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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


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.


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).


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


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.


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


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].


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).


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.


78

Table 4.2 - DSC data of pure and coated cotton fabric samples in air


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)


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


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.


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


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.


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


84


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


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.


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).


87



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.


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.


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).


90

Table 4.6 - DSC data of pure and coated cotton fabric samples in air


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.


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).


92


(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




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-


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.


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.


(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.


94


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


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.


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).


97



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.


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.


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.


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).


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).


102

Table 4.10 - DSC data of pure and coated cotton fabric samples in inert


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


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


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.


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.


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.


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.


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.


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


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


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.


112

Fig. 4.25 - FTIR spectra of CF residues obtained at different temperatures.


113

Fig. 4.26 - FTIR spectra of CF-INT residues obtained at different temperatures.


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).


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.


(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


116




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.


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.


117


(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.


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


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).


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.


121

Fig. 4.29 - SEM images of (1) UCF, (2) TCF and (3) TCF-1 samples at 5 µm

magnification (Series B).


122

Fig. 4.30 - SEM images of (1) UCF, (2) TCF and (3) TCF-1 samples at 2 µm

magnification (Series B).


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.


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


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.


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



127

Fig. 4.33 - DTA curves of (1) UCF, (2) TCF and (3) TCF-1 samples in air


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


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


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


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.


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


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


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).


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.

chapter 4shodhganga.inflibnet.ac.in/bitstream/10603/48036/10/10... · 2018-07-03 · chapter – 4...

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