Indian Journal of Fibre & Textil e Research Vol. 24, September 1999, pp. 197-207

Studies on combined fl ame-retardant and water-repellent treatments on cotton drill fabric

R Ind u Shekar, Ashok Yadav, Nishkam Kasturiya & Hans Raj

Textiles Division, Defence Materials and Stores Research & Development Establi shmen t, Kanpur 2m~ 0 1:1, India

Receil'ed 1 Decemher 1997; revised received alld accepted 4 Feh/"l{ory 1999

Bleached cotton drill fab ric was treated wit h phosphoms-based flame retardant foll owed by water and oil repe ll ents t(l achieve fl ame-retardant, water-repell ent and oil -repellent propert ies for critical appli cations such as nucl ear hiological chemi ca l protective suit s. The resul ts indi cate that by an effecti ve combination of above fini shin g agent s. sati sfa ctory performance could be achieved , although it is very diffi cult to understand the nature of reaction that takes place hetween a phosphorus-based fl ame retardant and the fluorocarbon-based water repell anl. The treated fabrics were evalu ated for flammabi lity, water repell ency and oi l repell ency. The effect of different add -on levels on important ph ys ical propcrt ies 1I',IS

also studi ed. The flame-ret ard ant hehaviour was persued through thermal studies. The flame- retardant and wate r-repcllent treated fabric wi th a total add-on level of 17.7% gave satisfactory results in terms of functio nal and phys ica l prope rt ies.

Keywords: Char length , Cotton fahric, Flame retarclant, Fluorocarbon, Oi l repell ent , Water repell en t

1 Introduction

The complex ity of renderi ng the li ght weight fab ri cs fl ame retardant by chemica l appli cation or by dope treatment fo r apparel, industrial, military and crit ical areas like nuclear biological chemical (NBC) protecti ve suits has generated a lot of interest among the va ri ous resea rch organizations th roughout the world. The flammab ility behaviour of tex ti les is influenced by a number of fac tors such as weight/uni t area, cloth cover, thickness, surface properties and finishing effects such as napped or lofty constructi ons 1.2.

Generall y, the heavy and tightl y woven fab ric constructions are less fl ammable than the I ight or open weave constructions although the above conclusions for both natural and syntheti c fabrics are not acceptable worldwide. This stems from the fac t that the above generali sations are based on onl y a very limited number of studies as scanty literature is ava il able on the effect of fabric structure on fini shing treatments such as fl ame retardancy, water repellency, etc and it does not carry the detai Is of fabric compos ition and geometry. Moreover, the high claims made by different organi za tions lack one or the other bas ic requirements, namely (i) carcinogenic and mutagenic nature of flame-retardant chemicals, (ii) very high add-on requirements to accompli sh functional properties which impair the physical and

comfort properties, (iii ) poor iaunderabili ty. and (iv) lack of sophis ticated instrument s whi ch measure fl ammabil ity to simulate the practi cal conditi ons.

In the recent pas t, due to th e significant advancement in the field of cOl1.bat tec hn ology, the present day soldier is exposed to very se ri oLls haza rds of atomic, thermonuclear fragmenta ti on, hiologica l and chemica l warfare as well as those of mu lti sensor system of reconnaissance, in te lli gence and surveill ance. The augmented prerequisites of its des igning have naturall y ex panded the prospec ts of research in military c lothing. However, each of these des igning prerequisites is contrary to one or the other and thi s makes the task of fabric engineer a complex one. Take the instance of achi ev ing water-repell ent nylon fabric for apparel purpose which almost requires jammed constructi on (max imum weavable) for optimum level of repell ency and at the same time has a air permeability of 30 cc/cm2/s, or a light-weigh l fl ame-retardant cotton fab ri c wherein it is nearl y impossible to get sati sfac tory fl ame-reta rdant properties along with the sa ti sfactory comfort properties like stiffness, wick ing, air permeability, etc.

This paper reports the results of ex peri mental investigations desi gned to study and develop oute r cotton fabric for NBC protecti ve clothing, wherein the

198 INDIA N 1. FIBRE TEXT. RES., SEPTEMBER 1999

fabri c is required to exhibit flame-retardant, water­repellent and oil-repellent properties alongwith sati sfactory physical properties. The implication of water-repellent treatment on FR properties is also briefly discussed.

2 Materials and Methods 2.1 Materials

Bleached cotton drill fabric having the following specifications was used :

weight , 195 g/m2 ; ends/cm, 28 ; picks/cm, 28 ; cloth cover, 25.8 ; porosity, 70% ; breaking strength (warp), 98 kg ; and breaking strength (weft ), 48 kg.

Glogard-DNP (solid contents 35 %), a fibre reactive organic phosphorus compound with metallic oxide, was used as a fl ame-retardant alongwith melamine res in from L&N Chemicals. FC-270, a f1u orochemical emulsion (solid contents 17%) from 3M Birla, was used as water and oil repe llent.

2.2 Methods

2.2.1 Fabric Preparation

The fabri c was initially scoured so as to remove the res idual fini shing agents before padding. It was then conditioned at 65 % R H for 2 h before fl ame-retardant treatment.

2.2.2 Flame-Retardant Treatment

Conditioned fabr ic samples were padded with an aqueous solution of a mi xture of Glogard-DNP and melamine resin by 2 dips and 2 nips through squeeze rollers and the wet pick up was maintained at 70-75 % (pneumatic pressure of 3.5 kg/cm2 on rollers). The padded samples were dried at 80-100°C and cured at 150-155°C for 3-3 .5 min . After curing, the samples were washed with 2 gpl Sandozin non-ionic detergent liquid and 2 gpl soda ash for 5 min and then washed with water and dried . The add-on obtained was calculated based on the intial weight of the fabric.

The FR pad bath concentration was varied from 30% to 50% to get the add-on levels of 12-20%. Melamine res in concentration was 10% of the FR concentration . The pH in different treatments was as foll ows: pH of two-step treatment , FR bath, 5-6 pH of single-bath (step) treatment, 5-6 pH of FC bath, 4.5-5 .5

Samples SI, S2 and S, were treated with FR and FC in two-step process, whereas the sample SB4 was subjected to single-step process wherein FR and FC were combined in the same bath .

In the second step, the FR-treated fa bric was impregnated with FC-270 by 2 dips and 2 nips and the conditions employed were identical to that of fl ame­retardant treatment, except that curing temperature was maintained at 170-175°C.

In an analogous treatment , the fabri c was subj ected to single bath treatment in which FR and FC were combined . In all the experiments, FC concentrati on was kept constant at 45 gpl.

2.2.3 Tests

Breaking strength , spray rating, stiffness and wing tear (s ingle rip) tests were perfo rmed accordin g to IS : 1969, IS : 390, BS : 3356 and BS : 4303 respec ti ve ly.

2.2.3.1 Measurement of Contact Angle

The contact angle was measured using the contact angle meter (model II) of Kerneco In struments Inc, Germany, as fo llows:

The specimen is set on the curette and a droplet is settled by usin g a microburette. The shadow of each drop is seen as arc of the c ircle in the fi e ld of goniometer. The contact angle is measured directl y by adjusting the movable scale to the target at the point of contact. The contact angle is the angle between the tangent line at the contact point and the hori zonta l line of the solid surface. In thi s case of adhesion wett ing, the contact angle (8) was measured us ing the protractor scale of the meter.

2.2.3.2 Oil Repellency Test

A test spec imen (2 .5 cm wide and 25 cm long) with the major axis parallel to the machine directi on was placed over a Whatman filt er paper No. I covering a 3.8 cm diam. cylindrical mandral and a load of 50± I g was attached to each end of the spec imen. A drop (4±1 mg) of diethylphthalate coloured with Cl disperse red II was all owed to fall through 5 mm on the upper surface of the specimen. At the end of 6 h, the specimen was carefull y removed and the filt er paper examined for penetrati on of the dyed liquid. The sample was considered to pass the test when minimum 7 out of 10 spec imens showed no penetration .

2.2.3.3 Determination of Phosphorus and Nitrogen Contents

The phosphorus content was dete rmined by gravimetric method based on prec ipitati on of ammonium phosphomolybdate and the nit rogen content by the Kjeldahl method .

INDU SHEKAR et al. : COlTON DRILL FABRIC 199

2.4 Thermal Behaviour Studies

The thermal studies were carried out on Dupont thermal system as detailed be low :

DSC: Dupont 2100 ; Rate, lOoC/min ; Flow, 20 ml/min ; and Atmosphere, nitrogen.

TGA: Dupont 2100 ; Rate, 50°C /min ; Flow, 60 ml/mjn ; and Atmosphere, nitrogen.

2.5 Surface Studies

The surfaces of the treated fibre and yam were studied with the help of scanning e lectron microscope SEM: Jeol 35 CF with Pol aron DC sputtering unit.

3 Results and Discussion

3.1 FR Properties

The results obtained on cotton drill fabric treated with Glogard-DNP for fl ame retardancy and with fluorocarbon (FC-270) for water and oi l repellency by single process and two-bath process using pad-dry­cure technique are shown in Table I . A comparison of the results of samples treated in two-bath process suggests that at comparable add-on levels, the sample S2FR with add-on of 16.7% shows the minimum char length of 7 .8 cm and 7.6 cm when both warp and weft are compared. Although a clear trend is seen for the char length in warp direction , the resu lts in weft direction are not clear. All the samples treated for flame retardancy and those treated for both flame

retardancy and water repellency (FR+FC) did not show after flame and after glow, suggest ing that an add-on level of 12% is sufficient enough to gi ve a char length of about 8-9 cm on medium weight fabrics. The difference is noticed basica ll y in terms of yield in char length . The char length va lues observed for sample S2FR at 1.2% phosphorus content and 3.4% nitrogen content are much less compared to those for sample S3FR ( 19.6% add-on) at somewhat higher phosphorus content ( 1.4%) and 3.2% nitrogen content. Thi s shows that phosphorus compounds, which contribute to fl ame retardancy, do not necessaril y show a linear relati onship with the amount of phosphorus added to the cotton fabri c with its char length . It is clear that the degree of flame retardancy is related to the amount of char and hence the general conception that to increase the degree of flame retardancy, the amount of fl ame retardant needed in the fabric to produce a given increment of flame retardancy is not va li d. Tesor023 reported that the amount of phosphorus compou nd needed to contribute a certai n degree of flame retardancy can be greatly reduced by incorporati on of compound s containing chlorine, bromine and nitrogen. Bajaj 12 reported the efficiency of phos phorus-based compounds in enhanc ing the flame-retardant properties by incorporating N-meth ylo l cross linki ng agents through N-P synergism. The data reveal the synergistic effect of nitrogen as we ll as flu orocarbon

Table 1- Results of fl ame-retardant . water-repellent and oi l-repellent treated fabrics

Substrate Add-on N P P Char Contact Water Oil

% % on in length angle repellency repellency

fabric Char cm deg rating rating

% % Warp Weft

SIFR 11.4 2.3 1.0 0.84 8.8 8.5 0 50 Fai ls

SIFR+FC 12.2 10.0 9.4 95 90 10/1 0

S2FR 16.7 3.4 1.2 0.80 7.8 7.6 0 50 Fail s

S2FR+FC 17.7 7.5 6.9 100 90 10/ 10

S3FR 19.6 3.2 1.4 0.90 8.3 7.9 0 50 Fai ls

S3FR+FC 20.4 8.5 8. 1 100 90 10/ 10

SB4FR+FC 16.4 2.2 0.8 0.70 7.5 8.8 98 50 10/ 10

SIFR. S2FR & S3FR: Samples treated wi th fl ame retardant

SIFR+FC, S2FR+FC & S3FR+FC : Samples treated with fl ame retardant + water repellent (FC)

SB4FR+FC: Sample treated with fl ame retardant and water repellent in single bath N- Nitrogen ; and P---Phosphorus

200 INDIAN 1. FIBRE TEXT. RES., SEPTEMBER 1999

(FC-270) in enhanc ing the flame-retardant properti es imparted to cotton fabric by Glogard-DNP and suggests that somewhat higher nitrogen content is requ ired to reach a char length in the range of 7 .5-S .3 cm in the case of two-step treatment.

It is a lso inte resting to note that the water-repe llent treatment given after the FR treatment has not affec ted the FR propert ies s igni f ican tly, except in sampl es SIFR+FC (12.2 % add-on) and S lFR+FC (20 .4 % add-on). Thi s is because of the non­compatabi lity of flame-re tardant G logard-DNP and FC, and treati ng the FR-trea ted fabri c w ith a wafer­re pe llent compound whic h can a lso contribute to FR properti es in antagon istic effect4

. This is reflected in the results of samples S IFR+FC and S.1 FR+FC but not in sample S2FR+FC ( 17.7% add-on), indicat in g th at the re may be an optimum comb in ati o n of FR and FC at which the mutua l influence of FR and FC is limited .

The effic iency o f FR+FC as a flame-re tardant and wate r-repe ll ent sys tem was examined by a single-bath treatment apart from a two-step sequenti a l treatment (Tab le I) . A comparison of the results o f single-bath process [SB4FR+FC (add-on , 16.4%) and S2FR+FC (add-on, 17 .7%)] shows (he same char length o f 7.5 cm in warp direction, bu t conside rabl y hi gh c har length in we ft direc ti on . However, dur ing testing, it was observed that burning behav iour was e rratic and did not show consistent results. This may be at tributed to the heterogeneous mi xture of padding so lution comprising aqueous-based FR-res in and emul sion­based Fe. The irregul ar burning of the fabric (SB.jFR+FC) observed during testing is attributed to the phys ical presence of FC on the surface, which is expected to retard the catalytic acti on of FR on the cellu los ic fabric . Kuryla and Papa) have expressed the complexity of the situation when the flame retardants used are stab le up to the poi nt of polymer degradation. In the present work also, FC has a hi gher decomposition temperature than the cellulose, making the reaction very compl ex to understand . A comparison of results obtained in the si ngle-step and two-step applications suggests that at comparable nitrogen content , a somewhat lower phosphorus content is required to achieve the char length of 7 .5 cm (warp), as observed when samples SIFR and SB4FR+FC are compared . Thi s may be attributed to the high degree of phosphorylation which occurs at high curing temperature after FR treatment , as the curing temperature was 170- 175°C in single-bath process compared to ISO-155°C in two-step process.

However, the situati on is less well-de fined whe n the samples are compared in the weft directi on to come to a logical conclusion.

3.2 Water Repellency and Oil RepcllcIll:Y

The use of fluorochemi ca ls to ,tite r the surface properties of text iles so as to achi eve low surrace energies is we ll known. On suc h su rfaces. liq uids w ith re lat ive ly low surface tensi o ns are he ld :I S drops with characte ri sti c con tact ang les('. The non-uniform surfaces of the textil es necess itate the need to consider both advancing and receding contac t ang les . However, in the capill ary sys te ms o f tex ti les. it is the ad vanc ing contact ang le on the fibres that cont ro ls spread ing and wickin£. In the present inves tiga tion. a ll the samp les treated with f1uorocarho n emu ls ion measured contac t ang les in the range o r 95- 100", wit h sample S2 measuring the hi ghest contac t ang le. Thi s is expected because the concentrati on or flu o rocarbon emul sion was kept constant (45 gpl ) in all the treatments . It is a lso obse rved that all the samples treated in two-step process passed the spray rating (rat ing 90). It is a lso interesting to note t il at out o f all the samples treated w ith flame-re tarda nt and wate r­repellent agents, onl y s in gle-bat h treated samp le SB~

fa iled in the water repe llency tes t. Even though no penetration of wate r th rough the ~, amp l e was observed, a distinct surface wetting was observed. The spray rating test be ing bas ica ll y a measure o f surface wett ing rathe r than a measure o r resista nce to penetration, the penetrati on aspect was not taken into considerati on . This resulted in the rating o f SO, whi ch is far from the satisfactory le ve l. Eve n th ough the contact angle of 9So was observed in s in gle-step applicat ion , whic h is more than 95" o bserved in sampl e S I, the spray rating observed in s ing le-bat h treated sample was 50, g ivi ng ampl e indicati on o f the non-uniform di stributi on of fluorocarbo n eillu is ion when combined w ith flame re tardant. This is expec ted because the extent of surface 'ove rage o f flu orocarbon emul s ion decides the values or co ntact ang le . In the spray rating test , the area o f the fabric subjected to water is very hi gh compa red to the area subjected in the contac t angle. Surprising ly, the flame retardant treated samples w ith a ratin g of SO in spray rating test measured 0° contact angle. T he repe lle ncy effect observed in the FR-treated samp le,' may be due to the presence of me lamine res in , hi gh c lo th cover and the high swellability of cotton ya rn s. The me lamine res in used along with FR a lso contributes for wate r repe llency and our conclusion is based on the views expressed by SunshineR

•

INDU SHEKAR el al. : COlTON DRILL FABRIC 20 1

The contact angle observations seem to correlate closely with oil-repellency ratings than the spray ratings, as all the samples treated with fluorocarbon emulsion by two-step and single-step processes passed the oil-repellency test with contact angles ranging in between 95-100°. The earlier work by Grajeck and Peterson'! shows the dependence of oil repellency of fabrics on the amount of flu orocarbon applied to the fabric

Table I also shows that all the samples (SIFR+FC, S2FR+FC, S,FR+FC and SB4FR+FC) after FC treatment passed the oil -repell ency test, irrespecti ve of the FR add-on . This is likely because the oi l repellency is basicall y influenced by the perfluoroalkyl group with optimal chain length ( I O-C) under controlled conditions at which water and oil repellency is achieved7

.,o

. In the present work , it was observed that even after 48 h under a tension of 50 g, the sample did not show any penetrati on even though

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the standard time was 6 h onl y. Thi s gives an indication of the superior oil-repell ent effect offered by fluorochemical s which is not ;1chieved by conventional water-repellent agents such as waxes, silicones, etc.

3.3 Differential Scanning Calorimetry

The DSC curves for the FR and FR+FC treated samples are shown in Fig. I and the peak temperatures of endotherms and exotherms of these fabrics are given in Table 2.

The DSC thermogram of sample SlFR (Fig. I a) shows a single endotherm. The endotherm begins at 105°C and has a shallow peak at 152" C and finally finishes at 200"C, followed by a large exot herm wi th it

well-defined peak at 304()C. The DSC curve of sample S3FR (Fig. Ic) shows a simil ar endotherm as that of S2FR at 150°C and a large exotherm 'vvhi ch reaches a max imum at 322°C. The end otherm ;1 ncl exotherm

2

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-1 14HO·C

-I -2L-~~ __ ~ ____ L-__ ~ __ ~

o 100 200 300 400 500 0 100 200 300 400 500 Tpmperature ,oe

Fi g. I-DSC thcnTIograms of FR and FR+FC treated co tton fabri c with differcnt add-on levcb: (a) S2FR, 16.7 %; (b) S2FR+FC, 17.7 %; (c) S, FR, 19.6 %; and (d) S ,FR+FC, 20.4 %

Table 2-DSC data of treated fabri cs

Substrate Endothcrmic temp .. °C Heat fl ow Exothermi c temp .. °C

Tj Tpk Tr JIg Tj Tpk T,

S2FR 105 152 200 73 255 304 40X

S2FR+FC Peak I 68 133 200 100 250 3 18 336

Peak 2 357 399 431 32

S.lFR 100 ISO 200 116 267 322 339

S.lFR+FC 80 141 200 112 277 323 339

T-- Initi ation ;Tpk--Peak : and T,-Final

I-Ieat fl ow

JIg

X6

9X

IJS

123

202 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1999

correspond to the flame retardant-melamine reSIn combination and substrate respectively. The thermograms in Fig. I a & I c also show that the endothermic peak in both the samples is unchanged, irrespective of the add-on levels. The DSC curves of S2FR and S,FR show that the endothermic pyrolysis reaction of the cellulose occurs at progressively lower temperature as the amount of FR (add-on level) increases, although the temperature difference is very marginal, indicating an optimum level of phosphorus and nitrogen contents at which the yield of char is maximum. This is supported by the char lengths, the sample S2FR showing a lower char length as compared to S,FR.

The DSC thermograms also give an indication of the total heat evolved (assuming that all the flammabl e gases are burnt) during exothermic decomposition. It may be seen from the results that in the case of sample S2FR (16.7 % add-on), the heat evolved is less (86 J/g) than that in case of sample SJFR ( 135 J/g) . The quantity of heat released by a FR­treated fabric has a linear relationship with the burning of a fabric, since the net effect of a FR is reflected in the reduction of heat produced by the burning fabric. The lower temperature at which the pyrolysis decomposition of cellulose fabric occurred after FR treatment gi ves sufficient information to elucidate that the flame-retardant Glogard-DNP works by condensed phase mechanism. However, it is difficult to come to such a conclusion based on DSC results alone. A systematic and more detaiied study is necessary to support the validity of the above conclusion.

Samples S2FR+FC and S,FR+FC show that the endotherm peak temperature is shifted further to a lower temperature. The exothermic peak temperature shows an increase in case of sample S2FR+FC, whereas the sample S,FR+FC shows no change after FC treatment.

It is well established in the literatures. I I that the FR compounds acting in the condensed phase basically function by undergoing decomposition at a lower temperature by producing acid fragments. These decomposition products of the FR compounds cause rapid and catalytic dehydration of cellulose through a carbonium ion mechanism leading to char formation and hence less flammable volatile gases are evolved.

3.4 Thermogravimetric Analysis

TGA curves of fabrics treated with flame retardant and water repellent are shown in Fig. 2 and· the data in

Table 3. The degradation pattern of the virgin cotton fabric was studied first and then those of the treated fabrics to understand the interacti ons between the cotton fabric and flame retardant and water repe llent. In the case of control fabric (Fig. 2e), the first stage of degradation may be attributed to the thermo-ox idati ve degradation of cotton fabric , which is tran sformed into carbonaceous residues which may undergo further decomposition in the later stages. The degradation curves obtained for the treated fabrics show two significant changes in the s lopes, indi cating two-stage degradation and weight loss. It Illay be seen from the curves that the onset of thermal breakdown starts at lower temperatures as compared to that in the untreated fabric . The shift In the thermal decomposition of cellulose (control fabri c) from :ni) C to 312°C (SJFR, Fig. 2c) and 30 1°C (S2FR, Fig. 2a) suggests that the thermal decompositi on of FR­treated fabric starts at a lower temperatu re l O

The first weight loss in S2 FR began near 300DC and this degradation corresponds to the thermal degradation of cellulose. Samples S2FR and S,FR show less weight loss compared to untreated fabri c in the temperature range of 300-350D C and the rate of weight loss is also significantl y reduced in the above temperature range. It is observed that the weight loss is more in the first stage compared to that in the second stage. The weight loss in sa mples S2 and S., was consistant and same (47 %) in the first step and around 38% in the second step after FR treatment. This gives an indication that the presence of flame retardant only alters the onset of thermal breakd own of cellulose and rate of weight loss, rather than the actual weight loss. However, the above sampl es showed varying level of weight loss after water­repellent treatment, sample S2 showing more weight loss (57%) compared to S, (48%) in the first stage of degradation. Weight loss remained consistant in the above samples after FR and FC treatments in the 2nd stage of degradation, irrespective of the add-on levels. The weight loss of the material during degradation was found to give an indication of an inc rease in the thermal stability of the treated fabri c compared with control. The high residue left at the end of degradation reaction in treated samples in the temperature range of 300-350DC is attributed to the pyrolysis of phosphorylated cotton .

The characteristics shape of the thermograms of the treated samples at the second stage which is absent in the control sample may be due to a sudden exothermic isomerisation because of the presence of FR and the

l

INDU SHEKAR et al. : COTION DRILL FABRIC 203

40

20

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100 305 ' 08'C 4

80

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Fig. 2-TGA thermogram of FR and FR+FC treated cotton fabric with different add-on levels: (a) Sl FR, 16.7%; (b) S2FR+FC, 17.7%; (c) S}FR, 19.6%; (d) S)FR+FC, 20.4%; and (e) Contro l

Table 3--TGA data of treated fabrics

Substrate Step I

T; Tr Wei ght DTG Dma,.

IIC IIC loss IIC

%

Control 337 345 63 34 1

S2FR 30 1 3 16 47 312

S2FR +FC 305 3 12 57 3 10

S)FR 312 325 47 322

S3FR+FC 3 12 324 48 322

TI - Initi ation ; and Tr-Final

rapid reacti on between the product and the cellulose. Phosphorus from vertica l burning shows that phosphorylated cotton fabric retained about 80-90 % phosphorus in char. The presence of high levels of phosphorus in char gives an indication that the flame retardant used in the present study function s by the condensed phase mechani sm. This is in agreement with the views expressed by Holme and Patel tJ

.

TG analysis shows that the FR has acted by catalytic dehydration of cellulose, as is evidenced by the alteration of decomposition path of cellulose in all the FR-treated samples, and the percentage residue obtained at the end of analysis reveals that the fabrics treated with

Step 2 % Rcs iduc at

T; Tr Weight DTG Dill'" SOOIlC "C "C loss "C

%

4.0

533 666 38 583 14.2

500 6 12 33 544 10.0

482 579 36 528 17.4

491 582 32 533 20.0

FR formulation and FR+FC formu lation have higher percentage residue compared to the control fabri c.

3.5 Physical Properties

3.5.1 Breaking Strength

The breaking strength val ues of contro l and treated fabrics are shown in Table 4 . The loss in breaking strength varied from 22% to 3 1 % in the warp direction and I % to 19% in the weft direc ti on after the flame-retardant treatment. The loss in strength was more in warp direction compared to weft direction in all the treated samples afte r the f1ame ­retardant treatment. When compared with the control,

204 INDI AN 1. FIBRE TEXT. RES., SEPTEMB ER 1999

the flame-retardant and water-repellent treated fabri cs incurred a loss in strength in the range of 20-25 % in warp direction and 6-21 % in weft direction.

Sample S I( 12.2% add-on) showed lowest retention of strength after FR+FC treatment in both warp and weft directions compared to samples S2 (17.7% add­on) and S, (20.4% add-on). This is surprising as we anticipated more loss in strength in those samples with higher add-on , because the increased crosslink density wou ld reduce the strength linearly . Curing the flame retardant impregnated fabric treated under ac idic conditions (pH 5-6) causes tendering which resu lts in strength losslo. Th is is seen from the results of FR and FC treated fabric (Table 4) . The change in strength is contro lled by the FR add-on %, crosslink dens ity, curing time and temperature, pH of the padding bath solution, etc.

Raising the curing temperature wi ll favour the decompos ition of FR, phosphorylati on of cellulose, and more crosslinking and diffusion of reactants. The increase in the curing time and temperature results in more degradati on of the fabric in the presence of latent ac id catalyst and causes loss in breaking strength . Low and medium weight fabrics are more prone to curing parameters th an the heavy fabrics . It is also observed that samples S2 and Sl ex hi bited more or less same strength retenti on in both warp and we ft directions after fl ame-retardant and water-repellent treatments. An increase in breaki ng strength is observed for all the samples (SI,S2, and S.l) in warp direction after FC treatment, whereas loss in strength is observed in weft direction . The loss in strength was less in weft direction compared to warp direction in both FR and FR+FC treated fabrics. Sample S I showed lowest retention of strength in both the directions after FR and FR+FC treatments. The loss in strength observed after FC treatment is diffi cult to elucidate as to whether the differences observed are

due to the chemical nature of FC in the treated samples or because of the hi gh curi ng temperature ( 170-1 75°C) employed after paddin g with Fe formu lation . The breaking strength retention in single­bath treatment is compatible with two-s tep process and no pronounced difference is observed.

3.5.2 Stiffness and Tear Strength

The stiffness and tear strength resu lts of contro l and treated fabrics are shown in Table 4. It is observed that the use of melamine res in wi th flame retardant imparts a sti ffe r hand to the t r~ a tcd fab rics, in additi on to the influence of FR add-on, curing ti me and curing temperature. Here, the function of the resi n used is three fo ld. Firstly, it reacts with FR and forms highly insoluble croslinked polymcr. Second ly, it contributes nit rogen which III assoc iati on with phosphorus compound enhances the \eve l of retardancy through P-N synergism. Third ly, it acts as a bi nding agent , thereby helping in meeting the durability requirements. Even though the use of melamine resin imparts a stiffer hand than that obtained with urea formaldehyde resin, the po lymer fo rmation is more efficient in the forme r as it readily condenses with FR. The hi gh sti ffness val ues observed in treated fab rics may also be attri buted to FC treatment and hi gh curing temperat urc used In both single process and two-step process.

Stiffness va lues are lowest for the sample SI ( 12.2% add-on) both after fl ame-retardan t and water­repellent treatments (Table 4) . Although the bending length values foll ow a definit e trend in warp di recti on, no clear trend is observed in the weft direc ti on. The bending length values after FR treatment increase with the increase in add-on leve l fro m I 1.4% to 19.6%, showing an increase of 78-l30% (warp) compared with the control fabri c. However, it is obse rved th at the increase in the va lueS of be nding

Tab le 4--Physical properties o f FR and FR+FC treated cotton fabrics

Substrate Breaking strengt h retention, % Sti ffness, c m Tear st rength, kg

Warp We ft Warp We ft Warp Weft

S ,FR 69 81 4.1 3.3 2.5 I. X SIFR+FC 75 79 4.3 3.4 2.5 Uj

S2FR 77 99 4.3 3.7 2.0 1.6

S2FR+FC 80 91 4.4 3.5 2.0 1.5

S,FR 78 98 4.5 4.0 1.6 1.6

S,FR+FC 79 94 4.7 3.7 1.6 1.5

SB4FR+FC 77 85 5.3 3.8 2.0 U

Control 100 100 2.3 1.7 3. 1 2.6

INDU SHEKAR et al. : COlTON DRILL FABRIC 205

Fig. 3--SEM photographs of FR and FR+FC treated cotton fabrics with different add-on levels: (a) S2FR (16.7 %). Sin gle lihre. 2000x; (b) S2FR (16.7%), Yarn , 200x; (c) SJFR ( 19.6%), Yarn , 200x; (d) S2FR+FC (17.7%), Yarn. 200x; (e) SJFR+FC (20.4%). Single lihre.

2000x; and (f) SB 4FR+FC ( 16.4%), Single fibre, 2000x

206 INDIAN 1. FIBRE TEXT RES ., SEPTEMBER 1999

length after FC treatment is marginal. The increase in va lues of bending length observed after FC treatment may be due to the double curing employed after FR and FC treatments. However, the fabric treated in single bath and subjected to single curing shows high bending length va lues contrary to our above observations. This may be due to the superfluous FR chemical on the fabric surface which remained there as no washing was carried out after the s ingle- bath treatment , unlike in the two step process wherein washing was carried out after the FR treatment. The absence of softeners like polyethylene wax emulsion in the fl ame-retardant formulation also contributes for high stiffness.

It may be seen from the results that the add-on level plays a significant role in tear strength. Sample S I FR with low add-on of I 1.4% shows hi ghest tear strength among all the treated samples. The reduction in tear strength (warp) has been found to be proportional to the add-on in the present work. This may be asc ribed to the minimum fibre-to-fibre bonding and more freedom for the bunching of threads due to low add-on le ve l, which is mainly responsible for hi gh tear strength observed for sample SIFR.

The tear strength resu lts are bas ically a function of s ing le thread strength, relati ve movement of ya rns at the time of testing and cloth cover. In the present work, the high cloth cover of the fabric , which further increases after treatment, reduces the tear strength as it prevents yam slippage which offers resistance to tear. The tear strength values rema ined more or less same in all the treated samples after FC treatment.

3.5.3 Surface Behaviour

The surface behaviour of fabrics treated with FR and FR+FC has been studied under SEM at different magnifications for both fibre and yam and is shown in Fig 3.

4 Conclusions

Cotton drill fabric was sequentially treated for fl ame retardancy and water and oil repellency in two­step process as well as in a single-step process, wherein the flame retardant and water-repellent was combined in single bath to study the overall functional performance of fabric in terms of flame retardancy and water and oil repellency . Cotton fabric modified with the increasing amount of flame retardant suggests the synergistic role of nitrogen in enhancing the flame retardant properties when N-P combination systems are compared . Satisfactory

results achieved in the sequentia l step (two-step) process with an overall add-on leve l of 17 .7 9'0 (FR+FC) sugges t that there is an optimum leve l of add-on at which the mutual antagoni stic influence of f lame retardant and fluorocarbon is minimuJl1. The functiona l and physical properti es of fabric trea ted to an add-on leve l of 17 .7% at 3.4% and 1.20/(' P contents have been found to be bette r compa red to those of the samples treated to add-on leve ls of 12.2%, 20.4% and 16.4%. Prac ti cal ex peri ence has shown the difficulty in ac hi evi ng combi ned flame retardancy and water and oil repe ll e ncy with satisfactory physical properties , because of the complexity of the combination of fl ame reta rdant (FR) and fluorocarbon (FC) and the compl ex natu re of reaction that takes place between FR and Fe. The phys ical presence of fluorocarbon on the surface of the fabric creates a layer which prevents the catalyt ic function of FR on cellulose, which, in tu rn , results in the deterioration of leve l of flame retardancy achi eved after fluorocarbon treatment. Comparable tear strength values were obtained with the sin g le-step process, while high stiffness and lower rete nti on of strength were observed in the case of s in g le- step process compared to two-step process after FR+FC treatment.

Thermal studi es carried out have de monstrated more clearly the interaction that occurs between the FR and FC and the cellulose, the reby g ivi ng a furth er insight into the operating mechani sm of the fl ame re tardant.

Acknowledgement

The authors are extremely thankful to Prof. G N Mathur, Director, DMSRDE, for encouragement and suggestions. They are also thankful to Mr. S C Agarwal, Mr. G D Pandey and Mr.Ram Narain for their assistance and cooperation during the work .

References Singh 0 P, Man·Made Text, India, 29 ( 19g6) 130.

2 Tesoro G C & Meiser C H (Jr), Text Res .l, 40 ( 1970) 430.

3 Tesoro G C, Sello S B & Willard J J, Text Res .I, 39 (1969) 180.

4 Thomas Mitchell , J Coated Fabr, 23 ( 1974) 298. 5 William C Kuryla & Anthony J Papa in FR (!/ IJO IYllil'J'ic

materials,vol 5 (Marcel Dekkar, Inc., New York). 1979,4-9. 6 Zisman W A, COlltact angle, H'ellabilit l' and adhesion.

Advances in Chemistry Series No . 43 (American Chemical Society), 1964, Chap. I .

7 Furmidge C G L, J Colloid Sci, I I ( 1962) 23.

8 Sunshine N B, FR of phenolic resins and l/rea and formaldehyde resin, FR of polymeri c materials, Vol 2, edited

.".

INDU SHEKAR el al. : COTION DRILL FABRIC 207

by William C Kuryl a and Anthon y J Papa (Marcel Dekkar, Inc., New York), 1973 , 218.

9 Grajeck E J & Peterson W H, Texl Res J, 32 ( 1962) 320. 10 Sahin Belgin, fill Texl BIIII, Dyeill g IPrilllinglFillishing, (3)

(1996) 26.

II Kaushik D P & Sharma J K, J Tc.\l Assoc, 55 (19'.>4) 25 . 12 Bajaj P, Chak rapani S & Jh a N K, Te.rl I?es .l, S4 (1984) 6 19. 13 Holme I & Patel S R, in /3/ellded 1('Xl i/es, edited hy M L

Gulrajani [Textile Association (Indi a), Mumhai J, 1981 . 354-37 1.