CHAPTER 4shodhganga.inflibnet.ac.in/bitstream/10603/48036/10/10... · 2018-07-03 · CHAPTER – 4...
Transcript of CHAPTER 4shodhganga.inflibnet.ac.in/bitstream/10603/48036/10/10... · 2018-07-03 · CHAPTER – 4...
Results and Discussion
69
CHAPTER – 4
RESULTS AND DISCUSSION
4.1.0 COTTON FABRIC COATED WITH INTUMESCENT FORMULATIONS
CONTAINING NANOCLAYS (SERIES A1)
4.1.1 Thermal study in air atmosphere (Series A1)
(A) TG analysis
Thermogravimetric analysis of pure cotton fabric (CF) and its coated cotton
fabric samples (CF-INT, CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-INT-
NME) was carried out using NETZSCH STA 449F1 TG instrument at heating rate of
10 oC/min in air atmosphere with flow rate 100 mL/min from ambient temperature to
700 oC with a sample weight of about 10 mg. TG curves of these samples are shown
in Figs. 4.1 and 4.2. The thermogravimetric analysis gives information on thermal
stability and degradation behaviour of polymeric materials. TG curves of samples
indicate the number of stages of thermal degradation, weight loss in each stage,
temperature at maximum weight loss rate and char yield. The thermal degradation
data of pure cotton fabric (CF) and its coated cotton fabric samples are given in Table
4.1, which includes T10wt% (temperature at 10 % weight loss), T50wt% (temperature at
50 % weight loss) and the residual mass i.e. char at 600 oC in air atmosphere.
Pure cotton fabric (CF) (Fig. 4.1) shows two stages of thermal degradation
[190] with major weight loss of 78.0 % in the first stage (100 - 360 oC) with DTG
peak at 330 oC. The onset temperature of degradation i.e. T10wt% and temperature at
mid-point of decomposition i.e. T50wt% pure cotton fabric are 313 and 331 oC,
respectively. During second stage of thermal degradation in the temperature range of
360 - 510 oC with DTG peak at 470 oC, 20.5 % weight loss takes place. The cotton
fabric degrades almost completely upto 500 oC leaving no char yield at 600 oC. The
major weight loss of pure cotton during first stage of thermal degradation is due to
dehydration, decomposition and formation of volatile products mainly laevoglucosan
[98, 191]. Later, in second stage of thermal degradation, the oxidation of
carbonaceous residue takes place [192]. Thermal degradation of pure ammonium
polyphosphate (APP) has already been studied and reported [193, 194] which releases
Results and Discussion
70
ammonia, phosphoric acid (PA) and water in first step leading to formation of the
highly cross-linked polyphosphoric acid (PPA) at higher temperature. The second step
of degradation of APP corresponds to the polyphosphoric acid evaporation on
decomposition and/or dehydration to P4O10 which later sublimes.
TG curve of CF-INT sample (Fig. 4.1) shows different behaviour with three
stages of the degradation producing char yield of 26.8 % at 600 oC. After coating with
intumescent (INT), the onset temperature of CF-INT sample is decreased by 44 oC
due to acid catalyzed dehydration of cellulose by phosphoric acid released from APP.
But the temperature at mid-point of decomposition is increased by 54 oC due to
formation of protective carbonaceous layer having cross-linked polyphosphate
structure of intumescent material on the surface of cotton fabric. The degradation rate
of CF-INT sample is reduced and delayed by limiting the heat and mass transfer. The
increase in thermal stability is observed in higher temperature range i.e. after 340 oC
as indicated by formation of higher amount of char. In the intumescent system,
carbonaceous material at surface protects the substrate from oxidation and flame. At
higher temperature (600 - 700 oC), a 13 % weight loss of CF-INT sample is observed,
which is probably due to oxidation of aromatic charred residue [195].
The phosphorylation of CF and degradation mechanism of CF-INT sample is
shown in Schemes 4.1 and 4.2 where intumescent material acts in a condensed phase
and catalyzes the reactions with formation of large amount of char. The ammonium
polyphosphate releases phosphoric acid which phosphorylates cellulose on C-6
position. Phosphorylated cellulose further decomposes with different path in
comparison to pure cellulose and forms conjugated double bonds in glucopyranose
rings leading to the formation of more char. Scheme 4.2 shows the formation of
intumescent carbonaceous layer by interactions of APP, pentaerytritol (PER) and
melamine (MEL) with the release of ammonia on the surface of cotton fabric and
Scheme 4.3 shows the decomposition of melamine simultaneously releasing ammonia
continuously.
Results and Discussion
71
Fig. 4.1 - TG curves of (1) CF, (2) CF-INT and (3) CF-INT-KLN samples in air
atmosphere (Series A1).
Fig. 4.2 - TG curves of (4) CF-INT-BNT, (5) CF-INT-NMT and (6) CF-INT-
NME samples in air atmosphere (Series A1).
Results and Discussion
72
Table 4.1 - TG data of pure and coated cotton fabric samples in air
atmosphere (Series A1)
Sample Stages Temp.
range
(oC)
Weight
loss
(%)
DTG
(oC)
T10wt%
(oC)
T50wt%
(oC)
Char at
600 oC
(%)
CF 1st
2nd
100-360
360-510
78.0
20.5
330
470
313 331 0.35
CF-INT 1st
2nd
3rd
100-310
310-600
600-700
40.0
32.5
13.3
286 269 385 26.8
CF-INT-KLN 1st
2nd
3rd
100-310
310-600
600-700
39.6
37.0
9.0
290 276 378 22.7
CF-INT-BNT 1st
2nd
3rd
100-310
310-600
600-700
40.4
37.4
7.4
284 270 372 21.5
CF-INT-NMT 1st
2nd
3rd
100-310
310-600
600-700
42.0
37.2
8.5
281 274 359 20.2
CF-INT-NME 1st
2nd
3rd
100-310
310-600
600-700
40.8
36.6
9.2
281 274 370 22.0
On incorporating nanoclays into intumescent system, no significant change in
thermal behaviour is observed. The weight loss in second stage is found increased in
the temperature range 310 - 600 oC and slightly reduced in third stage of degradation
in the temperature range 600 - 700 oC. The T50wt% temperature is reduced in all
samples containing nanoclays as compared to CF-INT sample due to catalytic action
of the nanoclays, which is also supported by decrease in DTG peaks. The T50wt%
temperature is highly decreased in case of sample containing NMT nanoclay. Onset
temperature of samples containing clays slightly increases in comparison to CF-INT.
The char yields formed are slightly decreased (20.2 - 22.7 %) at 600 oC in comparison
Results and Discussion
73
to CF-INT, which may be due to catalytic effect of clay on degradation process of
polymer (cotton) due to their large surface area.
At 500 oC, pure cotton fabric gives negligible char but after coating treatment
with intumescent, about 37 % residue is left at this temperature due to interaction
among the intumescent components and interaction of intumescent components with
cotton cellulose. The char layer insulates the underlying cotton material and reduces
the release of volatile products [98], thereby increasing the thermal stability of coated
cotton at higher temperature stage. There is a strong correlation between char yield
and fire resistance as the char is formed at the expense of combustible gases. The
presence of a char inhibits further flame spread by acting as a thermal barrier around
the unburned cotton material.
OOO
CH2OH
OH
OH
Cellulose
H3PO4 OOO
CH2O
OH
OH OOO
CH2
OH
OH
POH
OH
O
-H2O
-H3PO3
Heat
CharO
OO
CH2OH
O
OH
POHOHO
-H2O
-H3PO3
OOO
CH2OH
HO
Heat
H3PO4
Scheme 4.1 - Phosphorylation and pyrolysis of phosphorylated cotton cellulose.
Results and Discussion
74
PO
O
HO
PO
O
O H
P PA
P ER
O HO H
OHO
PO
H O O HO H
OHO
PO
O
OHOH
OO
PP
O
H O
OO
O HO H
OO
P
O
H O
M EL
O HO H
OO
PO
OHO
O HO H
OO
PO
O
O HO H
OO
PP
O
O
OO O H
O HOO
P
O
O
N
NN
H 3N
NH 2H 2N N
NN
H 3N
NH 2H 2N
N
NN
H 3N
NH 2H 2N
N
NN
H 3N
NH 2H 2N
O
( i)( ii)
(ii i)( iv)
( v)
( v i)
( v ii) ( v ii i)
O
Scheme 4.2 - Mechanism of formation of pentaerythritol diphosphate (PEDP)
melamine adduct.
He a t
He at
PO
OH 4N O
PO
O
O N H 4
H OPO H
O
O H
P A
Po lym e r iz a t io n
PO
O
H O
PO
O
O H
P P A
- N H 3
- NH 3
P E R
- H 2O OP
O
O H
O
M E L
OPOHO
O
OP
O
O H
OOPOO
O
N
NN
H 3N
N H 2H 2N
A P P
P E D P
Results and Discussion
75
N N
N NH2
NH2
H2N
(MEL)
Heat
N N
N
NH2
H2N
N N
N NH2
NH2
-NH3N
N
N
N
NN
NH2H2N
Melame Meleme
NH2
HN
Scheme 4.3 - Decomposition of melamine.
(B) DSC analysis
Differential scanning calorimetric (DSC) analysis of pure cotton fabric and its
coated cotton fabric samples was carried out from ambient temperature to 700 oC at a
heating rate of 10 oC/min in air atmosphere with flow rate of 100 mL/min using
NETZSCH STA 449F1 TG instrument. About 10 mg sample was examined in each
case. DSC curves of pure cotton fabric (CF) and its coated cotton fabric samples (CF-
INT, CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-INT-NME) are shown in
Figs. 4.3 and 4.4. The initiation and maximum temperatures, and nature of DSC peaks
are given in Table 4.2.
DSC curve of pure cotton fabric (CF) shows two major exothermic peaks with
maxima at 350 and 472 oC, respectively. First exotherm with maximum at 350 oC is
large, which may be due to dehydration (charring) and oxidation of the volatile
products (laevoglucosan a major volatile product) of thermal depolymerization of
cellulose. The second exotherm with maximum at 472 oC may be due to the oxidation
of charred residue formed [191].
DSC curve of CF-INT shows the first exotherm with maximum at 298 oC and
second exotherm at 338 oC, which are lowered in comparison to that of pure cotton
cellulose due to chemical interactions among coated additives and cotton cellulose
such as catalyzed dehydration of cellulose, phosphorylation of cellulose as well as
PER, cross-linking of APP and oxidation of products of thermal decomposition of
cellulose. APP and melamine components of intumescent system on decomposition
release phosphoric acid and ammonia, respectively. The third exotherm in DSC curve
of CF-INT with maximum at 490 oC may be due to cross-linking, deoxygenation and
aromatization reactions of the char residue formed in air atmosphere [196].
Results and Discussion
76
Fig. 4.3 - DSC curves of (1) CF, (2) CF-INT and (3) CF-INT-KLN samples in
air atmosphere (Series A1).
Fig. 4.4 - DSC curves of (4) CF-INT-BNT, (5) CF-INT-NMT and (6) CF-INT-
NME samples in air atmosphere (Series A1).
Results and Discussion
77
The shift of last exotherm of CF at 472 oC to higher temperature at 490 oC in
case of CF-INT is an indication of increase in thermal stability of material, which may
be attributed to the formation of carbonaceous layer generally called char at the
surface of fabric. The increase in char of cotton fabric on coating with intumescent
system is also observed in TG analysis (Table 4.1). The carbonaceous layer reduces
the heat and mass transfer between the substrate and the flame. As a result of this, it
insulates the cotton fabric from flame and atmospheric oxygen as indicated by
reduction in the size of peak to greater extent (Fig. 4.3). The acrylic based binder used
for coating may also act as a carbon source in the intumescent system, which has also
been demonstrated in earlier study [197]. The areas under oxidative exothermic peaks
are substantially decreased after intumescent coating, which indicates flame reducing
effects by intumescent and decreasing the oxidation of volatile products by preventing
the contact with atmospheric oxygen.
On incorporating the nanoclays into intumescent system, no significant
changes are observed in DSC curves except that the last exotherms maxima are
slightly shifted to lower temperatures because of catalytic activity of nanoclays being
having the large surface area. The CF-INT-NMT sample shows a very small first
exotherm and CF-INT-NME sample does not give the first exotherm (Fig. 4.4), which
may be due to overlapping of this exotherm with neighbouring exotherm.
Results and Discussion
78
Table 4.2 - DSC data of pure and coated cotton fabric samples in air
atmosphere (Series A1)
Sample DSC temperature (oC) Nature of peak
Initiation
temp.
Maximum
temp.
CF 337
445
350
472
Exo (large & sharp)
Exo (large & sharp)
CF-INT 274
317
435
298
338
490
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)
CF-INT-KLN 272
318
420
300
334
482
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)
CF-INT-BNT 270
314
420
297
346
485
Exo (small & sharp)
Exo (medium)
Exo (small & broad)
CF-INT-NMT --
315
435
305
335
478
Exo (very small)
Exo (medium)
Exo (small & broad)
CF-INT-NME 315
440
341
480
Exo (medium)
Exo (small & broad)
Results and Discussion
79
4.1.2 Flammability study (series A1)
4.1.2.1 Auto flammability test
The ATLAS 45o Automatic Flammability Tester (Model M233G AFC 45o
flammability chamber) was used to evaluate flammability of specimens according to
test standard ASTM D 1230 [181]. The 45° automatic flammability test is similar to
UL-94 vertical test. The fabric sample was mounted in a frame and held at an angle of
45° with test specimen of size 16.5 cm x 5 cm of the fabric. The specimen was then
exposed to a standard butane flame for 12 sec to cause ignition and then burning time
and burning characteristics were recorded. Auto flammability test was carried out for
pure cotton fabric (CF) and coated cotton fabric samples (CF-INT, CF-INT-KLN, CF-
INT-BNT, CF-INT-NMT & CF-INT-NME). The images of samples after
flammability test are shown in Fig. 4.5 and the flammability parameters are given in
Table 4.3.
In this study two factors are measured: One is ease of burning and other is
flame spread speed. According to ASTM D 1230 standard, a progressive burning of a
fabric at a distance of 12.7 cm from a flame is deemed to be failure of resistance to
burning. Flame spread speed was the time taken by a flame on burning material away
from the source of ignition to travel a specified distance under specified conditions.
The effect of coating on the fire properties was observed with flame spread speed.
The higher value of flame spread speed indicates the more propagation of fire. The
flame spread speed is decreased in case of the coated fabrics.
In case of pure cotton fabric (CF), the flame spreads quickly within 13 sec and
burned entire fabric after removing the ignition source (Fig. 4.5). Thus pure cotton
fabric failed in this flammability test. On the other hand, coated cotton fabric with
intumescent (CF-INT) shows no flame spread with formation of char spot of length
1.8 cm and passed this test (Table 4.3). Further, on addition of nanoclays with
intumescent for the samples (CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-INT-
NME), the auto flammability test is passed with formation of char spot. On addition
of nanoclays (except NME) into intumescent formulation, the char length is decreased
in the range 1.3 - 1.6 cm. These results indicated the better flame retardancy of the
coated cotton samples. This can be explained by the formation of protective barrier
Results and Discussion
80
layer of char on the surface of cotton fabric during the burning process which acted as
shield to the cotton and prevent it from the fire. The flammable volatiles are reduced
in the case of coated cotton fabric as indicated by increase in char formation.
4.1.2.2 Limiting oxygen index test
Limiting oxygen index (LOI) analysis of pure cotton fabric (CF) and its coated
cotton fabric samples (CF-INT, CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-
INT-NME) was performed using Limiting Oxygen Indexer IS: 13501-1992 RA 2008
instrument. LOI values were measured for pure and coated samples of size 150 mm x
50 mm and are given in Table 4.3. The oxygen concentration is reported in volume
percent. In limiting oxygen index test, higher the LOI values the better the flame
retardancy of the cotton fabric. LOI value for pure cotton fabric (CF) is 18 %, which
is increased to 27.5 % for coated cotton fabric with intumescent (CF-INT). LOI value
is further increased slightly up to 28.5 % on inclusion of different nanoclays in
intumescent formulation.
Any polymeric material or fiber with a LOI value of 21 % or lower will ignite
easily and burn rapidly in the presence of air and are classified as ”combustible”.
Polymeric material with a LOI values of 26-28 %, the polymer or fibre may be
considered flame retarded and are classified as ”self-extinguishing” [198]. Thus, both
flammability tests indicate that the intumescent coating has provided good flame
retardancy to coated cotton fabric.
Results and Discussion
81
Fig. 4.5 - Images of (1) CF, (2) CF-INT, (3) CF-INT-KLN, (4) CF-INT-BNT, (5)
CF-INT-NMT and (6) CF-INT-NME test samples after auto
flammability test (Series A1).
Table 4.3 - Flammability parameters of pure and coated cotton fabric samples
(Series A1)
Sample Auto flammability testLOI(%)
Flamespread time
(sec)
Charlength(cm)
Burningspeed(m/h)
Pass/Fail
CF 13 BEL# 41.53 Fail 18.0
CF-INT DNI** 1.8 -- Pass 27.5
CF-INT-KLN DNI 1.3 -- Pass 27.5
CF-INT-BNT DNI 1.6 -- Pass 28.0
CF-INT-NMT DNI 1.6 -- Pass 28.0
CF-INT-NME DNI 2.3 -- Pass 28.5**DNI-Did Not Ignite, #BEL-Burn Entire Length
Results and Discussion
82
4.1.3 Mechanical study (Series A1)
4.1.3.1 Stiffness measurement
The resistance of the fabric to stiffness was measured using Paramount
Stiffness Tester (BS 3356:1961). Test specimens measuring 12 cm x 2.5 cm were cut
in both warp and weft directions from different portions of the fabrics. The test was
repeated three times for all the samples and an average was calculated. Stiffness of
pure cotton fabric and its coated cotton fabric samples (CF-INT, CF-INT-KLN, CF-
INT-BNT, CF-INT-NMT & CF-INT-NME) was measured and is given in Table 4.4
The stiffness in warp wise direction of pure cotton fabric is 3.2 cm but for
cotton fabric coated with intumescent (CF-INT) the stiffness observed is 6.2 cm and it
remains almost same for the cotton fabric coated with intumescent containing
nanoclays for samples (CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-INT-
NME). In case of weft wise direction, stiffness value of 2.6 cm is observed for pure
cotton fabric and it is increased to 5.9 cm for intumescent coated cotton fabric (CF-
INT). On addition of nanoclays with intumescent, the stiffness is decreased in range
4.0 - 5.4 cm for samples (CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-INT-
NME).
4.1.3.2 Thickness measurement
The thickness of fabric was measured by the Prolific Thickness Tester
instrument (BS 2544:154). The thickness gauge was used to measure the thickness of
pure cotton fabric and coated fabric samples. Thickness at different places on sample
was measured and the mean was calculated. Thickness of pure cotton fabric and its
coated cotton fabric samples (CF-INT, CF-INT-KLN, CF-INT-BNT, CF-INT-NMT
& CF-INT-NME) was measured and is given in Table 4.4.
The observed thickness of pure cotton fabric is 2.2 mm and 2.9 mm for
intumescent coated cotton fabric (CF-INT). Thickness of coated cotton fabric samples
(CF-INT-KLN, CF-INT-BNT, CF-INT-NMT & CF-INT-NME) with intumescent
formulation containing nanoclays varies from 2.7 to 2.8 mm. Table 4.4 reveals that on
adding INT, stiffness increases in both warpwise and weftwise directions. But on
adding nanoclays no significant change in warpwise stiffness is observed but
weftwise stiffness is decreased.
Results and Discussion
83
The changes in thickness and stiffness values of coated cotton fabric samples
are observed not too high than pure cotton fabric which indicates that the properties of
cotton fabric are not affected.
Table 4.4 - Stiffness and thickness of pure and coated cotton fabric samples
(Series A1)
Sample Stiffness Thickness
(mm)Warpwise
(cm)
Weftwise
(cm)
CF 3.2 2.6 2.2
CF-INT 6.2 5.9 2.9
CF-INT-KLN 6.2 4.4 2.8
CF-INT-BNT 6.2 4.0 2.7
CF-INT-NMT 6.4 4.9 2.8
CF-INT-NME 6.4 5.0 2.8
Results and Discussion
84
4.2.0 COTTON FABRIC COATED WITH INTUMESCENT FORMULATIONS
CONTAINING NANOCLAY AND ADDITIVES (SERIES A2)
4.2.1 Thermal study in air atmosphere (Series A2)
(A) TG analysis
Thermogravimetric analysis of pure cotton fabric and its coated fabric samples
(CF-INT-ATH, CF-INT-KLN-ATH, CF-INT-ZB, CF-INT-KLN-ZB, CF-INT-ZL &
CF-INT-KLN-ZL) of this series was carried out using NETZSCH STA 449F1 TG
instrument at heating rate 10 oC/min with flow rate of 100 mL/min of air from
ambient temperature to 700 oC. The TG curves of above samples are shown in Figs.
4.6 and 4.7. The thermal degradation data of these samples are given in Table 4.5.
Thermal analysis of pure cotton fabric and intumescent coated cotton fabric
(CF-INT) samples has been discussed earlier in detail in section 4.1.1. TG curve for
CF-INT-ATH sample (prepared by coating cotton fabric with slurry containing
intumescent and aluminium trihydroxide), shows three stages of thermal degradation.
The weight losses for the first two stages (100 - 310 and 310 - 600 oC) are observed
almost same (40 %) with one DTG peak at 293 oC for both stages, which is considered
due to many reactions of coated cotton fabric such as dehydration and
dephosphorylation of cotton cellulose, and oxidation of volatile products and aromatic
charred residues [195]. Simultaneously, the dehydration and decomposition of ATH
occur in this temperature range and form alumina which becomes the part of the
carbonaceous residue and acts as a thermally insulating protective coating. Third stage
of thermal degradation (600 - 700 oC) of CF-INT-ATH gives 8.1 % weight loss,
which may be due to the oxidation of carbonaceous residue formed in previous stage.
The onset temperature of degradation of CF-INT-ATH sample is observed at 279 oC,
which is 10 oC higher as compared to CF-INT, and 34 oC lower as compared to CF.
The temperature at mid-point of decomposition (T50wt%) is 371 oC, which is 14 oC
lower as compared to CF-INT and 40 oC higher as compared to CF. When kaolin
nanoclay is added in formulation for CF-INT-KLN-ATH sample, no significant
difference is observed in weight loss pattern as well as in onset temperature except the
decrease in T50wt% by 16 oC as compared to CF-INT-ATH.
On incorporating zinc borate (ZB) additive in place of ATH for CF-INT-ZB
sample, no significant change is seen in TG curve except slight decrease in DTG
Results and Discussion
85
peak. The onset temperature of degradation of CF-INT-ZB sample is observed at
265 oC, which is 4 oC lower as compared to CF-INT, 14 oC lower than that of
CF-INT-ATH and 48 oC lower than that of pure cotton fabric. The T50wt% for CF-
INT-ZB sample is observed at 397 oC, which is 26 oC higher than that of CF-INT-
ATH, 12 oC higher as compared to CF-INT and 66 oC higher as compared to CF.
When kaolin nanoclay is added in formulation for CF-INT-KLN-ZB sample, the
T50wt% is decreased by 73 oC and a great decrease in char yield (8.4 %) is also
observed as compared to CF-INT-ZB (28.4 %). The addition of zeolite in INT slurry
in place of ATH and ZB did not give encouraging results (Table 4.5) for improvement
in flame retardancy of cotton fabric. The CF-INT-ZL sample shows onset temperature
at 272 oC, which is 41 oC lower than that of CF. When kaolin nanoclay is added to this
sample (CF-INT-KLN-ZL), the char yield is decreased slightly as compared to CF-
INT-ZL.
In this study, addition of ZB increases the thermal stability of coated fabric
and also contributes in increasing the char yield. It has been reported earlier that zinc
borates dehydrate endothermically and released water vapours which dilutes the
gaseous flammable products. Zinc borate can also change the oxidative
decomposition pathway of polymers but the reason for this is not known clearly
whether this is due to an inhibition effect of boron oxide or the oxidation of graphite
structure in the char [199, 200], or is purely due to the formation of a protective
sintered layer on fabric substrate.
Results and Discussion
86
Fig. 4.6 - TG curves of (1) CF, (2) CF-INT, (3) CF-INT-ATH and (4) CF-INT-
KLN-ATH samples in air atmosphere (Series A2).
Fig. 4.7 - TG curves of (5) CF-INT-ZB, (6) CF-INT-KLN-ZB, (7) CF-INT-ZL
and (8) CF-INT-KLN-ZL samples in air atmosphere (Series A2).
Results and Discussion
87
Table 4.5 - TG data of pure and coated cotton fabric samples in air
atmosphere (Series A2)
Sample Stages Temp.range
(oC)
Weightloss
(%)
DTG
(oC)
T10wt%
(oC)
T50wt%
(oC)
Char at600/700 oC
(%)CF* 1st
2nd
100-360
360-510
78.0
20.5
330
470
313 331 0.3/0.3
CF-INT* 1st
2nd
3rd
100-310
310-600
600-700
40.0
32.5
13.3
286 269 385 26.8/13.5
CF-INT-ATH 1st
2nd
3rd
100-310
310-600
600-700
40.0
38.4
8.1
293 279 371 21.1/12.9
CF-INT-KLN-ATH 1st
2nd
3rd
100-310
310-600
600-700
41.5
40.9
7.2
293 274 355 16.6/9.4
CF-INT-ZB 1st
2nd
3rd
100-310
310-600
600-700
38.3
32.6
9.4
286 265 397 28.4/19.0
CF-INT-KLN-ZB 1st
2nd
3rd
100-310
310-600
600-700
46.5
44.5
6.7
288 267 324 8.40/1.7
CF-INT-ZL 1st
2nd
3rd
100-310
310-600
600-700
41.7
37.7
10.8
288 272 353 19.6/8.8
CF-INT-KLN-ZL 1st
2nd
3rd
100-310
310-600
600-700
42.7
40.6
8.15
287 270 349 15.8/7.6
*Same samples from series A1.
Results and Discussion
88
(B) DSC analysis
Differential scanning calorimetric (DSC) analysis of pure cotton fabric and its
coated cotton fabric samples of this series was carried out from ambient temperature
to 700 oC at a heating rate of 10 oC /min in air atmosphere with flow rate of 100
mL/min. DSC curves of pure cotton fabric (CF) and its coated cotton fabric samples
(CF-INT-ATH, CF-INT-KLN-ATH, CF-INT-ZB, CF-INT-KLN-ZB, CF-INT-ZL &
CF-INT-KLN-ZL) are shown in Figs. 4.8 and 4.9. The initiation and maximum
temperatures, and nature of DSC peaks are given in Table 4.6. Differential scanning
calorimetric analysis of pure cotton fabric and intumescent coated cotton fabric (CF-
INT) has already been discussed in section 4.1.1.
DSC curve of CF-INT-ATH (Fig. 4.8) shows the first exotherm with
maximum at 290 oC and second exotherm with maximum at 322 oC and both peaks
are lowered in comparison to respective peaks of pure cotton fabric due to catalyzed
dehydration, phosphorylation and cross-linking processes. The third DSC exotherm of
CF-INT-ATH with maximum at 451 oC is considered to be due to aromatization
reactions of the char residue formed in air atmosphere [196]. The shift of last
exotherm of CF at 472 oC to lower temperature at 451 oC in case of CF-INT-ATH is
an indication of early start of aromatization reactions of char residue. On addition of
kaolin nanoclay in this sample (CF-INT-KLN-ATH), no difference is observed in
DSC curve as compared to CF-INT-ATH.
The intumescent coated samples containing ZB additive show significant
differences in DSC curves in which intensity of second or last exotherm peak is
reduced as well as shifted from 338 oC (CF-INT) to 498 oC temperature, which may
be due to dehydration as well as formation of a protective sintered layer. DSC curve
of CF-INT-ZB shows two exotherms at 281 and 498 oC, which are observed at lower
temperatures in comparison to the respective peaks of pure cotton fabric. On addition
of kaolin nanoclay along with ZB for this sample (CF-INT-KLN-ZB), a significant
difference in thermal behaviour is observed by DSC analysis as compared to other
combinations (Table 4.6). In case of CF-INT-KLN-ZB sample, the last exotherm is
observed at higher temperature (493 oC) in comparison of CF (472 oC), which
indicates synergy of ZB and kaolin, and increase in char formation at the fabric
surface by insulating cotton fabric from fire. The sample containing zeolite (ZL)
shows almost similiar DSC behaviour to samples containing ATH.
Results and Discussion
89
Fig. 4.8 - DSC curves of (1) CF, (2) CF-INT, (3) CF-INT-ATH and (4) CF-INT-
KLN-ATH samples in air atmosphere (Series A2).
Fig. 4.9 - DSC curves of (5) CF-INT-ZB, (6) CF-INT-KLN-ZB, (7) CF-INT-ZL
and (8) CF-INT-KLN-ZL samples in air atmosphere (Series A2).
Results and Discussion
90
Table 4.6 - DSC data of pure and coated cotton fabric samples in air
atmosphere (Series A2)
Sample DSC temperature (oC) Nature of peak
Initiation temp. Maximum temp.
CF* 337
445
350
472
Exo (large & sharp)
Exo (large & sharp)
CF-INT* 274
317
435
298
338
490
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)
CF-INT-ATH 280
305
414
290
322
451
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)
CF-INT-KLN-ATH 280
308
411
295
331
461
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)
CF-INT-ZB 259
403
281
498
Exo (small & sharp)
Exo (small & broad)
CF-INT-KLN-ZB 286
477
303
493
Exo (medium & sharp)
Exo (small & broad)
CF-INT-ZL 280
317
440
291
333
467
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)
CF-INT-KLN-ZL 269
310
407
285
320
469
Exo (small & sharp)
Exo (small & broad)
Exo (small & broad)*Same samples from series A1.
Results and Discussion
91
4.2.2 Flammability study by auto flammability test (Series A2)
The ATLAS 45o Automatic Flammability Tester was used to evaluate
flammability of cotton fabric and its coated cotton fabric samples (CF-INT-ATH, CF-
INT-KLN-ATH, CF-INT-ZB, CF-INT-KLN-ZB, CF-INT-ZL & CF-INT-KLN-ZL).
In this test, the fabric specimen of size 16.5 cm x 5 cm was mounted at an angle of
45° and exposed to a standard butane flame for 12 sec to record burning
characteristics. The images of samples after test are shown in Fig. 4.10 and test results
of these samples are given in Table 4.7.
Pure cotton fabric (CF), fails this test and burned entire fabric after removing
the ignition source. Other coated cotton fabric samples with intumescent containing
additives and nanoclay (CF-INT-ATH, CF-INT-KLN-ATH, CF-INT-ZB, CF-INT-
KLN-ZB, CF-INT-ZL & CF-INT-KLN-ZL) shows no flame spreading with formation
of char spot of char length in a range of 1.8 - 2.2 cm and passed this test. These
results indicate that coated cotton fabric samples with intumescent containing
additives and nanoclay exhibit good flame retardant property. The coated cotton
fabric samples exhibit good flame retardancy because the intumescent flame
retardants get swollen and forms protective char layer on the surface of burning
material to prevent it from heat and fire [98].
Fig. 4.10 - Images of (1) CF, (2) CF-INT-ATH, (3) CF-INT-KLN-ATH, (4) CF-
INT-ZB, (5) CF-INT-KLN-ZB, (6) CF-INT-ZL and (7) CF-INT-KLN-
ZL test samples after auto flammability test (Series A2).
Results and Discussion
92
Table 4.7 - Flammability parameters of pure and coated cotton fabric samples
(Series A2)
Sample Auto flammability test
Flame
spread time
(sec)
Char
length
(cm)
Burning
speed
(m/h)
Pass/Fail
CF* 13 BEL# 41.53 Fail
CF-INT* DNI** 1.8 -- Pass
CF-INT-ATH DNI 2.0 -- Pass
CF-INT-KLN-ATH DNI 1.8 -- Pass
CF-INT-ZB DNI 1.8 -- Pass
CF-INT-KLN-ZB DNI 2.2 -- Pass
CF-INT-ZL DNI 2.2 -- Pass
CF-INT-KLN-ZL DNI 1.9 -- Pass*Same samples from series A1.**DNI-Did Not Ignite, #BEL-Burn Entire Length
4.2.3 Mechanical study (Series A2)
4.2.3.1 Stiffness measurement
The resistance of the fabric to stiffness was measured using Paramount
Stiffness Tester with a test specimen of size 12 cm x 2.5 cm. The test was repeated in
both warpwise and weftwise directions of the fabrics for all the samples. Stiffness
values of pure cotton fabric and its coated cotton fabric samples (CF-INT-ATH, CF-
INT-KLN-ATH, CF-INT-ZB, CF-INT-KLN-ZB, CF-INT-ZL & CF-INT-KLN-ZL)
were measured and are given in Table 4.8.
The stiffness in warp wise direction of pure cotton fabric is 3.2 cm but for
coated cotton fabric samples (CF-INT-ATH, CF-INT-ZB & CF-INT-ZL), the
stiffness is observed in range of 5.7 - 6.2 cm and for samples containing kaolin
nanoclay along with additives (CF-INT-KLN-ATH, CF-INT-KLN-ZB & CF-INT-
KLN-ZL), the stiffness is observed in the range of 4.3 - 4.4 cm. In case of weft wise
direction, stiffness is observed 2.6 cm for pure cotton fabric and it is increased to 5.6 -
6.3 cm for samples containing nanoclay and additives (CF-INT-KLN-ATH, CF-INT-
Results and Discussion
93
KLN-ZB & CF-INT-KLN-ZL) and to 4.3 - 4.4 cm for samples containing additives
(CF-INT-ATH, CF-INT-ZB & CF-INT-ZL). Table 4.8 reveals that on addition of
nanoclay the warpwise stiffness is decreased and in weftwise stiffness is increased.
The addition of kaolin showed reverse effect on stiffness of fabric in warpwise and
weftwise directions.
4.2.3.2 Thickness measurement
The thickness of fabric was carried out on the Prolific Thickness Tester
instrument. The thickness of fabric samples was measured at different places on fabric
surface with thickness gauge and the mean was calculated. Thickness values of pure
cotton fabric and its coated cotton fabric samples (CF-INT-ATH, CF-INT-KLN-ATH,
CF-INT-ZB, CF-INT-KLN-ZB, CF-INT-ZL & CF-INT-KLN-ZL) were measured and
are given in Table 4.8. The observed thickness of pure cotton fabric is 2.2 mm and
thickness of cotton fabric samples coated with intumescent containing additives with
or without nanoclay (CF-INT-ATH, CF-INT-KLN-ATH, CF-INT-ZB, CF-INT-KLN-
ZB, CF-INT-ZL, CF-INT-KLN-ZL) are observed in range of 2.9 - 3.3 mm. The
change observed in thickness and stiffness values after coating is not so high that it
affects the properties of cotton fabric.
Table 4.8 - Stiffness and thickness of pure and coated cotton fabric samples
(Series A2)
Sample Stiffness Thickness(mm)Warpwise
(cm)Weftwise
(cm)CF* 3.2 2.6 2.2
CF-INT* 6.2 5.9 2.9
CF-INT-ATH 6.0 4.2 3.0
CF-INT-KLN-ATH 4.4 5.6 2.9
CF-INT-ZB 5.7 4.9 2.9
CF-INT-KLN-ZB 4.3 6.3 2.9
CF-INT-ZL 6.2 4.8 3.3
CF-INT-KLN-ZL 4.3 5.6 3.0* Same samples from series A1.
Results and Discussion
94
4.3.0 COTTON FABRIC COATED WITH INTUMESCENT FORMULATIONS
CONTAINING NANOCLAY, POLYMERS AND ADDITIVES (SERIES A3)
4.3.1 Thermal study in air and inert atmospheres (Series A3)
(A) TG analysis in air atmosphere
Thermogravimetric analysis of pure cotton fabric and its coated fabric samples
of this series containing nanoclay, additives and polymers (CF-INT-PVC, CF-INT-
KLN-PVC, CF-INT-PVA, CF-INT-KLN-PVA, CF-INT-PTFE, CF-INT-KLN-PTFE,
CF-INT-KLN-PVC-ATH & CF-INT-KLN-PVC-ZB) was carried out at heating rate
10 oC/min in air atmosphere with flow rate of 100 mL/min from ambient temperature
to 700 oC using NETZSCH STA 449F1 TG instrument. The TG curves of pure cotton
fabric and its coated fabric samples with slurry containing PVC, KLN, ATH and ZB
are shown in Fig. 4.11 and TG curves of cotton fabric samples coated with PVA,
PTFE and KLN are shown in Fig. 4.12. The various parameters such as T10wt%, T50wt%
and char yield at 600 oC of samples were evaluated to compare their thermal
behaviour and are given in Table 4.9. All samples of cotton fabric shows a weight loss
of about 2 % due to absorbed moisture upto 100 oC.
Thermal analysis of pure cotton fabric (CF) and intumescent coated cotton
fabric (CF-INT) has already been discussed in section 4.1.1. The CF-INT-PVC
sample containing PVC along with intumescent shows three stages of thermal
degradation in TG curve (Fig. 4.11). The first stage of degradation occurs in
temperature range of 100 - 320 oC with a weight loss of 44.4 % due to dehydration
and decomposition of coated cotton. The second stage of degradation occurs in
temperature range of 320 - 600 oC with a weight loss of 31.8 % due to oxidation of
volatile products. The third stage of degradation occurs in temperature range of 600 -
700 oC with a weight loss of 16.6 % due to oxidation of aromatic char residues. The
temperature at midpoint of decomposition (T50wt%) for CF-INT-PVC sample is
observed significantly lower by 28 oC in comparison of CF-INT, which may be due to
catalyzation by HCl released from PVC [201], and the generation of char is also
reduced.
On addition of KLN nanoclay alongwith PVC for CF-INT-KLN-PVC sample,
the thermal stability is increased as seen by increase in DTG peak by 11 oC. The CF-
INT-KLN-PVC sample is observed more thermal stable than CF-INT-PVC and also
Results and Discussion
95
gives more char yield at 700 oC. This effect is seen more prominent in presence of
KLN nanoclay at higher temperature in third stage of thermal degradation.
The destabilization of CF-INT-KLN-PVC-ZB and CF-INT-KLN-PVC-ATH
samples due to presence of ZB and ATH is seen clearly in their thermograms after
500 oC, i.e. by the end of second stage (Fig. 4.11). But these samples containing ZB
and ATH shows 5 % less weight loss in the third stage of thermal degradation in
temperature range 600 - 700 oC in comparison to that of CF-INT-KLN-PVC. The
reason for these facts may be due to formation of stable oxides of Zn and Al metals
along with carbonaceous residue at higher temperature stage which protects the
underlying polymer substrate.
On incorporating any polymer (PVC/PVA/PTFE) into intumescent system
separately, no major change in the thermal behaviour especially in first stage of
degradation is observed. The T50wt% temperature and DTG peak are reduced in all
samples containing additives (polymer, ZB and ATH) due to catalytic action of the
clay/additives and released acid from polymers. The amount of char residues left at
600 oC is also found decreased as compared to CF-INT sample, which may be due to
catalytic effects of clay on degradation process of polymer due to their large surface
area.
The incorporation of PVA instead of PVC for CF-INT-PVA sample gives
slightly higher thermal stability as well as higher char yield (Table 4.9), which may be
explained due to higher crosslinking effects of PVA having hydroxyl functional
group. On adding KLN to this sample, no further improvement in thermal properties
is observed.
On incorporation of PTFE polymer with or without nanoclay, TG curves
shows no improvement in thermal properties except increase in onset temperature of
degradation (Table 4.9), which may be due to less compatibility of PTFE for
formation of slurry and lack of uniform coating on the fabric.
Results and Discussion
96
Fig. 4.11 - TG curves of (1) CF, (2) CF-INT, (3) CF-INT-PVC, (4) CF-INT-KLN-
PVC, (5) CF-INT-KLN-PVC-ZB and (6) CF-INT-KLN-PVC-ATH
samples in air atmosphere (Series A3).
Fig.4.12 - TG curves of (7) CF-INT-PVA, (8) CF-INT-KLN-PVA, (9) CF-INT-PTFE
and (10) CF-INT-KLN-PTFE samples in air atmosphere (Series A3).
Results and Discussion
97
Table 4.9 - TG data of pure and coated cotton fabric samples in air
atmosphere (Series A3)
Sample Stages Temp.range(oC)
Weightloss(%)
DTG(oC)
T10wt%(oC)
T50wt%(oC)
Char at600 /700 oC
(%)CF* 1st
2nd
100-360
360-510
78.0
20.5
330
470
313 331 0.35/0.3
CF-INT* 1st
2nd
3rd
100-310
310-600
600-700
40.0
32.5
13.3
286 269 385 26.8/13.5
CF-INT-PVC 1st
2nd
3rd
100-320
320-600
600-700
44.4
31.8
16.6
284 263 357 23.0/6.4
CF-INT-KLN-PVC 1st
2nd
3rd
100-320
320-600
600-700
43.4
34.9
12.0
295 265 361 21.3/9.3
CF-INT-KLN-PVC-ZB 1st
2nd
3rd
100-320
320-600
600-700
45.0
39.2
7.3
290 263 341 15.1/7.8
CF-INT-KLN-PVC-ATH 1st
2nd
3rd
100-320
320-600
600-700
43.4
40.8
6.0
295 272 354 14.8/8.7
CF-INT-PVA 1st
2nd
3rd
100-330
330-590
590-700
44.3
29.8
15.8
290 266 370 24.3/9.3
CF-INT-KLN-PVA 1st
2nd
3rd
100-340
340-590
590-700
46.5
31.2
13.2
291 268 360 20.8/8.4
CF-INT-PTFE 1st
2nd
3rd
100-340
340-600
600-700
49.9
34.5
13.3
288 275 335 14.7/1.4
CF-INT-KLN-PTFE 1st
2nd
3rd
100-340
340-600
600-700
49.3
35.6
8.74
286 274 340 14.3/5.6
*Same samples from series A1.
Results and Discussion
98
(B) DSC analysis in inert atmosphere
DSC analysis of pure cotton fabric (CF) and its coated fabric samples of this
series containing nanoclay, additives and polymers (CF-INT-PVC, CF-INT-KLN-
PVC, CF-INT-PVA, CF-INT-KLN-PVA, CF-INT-PTFE, CF-INT-KLN-PTFE, CF-
INT-KLN-PVC-ATH & CF-INT-KLN-PVC-ZB) was carried out using a TA
instruments DSC Q-10 differential scanning calorimeter thermal analyzer from 40 to
550 oC temperature at a heating rate of 10 oC/min under constant nitrogen flow (50
mL/min). About 4 - 8 mg of samples were weighed in the aluminum pan and placed in
the DSC cell. DSC thermograms of samples are shown in Figs. 4.13 - 4.16. The initiation
and maximum temperatures along with heat flow and nature of DSC peaks were
measured and are given in Table 4.10. All the samples show an endothermic peak below
90 oC due to presence of moisture and this peak is not given in the Table 4.10.
DSC curve of cotton fabric (CF) in inert atmosphere shows a major
endothermic peak with maximum at 361 oC due to dehydration, depolymeization and
pyrolysis reactions with the formation of leavoglucosan, a major volatile product
[191, 195]. A broad exotherm with maximum at 450 oC is also observed which may
be ascribed to random chain scission, crosslinking and aromatization of char [202, 203].
DSC curve of CF-INT (Fig. 4.13) shows an endotherm with maximum at
272 oC due to the decomposition of APP releasing phosphoric acid,
phosphorylation and acid catalyzed dehydration of cotton fabric by acid and cross-
linking of APP [204]. The evolution of ammonia gas on decomposition of melamine
is also started in this temperature range of DSC peak. The next exotherm with
maximum at 290 oC may be attributed to charring process of cotton and endotherm at
303 oC due to decomposition of cotton fabric alongwith vaporization of volatiles
formed as well as continuous release of ammonia from melamine. The large
endotherm of CF is shifted from 361 oC to lower temperature at 303 oC in case of CF-
INT, which is an indication of blocking of OH group at C6 of cellulose (responsible
for formation of leavoglucosan) by phosphorylation and then subsequent
dephosphorylation of cellulose phosphate. Phosphoric acid obtained from
decomposition of APP and from dephosphorylation of cellulose phosphate catalyzes
the dehydration of cellulose moiety leading to the formation of carbonaceous char.
Results and Discussion
99
The CF-INT sample gives exotherm with maximum at 418 oC, which may be due to
deoxygenation and aromatization reactions of the char formed.
DSC curve of CF-INT-PVC (Fig. 4.13) shows almost similar pattern to that of
CF-INT sample. The small endotherm with maximum at 175 oC may be due to
melting of PVC and fusion of pentaerythritol. The CF-INT-PVC sample shows DSC
endotherm with maximum at 278 oC (due to dehydrochlorination of PVC [201],
decomposition of APP, phosphorylation and acid catalyzed dehydration of cotton
fabric, cross-linking of APP and release of ammonia on decomposition of melamine),
exotherm at 290 oC (due to charring of cotton), endotherm at 295 oC (due to
decomposition of cotton fabric and PVC alongwith vaporization of volatiles formed
as well as continuous release of ammonia from melamine).
On addition of clay to CF-INT-PVC, the exotherm peak at 290 oC for CF-INT-
KLN-PVC sample split into two exotherms with low intensity and also shifted to
higher temperatures at 295 and 312 oC indicating protection of cotton fabric substrate
from decomposition. This fact is also supported by shift of next endotherm from 303
to 328 oC (Fig. 4.14). On addition of ZB to CF-INT-KLN-PVC, no significant change
is seen except shifting of endotherm from 272 to 282 oC indicating some delay in
chemical action of intumescent.
In case of CF-INT-PVA sample, dual endotherms at 255 and 271 oC are
observed at lower temperature with reduced intensity in comparison to CF-INT. The
exotherm at 310 oC and endotherm at 332 oC are observed at higher temperature. On
addition of KLN to CF-INT-PVA, the exotherm at 310 oC due to charring is not
observed which may be due to overlapping with two intensive endotherms at 278 and
303 oC (Fig. 4.15). No significant difference in DSC curve of CF-INT-PTFE sample,
is seen in comparison to CF-INT. On adding KLN in CF-INT-PTFE, the endotherm at
285 oC and exotherm at 296 oC are split into dual endo and dual exo with reduced
intensities (Fig. 4.16) due to barrier effect of clay.
Results and Discussion
100
Fig. 4.13 - DSC curves of (1) CF, (2) CF-INT and (3) CF-INT-PVC samples in
inert atmosphere (Series A3).
Fig. 4.14 - DSC curves of (4) CF-INT-KLN-PVC and (5) CF-INT-KLN-PVC-ZB
samples in inert atmosphere (Series A3).
Results and Discussion
101
Fig. 4.15 - DSC curves of (6) CF-INT-PVA and (7) CF-INT-KLN-PVA samples
in inert atmosphere (Series A3).
Fig. 4.16 - DSC curves of (8) CF-INT-PTFE and (9) CF-INT-KLN-PTFE
samples in inert atmosphere (Series A3).
Results and Discussion
102
Table 4.10 - DSC data of pure and coated cotton fabric samples in inert
atmosphere (Series A3)
Sample DSC peak temp. (oC ) Heat flow(J/g)
Nature ofpeakInitiation Maximum
CF 308404
361450
84.8--
EndoExo
CF-INT 244281289378
272290303418
31.18.96.6
29.0
EndoExoEndoExo
CF-INT-PVC 169255279290
175278290295
--35.822.643.6
EndoEndoExoEndo
CF-INT-KLN-PVC 182238286296310385
187273295312328405
0.734.1
--7.6
10.64.4
EndoEndoExoExoEndoExo
CF-INT-KLN-PVC-ZB 169228294309318382
176282297315327418
0.9611.54.27.8
14.6
EndoEndoExoExoEndoExo
CF-INT-PVA 184245294319384
187255, 271
310332412
0.8--
11.513.612.1
EndoEndoExoEndoExo
CF-INT-KLN-PVA 184262292397
188278303418
0.626.229.4
--
EndoEndoEndoExo
CF-INT-PTFE 185270282297393
188285296300420
0.419.413.233.214.0
EndoEndoExoEndoExo
CF-INT-KLN-PTFE 193231294315384456
200239, 279297, 314
328400465
------
16.53.52.8
EndoEndoExoEndoExoExo
Results and Discussion
103
4.3.2 Kinetic study
The thermal degradation kinetic parameters were determined for five samples
(CF, CF-INT, CF-INT-KLN, CF-INT-ZB and CF-INT-PVC) by applying two
methods (Broido and Horowitz-Metzger) on TG data. The first stage of thermal
degradation was the main degradation stage in CF sample and for CF-INT, CF-INT-
KLN, CF-INT-ZB and CF-INT-PVC samples there were two main stages of thermal
degradation. Therefore, kinetic parameters were obtained for these two stages. The
values of activation energy (E), pre-exponential factor (A) and correlation coefficient
(R2) were calculated for the conversion in the range of α = 0.02 to 0.4 for first stage
and 0.4 to 0.9 for second stage at constant single heating rate of 10 oC/min. The plots
of ln[-ln(1-α)] versus 1000/T in case of Broido method and ln[-ln(1-α)] versus θ in
case of Horowitz-Metzger method for first and second stages of degradation of the
samples are shown in Figs. 4.17 - 4.24, respectively. Tables 4.11 - 4.12 represent the
kinetic parameters of samples obtained by Broido and Horowitz-Metzger methods.
By applying Broido method [177], the activation energy of value 169.1 kJ/mol
for major stage of degradation (first stage) of CF is calculated. The activation energy
in case of CF-INT (81.3 kJ/mol) becomes half than that of pure cotton fabric (CF).
The decrease in activation energy support catalyzation of the degradation reactions
such as dehydration and cross-linking reactions i.e. charring of the cellulose by APP
(a component intumescent). On adding kaolin clay in the intumescent formulation for
sample CF-INT-KLN, the activation energy (93.7 kJ/mol) is slightly increased in
comparison to CF-INT (81.3 kJ/mol) due to the slightly decrease in amount of
intumescent or may be because of protecting tendency of clay from degradation of
cotton substrate. No catalyzing effect of kaolin clay in presence of intumescent
formulation is seen in kinetic study. The addition of zinc borate in intumescent
formulation for CF-INT-ZB sample shows more decrease in activation energy (73.1
kJ/mol) as compared to CF-INT (81.3 kJ/mol), which may be due to catalyzation by
ZB in presence of intumescent due to charring reaction in cellulose. No effect is
observed on the rate of degradation reaction on addition of PVC in intumescent
formulation for sample CF-INT-PVC as indicated by its activation energy of value
83.6 kJ/mol, which is almost same as that of CF-INT (81.3 kJ/mol).
By applying Horowitz-Metzger method, the values of activation energy of CF,
CF-INT, CF-INT-KLN, CF-INT-ZB and CF-INT-PVC samples for first stage of
Results and Discussion
104
degradation are 179.8, 91.1, 94.3, 64.9 and 101.8 kJ/mol, respectively (Table 4.12).
The values of activation energy obtained by Horowitz-Metzger method are almost
similar as obtained by Broido method and the pattern of variation of activation energy
is also similar as that seen in Broido method.
The activation energy of second stage of degradation is also obtained by
applying both the methods (Table 4.11 and 4.12). Second stage activation energy is
observed less than that of first stage of thermal degradation for all samples. The
values of frequency factors of second stage of thermal degradation are very less in
comparison to that of first stage which may be explained due to the presence of cross
linked structure of cellulose at higher temperature stage. No catalyzing effect of
additives (KLN, ZB & PVC) on the rate of degradation is seen in second stage of
degradation. The activation energy is slightly increased on addition of kaolin clay in
intumescent system indicating protection of degradation of underlying cotton
substrate at higher temperature stage by formation of compact carbonaceous char
layer on cotton surface which is favourable at second stage for flame retardancy.
There may be competition between catalytic effect and protecting effect of
clay on degradation of cotton fabric. In second stage the protecting effect of clay in
presence of high char may be more compensated than the catalytic effect of clay on
degradation.
Results and Discussion
105
Fig. 4.17 - Plot of ln[-ln(1-α)] versus 1000/T using Broido method for first stage
of (1) CF and (2) CF-INT samples in air atmosphere.
Fig. 4.18 - Plot of ln[-ln(1-α)] versus 1000/T using Broido method for first stage
of (3) CF-INT-KLN, (4) CF-INT-ZB and (5) CF-INT-PVC samples in
air atmosphere.
Results and Discussion
106
Fig. 4.19 - Plot of ln[-ln(1-α)] versus 1000/T using Broido method for second
stage of (1) CF and (2) CF-INT samples in air atmosphere.
Fig. 4.20 - Plot of ln[-ln(1-α)] versus 1000/T using Broido method for second
stage of (3) CF-INT-KLN, (4) CF-INT-ZB and (5) CF-INT-PVC
samples in air atmosphere.
Results and Discussion
107
Fig. 4.21 - Plot of ln[-ln(1-α)] versus θ using Horowitz-Metzger method for first
stage of (1) CF and (2) CF-INT samples in air atmosphere.
Fig. 4.22 - Plot of ln[-ln(1-α)] versus θ using Horowitz-Metzger method for first
stage of (3) CF-INT-KLN, (4) CF-INT-ZB and (5) CF-INT-PVC
samples in air atmosphere.
Results and Discussion
108
Fig. 4.23 - Plot of ln[-ln(1-α)] versus θ using Horowitz-Metzger method for
second stage of (1) CF and (2) CF-INT samples in air atmosphere.
Fig. 4.24 - Plot of ln[-ln(1-α)] versus θ using Horowitz-Metzger method for
second stage of (3) CF-INT-KLN, (4) CF-INT-ZB and (5) CF-INT-
PVC samples in air atmosphere.
Results and Discussion
109
Table 4.11 - Kinetic parameters of pure and coated cotton fabric samples by
Broido method in air atmosphere
Table 4.12 - Kinetic parameters of pure and coated cotton fabric samples by
Horowitz-Metzger method in air atmosphere
Sample Broido method
Stage 1 Stage 2
E
(kJ/mol)
R2 A
(min-1)
E
(kJ/mol)
R2 A
(min-1)
CF 169.1 0.9457 1.1x1014 39.7 0.9056 191.2
CF-INT 81.3 0.9628 3.1x106 19.5 0.7877 1.0
CF-INT-KLN 93.7 0.9529 4.6x107 21.7 0.8699 1.9
CF-INT-ZB 73.1 0.9677 5.4x105 19.5 0.8509 1.1
CF-INT-PVC 83.6 0.9776 5.4x106 19.1 0.7478 0.9
Sample Horowitz-Metzger method
Stage 1 Stage 2
E
(kJ/mol)
R2 E
(kJ/mol)
R2
CF 179.8 0.9541 42.8 0.9310
CF-INT 91.1 0.9771 14.6 0.9983
CF-INT-KLN 94.3 0.9875 19.1 0.9978
CF-INT-ZB 64.9 0.9834 16.4 0.9984
CF-INT-PVC 101.8 0.9678 14.5 0.9981
Results and Discussion
110
4.3.3 FTIR analysis of char residues of samples
The Fourier transform infrared spectra of unheated and char residues of five
fabric samples (CF, CF-INT, CF-INT-KLN, CF-INT-ZB & CF-INT-PVC) were
obtained using Shimadzu IR affinity-I 8000 FTIR spectrophotometer in range 4000 to
400 cm-1 for 15 scans with a resolution of 4 cm-1 to study the changes taking place in
structure on heating. The residue of fabric samples were mixed with KBr and then
their FTIR spectra was taken. The residues were obtained by heating fabric samples in
furnace for 10 min at different temperatures (200, 250, 300, 350 oC) separately. Since
no difference in IR spectra of samples was observed after heating up to 200 oC,
therefore, spectra of samples obtained at 200 oC and higher temperatures are given in
this study.
The infrared spectra of residues of CF and CF-INT are shown in Figs. 4.25
and 4.26, respectively. The spectrum of cotton fabric sample obtained at 200 oC
consists of following characteristic bands: 3417 cm1 (O−H str.), 2893 cm1 (C−H str.),
1641 cm1 (absorbed water), 1444 cm1 (CH2 symmetrical bending), 1325 cm1 (C−H and
O−H bending), 1087 cm1 (antisym. C−O−C str.) and 1024 cm1 (C−O str.). These
bands show the characteristic bands of cellulose [205, 206].
At 250 oC, the band at 3417 cm1 (O−H str.) becomes very wide due to
elimination of OH group. The band at 2893 cm1 (C−H str.) remains as it at 250 oC
temperature. The band observed at 1641 cm1 due to absorbed water is also present at
250 oC with increased intensity, which may be due to presence of moisture as well as
C=C bonds formed due to dehydration. The intensity of bands at 1435 and 1342 cm1
is decreased and a broad spectrum is obtained. The spectrum of the sample remained
same on further heating at 300 oC except that a new band at 1702 cm1 (C=O) started
arising due to formation of carbonyl functionalities [204] in the cellulose moiety.
At 350 oC, the bands at 3417 cm1 (O−H str.) and 2893 cm1 (C−H str.) are
almost diminished. The band at 1641 cm1 is shifted to 1633 cm1 with less intensity
due to some skeletal rearrangement. The band at 1710 cm1 becomes very intense at
350 oC due to C=O bonds formation. A new small band at 1560 cm1 is appeared due
to conjugation (C=C or C=C=C). All bands in range 1000-1200 cm1 seen at 250 and
300 oC are merged into a new band at 1235 cm1 (C−O−C str.) due to cross-linking
Results and Discussion
111
where about 25 % solid residue remained (Fig. 4.1) from cotton cellulose. These
changes indicated the decomposition of cellulosic structure of cotton fabric at 350 oC.
The IR spectrum of intumescent coated cotton fabric sample (CF-INT) at 200 oC
(Fig. 4.26) gives additional bands at 1261 cm1 (P=O str.), 1105 cm1 (P−O−C str. and
skeletal vibrations involving C−O str.) and 895 cm1 (P−O−P str.) [207], which are
the characteristic bands of intumescent containing phosphorus compound. A band at
3282 cm1 shows the presence of N−H stretching of melamine alongwith the bands of
O−H stretching of cellulose and band at 1697 cm1 supported the presence of C=N
and NH2 group of melamine.
At 250 oC, a band at 1651 cm1 becomes more intense due to carbonizing effect.
The bands at 1230 and 1072 cm1 become less intense and merge into one intense band at
1110 cm1 at 250 oC may be due to P−O−C stretching in phosphorylated cotton cellulose.
The phosphorylation of cotton cellulose takes place due to release of phosphoric acid
from ammonium polyphosphate.
At 300 oC, a new intense band is appeared at 1703 cm1 due to C=O bonds
formation. The intensity of characteristic bands of glucosidic structure (1600 - 1100 cm1)
is decreased and merged into one intense band at 1070 cm1 at 300 oC. These
observations shows that dehydration and dephosphorylation reactions takes place at
this stage of degradation and also degradation of fabric started at early temperature
due to interaction of cellulose with intumescent components.
At 350 oC, bands at 3417 cm1 (O−H str.) and 2893 cm1 (C−H str.) are
disappeared. The bands at 1703 (due to C=O bonds formation), 1640 (P−O−H) and
1555 cm1 (C=C) are remained present at 350 oC. The bands at 1207 (P=O and
C−O−C) and 1000 cm1 (P−O−P) are appeared due to formation of pentaerythritol
diphosphate [208] and polyphosphate compounds on chemical interactions among
PER, APP and cellulose. The FTIR spectra of other coated samples (CF-INT-KLN,
CF-INT-ZB & CF-INT-PVC) containing kaolin, zinc borate and poly (vinyl chloride)
do not show any significant change in comparison to CF-INT.
Results and Discussion
112
Fig. 4.25 - FTIR spectra of CF residues obtained at different temperatures.
Results and Discussion
113
Fig. 4.26 - FTIR spectra of CF-INT residues obtained at different temperatures.
Results and Discussion
114
4.3.4 Flammability study by auto flammability test (Series A3)
The ATLAS 45o Automatic Flammability Tester (Model M233G AFC 45o
flammability chamber) was used to evaluate flammability of coated cotton samples (CF-
INT-PVC, CF-INT-KLN-PVC, CF-INT-KLN-PVC-ZB, CF-INT-KLN-PVC-ATH, CF-
INT-PVA, CF-INT-KLN-PVA, CF-INT-PTFE & CF-INT-KLN-PTFE). The specimens of
size 16.5 cm x 5 cm were exposed to a butane flame for 12 sec to cause ignition.
Images of coated fabric samples after flammability test are shown in Fig. 4.27 and the
flammability parameters are given in Table 4.13.
Fig. 4.27- Images of (1) CF, (2) CF-INT, (3) CF-INT-PVC, (4) CF-INT-KLN-
PVC, (5) CF-INT-KLN-PVC-ZB, (6) CF-INT-KLN-PVC-ATH, (7)
CF-INT-PVA, (8) CF-INT-KLN-PVA, (9) CF-INT-PTFE and (10) CF-
INT-KLN-PTFE test samples after flammability test (Series A3).
Results and Discussion
115
On addition of polymers and other additives along with intumescent
formulation for CF-INT, CF-INT-PVC, CF-INT-KLN-PVC, CF-INT-KLN-PVC-ZB,
CF-INT-KLN-PVC-ATH, CF-INT-PVA, CF-INT-KLN-PVA, CF-INT-PTFE & CF-
INT-KLN-PTFE samples, these samples did not ignite and char length remained the
same in the range of 1.7 - 2.2 cm. All the coated fabric samples of this series pass this
flammability test.
Table 4.13 - Flammability parameters of pure and coated cotton fabric samples
(Series A3)
Sample Auto flammability test
Flame
spread time
(sec)
Char
length
(cm)
Burning
speed
(m/h)
Pass/Fail
CF* 13 15 (BEL)# 41.53 Fail
CF-INT* DNI** 1.8 -- Pass
CF-INT-PVC DNI 1.7 -- Pass
CF-INT-KLN-PVC DNI 1.9 -- Pass
CF-INT-KLN-PVC-ZB DNI 1.9 -- Pass
CF-INT-KLN-PVC-ATH DNI 1.8 -- Pass
CF-INT-PVA DNI 2.2 -- Pass
CF-INT-KLN-PVA DNI 2.1 -- Pass
CF-INT-PTFE DNI 2.0 -- Pass
CF-INT-KLN-PTFE DNI 2.1 -- Pass*Same samples from series A1.**DNI-Did Not Ignite, #BEL-Burn Entire Length
Results and Discussion
116
4.3.5 Mechanical study (Series A3)
4.3.5.1 Stiffness measurement
The resistance of the fabric to stiffness was measured using Paramount
Stiffness Tester (BS 3356:1961) with a test specimen of size 12 cm x 2.5 cm in both
warp and weft directions of the fabrics. Stiffness of pure cotton fabric and its coated
cotton fabric samples (CF-INT, CF-INT-PVC, CF-INT-KLN-PVC, CF-INT-KLN-
PVC-ZB, CF-INT-KLN-PVC-ATH, CF-INT-PVA, CF-INT-KLN-PVA, CF-INT-
PTFE & CF-INT-KLN-PTFE) was measured and given in Table 4.14.
The stiffness observed for CF and CF-INT is 3.2 and 6.2 cm, respectively in
warp wise direction as mentioned earlier in section 4.1.3.1. The stiffness is increased
slightly for all coated cotton samples containing polymers and supporting additives in
range 6.3 - 6.8 cm. In case of weft wise direction, the observed stiffness for CF and
CF-INT is 2.6 and 5.9 cm, respectively. On addition of polymers and other additives
along with intumescent (CF-INT, CF-INT-PVC, CF-INT-KLN-PVC, CF-INT-KLN-
PVC-ZB, CF-INT-KLN-PVC-ATH, CF-INT-PVA, CF-INT-KLN-PVA, CF-INT-
PTFE & CF-INT-KLN-PTFE), the stiffness of fabric coated samples is observed in a
range 4.8 - 5.5 cm.
4.3.5.2 Thickness measurement
The thickness of pure cotton fabric and its coated cotton fabric samples was
measured using a thickness gauge under the name Prolific Thickness Tester (BS
2544:154). The thickness values of pure cotton fabric and its coated cotton fabric
samples (CF-INT, CF-INT-PVC, CF-INT-KLN-PVC, CF-INT-KLN-PVC-ZB, CF-
INT-KLN-PVC-ATH, CF-INT-PVA, CF-INT-KLN-PVA, CF-INT-PTFE & CF-INT-
KLN-PTFE) are given in Table 4.14.
The observed values of thickness of CF and CF-INT are 2.2 and 2.9 mm as
reported earlier in section 4.1.3.2. The thickness of all other coated cotton fabric
samples containing kaolin nanoclay, polymers and supporting additives is increased
and varied in range 2.9 to 3.4 mm. Table 4.14 reveals that the thickness of fabric
samples containing kaolin nanoclay is increased slightly as compared to samples
without containing kaolin nanoclay. The stiffness and thickness values of coated
fabric samples indicate that bending rigidity and hand properties are not change
significantly for the end use.
Results and Discussion
117
Table 4.14 - Stiffness and thickness of pure and coated cotton fabric samples
(Series A3)
Sample Stiffness Thickness
(mm)Warpwise
(cm)
Weftwise
(cm)
CF* 3.2 2.6 2.2
CF-INT* 6.2 5.9 2.9
CF-INT-PVC 6.8 4.9 3.3
CF-INT-KLN-PVC 6.3 4.8 3.4
CF-INT-KLN-PVC-ZB 6.8 5.5 2.9
CF-INT-KLN-PVC-ATH 6.4 4.6 3.2
CF-INT-PVA 6.4 5.2 3.1
CF-INT-KLN-PVA -- -- 3.3
CF-INT-PTFE -- -- 2.8
CF-INT-KLN-PTFE -- -- 2.9*Same samples from series A1.
Results and Discussion
118
4.4.0 COTTON FABRIC TREATED WITH PHOSPHORUS BASED MONOMER
BY ADMICELLAR POLYMERIZATION METHOD (SERIES B)
The samples of this series prepared by admicellar polymerization are mainly
of two types: untreated and treated cotton fabric samples in absence of binding agent
and treated cotton fabric samples containing binding agent. For three fabric samples
(untreated cotton fabric (UCF), treated cotton fabric without binding agent (TCF) and
treated cotton fabric without binding agent after first home laundering (TCF-1)), the
FTIR, SEM, elemental analysis, thermal analysis (TG & DTA) and flammability
studies were carried out. For the four samples containing binding agent (treated cotton
fabric containing binding agent (TCF-BA), treated cotton fabric containing binding
agent after first home laundering (TCF-BA-1), treated cotton fabric containing
binding agent after second home laundering (TCF-BA-2) and treated cotton fabric
containing binding agent after third home laundering (TCF-BA-3)), the durability and
flammability studies were carried out.
4.4.1 FTIR analysis (Series B)
FTIR spectra of untreated cotton fabric (UCF), treated cotton fabric (TCF)
and treated cotton fabric after first home laundering (TCF-1) were recorded using
Shimadzu IR affinity-I 8000 FTIR spectrophotometer in the wavenumber range from
4000 to 400 cm-1 for 15 scans with a resolution of 4 cm-1. The polymer film formed
on cotton fabric was analyzed by FTIR spectra. FTIR spectra of untreated cotton
fabric (UCF), treated cotton fabric (TCF) and treated cotton fabric after first home
laundering (TCF-1) are shown in Fig. 4.28.
The spectrum of untreated cotton fabric consists of following bands: 3427 cm1
(O−H stretching), 2912 cm1 (C−H stretching), 1631 cm1 (C=C and C=O stretching),
1425 cm1 (CH2 symmetrical bending), 1323 cm1 (C−H and O−H bending), 1151 cm1
(antisymmetrical C−O−C stretching), 1035 cm1 (C−O stretching) and 893 cm1 (C=O
stretching). These bands are characteristics bands of cellulose [205, 206] as shown in
Fig. 4.28.
The IR spectrum of treated cotton fabric (TCF) is observed to be quite similar
to that of untreated cotton fabric (UCF) except some extra P−O bands of phosphorus
compounds. These bands confirm interaction between cotton fabric and a phosphorus
species due to formation of bands at 1157 cm1 (P−O−C stretching and skeletal
Results and Discussion
119
vibrations involving C−O stretching), 1078 cm1 (P−O−C stretching). In treated
cotton fabric (TCF), highly intense bands at 1242 (P=O stretching) and 896 cm1
(P−O stretching) are observed, which are the characteristic bands of phosphonates,
representing a phosphorus based layer formed on cotton fabric [209-211].
In case of treated cotton fabric after first home laundering (TCF-1), bands at
902 (P−O stretching) and 1241 cm1 (P=O stretching) remain with the bands of cotton
cellulose. The bands observed at 1147 cm1 (P−O−C stretching and skeletal vibrations
involving C−O stretching), and 1078 cm1 (P−O−C stretching) are not seen indicating
removal of some phosphorus content from cotton fabric corresponding to the lack of
durability of flame retardant finish on cotton fabric. These results confirm the
presence of phosphorus layer on treated cotton fabric when compared with untreated
cotton fabric.
Fig. 4.28 - FTIR spectra of (1) UCF, (2) TCF and (3) TCF-1 samples (Series B).
Results and Discussion
120
4.4.2 Elemental and SEM analyses (Series B)
The surfaces of untreated cotton fabric (UCF), treated cotton fabric (TCF) and
treated cotton fabric after first home laundering (TCF-1) were examined by SEM
using a JEOL JSM 880. Samples for SEM were sputter coated with a thin layer of
gold. The morphology of untreated cotton, treated cotton and treated cotton after first
home laundering was examined by using SEM at magnification of 5 µm and 2 µm as
shown in Figs. 4.29 and 4.30.
The elemental analysis of samples was carried out at beam energy of 5 keV
using a ZEISS 960A SEM equipped with Oxford Link energy dispersive spectroscopy
(EDS) with a thin window and using IXRF EDS 2008 software. Elemental analysis
was carried out to know the amount of phosphorus content on the samples. The list of
content of phosphorus along with other elements for untreated cotton, treated cotton
and treated cotton after first home laundering is given in Table 4.15.
Fibres in untreated cotton fabric (UCF) are smooth and do not show any
polymer aggregates and striations are visible. By comparison, fibres from treated
cotton fabric (TCF) are rough and show a bumpy appearance, similar to other coatings
[196] indicating formation of a layer of phosphorus polymer on the fabrics. The
roughness of treated cotton fabric is higher than untreated cotton fabric. The surface
of treated cotton fabric after first home laundering (TCF-1) is smooth compared to
treated cotton fabric. Treated cotton after first home laundering shows regular surface
morphology as untreated cotton but not as smooth as untreated cotton.
Untreated cotton fabric has zero percentage of phosphorus content compared
to treated cotton fabric (2.28 %) and treated cotton fabic after first home laundering
(1.74 %). The decrease in phosphorus content for treated cotton fabric after first home
laundering can be explained by washout of unreacted monomer or oligomers on the
surface. The percentage of calcium and magnesium is increased for treated cotton
fabric after first home laundering resulting from exchange of ammonium ions during
washing.
Together FTIR, SEM micrographs and elemental analysis indicate that a thin
layer of phosphorus polymer is formed on cotton surface using admicellar
polymerization. The mechanism of formation of a phosphorus polymer is given in
Scheme 4.4.
Results and Discussion
121
Fig. 4.29 - SEM images of (1) UCF, (2) TCF and (3) TCF-1 samples at 5 µm
magnification (Series B).
Results and Discussion
122
Fig. 4.30 - SEM images of (1) UCF, (2) TCF and (3) TCF-1 samples at 2 µm
magnification (Series B).
Results and Discussion
123
NC NN CN
NN
CN2
AIBN
Free radical generation
H
HZ
CNCN
Z H
HZ
CN
Z
Z
ROPO
O
ORZ =
R = H or
PHEME
O
OCH3
CH2
O
O
HO NH
O
NC
Z Z
O
NH
OH
Initiation and propagation of polymer formation
NC
Z
Z
ONH
OH
NC
Z
Z
ONH
OH
NC
Z
Z
ONH
OH
NC
Z
Z
ONH
OH
Disproportionation
Chain termination
Scheme 4.4 – Polymerization of phosphorus based monomer.
Results and Discussion
124
Table 4.15 - Elemental analysis of untreated and treated cotton fabric, and
treated cotton fabric after first home laundering (Series B)
Element Sample
UCF TCF TCF-1
Carbon (%) 38.71 39.46 38.68
Oxygen (%) 60.93 57.80 58.22
Sodium (%) 00.15 00.16 00.06
Phosphorus (%) 00.00 02.28 01.74
Calcium (%) 00.20 00.28 00.81
Magnesium (%) 00.00 00.00 00.47
4.4.3 Thermal study in air atmosphere (Series B)
(A) TG and DTA analysis
The differential thermal analysis (DTA) and thermogravimetry analysis (TG)
of untreated cotton (UCF), treated cotton fabric (TCF) and treated cotton after home
launderings (TCF-1) were performed using a NETZSCH STA 449F1 TG instrument.
The DTA and TG studies were carried out with 10 mg samples in alumina crucibles
under static air from ambient temperature to 700 oC at a heating rate of 10 oC/min.
TG studies give information on the thermal stability and the decomposition product
of materials. The important parameters that were obtained from TG include T10 wt%,
T50 wt% and char yield. The TG and DTG thermograms of untreated cotton, treated
cotton fabric and treated cotton after first home laundering samples are shown in
Figs. 4.31 and 4.32. The thermal parameters used for comparing thermal stability are
given in Table 4.16. The DTA thermograms of cotton fabric samples are shown in
Fig. 4.33 and major DTA peaks are given in Table 4.17.
TG curve of untreated cotton fabric (UCF) shows that it degrades completely
with no significant char yield at 600 oC and shows two stages of thermal degradation.
The first stage (100 - 350 oC) of degradation occurred due to oxidative thermal
degradation of cotton [190] where large amount of flammable volatile components are
formed with a weight loss of 76 %. This stage is also supported by first DTA
Results and Discussion
125
exotherm with a maximum at 330 oC. The second stage (350 - 700 oC) of thermal
degradation may be due to oxidation of carbonaceous residue [192] formed during
first stage of thermal degradation with a weight loss of 24 %, which corresponds to
second DTA exotherm with a maximum at 455 oC.
TG curve of treated cotton fabric (TCF) shows three stages of thermal
degradation. The first stage (100 - 285 oC) of degradation of treated cotton is occurred
due to catalyzed dehydration with 45 % weight loss and supported by first DTA
exotherms with a maximum at 265 oC. The second stage (285 - 540 oC) of thermal
degradation with weight loss of 41 % indicates phosphorylation and dephosphorylation of
cotton which exhibit typical condensed phase flame retardant activity due to presence
of phosphorus [212] and it corresponds to second DTA exotherm with a maximum at
325 oC. The third stage (540 - 700 oC) of degradation of treated cotton is occurred due
to oxidation of char residues. For treated cotton, the onset temperature (T10wt%) is
lower about 70 oC and gives a higher char yield (9.0 %) as compared to UCF. This is
due to decomposition of phosphorus polymer before the substrate to interfere with its
burning process.
The degradation behaviour of treated cotton after first home laundering (TCF)
is almost same as that of untreated cotton. The first stage of degradation of treated
cotton after first home laundering is supported by first DTA exotherm with a
maximum at 335 oC. The second stage of thermal degradation gives rise to second
DTA exotherm with a maximum at 460 oC (Fig. 4.33). The decomposition
temperature of TCF-1 is higher than that of TCF and nearly same as that of UCF
which indicates decrease in the flame retardancy of washed cotton fabric. The char
yield for treated cotton fabric after wash is 10 % at 600 oC, which is slightly more
than treated cotton may be due to presence of salts in detergent used for laundering.
Results and Discussion
126
Fig. 4.31 - TG curves of (1) UCF, (2) TCF and (3) TCF-1 samples in air
atmosphere (Series B).
Fig. 4.32 - DTG curves of (1) UCF, (2) TCF and (3) TCF-1 samples in air
atmosphere (Series B).
Results and Discussion
127
Fig. 4.33 - DTA curves of (1) UCF, (2) TCF and (3) TCF-1 samples in air
atmosphere (Series B).
Table 4.16 - TG data of untreated and treated cotton fabric, and treated cotton
fabric after first home laundering in air atmosphere (Series B)
Sample Stages Temp.range
(oC)
Weightloss
(%)
DTG(oC)
T10wt%
(oC)
T50wt%
(oC)
Char at600 oC
(%)
UCF 1st
2nd
100-350
350-700
76
24
310
445
298 316 0.0
TCF 1st
2nd
3rd
100-285
285-540
540-700
45
41
9
250
475
610
230 308 9.0
TCF-1 1st
2nd
100-370
370-700
57
32
308
475
290 320 10.0
Results and Discussion
128
Table 4.17 - DTA data of untreated and treated cotton fabric, and treated cotton
fabric after first home laundering in air atmosphere (Series B)
Sample DTA peak temp. (oC) Nature of peak
Initiation
temp.
Maximum
temp.
UCF 312
392
330
455
Exo (large & sharp)
Exo (large)
TCF --
270
402
265
325
480
Exo (very small)
Exo (broad)
Exo ( broad)
TCF-1 292
425
335
460
Exo (medium & sharp)
Exo (broad & small)
4.4.4 Flammability study by auto flammability test (Series B)
The burning behaviour of untreated cotton fabric (UCF), treated cotton fabric
(TCF) and treated cotton fabric after 1st home laundering (TCF-1) was studied using
the ATLAS 45o Automatic Flammability Tester. The burning behaviour of untreated
cotton fabric, treated cotton fabric and treated cotton fabric after first home laundering
samples at the ignition time of 12 sec is compared in Fig. 4.34 and flammability
parameters are given in Table 4.18.
For untreated cotton fabric (UCF) sample, after removing the ignition source,
flame spreads easily within 41 sec and burned entire fabric length to ashes. The
untreated cotton fabric sample shows both surface flash as well as base burn thus
failing the 45o flammability test with ‘Class 3’ flammability. For treated cotton fabric
(TCF) sample, only a spot of char with char length 1.0 cm was formed on the fabric in
burnt area, after removing the ignition source with no flame spreading may be due to
the catalytic effects in the crosslinking and dehydration reactions [81, 213]. For
treated cotton fabric after first home laundering (TCF-1) sample, the fabric burnt with
entire length but with formation of char. There is no ash formation as in case of UCF
sample. This shows that phosphorus is there after washing which helps in char
formation. The treated cotton fabric only had surface flash without base burn, thus
Results and Discussion
129
achieving ‘Class 1’ flammability and passed this test. The decreased char length,
flame spread time and change from ‘Class 3’ to ‘Class 1’ of treated cotton fabric
indicated a great improvement in the flame retardancy. This can be explained by two
factors: first is the presence of protecting layer [206] of char formation on the surface
of treated cotton fabric during the combustion process which acts as barrier for
underlying cotton from the flame and delay the degradation, and second is the
reduced amount of flammable volatiles. The ultrathin film coating of a phosphorus-
containing flame retardant on the cotton fabric surface indicates that admicellar
polymerization of monomer (phosphoric acid 2-hydroxy ethyl methacrylate ester)
successfully imparts flame retardancy.
Fig. 4.34 - Images of (1) UCF, (2) TCF and (3) TCF-1 after flame test (Series B).
Table 4.18 - Flammability parameters of untreated and treated cotton fabric,
and treated cotton fabric after first home laundering (Series B)
Flammability
parameters
Sample
UCF TCF TCF-1
Flame spread time (sec) 41 DNI** 29
Char length (cm) BEL# 1.0 BEL**DNI-Did Not Ignite, #BEL- Burnt Entire Length
Results and Discussion
130
4.4.5 Durability of treated cotton fabric (Series B)
The presence of phosphorus polymer layer deposition on the treated cotton
fabric is the most effective parameter in char formation and decreasing the
flammability of the treated fabrics. But in absence of the binding agent, the coating is
not stable to washing and subsequent flame retardancy is poor (Fig. 4.34). To
improve durability the addition of the binding agent is necessary. Therefore, by taking
different monomer and binding agent concentrations, a suitable and best condition
was find out for durable flame retardant treatment.
(A) Effect of monomer concentration on flammability
The monomer concentration was increased from 20 to 100 mM but the
concentrations of surfactant (0.45 mM), initiator (0.01 mM) and binding agent
(3.6 mM/g) were kept constant. The effect of different monomer concentrations on
the flammability of cotton fabric was studied. With increase of monomer
concentration the amount of phosphorus content on cotton fabric is increased. Table
4.19 shows the flame spread time and char length on cotton fabric with different
monomer concentrations. Table 4.19 reveals that minimum monomer concentration
required for a flame retardant is 60 mM. Similarly, with increase in phosphorus
monomer concentration, flame retardant property of fabric was also increased [209]. The
monomer concentration of 100 mM is good enough for the durable flame retardant
cotton fabric.
(B) Effect of binding agent concentration on flammability
The effect of different concentrations (ranged from 1.2 to 7.2 mM/g) of
binding agent with the constant concentrations of surfactant (0.45 mM), initiator (0.01
mM) and Monomer (100 mM) on flame retardancy of cotton fabric was studied.
Lower levels of binding agent failed to provide any durability to cotton fabric as the
fabric burnt completely after one wash (Table 4.20). The concentrations at the upper
end of the range examined yield durable flame retardancy, but the fabric is stiff by
hand feel as compared to lower concentrations of binding agent. The intermediate
amounts (3.2 and 3.6 mM/g) of binding agent are found to be effective for imparting
flame retardancy as the treated fabric is durable for two washes (Fig. 4.35) and fabric
is not stiff after treatment. The best results obtained by varying the monomer and
binding agent concentrations are shown in Fig. 4.35 and flammability parameters are
given in Table 4.21.
Results and Discussion
131
Table 4.19 - Effect of monomer concentration on flame retardancy of treated
cotton fabric (Series B)
Monomerconc.(mM)
TCF-BA TCF-BA-1 TCF-BA-2 TCF-BA-3Charlength(cm)
Flamespread
time(sec)
Charlength(cm)
Flamespread
time(sec)
Charlength(cm)
Flamespread
time(sec)
Charlength(cm)
Flamespread
time(sec)
20 BEL# 47 NT** NT NT NT NT NT
50 BEL 48 NT NT NT NT NT NT
60 2.0 DNI* BEL 72 NT NT NT NT
70 1.0 DNI BEL 48 NT NT NT NT
80 1.8 DNI BEL 64 NT NT NT NT
90 1.0 DNI 2.0 DNI BEL 49 NT NT
100 1.0 DNI 1.2 DNI 1.2 DNI BEL 23*DNI-Did Not Ignite, #BEL-Burn Entire Length, **NT- Not Tested
Table 4.20 - Effect of binding agent concentration on flame retardancy of
treated cotton fabric (Series B)
Bindingagentconc.(mM/g)
TCF-BA TCF-BA-1 TCF-BA-2 TCF-BA-3
Charlength(cm)
Flamespread
time(sec)
Charlength(cm)
Flamespread
time(sec)
Charlength(cm)
Flamespread
time(sec)
Charlength(cm)
Flamespread
time(sec)
1.2 2.0 DNI* BEL# 23 NT** NT NT NT
2.4 1.8 DNI BEL 60 NT NT NT NT
2.8 1.5 DNI 10.0 DNI BEL 42 NT NT
3.2 1.2 DNI 3.0 DNI 1.0 DNI BEL 41
3.6 1.0 DNI 1.2 DNI 1.5 DNI BEL 56
5.0 1.0 DNI 1.0 DNI 1.2 DNI BEL 23
7.2 1.0 DNI 1.5 DNI 1.9 DNI 2.2 NT*DNI-Did Not Ignite, #BEL-Burn Entire Length, **NT- Not Tested
Results and Discussion
132
Fig. 4.35 - Images of (1) TCF-BA-1, (2) TCF-BA-2 and (3) TCF-BA-3 test
samples after flammability test (Series B).
Table 4.21 - Flammability parameters of untreated and treated cotton fabric,
and treated cotton fabric after first, second and third home
laundering (Series B)
Flammability
parametersUCF TCF-BA TCF-BA-1 TCF-BA-2 TCF-BA-3
Flame spread Time
(sec)41 DNI** DNI DNI 23
Char length
(cm)BEL# 1.0 1.2 1.2 BEL
**DNI-Did Not Ignite, #BEL- Burnt Entire Length
Results and Discussion
133
The effects of the presence of binding agent and monomer versus char length
on treatment to cotton fabric are shown in Fig. 4.36. The binding agent concentration
was optimized based on the durability and char length of fabric. If the char length of
treated fabric decreases, the performance of fabric increases as phosphorus polymer
linkage to cotton fabric is strongly adhered. As the concentration of monomer is
increased, the char length of cotton fabric decreased indicating formation of polymer
layer on cotton surface. The fabric burnt to its entire length in 60 sec for binding agent
concentration below 60 mM. At higher monomer concentrations around 90 and 100
mM, the char length is 1.0 cm. The char length of treated cotton fabric increased with
home launderings. It seems odd that flame retardancy is decreased even though the
mass of polymer remains largely unchanged. We suggest reduced performance may
result from substitution of calcium and magnesium for ammonium ions which have
the potential to yield acidic moieties on thermal degradation that can act as catalysts.
Fig. 4.36 - Effect of concentration of monomer and binding agent vs char length
of treated cotton fabric (Series B).
Results and Discussion
134
4.4.6 Gravimetric analysis
Gravimertic analysis was carried out by weighing the cotton fabric samples
before treatment, after treatment and after home launderings. The weight gain for
fabric before and after treatment shows how much polymer is formed on the fabric.
Table 4.22 lists the amount of weight gained after treatment.
Table 4.22 - Gravimetric analysis of untreated and treated cotton fabric, and
treated cotton fabric after home launderings (Series B)
Sample UCF TCF-BA TCF-BA-1 TCF-BA-2
Weight measurement (g) 2.74 4.19 3.99 3.86
The weight gained by fabric after treatment is about 1.45 g indicating
formation of polymer on the surface of cotton fabric. After first and second home
launderings, fabric weight decreased to 3.86 g which indicates that home laundering
does not remove the coating completely from fabric surface. Therefore, the
percentage retention of the phosphorus monomer on the cotton fabric indicates that
the polymer bound to cotton surface is durable till two home launderings.