figure 4.4 also indicate the increase in graft add-on with

increase in potassium persulphate concentration which may be due to increase in the

number of radicals generated. A further increase in initiator concentration decreased the

graft add-on possibly due to homopolymer formation which occurs simultaneously

causing reduction in concentration of available monomer for grafting. It is well known

that high initiator concentrations lead to short chain polymers, therefore it can be

expected that a higher concentration of KPS might result in decreasing graft add-on.

After optimizing the parameters like temperature, time and initiator the monomer

concentration was varied in order to get efficient utilization of monomer (AA) in grafting.

The graft add-on (%) was found to be increasing significantly initially with increasing

monomer concentration from 50 to 100 gpl and then to relatively lower extent from 100

to 200 gpl. This is because of more availability of monomer for grafting initially, while

at higher concentration, the homopolymer formation is dominant compared to grafting

causing only slight increase in graft add-on. However efficiency of grafting decreased at

higher concentration of AA. Hence 100 gpl concentration was found to be optimum for

grafting. The continuous grafting of acrylic acid onto cotton however seems to be

advantageous in the cases where the lower graft add-on is desired with better efficiency.

In all the parameters optimized are as follows; process pad-cure, curing temperature-

1400C, curing time-5min, initiator conc-15gpl, and monomer concentration-100gpl.



Table 4.1: Effect of different parameters on grafting of AA on cotton

Sr. No.

Process Temperature (Drying/Curing)

(0C)

Time (Drying/Curing) (Min.)

Initiator conc. (gpl)

Monomer conc. (gpl)

Graft add-on (%)

1. Process selection A Pad-Dry 80 5 15 100 1.45

B Pad-Cure 140 5 15 100 2.65 C Pad-Dry-Cure 80/140 5/5 15 100 2.29 2. Effect of Temperature A Pad-Cure 100 5 15 100 1.30 B 120 5 15 100 1.88 C 130 5 15 100 2.63 D 140 5 15 100 2.65 E 150 5 15 100 2.50 F 180 5 15 100 1.50 3. Effect of Time A Pad-Cure 140 1 15 100 2.18 B 140 2 15 100 2.21 C 140 3 15 100 2.33 D 140 4 15 100 2.45 E 140 5 15 100 2.65 F 140 8 15 100 2.67 G 140 10 15 100 2.670 4. Effect of Initiator conc. A Pad-Cure 140 5 5 100 2.22 B 140 5 10 100 2.39 C 140 5 15 100 2.65 D 140 5 20 100 2.12 E 140 5 25 100 1.73 5. Effect of monomer conc. A Pad-Cure 140 5 15 50 1.40 B 140 5 15 100 2.65 C 140 5 15 150 3.61 D 140 5 15 200 3.79



Figure 4.4: Optimization of parameters for AA grafting onto cotton

4.3.1.3 Effect of Grafting on Textile Properties of Cotton

Even though graft add-on varied with the parameters of grafting as represented in Table

4.1, it was not the only factor affecting the textile properties especially in the case of

mechanical properties which were greatly affected by the parameters like high

temperature, increased reaction time, higher concentration of initiator causing

degradation of cellulose chains and higher concentration of acrylic acid reacting with

hydroxyl groups of cellulose rather than participating in grafting. In order to study the

effect of all these parameters on the mechanical properties, the grafted samples were

evaluated for their mechanical properties and results are summarized in Table 4.2.

Results in Table 4.2 indicate the increased moisture regain with increase in graft add-on

0

0.5

1

1.5

2

2.5

3

100 125 150 175 200

Gra

ft a

dd-o

n (%

)

Cuting temperature (0C)

0

1

2

3

0 2 4 6 8 10

Gra

ft a

dd-o

n (%

)

Curing time (min)

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25

Gra

ft a

dd-o

n (%

)

KPS conc. (gpl)

00.5

11.5

22.5

33.5

4

0 50 100 150 200

Gra

ft a

dd-o

n (%

)

AA concentration (gpl)



giving 7.01% increase in moisture regain for optimum grafted sample (with graft add-on

2.65%) when compared with that of ungrafted sample. This enhancement in moisture

regain was due to the introduction of polyacrylic acid in molecular structure of cellulose

substrate during grafting. Even though the enhancements in moisture regain were of

lower extent, the property enhancement seems to be dependent on graft add-on level

which was quite lower in case of continuous grafting. However, the carboxyl content was

also increased with increase in graft add-on resulting in increased hydrophillicity of

grafted sample. The moisture regain of grafted product was further increased after

treatment with sodium hydroxide which forms corresponding salt showing 22.39%

increase for sample with optimum graft add-on over that of ungrafted sample. The

sodium carboxylate group has much higher moisture absorption capacity than did the

protonated carboxylic group and hence there was an enhancement in moisture regain of

grafted cotton.

The whiteness index decreased with increase in graft add-on which may be due to

increase in carboxyl content of the product and also the ester group formation between

the free acrylic acid and hydroxyl groups of the cellulose. The whiteness index decreased

with reaction temperature irrespective of the increase or decrease in graft add-on levels

indicating the negative effect of higher curing temperatures on whiteness. In case of time

parameter, the whiteness decreased with increase in reaction time keeping all other

reaction parameters constant; however, the effect of time on the whiteness seems to be

less significant as compared to that of reaction temperature. The whiteness index was also

decreased with increase in initiator concentration irrespective of graft add-on. The

increase in concentration of acrylic acid also resulted in decreased whiteness mainly due

to increase in graft add-on since all other parameters were constant. Tensile strength and

tearing strength found to be negatively influenced by grafting reaction, the individual

extent of which depend on the combination of various parameters of grafting. Tensile

strength decreased with increased curing temperature, increased reaction time, increased

initiator concentration and increased acrylic acid concentration. The similar trend was

found in case of tearing strength. In general, tensile strength depends on the distribution

of the force though out the dimension of the fabric when fabric was pulled between the

jaws during testing. Grafting reaction resulted in deposition of the side chain on the



cellulose backbone consuming the hydroxyl groups and preventing the H-bond formation

between them. Grafting also resulted in stiffness of the fabric facilitating the failure at

lower load. The degradation of cellulose chains during grafting can be other probable

reason.

Table 4.2: Effect of grating on textile properties

Sample No.

Graft add-on

(%)

W.I. Carboxyl content

(meq/100gm)

Moisture regain

(%)

T.S. (Kg)

Te.S. (gm)

CRA (0)

B.L. (cm)

UG 0.0 70.05 4.40 6.23(6.28) 36.34 1920 106 1.10 2A 1.30 59.90 18.44 6.444(6.94) 28.76 1472 144 1.15 2B 1.88 48.35 27.616 6.540(7.234) 26.76 1440 155 1.20 2C 2.63 35.51 38.361 6.653(7.61) 26.51 1440 175 1.25 2D 2.65 33.37 39.035 6.667(7.625) 23.22 1408 175 1.30 2E 2.50 24.02 35.853 6.633(7.54) 22.51 1152 173 1.37 2F 1.50 18.22 23.766 6.477(7.04) 17.31 960 145 1.47 3A 2.18 42.65 26.19 1472 160 1.20 3B 2.21 37.94 25.94 1472 163 1.20 3C 2.33 35.93 23.84 1440 165 1.25 3D 2.45 33.48 22.87 1408 170 1.25 3E 2.65 33.37 23.22 1408 175 1.30 3F 2.67 27.70 20.52 1120 176 1.37 3G 2.67 26.82 19.17 992 176 1.40 4A 2.22 46.00 26.72 1440 162 1.20 4B 2.39 34.60 24.56 1408 167 1.30 4C 2.65 33.37 23.22 1408 175 1.30 4D 2.12 25.55 17.04 1088 159 1.45 4E 1.73 26.58 12.16 928 153 1.40 5A 1.40 52.76 24.07 1408 144 1.20 5B 2.65 33.37 23.22 1408 175 1.30 5C 3.61 24.36 19.14 1216 177 1.60 5D 3.79 16.89 17.89 960 180 1.70

*T.S.-Tensile strength, Te.S.-Tearing strength, W.I.-Whiteness Index, B.L.-Bending length

Crease recovery angle, which is the measure of ability of the fabric to resist the formation

of creases, increased with increase in graft add-on independent of reaction parameters.

The addition of side chain prevents the H-bond formation between hydroxyl groups and

hence increases the ability of fabric to recover from the crease. The polymer deposition,

which was considered to be one of the mechanisms of crease recovery, also resulted in



increased CRA. However, the bending length increased with increase in graft add-on

indicating the increased stiffness after grafting.

4.3.1.4 Effect of Grafting on Cationic Dyeing of Cotton

The acrylic acid grafted cotton was studied for its enhanced dyeability towards cationic

dyes and results are summarized in Table 4.3 and presented graphically in Figure 4.5.

The colour strength increased with increase in graft add-on for both the cationic dyes.

The increase in graft add-on resulted in increase in carboxyl content of the cotton fabric

(refer Table 4.2) hence providing more attachment points for cationic dye molecules

resulting in enhanced colour values. The optimum grafted sample (with graft add-on of

2.65%) showed the increase in colour strength, compared to that of ungrafted bamboo

rayon, by 334.04% for Bismark Brown and 1436.77% for Methylene Blue dyes. Since in

this case the cotton is grafted in fabric form and by using padding method, the grafting is

more or less controlled by the mangle pressure. Since the even padding of monomers can

be carried out, the grafting was expected to be even thoughout the width and length of the

fabric. The fabrics dyed using cationic dyes showed the even along the fabric. Hence

grafting of fabric using padding process can be claimed as method for obtaining uniform

grafting on the substrates.

The fastness properties of the dyed samples were improved for both the dyes. Cationic

dyes are known for inferior fastness properties on cellulose and hence improvement in

fastness properties for grafted product may be attributed to increase in carboxyl groups

which provide better attachment to the sites for dye molecules and hence offering

resistance to removal in washing or rubbing. Improvement in light fastness is due to

larger amount of dye being adsorbed on the fibre as compared to when graft copolymer

was absent. The samples with optimum graft add-on showed 3 grade improvement in

light fastness and 1 to 2 grade improvement in rubbing fastness.



Table 4.3: Effect of grafting on dyeing properties with cationic dyes

C*- Change in shade, S*-Staining

Figure 4.5: Effect of AA graft add-on (%) on colour values of cationic dyeing

0

5

10

15

0 1.3028 1.45 1.5 1.8819 2.2974 2.5034 2.6306 2.65

K/S

Graft add-on (%)

Bismark brown GMethylene blue

Graft add-on

(%)

K/S L* a* b* Washing fastness

Rubbing fastness

Light fastness

C* S* Dry Wet

Dye used-Bismark Brown G (λmax -470nm) 0.00 1.2038 72.71 11.76 27.32 1-2 3 3 3 1 1.3028 1.9792 63.70 17.90 22.67 4 3-4 4 3 3 1.45 2.1963 65.06 17.54 27.47 4 3-4 4 3 3 1.50 2.4768 61.09 10.77 23.95 4 3-4 4 3 3 1.8819 2.9519 60.82 17.49 28.09 4 3-4 4 3 3 2.2974 3.6239 59.15 18.30 30.46 4 3-4 4 3 3 2.5034 4.9859 56.66 23.18 34.19 4 3-4 4 3 3 2.6306 5.1024 53.03 14.80 28.61 4 3-4 4 3 4 2.65 5.2250 55.03 19.07 32.45 4 3-4 4 3 4 Dye used-Methylene Blue (λmax -670nm) 0.00 0.8797 74.24 -12.47 -15.26 1-2 3 3 3 1 1.3028 6.7719 52.51 -11.56 -34.59 3 3 3 2-3 2 1.45 6.9481 52.77 -11.93 -34.84 3 3 3 2-3 2 1.50 8.2594 50.75 -10.81 -36.15 3 3 3 2-3 2 1.8819 9.7015 50.03 -11.53 -35.13 3 3 3 2-3 3 2.2974 12.397 46.82 -10.27 -36.53 3-4 3 3 3 3 2.5034 13.117 43.21 -7.77 -37.47 3-4 3 4 3 3 2.6306 13.439 43.91 -8.23 -37.15 3-4 3 4 3 4 2.65 13.519 43.55 -8.32 -36.64 3-4 3 4 3 4



4.3.2 Grafting of Acrylamide onto Cotton vis a vis Dyeing with Acid Dyes

4.3.2.1 Evidence of Grafting

Acrylamide was grafted onto cotton by continuous mode of grafting and characterized in

order to validate the grafting reaction. The FTIR spectrum of grafted cotton sample (refer

Figure 4.6) showed peaks at 1662.5 cm-1 (C=O) stretching, 3335 cm-1 (-NH2). The

presence of –NH stretching in the FTIR spectrum of grafted cotton, which is due to

introduction of polyacrylamide graft on to cotton backbone, confirmed the grafting of

acrylamide on to cotton fabric.

Figure 4.6: FTIR spectrum of ungrafted cotton and AAm-g-Cotton

Figure 4.7 shows the thermogram of ungrafted and grafted cotton samples (AAm-g-

Cotton). In the initial stage weight loss values of both samples were 6.27% and 5.00% at

250 0C, respectively. Between 250 0C to 350 0C, the drastic decomposition of the samples

resulted in to significant weight loss which was 58.15% for ungrafted and 51.74% for

AAm-g-Cotton at 350 0C. However, beyond 350 0C the loss in weight was slowed down

and finally at 450 0C, weight loss values observed were 96.75% for ungrafted and

80.30% for AAm-g-Cotton, respectively. This clearly indicates relatively higher thermal

stability of the grafted sample as compared to that of ungrafted cotton. This could be

attributed to the formation of side chain network as a result of grafting of acrylamide onto

cellulose backbone increasing molecular weight.



Figure 4.7: TGA of ungrafted cotton and AAm-g-Cotton

SEM micrograph (refer Figures 4.8 A and B) of grafted cotton clearly show a surface

deposition, which is absent in unmodified substrate. This further confirms the presence of

grafted acrylamide onto cellulose backbone.

A B


4.3.2.2 Optimization of Grafting Parameters

The effect of various parameters on graft add-on of acrylamide onto cotton has been

summarized in Table 4.4 and presented graphically in Figure 4.9. The experiments

similar to that of acrylic acid grafting were conducted. The initial attempt was to select a



process for the optimum grafting using padding technique and hence the three commonly

used padding techniques namely pad-dry, pad-cure and pad-dry-cure were screened and

the result of grafting are presented in Table 4.4 and Figure 4.9. The pad-cure method was

found to provide highest level of grafting when compared with that of other two methods.

This may be because the reaction kinetics principle as also observed in earlier case. In the

pad-cure process, the monomer was padded onto cotton and cured at a high temperature

where the probability of grafting was highest due to presence of initiator and monomer in

the wetted fabric. The pad-dry can be the case where fabric is dried at much lower

temperature (80 0C) after padding and the rate of reaction was quite lower than that at

higher temperature in pad-cure processes. In pad-dry-cure process, the grafting occurred

during drying and even though curing was carried out the fabric was not in the wetted

state so the movement of the monomers was restricted not facilitating grafting. The

curing process (after padding) is advantageous in the cases where the crosslinking is

supposed to happen during curing. However in this case of continuous grafting, the

process seems to be not advantageous compared to pad-cure process.

The pad-cure process was varied for its parameters to get optimum grafting. With

increase in curing temperature from 100 0C to 140 0C, graft add-on increased while

beyond 140 0C, further increase in temperature resulted in decrease in graft add-on. The

increase in graft add-on with temperature is because of higher rate of dissociation of

initiator as well as the diffusion and mobility of monomer from aqueous phase to

cellulose phase. With increase in temperature beyond 140 0C, the radical termination

reaction might be accelerated, leading to decrease in graft add-on and also increase in

extent of homopolymerization. This may be, possibly due to recombination of growing

homopolymer chain radicals; a possibility at higher temperatures. The effect of

temperature of grafting on the graft add-on was found to be applicable in the case of

continuous grafting.







on. The higher curing time however, can result in loss in mechanical properties of cotton









After optimizing the parameters like temperature, time and initiator the monomer

concentration was varied in order to get efficient utilization of monomer (AAm) in

grafting. The graft add-on increased significantly initially with increasing monomer

concentration from 50 to 100 gpl and then to relatively lower extent from 100 to 200 gpl.

This is because of more availability of monomer for grafting initially, while at higher

concentration, the homopolymer formation is dominant compared to grafting causing

only slight increase in graft add-on; however efficiency of grafting decreased. Hence

100gpl concentration was found to be optimum for grafting. The continuous grafting of

acrylamide onto cotton however seems to be advantageous in the cases where the lower

graft add-on is desired and with better efficiency.

The optimized parameters in case of acrylamide grafting onto cotton were found identical

to that of acrylic acid grafting i.e. process pad-cure, curing temperature-1400C, curing

time-5min, initiator conc-15gpl, and monomer concentration-100gpl.



Table 4.4: Effect of different parameters on grafting of AAm on cotton

Sr. No.

Process Temperature (Drying/Curing)

(0C)

Time (Drying/Curing) (Min.)

Initiator conc. (gpl)

Monomer conc. (gpl)

Graft add-on (%)

1. Process selection A Pad-Dry 80 5 15 100 1.836 B Pad-Cure 140 5 15 100 3.60 C Pad-Dry-Cure 80/140 5/5 15 100 2.39 2. Effect of Temperature A Pad-Cure 100 5 15 100 1.426 B 120 5 15 100 2.447 C 130 5 15 100 3.440 D 140 5 15 100 3.60 E 150 5 15 100 3.062 F 180 5 15 100 3.047 3. Effect of Time A Pad-Cure 140 1 15 100 2.325 B 140 2 15 100 2.529 C 140 3 15 100 2.837 D 140 4 15 100 3.555 E 140 5 15 100 3.60 F 140 8 15 100 3.062 G 140 10 15 100 3.047 4. Effect of Initiator conc. A Pad-Cure 140 5 5 100 1.825 B 140 5 10 100 3.034 C 140 5 15 100 3.60 D 140 5 20 100 2.942 E 140 5 25 100 2.645 5. Effect of monomer conc. A Pad-Cure 140 5 15 50 1.681 B 140 5 15 100 3.60 C 140 5 15 150 4.302 D 140 5 15 200 4.600



Figure 4.9: Optimization of parameters for AAm grafting onto cotton

4.3.2.3 Effect of Grafting on Textile Properties of Cotton

Even though graft add-on varies with the parameters of grafting as represented in Table

4.5; it is not the only factor affecting the textile properties especially in the case of

mechanical properties which was greatly affected by the parameters like high


degradation of cellulose chains and higher concentration of acrylamide imparting

stiffness. Acrylamide, being nonionic, do not possess the functional groups reacting with

cellulose but do affect the textile properties varying with reaction parameters. In order to

0

1

2

3

4

100 120 140 160 180

Graf

t add

-on

(%)

Curing temperature (0C)

0

1

2

3

4

0 2 4 6 8 10

Gra

ft a

dd-o

n (%

)

Curing time (min)

0

1

2

3

4

0 10 20 30

Graf

t add

-on

(%)

KPS conc. (gpl)

0

1

2

3

4

5

0 50 100 150 200

Gra

ft a

dd-o

n (%

)

AAm conc. (gpl)



study the effect of all these parameters on the mechanical properties, the grafted samples

were evaluated for their mechanical properties and results are summarized in Table 4.5




regain was due to the introduction of hydrophilic monomer (acrylamide) in molecular

structure of cellulose substrate during grafting increasing its hydrophilicity. Even though

the enhancements in moisture regain were of lower extent; the property enhancement

seems to be dependent on graft add-on level which was quite lower in case of continuous

grafting. The moisture regain of grafted product was further increased after treatment

with sodium hydroxide showing 30.85% increase for sample with optimum graft add-on

over that of ungrafted sample. This may be attributed to conversion of –CONH2 groups to

–COOH and –COONa groups after saponification. The absorbency behavior may be

interpreted by postulating that the collaborative absorbent effect of –CONH2, -COONa,

and –COOH groups is superior to that of single –CO NH2, -COONa, and –COOH groups

(Wu et al., 2003).


increase in nitrogen content of the product and also due to effect of heat, during curing on

cellulose backbone. The –NH2 group is known to impart yellowness to the applied

substrate resulting in lowering of whiteness index. The whiteness index decreased with

reaction temperature irrespective of the increase or decrease in graft add-on levels




less significant as compared to that of reaction temperature. The whiteness index was also

decreased with increase in initiator concentration irrespective of graft add-on (%). The

increase in concentration of acrylamide also resulted in decreased whiteness mainly due

to increase in graft add-on since all other parameters were constant.

Tensile strength and tearing strength found to be negatively influenced by grafting

reaction, the individual extent of which depend on the combination of various parameters



of grafting. Tensile strength decreased with increased curing temperature, increased

reaction time, increased initiator concentration and increased acrylic acid concentration.

The similar trend was found in case of tearing strength. In general tensile strength

depends on the distribution of the force though out the dimension of the fabric when

fabric was pulled during testing. Grafting reaction resulted in deposition of the side chain

on the cellulose backbone consuming the hydroxyl groups and preventing the H-bond

formation between them. Grafting also resulted in stiffness of the fabric facilitating the

failure at lower load. The degradation of cellulose chains during grafting can also be the

probable reason for decrease in strength properties on grafting.

However, the decrease in mechanical properties and whiteness of the cotton fabric was of

the lower order compared to that in case of acrylic acid grafting probable due to absence

of reaction between hydroxyl groups of cellulose and carboxylic group of acid and the

hydrolysis of cellulose in presence of strong acid like acrylic acid at enhanced curing

temperatures.





which was considered to be one of the mechanisms of crease recovery, also results in






Sample No.

Graft add-on

(%)

W.I. Moisture regain

(%)

T.S. (Kg)

Te.S. (gm)

CRA (0)

B.L. (cm)

UG 0.0 70.05 6.23(6.28) 36.34 1920 106 1.10 2A 1.426 70.02 6.440(7.021) 30.71 1504 150 1.20 2B 2.447 68.38 6.507(7.553) 29.73 1504 160 1.25 2C 3.440 61.16 6.618(8.069) 27.33 1472 175 1.35 2D 3.60 60.74 6.621(8.152) 23.68 1440 180 1.40 2E 3.062 49.96 6.599(7.872) 22.61 1440 164 1.35 2F 3.047 48.78 6.451(7.864) 19.33 992 162 1.35 3A 2.325 61.67 27.00 1568 160 1.25 3B 2.529 61.46 26.02 1536 165 1.30 3C 2.837 61.39 24.12 1504 167 1.35 3D 3.555 61.12 22.94 1472 177 1.40 3E 3.60 60.74 23.68 1440 180 1.40 3F 3.050 56.88 22.20 1184 180 1.35 3G 3.010 48.77 21.39 1040 181 1.35 4A 1.825 68.85 27.94 1504 156 1.25 4B 3.034 63.01 25.10 1472 170 1.35 4C 3.60 60.74 23.68 1440 180 1.40 4D 2.942 62.83 19.19 1184 161 1.35 4E 2.645 63.54 17.44 992 160 1.30 5A 1.681 68.29 24.60 1440 154 1.25 5B 3.60 60.74 23.68 1440 180 1.40 5C 4.302 42.12 20.50 1248 182 1.60 5D 4.600 39.17 19.72 992 182 1.65 *T.S.-Tensile strength, Te.S.-Tearing strength, W.I.-Whiteness Index, B.L.-Bending length

4.3.2.4 Effect of Acrylamide grafting on acid Dyeing of Cotton

The dyeability of the textile fibres can be increased by introducing suitable functional

groups in the fibre structure, so that they become the centres of adsorption or reaction

with the appropriate class of dye molecules. The dyeability can also be enhanced by

bringing about opening up of the fibre structure, thus creating additional accessibility for

the dye molecules. During grafting both the criterias are relevant (Lokhande et al., 1984).



The acid dyes generally only tint cellulose. The direct dyes, on the other hand, require

large quantity of salt for exhaustion. Grafting of cellulose with acrylamide is another tool

for making cellulose acid dyeable, as –CONH2 groups introduced in the fibre structure as

a result of grafting provide sites for salt linkage formation during acid dyeing of grafted

cotton. Results in Table 4.6 and figure 4.10 indicate the increase in colour strength, for

both the acid dyes with increase in graft add-on of grafted cotton. With graft add-on of

3.60%, the increase in colour strength was 324.73% for Acid blue 13 and 514.53% for

Acid orange dye, as compared that of ungrafted cotton. The results are quite obvious as

the attachment points for acid dyes increased with increase in graft-add on, the more dye

will be taken by the grafted cotton having higher graft add-on resulting in higher colour

values.

The fastness properties of the dyed samples were also improved for both the dyes. The

improvement in fastness properties for grafted product may be attributed to increase in -

CONH2 groups which provide better attachment to the sites for dye molecules and hence

offering resistance to removal in washing or rubbing. Improvement in light fastness was

due to larger amount of dye being adsorbed on the grafted fibre, as compared to that on

ungrafted fibre. The samples with optimum graft add-on showed 1-3 grade improvement

in wash fastness, 1 to 2 grade improvement in rubbing fastness and 3-4 grade

improvement in light fastness.



Table 4.6: Effect of AAm grafting on acid dyeing properties


Figure 4.10: Effect of AAm graft add-on (%) on colour values of acid dyeing

0

0.5

1

1.5

2

2.5

0 1.4259 1.836 2.4472 3.0617 3.44 3.6

K/S

Graft add-on (%)

Acid Blue 13

Acid orange 92

Graft add-on (%)


Rubbing fastness

Light fastness

C* S* Dry Wet

Dye used-Acid Blue 13, λmax -590nm

0.00 0.3057 76.19 -0.66 -7.94 2 3 2-3 2 1 1.4259 0.8063 62.46 2.87 -4.50 3-4 4 4 3-4 3 1.836 0.8650 62.28 1.21 -5.60 3-4 4 4 3-4 4 2.4472 0.9859 61.65 -0.31 -8.82 3-4 4 4 3-4 4 3.0617 1.0171 61.25 0.92 -11.22 3-4 4 4 3-4 4 3.4400 1.2046 59.84 0.51 -15.19 3-4 4 4 3-4 5 3.60 1.2982 58.21 1.82 -14.74 4 4 4 3-4 5 Dye used-Acid Orange 92, λmax -490nm 0.00 0.3303 82.49 15.26 11.95 2 3 2-3 2 2 1.4259 1.6454 69.67 30.93 24.88 4 4-5 4-5 3-4 4 1.836 1.8154 67.21 28.82 24.00 4 4-5 4-5 3-4 5 2.4472 1.8877 67.90 30.46 25.04 4 4-5 4-5 3-4 5 3.0617 1.9115 67.85 30.01 25.48 4 4-5 4-5 3-4 5 3.4400 1.9771 66.65 28.02 24.42 4-5 4-5 4-5 4 5 3.60 2.0298 68.78 32.81 28.41 4-5 4-5 4-5 4 5



4.3.3 Grafting of AA-AAm onto cotton by continuous grafting 4.3.3.1 Evidence of grafting

After studying the continuous grafting of acrylic acid (AA) and acrylamide (AAm) onto

cotton individually, the mixture of AA and AAm were grafted onto cotton in order to

study the synergism of monomers in continuous system. The mixture of AA-AAm was

grafted onto cotton and the grafted fabric (AA.AAm-g-Cotton) was characterized in order

to validate grafting. The FTIR spectrum of grafted fabric (refer Figure 4.11) when

compared with that of the ungrafted fabric clearly indicates the peaks at 1715 cm-1 and

3350 cm-1 which are due to introduction of –COOH and -NH2 group which is due to

introduction of graft side chains on to cellulose backbone.

Figure 4.11: FTIR spectra of ungrafted cotton and grafted AA.AAm-g-Cotton

Figure 4.12 shows the thermogram of ungrafted and grafted cotton samples (AA.AAm-g-

Cotton). In the initial stage weight loss values of both samples were 6.27% and 5.80% at

250 0C, respectively. Between 250 0C to 350 0C, the drastic decomposition of the samples

resulted in to significant weight loss which was 58.15% for ungrafted and 46.34% for

AA.AAm-g-Cotton fabric at 350 0C. However, beyond 350 0C the loss in weight was

slowed down and finally at 450 0C, weight loss values observed were 96.75% for

ungrafted and 81.70% for AA.AAm-g-Cotton, respectively. This clearly indicates the

relatively higher thermal stability of the grafted sample compared to that of ungrafted



cotton. This could be attributed to the formation of side chain network as a result of

grafting of acrylic acid-acrylamide blend onto cellulose backbone increasing molecular

weight.

Figure 4.12: TGA of ungrafted cotton and AA.AAm-g-Cotton

SEM micrograph (refer Figure 4.13) of grafted cotton clearly show a surface deposition,

which is absent in unmodified substrate.

A B




This further confirms the presence of acrylic acid and acrylamide grafted chains on

cellulose backbone.

4.3.3.2 Optimization of grafting parameters

The mixture of AA and AAm were grafted onto cotton by padding technique and the

effect of various parameters of grafting on graft add-on of monomers onto cotton

backbone are summarized in Table 4.7 and presented graphically in Figures 4.14 and

4.15. The initial attempt was to select a process for the optimum grafting using padding

technique and hence the three commonly used padding techniques namely pad-dry, pad-

cure and pad-dry-cure were screened. Like in the case of individual AA and AAm, the

pad-cure method was found to provide highest level of grafting in mixture of AA-AAm

grafting when compared with that of other two methods. This may be because the

reaction kinetics principle. In the pad-cure process, the monomer was padded onto cotton

and cured at a high temperature where the probability of grafting was highest due to

presence of initiator and monomer in the wetted fabric. The pad-dry can be the case

where fabric is dried at much lower temperature (80 0C) after padding and the rate of

reaction was quite lower than that at higher temperature in pad-cure processes. In pad-

dry-cure process, the grafting occurred during drying and even though curing was carried

out the fabric was not in the wetted state so the movement of the monomers was

restricted not facilitating grafting. The curing process (after padding) is advantageous in

the cases where the crosslinking is supposed to happen during curing. However in this

case of continuous grafting, the process seems to be not advantageous compared to pad-

cure process.

The mixture of AA-AAm was found to give higher level of grafting compared to

individual monomers. In order to study the ratio of AA to AAm to get optimum graft

add-on, the ratio of AA and AAm were varied keeping the total monomer concentration

constant. The results in Table 4.7 and Figure 4.14 clearly indicate the enhanced graft add-

on when using binary mixture of acrylic acid (AA) and acrylamide (AAm) as compared

to individual monomers keeping the total monomer available constant (100gpl). The graft

add-on increased as acrylic acid was gradually replaced by acrylamide in the blend.

During the grafting of AAm-AA binary mixtures onto cotton fabric, the synergistic



influence has been witnessed giving enhanced grafting. Obviously, it indicates that the

rate of grafting is enhanced at the expense of the rate and the extent of homopolymer

formation, resulting in the increase in the efficiency of grafting. This also implies that

AAm and AA monomer molecules are present in solution with some kind of association

between the two, which increases or decreases depending upon their relative proportion

in the bath. Obviously, it is maximum, when they are present in 50:50 ratio. It is,

therefore, possible that the AAm and AA monomer molecules form a labile complex, and

the extent of its formation will be the highest, when the monomers are present in equal

proportion. The complex formation seems to have considerable influence in changing the

rates of reaction during the grafting process: (i) due to the complex formation mobility of

the reacting species in the solution is reduced, thereby retarding the rate of

homopolymerization; (ii) when one monomer molecule diffuses inside the fiber structure,

it automatically carries another monomer molecule present in the complex, thus

increasing the monomer concentration in the fibre phase-a very favourable situation for

higher graft-copolymer formation; (iii) when the monomer molecule reacts with the free

radical on the backbone of the cellulose, the chain propogation is enhanced due to the

complex, and, hence, a higher amount of monomer molecules is utilized resulting in the

synergistic influence. Similar contentions have been supported in the literature on

grafting studies with reference to polyester and lignocellulosic substrates, respectively

(Lokhande & Teli, 1984; Teli & Sheikh, 2011).

The parameters of pad-cure process were varied to get optimum grafting using 50:50

ratio of AA and AAm (refer Table 4.7 and Figure 4.15). With increase in curing

temperature from 100 0C to 140 0C, graft add-on increased while beyond 140 0C, further

increase in temperature resulted in decrease in graft add-on. The increase in graft add-on

with temperature is because of higher rate of dissociation of initiator as well as the

diffusion and mobility of monomer from aqueous phase to cellulose phase. With increase

in temperature beyond 140 0C, the radical termination reaction might be accelerated,

leading to decrease in graft add-on and also increase in extent of homopolymerization.

This may be, possibly due to recombination of growing homopolymer chain radicals; a

possibility at higher temperatures. The effect of temperature of grafting was found to be

more pronounced in case of continuous grafting.







on. The higher curing time however, resulted in loss in mechanical properties of cotton









After optimizing the parameters like temperature, time and initiator the monomer total

concentration was varied keeping the ratio of AA:AAm as 50:50 in order to get efficient

utilization of monomer in grafting. The graft add-on was found to be increasing

significantly initially with increasing monomer concentration from 50 to 100 gpl and then

to relatively lower extent from 100 to 200 gpl. This is because of more availability of

monomer for grafting initially, while at higher concentration, the homopolymer formation

is dominant compared to grafting causing only slight increase in graft add-on; however

efficiency of grafting decreased. Hence 100gpl concentration was found to be optimum

for grafting. The continuous grafting of mixture of AA-AAm onto cotton however seems

to be advantageous in the cases where the lower graft add-on is desired and dual

modification of cotton is required with better efficiency.

The optimized parameters in case of AA-AAm blend grafting onto cotton were found

identical to that of individual AA and AAm grafting i.e. process pad-cure, AA:AAm

50:50, curing temperature-1400C, curing time-5min, initiator conc-15gpl, and total

monomer concentration-100gpl.; however, the level of grafting was much higher in

blends than individual cases ensuring efficient utilization of monomer.



Table 4.7: Effect of different parameters of on grafting of AA-AAm on cotton

Sr. No.

Process AA:AAm (w/w)

Temperature (Drying/Curing)

(0C)

Time (Drying/Curing)

(Min.)

KPS conc. (gpl)

AA-AAm conc. (gpl)

Graft add-on

(%)

1. Process selection A Pad-Dry 50:50 80 5 15 100 3.556 B Pad-Cure 50:50 140 5 15 100 4.022 C Pad-Dry-

Cure 50:50 80/140 5/5 15 100 3.896

2. Effect of blend composition A Pad-Cure 100:0 140 5 15 100 2.65 B Pad-Cure 75:25 140 5 15 100 3.289 C Pad-Cure 50:50 140 5 15 100 4.022 D Pad-Cure 25:75 140 5 15 100 3.721 E Pad-Cure 0:100 140 5 15 100 3.60 3. Effect of Temperature A Pad-Cure 50:50 100 5 15 100 1.505 B 50:50 120 5 15 100 2.675 C 50:50 130 5 15 100 3.790 D 50:50 140 5 15 100 4.022 E 50:50 150 5 15 100 3.837 F 50:50 180 5 15 100 3.627 4. Effect of Time A Pad-Cure 50:50 140 1 15 100 2.888 B 50:50 140 2 15 100 3.126 C 50:50 140 3 15 100 3.229 D 50:50 140 4 15 100 3.885 E 50:50 140 5 15 100 4.022 F 50:50 140 8 15 100 4.035 G 50:50 140 10 15 100 4.027 5. Effect of Initiator conc. A Pad-Cure 50:50 140 5 5 100 2.224 B 50:50 140 5 10 100 3.770 C 50:50 140 5 15 100 4.022 D 50:50 140 5 20 100 4.009 E 50:50 140 5 25 100 3.699 6. Effect of monomer conc. A Pad-Cure 50:50 140 5 15 50 1.751 B 50:50 140 5 15 100 4.022 C 50:50 140 5 15 150 4.458 D 50:50 140 5 15 200 5.180



Figure 4.14: Effect of AA:AAm ratio on graft add-on

Figure 4.15: Optimization of grafting parameters for AA.AAm onto Cotton

0

1

2

3

4

5

1:00 0.75:0.25 0.5:0.5 0.25:0.75 0:01

Graf

t add

-on

(%)

AA:AAm ratio

0

1

2

3

4

5

100 120 140 160 180

Gra

ft a

dd-o

n (%

)

Curing temperature (0C)

0

1

2

3

4

5

0 2 4 6 8 10

Gra

ft a

dd-o

n (%

)

Curing time (min)

0

1

2

3

4

5

0 5 10 15 20 25

Gra

ft a

dd-o

n (%

)

KPS conc. (gpl)

0

1

2

3

4

5

6

0 50 100 150 200

Graf

t add

-on

(%)

Monomer conc. (gpl)



4.3.3.3 Effect of grafting on textile properties of cotton

Even though graft add-on varies with the parameters of grafting as represented in Table

4.7; it is not the only factor affecting the textile properties especially in the case of

mechanical properties which was greatly affected by the parameters like high


degradation of cellulose chains and higher concentration of acrylamide imparting

stiffness. In case of grafting of AA-AAm onto cotton by padding technique the grafting

of both monomers, level of grafting, excess AA reacting with hydroxyl groups forming

ester, polymer deposition offering stiffness and the acid hydrolysis of cellulose and

drastic reaction conditions affect the textile properties of cotton.

In order to study the effect of all these parameters on the mechanical properties, the

grafted samples were evaluated for their mechanical properties and results are

summarized in Table 4.8




regain was due to the introduction of hydrophilic monomers AA and AAm in molecular

structure of cellulose substrate during grafting increasing its hydrophilicity. Even though

the enhancements in moisture regain were of lower extent; the property enhancement

seems to be dependent on graft add-on level which was quite lower in case of continuous

grafting. However, the increase in moisture regain was of higher order as compared to

that in case of individual monomers. The moisture regain of grafted product was further

increased after treatment with sodium hydroxide showing 36.31% increase for sample

with optimum graft add-on over that of ungrafted sample. This may be attributed to

conversion of –CONH2 groups to –COOH and –COONa groups after saponification. The

absorbency behavior may be interpreted by postulating that the collaborative absorbent

effect of –CONH2, -COONa, and –COOH groups is superior to that of single –CO NH2, -

COONa, and –COOH groups (Wu et al., 2003).


increase in AA-AAm in cellulose increasing nitrogen content of the product and also due



to effect of heat, during curing, on cellulose backbone. Acid hydrolysis of cellulose also

imparts yellowness. The –NH2 group is known to impart yellowness to the applied

substrate resulting in lowering of whiteness index. The whiteness index decreased with

reaction temperature irrespective of the increase or decrease in graft add-on levels




less significant as compared to that of reaction temperature. The whiteness index also

decreased with increase in initiator concentration irrespective of graft add-on. The

increase in concentration of monomer also resulted in decreased whiteness mainly due to

increase in graft add-on since all other parameters were constant.

Tensile strength and tearing strength was found to be negatively influenced by grafting

reaction, the individual extent of which depend on the combination of various parameters

of grafting. Tensile strength decreased with increased curing temperature, increased

reaction time, increased initiator concentration and increased acrylic acid concentration.

The similar trend was found in case of tearing strength. In general tensile strength

depends on the distribution of the force though out the dimension of the fabric when

fabric as pulled during testing. Grafting reaction resulted in deposition of the side chain

on the cellulose backbone consuming the hydroxyl groups and preventing the H-bond

formation between them. Grafting also resulted in stiffness of the fabric facilitating the

failure at lower load. The degradation of cellulose chains during grafting can be the

probable reasons for decrease in mechanical properties of cotton after grafting.

However, the decrease in mechanical properties and whiteness of the cotton fabric was of

the lower order compared to that in case of individual acrylic acid grafting probable due

to absence of reaction between hydroxyl groups of cellulose and carboxylic group of acid

and the hydrolysis of cellulose in presence of strong acid like acrylic acid at enhanced

curing temperatures since the availability of free acrylic acid may be decreased because

of the formation of labile complex between AA and AAm (Lokhande & Teli, 1984; Teli

& Sheikh, 2011). .







which was considered to be one of the mechanisms of crease recovery, also results in




Sample No.

Graft add-on

(%)

W.I. Moisture regain

(%)

T.S. (Kg)

Te.S. (gm)

CRA (0)

B.L. (cm)

UG 0.0 70.05 6.23(6.28) 36.34 1920 106 1.10 2A 1.505 68.21 6.5898(7.1077) 31.12 1504 152 1.20 2B 2.675 67.48 6.8697(7.7514) 31.08 1504 160 1.40 2C 3.790 50.76 7.1362(8.3643) 29.20 1472 184 1.45 2D 4.022 45.75 7.1917(8.4920) 24.91 1408 193 1.55 2E 3.837 46.48 7.1474(8.3902) 23.53 1152 187 1.55 2F 3.627 44.96 7.0972(8.2747) 19.44 992 180 1.55 3A 2.888 58.07 28.37 1504 165 1.30 3B 3.126 57.86 26.74 1472 167 1.35 3C 3.229 55.74 24.95 1472 172 1.35 3D 3.885 50.76 24.86 1440 190 1.45 3E 4.022 45.75 24.91 1408 193 1.55 3F 4.035 40.46 22.36 1184 194 1.55 3G 4.027 36.93 21.62 1040 194 1.55 4A 2.224 67.77 30.10 1664 160 1.35 4B 3.770 67.48 27.53 1504 184 1.45 4C 4.022 45.75 24.91 1408 193 1.55 4D 4.009 60.75 19.25 1072 191 1.55 4E 3.699 63.17 18.99 1024 182 1.50 5A 1.751 68.01 25.347 1568 155 1.25 5B 4.022 45.75 24.91 1408 193 1.55 5C 4.458 33.71 21.13 1248 197 1.60 5D 5.180 33.69 19.97 992 200 1.65

*T.S.-Tensile strength, Te.S.-Tearing strength, W.I.-Whiteness Index, B.L.-Bending length



4.3.3.4 Effect of Grafting on Cationic Dyeing of Cotton

The grafting of AA-AAm onto cotton modify it in a dual way due to introduction of

functional groups like –COOH and –CONH2. The pure cellulose (cotton) on one hand do

not possess the groups for the attachment of cationic dye; while on the other hand lacks

the groups where plannar acid dye can attach. Hence the grafted cotton was expected to

have increased dyebility towards such dyes. In order to confirm the dyeability imparted,

the grafted cotton was studied for its dyeability towards both cationic and acid dyes and

results are summarized in Tables 4.9 and 4.10 and presented graphically in Figures 4.16

and 4.17.

Results in Table 4.9 and Figure 4.16 indicate the increase in colour strength with increase

in graft add-on for both the cationic dyes. The increase in graft add-on resulted in

increase in carboxyl content of the cotton fabric (refer Table 4.8) hence providing more

attachment points for cationic dye molecules resulting in enhanced colour values. The

optimum grafted sample (with graft add-on of 4.022%) showed the increase in colour

strength, compared to that of ungrafted cotton, by 163.27% for Bismark Brown and

1137.7% for Methylene Blue dyes. Since in this case the cotton was grafted in fabric

form and by padding method, the grafting was more or less controlled by the mangle

pressure. Since the even padding of monomers can be carried out, the grafting was

expected to be even thoughout the width and length of the fabric. The fabrics dyed using

cationic dyes showed even dyeing along the fabric. Hence grafting of fabric using

padding process can be claimed as method for obtaining uniform grafting on the

substrates.

The fastness properties of the dyed samples were also improved for both the dyes.

Cationic dyes are known for inferior fastness properties on cellulose and hence

improvement in fastness properties for grafted product may be attributed to increase in

carboxyl groups which provide better attachment to the sites for dye molecules and hence

offering resistance to removal in washing or rubbing. Improvement in light fastness is

due to larger amount of dye being adsorbed on the fibre as compared to when graft

copolymer was absent. The samples with optimum graft add-on showed 3 grade

improvement in light fastness and 1 to 2 grade improvement in rubbing fastness.



Table 4.9: Effect of grafting on dyeing properties with cationic dyes


Figure 4.16: Effect of AAAAm graft add-on (%) on colour values of cationic dyeing

0

2

4

6

8

10

12

0 1.505 2.675 3.79 4.022 3.837 3.627

K/S

Graft add-on (%)

Bismark brown G

Methylene blue

Graft add-on (%)


Rubbing fastness

Light fastness

C* S* Dry Wet

Dye used-Bismark Brown G, λmax -470nm

0.00 1.2038 72.71 11.76 27.32 1-2 3 3 3 1 1.505 1.9063 64.13 14.06 22.06 4 3 4 3 3 2.675 2.3227 63.58 16.33 26.72 4 3-4 4 3 3 3.790 3.1605 58.47 11.37 25.80 4 3-4 4 3 3 4.022 3.1693 58.38 10.98 25.72 4 3-4 4 3 4 3.837 2.8772 61.09 15.58 27.79 4 3-4 4 3 3 3.627 1.9545 65.20 19.45 24.52 4 3-4 4 3 3 Dye used-Methylene Blue G, λmax -670nm 0.00 0.8797 74.24 -12.47 -15.26 1-2 3 3 3 1 1.505 3.7170 60.08 -14.36 -27.07 3 3 3 2-3 2 2.675 7.1961 51.83 -10.78 -35.49 3 3 3 2-3 2 3.790 10.455 48.96 -11.29 -35.63 3 3 3 2-3 2 4.022 10.888 45.97 -9.97 -35.18 3-4 3 3 3 3 3.837 8.8850 51.71 -12.76 -34.08 3-4 3 3 3 3 3.627 3.9294 58.84 -13.90 -28.00 3-4 3 4 2-3 3



4.3.3.5 Effect of AA-AAm grafting on Acid Dyeing of Cotton

The dyeability of the textile fibres can be increased by introducing suitable functional

groups in the fibre structure, so that they become the centres of adsorption or reaction

with the appropriate class of dye molecules. The dyeability can also be enhanced by

bringing about opening up of the fibre structure, thus creating additional accessibility for

the dye molecules. During grafting both the criterias are relevant (Lokhande et al., 1984).

The acid dyes generally only tint cellulose. The direct dyes, on the other hand, require

large quantity of salt for exhaustion. Grafting of cellulose with acrylamide or blend of

monomers containing AAm is another tool for making cellulose acid dyeable, as -CONH2

groups introduced in the fibre structure as a result of grafting provide sites for salt linkage

formation during acid dyeing of grafted cotton. Results in Table 4.10 indicate the

increase in colour strength, for both the acid dyes with increase in graft add-on of grafted

cotton. With graft add-on of 4.022%, the increase in colour strength was 201.21% for

Acid blue and 460.1% for Acid orange dye, as compared that of ungrafted cotton. The

results are quite obvious as the attachment points for acid dyes increased with increase in

graft-add on, the more dye will be taken by the grafted cotton having higher graft add-on.

The fastness properties of the dyed samples were also improved for both the dyes. The

improvement in fastness properties for grafted product may be attributed to increase in -

CONH2 groups which provide better attachment to the sites for dye molecules and hence

offering resistance to removal in washing or rubbing. Improvement in light fastness is

due to larger amount of dye being adsorbed on the grafted fibre, as compared to that on

ungrafted fibre. The samples with optimum graft add-on showed 1-3 grade improvement

in wash fastness, 1 to 2 grade improvement in rubbing fastness and 3-4 grade

improvement in light fastness.



Table 4.10: Effect of grafting on dyeing properties with acid dyes


Figure 4.17: Effect of AAAAm graft add-on (%) on colour values of acid dyeing

0

0.5

1

1.5

2

0 1.505 2.675 3.79 4.022 3.837 3.627

K/S

Graft add-on (%)

Acid blue 13

Acid orange 92

Graft add-on (%)


Rubbing fastness

Light fastness

C* S* Dry Wet

Dye used-Acid Blue G, λmax -590nm

0.00 0.3057 76.19 -0.66 -7.94 2 3 2-3 2 1 1.505 0.5881 66.88 2.04 -4.17 3-4 4 4 3-4 3 2.675 0.6425 67.18 0.48 -0.70 3-4 4 4 3-4 4 3.790 0.8402 63.57 1.10 -9.72 3-4 4 4 3-4 4 4.022 0.8601 62.72 1.34 -7.66 3-4 4 4 3-4 4 3.837 0.9081 62.48 -0.33 -7.37 3-4 4 4 3-4 5 3.627 0.9208 60.36 3.47 -4.87 4 4 4 3-4 5 Dye used-Acid Orange, λmax -490nm 0.00 0.3303 82.49 15.26 11.95 2 3 2-3 2 2 1.505 1.2291 72.23 28.55 22.22 4 4-5 4-5 3-4 4 2.675 1.5484 70.23 30.40 24.35 4 4-5 4-5 3-4 5 3.790 1.6787 67.58 27.80 25.27 4 4-5 4-5 3-4 5 4.022 1.7693 67.73 28.73 24.37 4 4-5 4-5 3-4 5 3.837 1.8287 67.88 30.61 24.63 4-5 4-5 4-5 4 5 3.627 1.8500 68.35 30.55 25.42 4-5 4-5 4-5 4 5



Hence it can be concluded that the continuous grafting of vinyl monomers onto cotton

fabric was successfully carried out using padding technique. The suitable padding

technique was optimized to get optimum graft add-on. The various parameters of the

grafting reaction were optimized. All the grafted cotton fabrics showed increased thermal

stability. The mechanical properties like tensile strength and tearing strength decreased to

some extent in all the cases. Crease recovery angles improved with some stiffness being

imparted to the grafted fabric. The grafted fabric showed the enhancement in dyeability

towards acid and cationic dyes depending on the type of monomer used for grafting. The

grafted fabric dyed uniformly indicating the uniformity of grafting. The continuous

grafting using padding technique hence claimed to be efficient, uniform and operation

friendly grafting method for textile fabrics.

Documents

CONTINUOUS GRAFTING OF VINYL MONOMERS …shodhganga.inflibnet.ac.in/bitstream/10603/13569/12/12...Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing Performance Enhancement