I ndian Journal of Fibre & Texti le Research Vol. 3 1 , September 2006, pp. 444-449

Effects of silicone-based softener on the easy-care finished cotton fabric

F Talebpour"

Art Department, Alzahra University, Tehran, Iran

and

I Holme

Department of Textile Industry, Leeds University, Leeds, UK

Revised received alld accepted 26 Jllly 2005

The effects of an easy-care fi nish, namely DMeDHEU and DMeDHEU plus si l icone softener, on physical propert ies of bleached cotton fabric have been studied. It is obvious that easy-care finish imparts marked increase in the fabric crease resistance along with the increase in static and k inetic frictions. The application of s i l icone softener on top of the easy-care finished fabric decreases the fabric friction and a further increase in the crease recovery angle is also observed. Easy-care tinish ing marginally changes the bending length, which is reduced to some extent by the application of s i l icone softener.

Keywords: Bending length, Cotton fabric, Crease recovery angle, Easy-care finish, Kinetic friction, Static friction, S i l icone softener

IPC Code: I nt. CI .8 D06C29/00

1 Introduction The term easy-care means that a fabric does not

crease during use and any crease after washing is easily removed from the fabric. Cotton fabrics are very comfortable to wear because of thei r good natural properties, but during drying after washing they show dimensional vanatlons that impart shri nkage to the fabric . Creasing of the cotton fabrics depends on the structural properties of the fibres. Nowadays, crease resistance is obtained by easy-care finishing which stiffens the cotton fibres by covalent cross-l inking and therefore, res istance to bending, creasing and recovery from deformation can be promoted. ' The process mainly consists of cross­l inking of the cotton fibre hydroxyl groups with a cross-l inking agent; the poss ib i l i ty of displacement of fibre chain molecules decreases. I t has been demonstrated that the degree of cross-l inking has a profound effect on the crease recovery angle and dimensional stabil ity of cotton fabric .2

The widely used cross-l inking agents i n easy-care finishing are formaldehyde-containing reactants, including DMDHEU and etherifi ed DMDHEU with lower formaldehyde levels.' The modern trend in easy-care finishing i s moving towards the use of low formaldehyde and zero formaldehyde fi bre cross-

"To whom all the correspondence should be addressed. E-mai l : fartalebpour@yahoo.coll1

l i nk ing agents.2 It has been considered that the textile fi nishing resins on the bas is of DMDHEU may contain up to 1 % free formaldehyde. According to EU regulation, the products contain ing formaldehyde concentration 2:0.2% have to be classified as skin sensitizer.4

Therefore, the i ncreasing demand for wrinkle resistant cotton apparel in the market leads to a need to develop formaldehyde free durable press fin ishes.s

Effective cross-l inking reactants should be very stable, soluble in water and remain colourless during heat curing . Moreover, they should not be toxic, odorous or i rritating and should be available at low cost. The non-formaldehyde durable press fi n ish system demonstrates superior durable press properties, h igh fabric strength retention and good laundering durabil ity.

On the other hand, the application of softeners to texti le materials i s principally for improving the handle, drape and sewing properties of the materials. Many types of chemical softeners are avai lable with different concentrations and proportions of ingredient such as s i l icones.6 S i l icone softeners have l i ttle affi ni ty towards texti le materials because they do not carry any charge. Therefore, they are compat ible with other fin ishing agents and can be appl ied to both natural and man-made fibres. Due to weak lion-ionic attraction forces, the affin i ty is very low and hence they cannot be applied by exhaust ion methods. Other

TALEBPOUR & HOLME: EASY-CARE FINISHED COTION FABRIC 445

application methods such as padding, spraying or foaming can however be used. They impart good lubrication and antistatic effects on the fabric but they are less durable and can be washed off easi ly. An important property of thi s group of softeners is their compatibil i ty with al l types of dyes and fin i shes so that they can be applied during dyeing and finishing processes.7.8

The non-ionic s i l icone-based products have been commerciali sed s ince 1 940s. They consist of long l i near chains with alternate s i l icon and oxygen atoms. Usually, two organic groups such as methyl groups are attached to each si l icon atom. These can be better described as polysiloxanes. The polysiloxane chain l ies flat on the fabric surface and produces a soft handle. Besides the soft handle, they improve other physical properties such as tear strength, abrasion resistance and crease res istance. Also, they can confer water repellency to the fabrics. The water-repellency resulting from the application of s i l icones is attributed to the non-polar methyl groups. Nearly 80% of the si l icones used in the textile industry are based on dimethyl siloxanes which are mainly used as water­repellents, anti-foams, lubricants and soften ing agents. Among the textile softeners, s i l icones are the most expensive types. The s i l icone softeners require a catalyst and a cross-li nker system to produce the best d b ' I ' 9 ura I i ty .

The softener acts as a lubricant; it fi l ls the spaces between the fibres and yarns and covers the surface of the yarns as a thin layer to reduce fri ction between fibres and yarns. Therefore, the Coulomb theOl'/ o

which was based on cold-welding has been prevented by this th in layer. It is clear that by decreasing the friction, the smoothness of the fabric will be improved. The appl ication of softener to natural fibres is at the final stage of wet processing such as dyeing, finishing or rinsing. They can be applied either alone or combined with other treatments. Generally, non­ionic softeners are applied by the pad-dry method. In the present paper, the effect of s i l icone-based softener on the physical properties of easy-care finished cotton fabric has been reported.

2 Materials and Methods

2. 1 Materials

Bleached cotton fabric [plain ( 1 / 1 ) ; endslcm, 24; pickslcm, 2 1 ; and weight, 1 26.5 g/m2] were used for the study .

The main chemicals used during the experiments were zero-formaldehyde cross-l inking agent (Arkofix V37S l ) together with a suitable catalyst (V388 1 ) . Both the products were supplied by Hoechst Ltd, UK. Solusoft W A from Hoechst was used as the wetting agent at a concentration of 1 5 giL in all the ex peri men ts.

A reactive s i l icone-based softener (Q2-8376), obtained from Dow Corning Limited, was used for fabric treatment. I t i s a milky colour s i l icone dispersion compatible with all addit ives in fin ishing especially with chemicals used in easy-care finishing of cellulosic materials . To produce a desirable pH medium, the addition of acetic acid i s recommended.

2.2 Methods

In i tial ly, bleached cotton fabric was treated with different concentrations of DMeDHEU (50, 1 00, 1 50, 200 giL) to impart easy-care properties. During testing, each sample was dipped in a prepared pad bath and squeezed i n an Ernst Benz Laboratory Two­Bowl Pad Mangle. The padded fabric was then dried in a stenter at l l O- 1 30°C. Curing was done in a Werner Mathis Curing Oven at 1 50°C for 90 s and no washing-off process was carried out after curing.

S i l icone-based softener (20 giL) was then applied to the treated samples by a pad-dry technique. Each prepared sample was padded through a laboratory pad mangle and then dried in a Benz Drying Oven at 1 20°C for 2 .5 min . Care was taken to keep the samples free from any tension or crease. All samples were conditioned in the standard atmosphere for at least 48 h prior to testing. To compare the variation in physical properties of the samples, a blank sample treated with the catalyst, wetting agent and si l icone softener without adding cross-linking agent was also prepared. The contents of each pad bath i ncluded: Arkofix V37S 1 - 0,50, 1 00, 1 50,200 giL; Catalyst V388 1 - 1 0 giL; and s i l icone-based softener-20g/L.

Shirley stiffness tester was used for the measurement of bending length . Fabric sample of 1 5 .2 cmx2.S cm size was cut from the warp as well as weft direction. The strip of the fabric was mounted on a horizontal platform i n such a way that it overhangs and bends downwards and bending length was measured.

Test on cotton fabrics for the crease recovery angle was carried out by the Shirley Crease Recovery Tester. A sample of the size 5 cmx2.S cm was cut

446 INDIAN 1 . FIBRE TEXT. RES., SEPTEMBER 2006

from the both warp and weft directions. The sample was carefully folded into half, kept between two glass plates and a 907 g weight was placed on the top. After 1 min the load was removed and the sample was placed on the fabric clamp in the tester and allowed to recover from creasing. Finally, the fabric crease recovery angle was read and recorded. The same procedure was carried out for measuring wet crease recovery angle for which the sample was first wetted out in water which was left under the testing conditions for one day. Each sample was immersed in water for I min and then placed between two pieces of blotting paper for 2 min to remove excess water.

The fabric friction of treated materials was measured by the dragging method using an Instron Tester described by Ajayi . 1 1 The measurement was based on the horizontal motion of a sledge over a stai nless steel flat plate.

3 Results and Discussion The total experiment was divided into two parts: ( i )

application of easy-care fin i sh on bleached cotton fabric and ( i i ) appl i cation of a s i l icone softener on top of the easy-care finished fabric.

The chemical add-on values for all treated samples were measured and the results are shown in Table I . After reconditioning all the samples in the standard atmosphere, the physical properties of the samples were measured and are shown in Tables 2 and 3 .

3.1 Crease Recovery Angle (CRA)

Figures I and 2 show the variations in dry and wet crease recovery angles of the treated fabrics. The application of cross-l inker i mproves the crease recovery angle of the fabric. On the other hand, the application of s i l icone-based softener plus DMeDHEU increases the fabric crease recovery angle more than that observed on treatment wi th DMeDHEU alone. The blank treated sample exhibits a higher eRA than the untreated fabric, which may be due to the effect of the softener that promotes more inter-fibre slippage. On the other hand, by using the cross-linking agent the possib i l i ty of d isplacement of fibre chain molecules decreases. Formation of cross­l inks between adjacent cellulosic chains aids the fabric to recover from any crease and returns to its in i tial uncreased state.

The results of these tests are found to be i n agreement with the results of Rooks. ' 2 He observed that the crease recovery of the fabric increases after easy-care treatment and a further increase i n crease

T<lble I-Chemic<ll add-on of tre<lted samples

Sample DMeDHEU S i l i cone Add-on, % giL softener DMeDHEU DMeDH EU+

giL S i l icone

I 0 20 0 1 .60 2 50 20 2.52 3.08 3 1 00 20 5.04 5.60 4 1 50 20 7.56 8. 1 1 5 200 20 1 0.08 1 0.64

Table 2-Physical properties of easy-care finished fabrics

Property DMeDHEU, giL Untreated 0 50 1 00 1 50 200

CRA (dry), deg

Warp 76.5 85.3 97 1 1 1 .3 1 1 1 .3 1 1 7 Weft 74.8 8 1 .3 98.3 107.3 1 20.7 1 1 5 .3

DCRA, deg 1 5 1 .3 1 66.6 1 95.3 2 1 R .6 232 232.3 SO 1 .4 1 .2 2 1 . 1 1 .5 1 .8 CRA (wet), deg

W<lrp 74.5 78.3 1 02 1 03.6 1 02 1 07.3 Weft 72 88.3 98.3 1 03.4 1 04.6 1 0 1

WCRA, deg 1 46.5 1 66.6 200.3 207 206.6 208.3 SO 1 .5 1 .6 2 1 .5 1 . 7 1 .5 Bending length, 111111

W<lrp 25.3 24.8 24.8 25 25 26.2 Weft 2 1 .9 1 8 .8 1 7 .8 1 8 .8 1 9 .3 1 9 .2

Friction

Static 0.29 0.32 0.23 0.28 0.32 0.36 Kinetic 0.22 0.20 0. 1 7 0.23 0.24 0.24

T<lble 3-Physical properties of DMeDHEU+s i l icone (20g/L) treated fabrics

Property DMeDHEU, giL 0 50 1 00 1 50 200

CRA (dry), deg

Warp 108.6 1 1 7.3 1 2 1 .6 1 28.3 1 32.6 Weft 1 0 1 .6 1 14.3 1 1 7.3 1 24.6 1 25.3

DCRA, deg 2 1 0.2 23 1 .6 238.9 252.9 257.9 SO 5.5 6 2 5 7.5 CRA (wet), deg

W<lrp 1 00 98 1 05.6 1 1 0 1 08

Weft 99.6 95.3 99.3 1 04.3 1 1 4.3 WCRA, deg 1 99.6 1 93.3 204.9 2 1 4.3 222.3 SO 5 7 6 7

Bending length. mill Warp 22 20.6 22.2 2 1 .7 22 Weft 1 6.3 1 6.9 1 7 .4 17 . 1 1 7 .2

Friction Static 0.26 0.22 0.26 0.25 0.25

Kinetic 0. 1 7 0. 1 4 0. 1 5 0. 1 4 0. 1 5

TALEBPOUR & HOLME: EASY-CARE FINI SHED COTTON FABRIC 447

280

240 '6C .. ." � 200

� 160

120 o 2

T __ - i

....L DMeDHEU+Silicone DMeDHEU

4 6 8 10 12 Chemical Add-on %

Fig. I-Effect of s i l icone-based softener on DCRA of the easy­care finished fabric

240 �----------------------------'

200

120 o 2 4

--.- DMeDHEU+Silicone .-•... DMeDHEU

6 8 10

Chemical Add-on % 12

Fig. 2-Effect of s i l icone-based softener on WCRA of the easy­care finished fabric

recovery is also observed by the application of cross­l inking agent plus s i l icone-based softener. The stiff and boardy handle of the DMeDHEU-treated fabric i s changed to a smooth and lively handle by the s i l icone softener appl ication. An effective softener should impart surface lubric i ty , flexibi l i ty and ease of compressibi l i ty to the fabric . The use of a s i l icone­based softener can also i mpart a h igh degree of water repellency which is an undesirable property in easy­care finishing. Wetabil i ty or absorbency is one of the several factors that determine the suitabi l i ty of apparel for a particular end-use. Figure 3 shows the i ncrease in DCRA of the DMeDHEU-treated samples after treatment with the s i li cone softener. I t i s clear from Fig. 3 that the s i l icone softener can markedly affect the DCRA at a lower DMeDHEU add-on values. Application of h igher amounts of DMeDHEU in the

300 f;] DMeDHEU+Silicone fil DMeDHEU

DMeDHEU Concentration (gIL)

Fig. 3-The i ncrease in dry crease recovery angles of the treated samples as compared to untreated fabric

presence of s i l icone softener has no further beneficial effect in terms of easy-care properties. The appl ication of s i l icone-based softener at 50 giL DMeDHEU concentration i ncreases DCRA about 36.3° and the fabric DCRA reaches to 23 1 .6° which i s very close to 232 .3° , i .e. DCRA of DMeDHEU­treated fabric at 200 giL. Therefore, by the application of 50 giL DMeDHEU plus 20 giL si l icone-based softener the crease resistance of the treated fabric i s same as that of the fabric treated with 200 giL DMeDHEU. Better easy-care properties can be gained at a lower DMeDHEU add-on using a si l icone softener. In all the samples tested, the si l icone softener promotes a h igher fabric crease recovery angle.

3.2 Fabric Friction

The overall effect of the appl ication of sil icone softener on easy-care fin ished fabric i s depicted in Fig. 4. I t i s observed that the easy-care finishing results in fabric wi th a h igher coefficient of fabric friction . Commercially, the fin ished fabrics are treated with a softener to keep the physical properties at the tolerable l imits. The softener acts as a fibre lubricant and reduces fabric friction. It is observed from Fig. 4 that although there i s an i ni tial i ncrease i n fabric friction for the DMeDHEU plus s i l icone-treated fabrics, thi s is lower than that observed i n the absence of softener. The fabric friction above 5% DMeDHEU add-on decreases sl ightly, whereas i n the absence of s i l icone softener there i s an i ncrease i n fabric friction. The above results can be interpreted in terms of the easy-care finishing, i ncreasing the fabric friction and the softener treatment decreases the fabric friction. In

448 INDIAN J. FIBRE TEXT. RES. , SEPTEMBER 2006

0.5 -.---------------,

Static

l····· ····· ·· ·i ..... ..... .......

......

....

0.3- ·· .... �.1.············· 53 0.2-'C .. · .... ·DMeDHEU � ""&""'DMeDHEU+Silicone

8 O.I-+---.--,...--.---,.--.,..--.--...-oy--......---r--r---l Ci! O.4 "}---------------, = co :e ·c

Kinetic .. · ... · DMeDHEU

� 0.3 --.-- DMeDHEU+Silicone

I .. · ····· · .. ···f .... · .... ·· .. -J 0.2 ......... �,... ..

...

_ .

.

.

.

_

.... _

.. -jlt---..... I�--t-I

O.I+---.--,...--.---,.--.-.--...-oy--......---r--r--4 o 2 4 6 8 10 12

Chemical Add-on %

Fig. 4-Effect of s i l icone-based softener on static and kinetic frictions of easy-care fin ished fabric

comparison with the easy-care treated fabrics, the easy-care plus softener-treated samples show significantly lower values of fabric friction . Therefore, even at h igher DMeDHEU concentrations the si l icone softener must cover the fibre surfaces and signifi cantly decreases the fibre friction.

The kinetic coefficient of fabric friction in the DMeDHEU/sil icone-treated samples i s lower than that of the DMeDHEU-treated fabrics and the value i s only changed marginally by the appl i cation of higher quantities of cross-linker. Therefore, the s i l icone softener is more effective to decrease the kinetic coefficient of friction of the samples at different DMeDHEU concentrations and there is no need to apply a higher quantity of softener for higher amounts of DMeDHEU to decrease the fabric k inetic friction .

3.3 Bending Length

I n easy-care fin ished fabrics the bending length i n the warp direction changes marg inally . Application of si l icone softener reduces the bending length i n both directions to some extent. Thi s effect is due to the deposition of softener on the surface of fibres which reduces i nter-fibre friction and led to a lower bending length . By the appl ication of s i l icone softener on top of the easy-care finished fabric the bending length init ial ly i ncreases to a small extent and then

28-r----------------, Warp

26

24

I 22

,f; 20 Oil --A-- DMeDHEU � 18 �--.-���-��-D-M�e-D�HE-U�+-S�ili-c-on

�e-�� .� 22 -r----------------,

." 5 Weft ill 20 -

18-

16-

_ .. --....... .

....

...

.

. � .. " ----- -_._ . ... . - -._-.- '.

--r- DMeDHEU 14-t---._'T"" ........ --,_�_D;..;;M�eD;..;;HE;;;;;;;..U;;...+TS;.;;;ili;;.;;· c,;.;.on;;;.;t

.-........ ---i

o 2 4 6 Chemical Add-on %

8 10 12

Fig. 5-Effect of s i l icone-based softener on bending length in the warp and weft directions

decreases ; the values however, are lower than those of the corresponding DMeDHEU-treated fabrics. The bending length in both the warp and weft directions tends to level off after 5% chemical add-on. In other words, the appl ication of h igher amounts of DMeDHEU in presence of si l icone softener shows no beneficial effect on the flexibi l i ty of the fabric . The i mprovement i n flexibi l i ty could be enhanced by using a s i l icone softener at lower DMeDHEU add-on (Fig. 5) .

4 Conclusions

4.1 Fabric DCRA can be i ncreased by cross-linking the fibres; only a small amount of cross-l inker i s required to i mpart a significant i ncrease in the fabric res istance. By i ncreasing the D MeDHEU concentration i n the pad bath, crease resistance of the fabric i ncreases. B lank treated sample exhibits a lower DCRA than a DMeDHEU-treated fabric, i mplying that this reagent can i ncrease the fabric easy-care properties due to the cross-l inking reaction.

4.2 Fabric crease recovery angle i ncreases more by the appl ication of s i l icone softener plus DMeDHEU. Both the formation of cross-l i nks between adjacent molecular chains and appl ication of s i l icone softener to promote more in ter-fibre s l ippage results i n h igher fabric crease resis tance in both the wet and dry states.

TALEBPOUR & HOLME: EASY-CARE FINISHED COTTON FABRIC 449

At a lower DMeDHEU add-on value, the s i l icone softener can markedly affect fabric DCRA. The application of higher amounts of cross- l inker i n the presence of a s i li cone softener has no benefic ial effect in terms of the easy-care properties.

4.3 The easy-care finishing w ith DMeDHEU in the presence of an acid catalyst decreases the fabric friction. The covalent cross-links between fibre molecular chains and the cross-l inker reinforce the fibre substances in the amorphous regions. However, by i ncreasing the cross- l inker concentration due to the saturation of the free hydroxyl groups the excess DMeDHEU deposits on the fibre surfaces and fabric friction increases. The k inetic coefficient of fabric friction is less affected by the cross- l inker concentration and does not show marked changes but the application of si l icone-based softener on top of the easy-care fin ished fabric, i .e. treated with DMeDHEU-a zero-formaldehyde easy-care fin i sh, decreases the static friction of fabric. Even at a h igher DMeDHEU add-on level the s i l icone softener covers the fibre surfaces and significantly decreases the fibre friction.

4.4 Bending length affects fabric stiffness and drape characteristics. The fabric having h igher bending length hampers comfort of the user. The bending length of the fabric increases by increasing add-on value. This can be attributed to the cross

l inking between DMeDHEU and cellulose fibres. An i ncrease in Arkofix V 375 1 add-on i ncreases the fabric bending length and stiffness. By the application of s i li cone softener on top of the easy-care fin ished fabric the bending length in i ti al ly i ncreases and then decreases; the values however are lower than those of the corresponding DMeDHEU-treated fabrics. The bendi ng length in both the warp and weft directions tends to l evel off after 5% chemical add-on .

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( 1982) 248-25 l . 2 Petersen H A, Cross- l inking with Formaldehyde- Containing

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4 Techllical /II/ormation, TIrr344e (BASF), 1 999, I I . 5 Charles Q Y, Am Dyest Rep, May ( 1 999) 1 1 - 15 . 6 Mooney W, Text MOllth, October ( 1 980) 32-34. 7 Mehra R H, Mehra A R & Mehra A R, Colourage, 38(8)

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(Butterworth Scientific Publications, London), 1959, 1&57. I I Ajayi J 0, Text Res J, 62 ( 1 992) 52. 1 2 Rooks R J, Text Chem C% r, 4 ( I ) ( 1 972) 47.