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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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 128
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 129
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 130
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 131
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 132
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 133
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 134
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)
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 135
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 136
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 137
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 138
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 139
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 140
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
Figure 4.8: SEM photograph of ungrafted (A) and grafted cotton (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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 141
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.
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-
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 142
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 4.4 and Figure 4.9 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 (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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 143
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 144
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
temperature, increased reaction time, higher concentration of initiator causing
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)
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 145
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
Results in Table 4.5 indicate the increased moisture regain with increase in graft add-on
giving 6.28% increase in moisture regain for optimum grafted sample (with graft add-on
3.60%) when compared with that of ungrafted sample. This enhancement in moisture
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).
The whiteness index decreased with increase in graft add-on which may be due to
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
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 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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 146
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.
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 results in
increased CRA. However, the bending length increased with increase in graft add-on
indicating the increased stiffness after grafting.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 147
Table 4.5: Effect of grating on textile properties
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).
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 148
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 149
Table 4.6: Effect of AAm grafting on acid dyeing properties
C*- Change in shade, S*-Staining
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 (%)
K/S L* a* b* Washing fastness
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 150
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 151
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
Figure 4.13: SEM photograph of ungrafted (A) and grafted cotton (B)
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 152
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 153
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 154
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, resulted in loss in mechanical properties of cotton
fabric and hence 5 min curing time was taken as optimum.
Results in Table 4.7 and Figure 4.15 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 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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 155
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 156
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)
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 157
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
temperature, increased reaction time, higher concentration of initiator causing
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
Results in Table 4.8 indicate the increased moisture regain with increase in graft add-on
giving 15.43% increase in moisture regain for optimum grafted sample (with graft add-on
4.022%) when compared with that of ungrafted sample. This enhancement in moisture
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).
The whiteness index decreased with increase in graft add-on which may be due to
increase in AA-AAm in cellulose increasing nitrogen content of the product and also due
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 158
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
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 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). .
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 159
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 results in
increased CRA. However, the bending length increased with increase in graft add-on
indicating the increased stiffness after grafting.
Table 4.8: Effect of grating on textile properties
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 160
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 161
Table 4.9: Effect of grafting on dyeing properties with cationic dyes
C*- Change in shade, S*-Staining
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 (%)
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 1.505 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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 162
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.
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 163
Table 4.10: Effect of grafting on dyeing properties with acid dyes
C*- Change in shade, S*-Staining
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 (%)
K/S L* a* b* Washing fastness
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
Continuous Grafting of Vinyl Monomers onto Cotton vis a vis Dyeing
Performance Enhancement of Fibrous Polymers Page 164
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.