Indian Journal of Fibre & Texti le Rescarch Vol. 3 1 , June 2006, pp. 330-334

Application of flame retardant products to knitted fabric

G Ozcan", H Dayiog lu & C Candan

Texti le Engineering Departmcnt, Istanbul Technical Un ivcrsity, Istanbul , Turkey

Received 1 Septelllber 2004; revised received 31 January 2005; accepted 1 1 April 2005

The effect of durable flame retardant products on knitted fabric flammabi l i ty has been studied. F irstly, the non-durable, semi-durable and durablc flame retardants were applied to the bleached knitted cotton fabrics to observe their effects on fabric flammabi l ity and then phosphorus-based durable flame retardant products were applied to bleached fabrics at different concentrations, curing temperatures and curing times alternatively to evaluate the effect of thei r treatment parameters on fabric burning behaviour. The burning behaviour and weight loss values of all the fabrics were evaluated using the standard vertical flammabi l ity test method. The resul ts evaluated using an SPSS statistical program show that the flame retardant concentrat ion, curing temperature and curing t ime are vcry important parameters to obtain FR fabrics having good flame resistance and acceptable handle and appearance.

Keywords: Cotton, Flame retardant fabric, Knitted fabric IPC Code: Int. C1.8 C09K2 1100; D06M I IIOO

1 Introduction

Flame retardancy may be conferred on texti le materials by the use of inherently flame resistant fibres, changing of fibre molecular structures by co­polymerization and chemical modification methods (as in modacry l ic fibres or FR-polyester), i ncorporation of flame retardant additives during the production of man-made fibres (FR-viscose) or application of flame retardant products to textile substrates by a chemical after-treatment processes. 1 .2

Chemical after-treatments i nclude surface or topical treatments, coatings and functional fi n ishes, which become a part of final fibre structure. Durabi l i ty of flame retardant fin ishes general ly depends on their adherence or bond strength to the fibre surfaces or molecular structures. Generally, the flame retardant (FR) products and their flame retardancy effects are c lassified as non-durable, semi-durable and durable. Durabil ity i s determined by launderabi l i ty, aftercare and defined cleansing requirements, weatherabi l i ty, and exposure to l ight, heat and atmospheric agents. U

Non-durable FR products are deposited on and between the fibres and no crosslinki ng takes place. These products adhere on fibre surfaces . Some non­durable FR fin ishes can resist dry-cleaning process depending on their constitution. Diammonium phosphate, borax and boric acid mixtures, ammonium sulphate, ammonium bromide and ammonium salts of

"To whom all the correspondencc should be addressed. E-mai l : olcangul@ itu.edu.tr

amidosulphonic acid are often used as non-durable flame retardant products.2,3 Semi-durable flame retardant products may crossl ink to fibre reactive groups. Flame retardancy can be maintained for 5- 1 5 times to dry or aqueous cleaning processes, depending on their constitution. Halogenated products, such as chlorinated paraffin, polyvinyl chloride, polyvinyl idene chloride, metal oxides (especial ly antimony trioxide i n combination with halogen compounds such as hexabromocyclododecane or chlorinated paraffin) and s imple phosphorus/nitrogen compounds, are often used as semi-durable FR products2 unless applied together wi th a resin . Durable FR products bond to the reactive groups of fibre molecules or penetrate ins ide the fibre. Durable FR products often consist of organophosphorus condensates especially in the presence of cellulosic fibres. '

The efficiency of the FR finish on a texti le fabric depends on a number of factors, e.g. fibre composition, fabric construction, FR compatibi l ity with other fin ishes, end use and durab i l i ty . 1 .2,4

Successful FR fin i shes should combine acceptable levels of flame retardancy at an affordable cost and be appl icable to textile fabrics using conventional textile finishing and coating equipment. ' ,2

Flammabi l i ty i s of major concern with respect to apparel fabrics, furnishing textiles and clothing for defence personnel . By the appropriate appl ication of flame retardant the probabi l i ty of a texti le material catching fire and danger of fire spread is considerably

OZCAN el al. : APPLICATION OF FLAME RETARDANT PRODUCTS TO KNITTED FABRIC 33 1

reduced, so that i t i s possible to find enough time to escape or extinguish the fire. More recently, considerable number of studies on the effects of flame retardant on pyrolytic degradation of cellulosic materials and on burni ng behaviour of textiles has been reported.4. 1 6 The present study is aimed at observing how and at which level of application parameters (such as flame retardant concentration, curing temperature and curing t ime), the flame retardant fini shes affect the flame resistancy of the cotton knitted fabric.

2 Materials and Methods

To investigate the effects of flame retardant type on flame resistance of knitted cotton fabric, non-durable, semi-durable and durable flame retardant products were chosen and applied to the bleached knitted fabrics at recommended levels by their suppl iers . Phosphorus-based durable flame retardant species were applied to the b leached cotton fabric each at five different concentrations, five different curing temperatures and five different curing times to evaluate the effect of their treatment parameters on fabric burning behaviour. The burning behaviour and weight loss values of al l the fabrics were evaluated using the BS 5438 ( 1 976) vertical flammabi li ty test method. Finally, the experimental results were evaluated using an SPSS statistical program.

2.1 Materials

SU 40-diammonium phosphate-based (non­durable), PF-phophorus/nitrogen compound-based (semi-durable) and PR 20-organo phosphorus-based (durable) flame retardants were obtained from SET AS

Chemical Company and Lefasol P448-organo phosphorus-based (durable) flame retardant was obtained from Lefateks Chemical Company. Phosphoric acid was used for catalysing the finishing process and Na2C03 was used for neutralizing stages of durable flame retardant appl ications for PR 20. Wet pick-up of the fabrics was about 80% and drying temperature was 1 20aC for all FR finish ings. The curing temperature was kept constant at 1 50aC for the durable flame retardant (PR20).

In thi s study, FR type, FR concentration, curing t ime, curing temperature and washi ng process of FR fabrics were considered as variables for analysis. The fabrics used were Ne 30/ 1 cotton s ingle jersey knitted and bleached. Al l fin ish ing processes were applied to the fabrics according to their anticipated commercial appl ication and were performed in laboratory type padding and dyeing machine. Finishing formulations and after-treatments are given in Table 1 . Flammabil i ty test was repl icated four t imes for each sample and a total of 84 samples were tested to evaluate the effects of fin ishes.

2.2 Methods

Vertical flammabil i ty test method [BS 5438 ( 1 976) Part 2] was used to evaluate the fabric flammabi l i ty. The test specimen strips ( 1 7 cm x 22 cm) were conditioned at 20±2°C and 65± 2% RH for 24 h before testing. The conditioned specimens were mounted on a suitable clamp and placed in a standard cabinet, which allows 2 mrnls airflow. A standard flame was applied at the bottom edge of the fabric for 30 s under controlled conditions. All flammabi l i ty tests were conducted under ambient temperature and

Table I-Finishing formulations and after treatments

B leaching

H202 (m1/400 ml), 1 .6 Na2COJ(g/400 ml), 0.4 Wetting agent (g/400 ml), 0.4

Sodium sil icate

(mll4oo ml), 0.4

Liquor ratio, 1 :20 Temperature (0C), 85 Time (h), I Washing with cold water

Non-durable (SU 40) and semi-durable (PF) FR finishes

SU40 (giL), 300 Phosphoric acid (giL), 2 Wet pick up (%), 80

Drying temp (0C), 1 20 Liquor ratio, 1 :90 Active agent content

SU : 37% PF : 46%

Washing with cold water

Durable FR finishes PR 20

PR 20 (gIL), 300

Phosphoric acid (gIL), 22 Wet pick up (%), 80

Drying temp (OC), 1 20

Curing temp. (0C) for 5 min, 155

Liquor ratio, 1 :90

Lefasol P448

Lefasol P448(g/L), 300 Phosphoric acid (gIL), 22

Wet pick-up ( %), 80

Drying temp. (0C), 120

Curing temp. (0C) for 5 min, 1 50

Liquor ratio, 1 :90 Active agent content (%), 88 Active agent content (%), 80

After the treatment, the fabrics were washed with 1 0glL sodium carbonate at 85°C for 2 times, again washed w ith 5gIL sodium carbonate at 40°C and then rinsed in cold water 4 t imes.

332 INDIAN J. FIBRE TEXT. RES. , JUNE 2006

relative humidity in the laboratory. This flammabil ity test method normally measures char and damaged length. However, these measures do not always represent the real destroyed area of the fabric for many cases. Therefore, i t was decided to use another parameter (weight loss), which wi l l g ive more real istic approach to evaluate fabric destruction. I t i s clear that the parameters selected are interrelated or dependent on each other; h igh weight loss would definitely show a high area destroyed, though the reverse would not necessarily be true. For these reasons, char length and weight loss were measured for all specimens. Before and after testing the test specimens were weighed and the weight loss value was determined using the following relationship :

Weight loss In itial weight of specimen - Last weight of specimen

(%) In i t ial weight of specimen

The results were evaluated statistically wi th the help of analysis of variance (ANOY A) tables to indicate the significance of the effect of fi nishing treatments and then regression analysis was used to show the relations between applied finishing process and the fabric flammabi l i ty . Each variable used in the study was considered signi ficant if the probability level was 0.05 or less and highly significant if the probabi l i ty level was 0.0 1 or less. Polynomial regression analysis resul ts are shown in Table 2 .

3 Results and Discussion

3.1 Effect of Flame Retardant Type

With respect to the effect of non- durable, semi­durable and durable FR finishing agents on vertical strip test behaviour, results from the analysis of variance and polynomial regression analysis (R2= 98.9% and significance =< 0.00 1 ) show that the weight loss values of the fabrics are highly affected

from FR types (Table 2) . When the FR type changes to a durable FR product, there i s a decrease in the weight loss of the fabrics. Figure 1 shows the relation between FR type and weight loss behaviour of the fabrics.

This decrease in the weight loss values can probably be attributed to the enhanced active agent content of the flame retardant products generated by the durable FR product. The increase in active agent content results in an increase i n degree of flame retardance consuming more combustion energy and producing less flammable volatiles and hence reduced weight loss.

3.2 Effect of FR Concentration

To determine the effect of FR finish concentration on flame resistance of the knitted fabric, the durable FR finish (organo phosphorus based, PR20) was selected and applied to the fabrics with five different add-ons (200, 250, 300, 350 and 400 giL). Each sample was dried at 1 20°C and cured at 1 60°C for 3 .5 min . Linear regression analysis (R2= 73.3%, F=49.4 1 , and significance« O.OO 1 ) indicates that the concentration of finishing agents considerably

,:[1 ,..---------------,

? l(1 � <n <n o

�J l(1 �

[I Non-durable

(SU 40) Semi -durable Durable

( PF) ( PR20)

Fig. I - Relationship between FR types and weight loss after ignition of the fabrics

Table 2-Polynomial regression analysis results [Dependent variable-Weight loss I

I ndependent variable Rsq df F S igf b() b l b2

FR type 0.988 9 382. 1 5 0.000 54.22 -42. 1 7 8.39

FR concentration 0.960 1 7 205.53 0.000 389. 1 5 -2.2 1 0.003

Curing temperature 0.235 1 7 2.6 1 0. 1 03 225.96 -2.61 0.008

Curing t ime 0.9 19 1 7 96.53 0.000 3 1 .96 - 1 1 .79 1 .2 1

Washing cycle 0.977 9 1 9 1 . 1 4 0.000 5.35 3.53 -0.062

Rsq-Coefficient of determination; df- Degree of freedom; F-Ratio between the treatment mean square and the error mean square; Sigf-Significance; and boo b l > and b2 are the regression coefficients. Mathematical equation-Quadratic model whose equation is Y= bo + (bl *t) + (b2*t\ where Y-Dependent variable, and t- Independent variable.

OZCAN el (Ii . : APPLICATION OF FLAME RETARDANT PRODUCTS TO KNITTED FABRIC 333

influences flame resistance of the fabrics (Table 2). Figure 2 shows that the weight loss decreases significantly as the FR concentration is increased.

Flame retardant application from bath l iquor concentration above 350 giL generates excessive harshness of handle although high flame resistance is obtained.

3.3 Effect of Curing Temperature

Keeping the FR concentration fixed at 300 giL, the temperature of curing was varied from 1 40°C to 1 80°C for 3 .5 min for durable FR Lefasol P448. Polynomial regression analysis (R2= 1 3 .2%, F=2.75, significance = 0. 1 1 5 ) shows that the cUring temperature has no significant effect on flame resistance of the fabrics (Table 2). It is observed that the highest curing temperature of 1 80°C does not add to flame resistance when compared with the s imi lar sample cured at 1 60°C. All the samples that were cured above 1 60°C are found to show undesirable yellowing. The samples that were cured under 1 50°C were ignited and continued to burn. This can be attributed to incompleted FR curing process and removal of retardant after washing off. The effect of change in curing temperature on flame resistance in term of weight loss of the knitted fabrics i s shown in Fig. 3 .

3.4 Effect o f Curing Time

Keeping the FR concentration fixed at 300 giL and the curing temperature at 1 60°C, the time of curing process was varied from 2 min to 6 min. Polynomial regression analysis (R2=9 1 .9%, F=96.5, significance« 0.00 I ) indicates that the flame resistance of the fabrics is influenced by the curing time (Table 2). Figure 4 shows that the flame resistance of the fabrics increases as the curing time increases from 2 min to 5 min. The lowest weight loss 80r-------------� ,-.. 60

e l:l 40 .3 � 20 . ., � 0

200 250 300 350 400 FR Cone. (giL)

Fig. 2 -Relationship between name retardant concentration and weight loss after ignition

values are obtained at 4 min and 5 min . I t i s assumed that the observed high weight losses at 2 min and 3 min are probably caused by the incomplete condensation of the flame retardant during these curing t imes. On the other hand the samples cured at 6 mll1 show a slight reduction i n FR properties and undesirable yellowing. This clearly i nd icates that the t ime and temperature of curing stage of the FR finish are very important parameters to obtain FR fabrics having good flame resistance, and acceptable handle and appearance.

3.5 Effect of Washing Process

Many FR cotton products are washed under severe conditions. " In this study, after the durable FR fin i shing agent was appl ied to the knitted fabrics according to the supplier recommendations for commercial use (300 giL), the FR fabrics obtained were washed 5 and 50 times according to the I SO 1 05 C06 washing standard at 40°C for 30 min. Polynomial regression analysis shows that as the washing cycles increase, the weight loss also i ncreases which is inversely proportional to the flame res istance. This clearly indicates that wi th every additional wash there i s a defi nite amount of loss in flame retardant finish. Figure 5 shows the relation between the washing process and the fabric flame resistance.

It is interesting to note that after 51h washing cycle ,-.. 14r----------------. � '" .3 10 ! 6\--�--�-���� 1 40 150 160 170 180 1 90

Curing Temperature ('C)

Fig. 3 -Effect of curing temperature on fabric name resistance as weight loss after ignition

14 .,-------------------,

4 2 ��� __ -__ -��

2 3 4 5 6 7 Curing Time (min)

Fig. 4 - Effect of curing t ime on flame resistance of the fabrics

334 INDIAN 1. FIBRE TEXT. RES., JUNE 2006

30 r-----------------------�

o o 5

Washing Cycle 50

Fig. 5 - Effect of washing cycle on fabric flame resistance

the weight loss after ignition of the fabrics increases by approximately 5 t imes compared to their ini tial value. The h ighest weight loss value is obtained after 50th wash cycle.

4 Conclusions The studies show that the applied FR types and

application conditions considerably i nfluence knitted fabric flame resistance. With the durable flame retardant, an increase in FR concentration causes flame resistance to increase although fabrics become harsh to handle above 350 giL of FR application . Curing temperature has no significant effect on flame resistance of the fabric, but all samples that were cured at above 1 60°C are found to show unacceptable yellowing. This effect most l ikely has resulted from damage to cotton cellulose above this temperature. Flame resistance of the fabrics i ncreases as the time of curing increases and samples cured for 6 min show the considerable yellowing. In normal commercial flame retardant finishing at 1 60°C, the curing times of the order of 3-5 min are acceptable and l ittle or no yellowing occurs. Yellowing observed in this work is probably a consequence of poor temperature control and higher heating rates typically observed in small­scale experimental work. These results clearly indicate that the FR concentration, curing temperature and curing t ime are very important parameters to

obtain FR fabrics having good flame resistance and acceptable handle and appearance.

The i ncrease in weight loss with every additional wash of the FR fabrics also shows that every additional wash of the FR-finish fabrics causes considerable loss of flame retardant finish although they keep some level of flame retardance.

Acknowledgement The authors are thankful to the Seta� Chemical

Company and Lefatex Chemical Company, Turkey, for chemical supports and to B i lkont Company, Turkey, for permi tting to use their plant for producing test fabrics. Appreciation i s extended to l .T .U. Textile and Cloth ing Qual i ty Control and Research Laboratory for the support to perform experimental work.

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