Ind ian Journal o f Fibre & Text il e Resea rch Vol. 28. September 2003 . pp. 3 12-32 1

Effect of solvent pretreatment and selective dye bath additives on physical properties and dyeing behaviour of microdenier polyester fabric

A K Samanta", A Konarb, D Ghosh & S Acharya

Text il e Chem istry Sec ti on, Institu te o f Jute Technology , 35 Ba ll ygu nge C ircu lar Road, Kolkata 7000 19, Ind ia

Received 2 November 200/ : accepted I January 2002

Polyester microdenier (0.8 dpf) and norma l de nie r (2 .1 7 dp f) multifil ament fabr ics have been subjected to swe lling pretreatmen t in sing le and mixed solvents of va rying ratio at room temperature fo r d iffere nt d ura ti ons prior to dye ing wi lh disperse dye. T he treated fab ri cs have been evaluated for changes in denie r. weight loss. a rea shri nkage. break ing tenacity, break ing e longat ion. c ritical d issolution ti me, surface depth o f colour. dye uni formity and light fastness . Among the th ree s ingle so lve nts used, the pretrea tme nt wi th 100% xy lene fo r 60 mi n at room tem perature shows s igni ficant improve ment in surface depth of colour and belle r balance of above properti es for both mi crodenier and normal denier polyester fabrics . T he use of a mixtu re of xy lene and dimethyl fo rmamide in the ratio of 1:2 for 60 min at room te mperat ure shows the hi ghest increase in surface depth of colour without much affec ting the above phys ical propert ies. Dye bath add itives li ke an tioxidant and UV absorber were used and UV absorbers are proved to be bene fi c ia l fo r improving li ght fas tness. Among a ll the UV absorbers used, benzophe none shows the best results even at a very low dose( 0 .5%).

Keywords : C rit ical d issoluti on ti me, Dye uni formity, Light fast ness, Mic rodenie r polyester fab ric. Po lyester fab ric, Solvent pre treatment

1 Introduction The demand of microdenier po lyester fabric is

increasing day by day due to its many advantages 1

over normal deni er po lyeste r fabric. Microdenier f ilament fab ri c imparts softness, better drape, good wearing comfo rt, good brea thability, bulkiness, high level of aestheti c appeal and hi gh cover in the resul tant fa bric. However, mi crodeni er fab ri c causes many practica l problems l.

1 in its wet process ing. There fabrics sho'vv lig hter surface depth of colour, non·· uni fo rm dye ing and poor co lour fas tness properties. It is know n2 that microdenier fibre/ filament/fab ri c has more specif ic surface area than that of normal denier f ibre/ fi lament /fabric. Therefore, the ex posure of hi gher surface area du ring its wet process ing and less dye concentration per specific surface area for a particu lar shade are inev itab le, resulting in li ghte r appearance of depth of colour. Poor light fastness is resul ted due to the exposure of hi gher surface area to the light during its use. Level dyeing is di ffic ult due to the higher rate of

"To whom all the correspondence should be addressed. Phone: 2476529912475 1985; Fax:009 1-033-24750996: E-mail : ijt @caI2.vsnl.net. in b Present address : Auro Tex tiles ( Vardhman Groups), Sa i Road, Baddi, Solan 173205, India

dye strike/absorpti on fo r great.e r surface area coupled with mo re amorphous fibre structure 111 the microfibre.

Solvent treatment on normal den ier polyester fa bri c and its effect on dyeing properties has been a lready studi ed by many sc ienti sts,·5, but there is littl e informati on6 ava il able o n effect of solvent pretreatment on dye ing behav io ur of microdenier polyeste r fab ri c .

The organic solvent acts on po lyester e ither by plasti c izing or swelling acti on with o r without some molecul ar deg radat ion, creating more vo ids and red ucing g lass transiti o n temperature7

•R

• T he swelling agent di ffuses into po lymer matri x, swell s the po lymer, breaks some weak inte rmo lecul ar forces between polymer chains and produces inc reased segmenta l mobility. This reduces glass transition temperature (Tg), causes some structura l rearrangement9

.IO and rebuilts the secondary inte r­

mo lecular fo rces in a pl asti c ized poly meric fibre, in vo lvi ng also the sliding , rotation and phys ical separation of crysta lline lamalle " with permissible h . k 1?· 14 Th ' . d h . s fi n age -. IS arI ses ue to t e ex tensIve

penetration of the ori ented on-crystall ine domains with contractio n of oriented po lymer with or w ithout marg inal tensile strength loss. At the same time, there is an increase in access ibility in non-c rystalli ne zone

SAMANTA et af. : MICR ODENIER POLYESTER FA BRIC 3 13

for better segregation of crystallites and non­crystallites, as observed by Warwicker ' 5. Again , the effect of pretreatment with sing le solvent and with mi xture of solvents may not be the same. Inter-sol vent interactions can lead to synergistic effect'6 depending on the ratio of individual solvent and their resul tant solubility parameters.

Weigmann et al. 17 studied the effect of DMF treatment on fine structure of polyester. Bobeth IH

investigated the progressive swelling of continuous fil ament of polyester in pheno l. Brennecke and RichterS and Haga l9 studied the swelling of po lyester in vari ous organic solvents. Ribnick et al. 20 studied the interaction of 26 solvents with different tex tile fibres. Chattopadhyay and Samanta2 1 reported the selecti ve sol vent pretreatment of po lyester yarn fo r achieving subsequent atmospheric dye ing. Chattopadhyay et al. 16 studied the e ffect of solvent mi xture treatment to obtain dye uniformity and to homogeni ze physical/structural vari ation of textured polyester fil aments. But, little studl has been done on the solvent swellinglpretreatment for microdeni er polyester materials.

Th d· 1 27 -24 d h ere are some stu les ' - reporte on t e chemical processing of microdenier po lyester fabri cs, mainly devoted to preparatory chemical process ing, selection of corresponding machineries, proper after­wash, selection of dyes, care in dyeing procedure, etc . The present work was, therefore, undertaken to study the effect of pretreatment of po lyester microdenier fabric with three diffe rent sing le solvents (DM F, acetone and xy lene) and with varying ratio of solvent mixtures on surface depth of colour, dye uniformity, tota l colour di fference and other fabric properties.

Disperse dyes show lower fas tness to light2s.26 on

polyester microfibres as compared to that on conventional normal denier po lyester fibres because of the greater fibre surface area that is exposed to light. The decreased light fas tness can be of the order of 0 .5-1 _5 units, depending on fibre fineness and fabric construction_ The effec t of suitable dye bath additi ves , like UV absorber and antioxidant, on light fastness of microdenier po lyester fabric was also studied in the present work .

2 Materials and Methods 2.1 Materials 2.1.1 Fabric

Plain weave fabri c (34 endslcm and 27 picks/cm) of normal denier (2. 17 dpf) po lyester multifiiament yarn (78 denier, 36 fil aments and zero twist) both in

warp and weft and pl ain weave fabric (38 endslcm and 36 picks/cm) of mi crodenier (0 .80 dpf) po lyester multifilament yarn (80 denier, 100 fil aments and zero twist) both in warp and weft were used for the study.

2.1.2 Solvents, Dye and other Chemicals Dimethyl fo rmamide (OM F), xy lene, acetone,

sodium hydrox ide, hydros, acetic ac id,a ll o f LR grade, were used.

A di sperse dye (Foron Rubine S-2GLFI ) of Mis Sandoz (Indi a) Ltd was used for dye ing. Sandac id­PBI liquid (a di spersing agent) of Mis Sandoz (Indi a) Ltd, e lectrofix LD liquid (dye auxili ary) and nonidet­P-40 (non-ioni c surfac tant) were used fo r thi s study.

UV absorbers, like sodium azide, benzophenone, 1,2,3-benzotri azo le of Mis Loba C hern Pvt Ltd, methyl ethyl ketone of SO fine Chern Ltd and antioxidant, like lauryl thio di-propionate (L TOP), were used.

2.2 Methods 2.2.1 Scouring of Fabric

Scouring of polyester fabrics was done by treating the fabrics in the solution containing 4 giL soda ash, I giL caustic soda, 2 giL surfac tant (nonidet-P-40), keeping the material-to- liquor ratio of I :50, at 60° C fo r 30 min in a launderometer.

2.2.2 Solvent Pretreatment Scoured po lyester fabric sampl es were treated with

diffe rent organic solvents under relaxed condi ti ons for different durations (60 and 120 min) at room

temperature (30 ± 2°C) with a material-to-liquor rati o of I :50. In case of mi xed solvents, the treatments were carried out onl y fo r 60 min under relaxed condition. The solve nt pretreated fab rics were thoroughly rinsed and then washed with dilute acetic ac id (0 .5%, v/v) for DMF-treated samples and wi th carbon tetrachloride for xy lene- and acetone- treated samples. Finally, the samples were washed with water and dried in air.

2.2.3 Dyeing

Polyester fabric pi eces were dyed with selec ted disperse dye using laboratory HT/HP beaker dye ing machine as per the standard dye ing procedure27 us ing the fo llowing recipe: di sperse dye, 2% on weight of fabric (owf); di spers ing agent, 0 .5 giL; electrofi x- LD liquid, 1 giL; and acetic ac id traces to maintain the pH at 4.5 - 5 .

Dyeing was started at 60°C and the temperature was raised to l300C at the rate of 20C/min _ The

3 14 INDI AN J. FIBRE TEXT. RES. , SEPTEMBER 2003

dyeing was continued fo r another 40 min and then the dyebath was cooled to 80°e. The disperse dyed pol yester fabri cs were then reducti on cleared by treating with 2 gil hydros and 2 gil caustic soda at 60° e for 30 min, washed and dried in air.

2.2.4 Application of UV Absorber / Antioxidant in Dye Bath The mi crodenier polyester fabric samples were

dyed hav ing U V absorber / antiox idant in the dye bath at different concentrati on (0 .5, I, 1.5 and 2% owf) . For the ease of appli cation, sodium azide in water, 1,2,3-benzotri azo le in hot water, benzophenone in butano l with vigorous stirring and LTDP in warm propanol (propane-2-01) were made soluble before thei r addition in dye bath .

2.3 Test Methods 2.3.1 Measurement of Mechanical Properties

Breaking tenac ity and breaking elongation for contro l and treated fa brics were measured on Instron uni versal tensile testing machine (44 11 ) as per the IS : 1969- 1968 method28 using the test specimen of size 50 mm x 20 mm (rave lled strip specimen) and traverse speed of 40 m/min . Average of 10 readings was taken for each sample .

2.3.2 Moisture Regain The untreated and solvent (single and mixture)

pretreated samples were dried in an oven at 1000e until constant weight was obtained and these weights (bone dry weight) were recorded. The samples were then kept in the des iccato r for conditioning at 65% relative humidity and 27°e. Thi s condition was achieved by keeping the samples in the atmosphere of saturated NaN03 solution ins ide des iccator for 48 h. The weights were again recorded with the help of microbalance and the moisture regain percentage was calculated on bone-dry weight bas is.

2.3.3 Shrinkage Area shrinkage of the fabri c after each chemical

treatment was measured by calcul ating the difference in area of a given segment ( lOcm x lOcm ) of the fabric before and after the treatment using the standard procedure29

. Average of 5 readings was taken in each case.

2.3.4 Weight Loss Weight loss of the fabric was calculated by taking

the di fference in weight o f a g iven segment of the oven-dried fabric before and after the given treatment

using the standard procedure30. Average of 5 readings

was taken in each case.

2.3.5 Critical Dissolution Time The yarns from both untreated and treated

polyester fabrics were rave led and single loop fro m such ravelled fi laments was formed having 11/4 in . diameter. It was hung from a stainless steel rod with a pretension load o f 0 .007 g/den. The fi lament yarn in thi s form was then introduced into 100% phenol kept in a wider diameter test tube at 400e and the time taken for the weight to fall down was recorded by using a stop watch fo llowing the standard procedure ' 0.

A verage of 5 readings was taken for each sample.

2.3.6 P'er cent Change in Denier Thi s test was carried out to find out the change in

count of the yarn after solvent swelling action with respect to the count of the parent yarn in fabric. The denier of both the fil ament yarns (normal den ier and microdenier) , ravelled from each treated and untreated fabrics, was measured after removal of crimp with suitable pretension load (0.00 16 g/den) following the standard procedure31.

2.3.7 Surface Depth of Colour/Colour Strength and Related Pal-ameters

Surface colour strength value was estimated in terms of KlS value (Kubelka-Munk-Functioni 2 using the following relationship :

(1- RAmax ) 2

KIS=-- - -2RA max

where K is the coefficien t of al;>sorption ; S, the coefficient of scattering ; R, the reflectance of the substrate; and A,lIax . the maximum absorbance wavelength.

The KlS value of the dyed samples was obtained from the Macbeth 2020 Plus re flectance spectrophotometer interfaced with associated computer-aided colour measuring and matching software. The total colour difference(L'lE) and dye Ul ni formity were also obtained using the Macbeth eeM system and associated software and the following relationship:

6 £ = ~(LlL) 2 + (L\a )2 + (L\b) 2

where L is the lightness/ darkness; a, the redness/greenness; and b, the yellownesslblueness.

Dye uniformity was measured by taking ey % of KIS values at 10 different points of dyed fabric

SAMANTA et al.: MICR OOENIER POLYESTER FAB RI C 3 15

2.3.8 Light Fastness

Light fastness of the dyed polyester fabrics was assessed on a MBTF (Mercury Bulb Tungsten Filament Lamp, 500 watts) microscale light fastness tester of Shirley Development Ltd, UK. A series of strips of dyed specimen was mounted along with the eight blue wool standard fabric strips on a cardboard. Strips of dyed polyester fabric samples were exposed to MBTF lamp by mounting the fabric sample strips on the cardboard hanged to a metal frame of MBTF tester, where one fourth of each sample was covered by black paper and three fourths of it was kept open for exposure. The effect of light on the colour, i.e. fading behaviour, was examined by lifting the black cover from time to time along with examining the fading of blue wool standards. The light fastness of the specimen was assessed by the fading of blue wool standards as per the IS : 2454-1967 method33

3 Results and Discussion 3.1 Effect of Single Solvent Pretreatment on Fabric Properties 3.1.1 Effect on Weight Loss, Shrinkage and Tensile Properties

Table I shows that the weight loss and shrinkage increase with the increase in treatment time from 60 min to 120 min, irrespective of the type of solvent used. The results also show 1.61-2.88% weight loss

for the polyester normal denier and microden ier fabrics . The weight loss is found to be the highest fo r 100% xylene and lowest for 100% acetone for both 60 min and 120 min treatment time.

Table I shows about 3.98 -9.76% shrinkage fo r microdenier fabric. It is found to be the highest for acetone and lowest for xylene for both 60 min and 120 min treatment time, which is just opposite to the value obtained in case of the weight loss. On the other hand, the DMF treatment causes moderate weight loss and shrinkage among the three solvents used.

The above results may be ex plained by the consequences of two opposing influences: (i) wei ght loss by the removal of res idual processing oil/surface finish (remaining part after scaring) and surface oligomers, including little surface dissolution of the fibrous material ; and (ii) area shrinkage due to the swelling and stress re laxation of the polymeric chain , which is also facilitated by plasticization effect of the solvents. Obviously, the results obtained indicate the predominance of second influence for all the solvents used.

The data on tensile properties (Table I) show that on solvent pretreatment, either there is very marginal decrease or almost no change in the breaking tenacity , irrespective of the treatment time and solvent type.

Table I - Effect of single solvent pretreatment on physical properties of normal denier and microdenier polyester fabrics

[Treatment temperature, 30 ± 2°C]

Fabric Increase in Weight Area Moisture Breaking Breaking COT denier loss shrinkage regai n tenacity elongation

% % % % cN/tex %

NO MO NO MO NO MO NO MO NO MD NO MO NO MO

Untreated 0.40 0.80 20.46 17.03 38.82 39.78 80 75

Treated with

100% OMF 60 min 0.85 2.44 2.58 2. 15 3.96 4. 12 1.02 1.95 20.44 16.98 46. 14 49 .12 49 43 120 min 2.54 2.58 2.72 2.4 1 5.22 5.82 1.51 2.03 20.45 17 .02 48.26 50.56 37 32

100% Xylene 60 min 0.3 1 2.23 2.66 2.45 2.0 3.98 0.82 1.37 20.42 16.66 43.02 48.86 62 58 120min 1.56 2.48 2.88 2.68 3.92 4.27 1.04 1.94 20.43 16.75 46.32 49.80 50 40

100% Acetone 60 min 1.53 2.84 1.61 1.74 5.92 6.24 0.6 1 1.1 3 20.25 16.77 48.40 5 1.66 70 62 120min 2.83 2.97 2. 16 2. 11 5.94 9.76 0.96 1.50 20.3 1 16.83 48.78 51.92 58 45

ND--Normal denier; and MD--Microdenier

316 INDIAN J. FIBRE TEXT. RES. , SEPTEMBER 2003

The breaking e longati o n inc reases after so lvent trea tment fo r a ll the three solvents used . The marg ina l increase in breaking e lo ngation is a lso observed with the inc rease in treatment time, irrespec ti ve o f the type of solvent used . However, the % increase in breaking ciongati on is max imum in case o f acetone.

The above findin gs towards tensile properties may be attributed to the poss ible di so ri entation o f polymeric cha in and increased access ibility to ex terna l agents, indicated by the lowering of C OT values (Table I). The inc rease in e lo ngation is the clear mani fes tatio n of shrinkage th at occurs during the swelling trea tment and solvent-induced cha in re laxa ti o n.

3.1.2 Effect on Critical Dissolution Tillie, Moisture Regain and Change in Filament Denier

It is observed from Tabl e I that the critica l dissolu tion time (C OT) decreases significantly with the increase in so lvent treatme nt time, irrespec tive of the type of so lvent and fabric used . However, the effect is always predominant fo r po lyester microdenier fabric than the no rmal denie r po lyester fabric. The effect is mo re pronounced in the case of DMF and xy lene treatments. Acetone treatment shows comparatively less reduction in C OT va lues.

C OT value gives an indirect pic ture of the microstructure of the fibre/fil ament in the fa bric assembl y. The drop in C OT va lue is a c lear indi cation of loosening of struc tura l assembly o f po lyeste r fil ament by re laxati on and di sori entati o n of chain s as we ll as increased loca li zati o n of c rysta lline and non­crysta lline reg ions, causi ng inc reased access ibil ity of externa l agents as studi ed by Galil 34. Hig her C OT va lue, o n the o ther hand , indi cates hi gher density or crysta llinity of the fibre po lymer.

Tabl e I shows that the so lven t pretreatment improves the mo isture regain fo r both pol yester microdenier and normal denie r fabrics. Moisture regain is fo und to be the hi ghest fo r DMF treatment and lowest fo r acetone treatment. The inc rease in moisture regain on sol vent treatment is a clear indication of increased access ibility o f polymer system which may be expla ined by better segregation of crys ta lline and non-crysta lline regions, parti a l di ssol ving/perfectioni ng of crystallites7

.34 as well as

ex pected increase in vo ids (number and/or size) on solvent swe lling. The loss in amorphous orientation on solvent treatment, as observed earlie r by Subramanian et al. 35, may be the another facto r for

ilcreased access ibility o f po lyester po lymer towards ex te rna l agents/moisture/dyes.

Per cent inc rease in fil ament yarn denie r o n solvent treatment and comparative ly higher inc rease in deni er for microdeni er po lyester fabric are a lso observed (Table I). This can be ex pla ined by sh rinkage consequent to swelling and stress re laxation of po lymer chain , causing overa ll inc rease in denie r.

3.2 Effect of Mixed Solvent Pretreatment on Fahric Properties 3.2.1 Effect on Weight Loss, Shrinkage and Tensile Properties

The effec t o f o rganic solvents mixture o n shrinkage of po lymeri c fibres depends on the ex tent to which the co mpone nts interac t with each othe r. Such inter­so lvent in te racti o ns can lead to sy nergism. It is considered to be appropriate to se mi xture of so lvents to bring the solubi lity parameter much closer to that of total so lubility paramete r o f po lyeste r fibre36

(8=1 0. 7) so that the actio n of mi xtu re of solvent beco mes more effec tive for better ba lance of property paramete rs o f the fa bric. It is a lso reported4

.7

.37 that the

max imum interacti on with polyester polymer occurs

at two regio ns of solubi lity pa rameter (b l =9.8 & 82=1 2. 1). In these regions, the solvent e ither inte racts w ith aro mati c or w ith a lipha ti c residue of the polye te l' repeat unit.

Weight loss, area shrinkage and tensile properti es o f the fabri cs treated with diffe rent proportions o f

DMF (b=1 2. 14)1aceto ne (b= IO.O) and DM F/xy lene

(b=8.7) mixed solvents are shown in Table 2. These two types o f mixture we re se lected o n the bas is of the data show n in Table I and indi vidual so lubility parameter va lues fo r the ir max imum poss ible interaction with po lyes te r fabri c. Again , it was a lso tho ught to be appropri ate to carry out mixed solvent treatment for o nly 60 min durati on as no s ignifi cant impro vement in tex til e- re lated pro perti es was observed fo r hi gher durati o n ( 120 min) in case of sing le solvent.

It is observed from Table 2 that the weigh t loss on mixed solvent treatment is highest for aceto ne/DMF (2: 1) mix ture and for xy lene/DMF (1 :2) mi xtu re in case of both po lyeste r microdenie r and normal denier fabrics.

The weighted average solubility parameter for 2: I acetone/DMF mixture is calculated to be 10.7 which is exactl y equal to the most w idely accepted theoretical value of solubility paramete r of polyester fibre . Again , the solubility parameter of 1:2 xylene/DMF mixture is also the closest (10.96) to it.

SAMANTA et at.: MICR ODENIER POLYESTER FABRIC 317

Table 2 - Effect of mixed solvent pretreatment on physical properties of normal denier and microdenier polyester fabrics ITreatment time. 60 min: and Treatment temperature. 30 ± i'Cl

Fabric Increase in Weight loss Area Moi sture regain

%

Breaking tenacity cN/tex

Breaking e longation

%

CDT denier % shrinkage

% %

ND MD ND MD ND

Untreated

Treated with

Acetone: DMF(3:I ) 1.03 2.75 2.25 2. 11 2.0

Acetone: DMF (2: I ) 0.67 2.58 2.79 2.59 2.0

Acetone: DMF ( I: I) 1.32 2.3 1 2.27 2. 10 3.96

Acetone: DMF ( I :2) 1.8 1 1.48 1.55 2.45 3.96

Acetone: DMF (I :3) 0.50 2.93 1.99 2.32 2.0

Xylene: DMF (3: I) 0.79 0.65 2.58 2.61 2.0

Xylene: DMF (2: I) 0.59 2.86 1.16 2.71 2.0

Xylene: DMF ( I: I) 1.42 2.0 1 2.42 2.58 3.96

Xylene: DMF (1:2) 1.00 0.35 2.85 2.84 2.0

Xylene: DMF ( 1:3) 0.72 2.99 2.66 2.75 '2.0

ND--Normal denier; and MD-Microdenier

Hence, the maximum weight loss occurs in both these cases.

The area shrinkage on mixed solvent treatment of microdenier polyester fabric is found to be higher as compared to that of normal denier polyester fabric. However, no particular trend is observed for both types of mixed solvents (acetone/OMF and xylenelDMF mixtures) at their varying ratio.

Table 2 shows that there is almost no change in breaking tenacity of both the polyester fabric, irrespective of the type of so lvents mixed or their ratio. After mixed sol vent treatment, the breaking elongation significantly increases in all the cases. However, the higher elongation observed in the case of polyester microdenier fabric may be corroborated by the higher shrinkage of polyester mjcrodenier fabric as compared to normal denier polyester fabric for the same mixed solvent treatment.

3.2.2. Effect 011 CDT, Moisture Regain and Change in Filament Denier

It is clear from Table 2 that the critical dissolution time decreases with the increase in proportion of OMF in the solvent mixture. The lowest COT value is observed in case of 1:3 acetone/OMF and 1:3 xylenelDMF mixtures for both the fabrics. In both these mixed solvent systems, the dropping trend in COT value increases with increase in proportion of

MD ND MD ND MD ND MD ND MD

0.4 0 .8 20.46 17.03 38.82 39.78 80 75

5.92 0.50 1.45 20.4 1 16.92 42.36 51.66 68 58

5.92 0.89 1.95 20.45 17 .01 43.26 52.02 64 55

4.0 0.48 1.47 20.43 16.92 48.22 49.22 60 52

3.96 0.45 1.46 20.37 17 .00 46.30 48.72 56 49

5.92 0.63 l.l8 20.43 16.64 43.46 51.04 53 46

2.5 0.43 1.04 20.43 16.95 43.48 45.14 60 56

5.92 0.77 1.62 20.38 16.68 43 .56 50.84 58 53

3.96 0.45 1.57 20.44 16.86 48.06 48.94 55 50

2.32 0.98 1.89 20.37 17.02 43 .30 46.14 53 47

5.92 0.48 1.72 20.35 16.75 43.04 51.07 50 45

acetone or xylene, keeping OMF proportion constant in the mixture. The drop in COT value also decreases with the increase in proportion of OMF, keeping the proportion of acetone or xylene constant in their respective solvent mixtures.

The drop in COT value may be due to the increased localization of crystalline and non-crystalline regions which might have led to increased access ibility of the polymer materials towards external agents.

For the mjxed solvent treatments , the moisture regain values (Table 2) increase possibly due to the increase in voids after swelling treatment and loss of amorphous orientation.

The per cent increase in filament denier is observed on mixed solvent treatment. It is a resultant effect of two opposite influences, i.e. weight loss and shrinkage, which have occurred simultaneously on solvent pretreatment. The reduction in weight reduces the denier while shrinkage of fabric increases the denier. Here, probably the shrinkage factor overweighs the weight loss factor and, therefore, the resultant denier increases.

3.3 Effect of Solvent Pretreatment on Surface Depth of Colour and Dye Uniformity

It is observed from Table 3 that the surface colour strength (average KJS value) of solvent pretreated

318 INDIAN J. FIBRE TEXT. RES .. SEPTEMBER 2003

Table 3 ---Effect of single and mixed solvent pretreatment on dyeing behav iour of normal denier and microden ier poiyes ter fabrics [Dye-- Foron Rubine S-2GFLI (2% shade): and Treatment temperature-- 30 ± i' CI

Fabric Treatment Average % increase Dye Total colour Light time KIS in KlS va lue uniformity difference ( l::,. £) fastness mill value (CY % of KIS) rati ng

ND MD ND MD ND MD ND MD ND MD

Untreated 14.26 10.31 1.89 2.93 5 3-4

Treated with

100% DMF 60 14.95 12. 17 4.84 18.04 1.78 2.08 0.58 2.30 5 3-4 120 16.81 12.26 17.88 18.9 1 1.57 2.62 1.47 2.58 5 3-4

100% Xy lene 60 16.79 12.57 17.74 21.92 1.13 1.21 1.75 1.37 5 3-4 120 16.83 12.61 18.02 22.31 2.03 1.48 1.21 1.31 5 3-4

100% Acetone 60 15.78 10.81 10.66 4.85 1.61 1.49 1.50 3.39 5 3-4 120 16.66 10.89 16.83 5.63 0.96 1.49 0.80 0.29 5 3-4

Acetone: DMF(3: I) 60 15.82 12.34 10.93 19.69 1.57 1.41 2.64 2.2 1 5 3-4

Acetone: DMF(2:1) 60 15.95 12.53 11.85 21 .53 1.33 1.01 2. 10 2.11 5 3-4

Acetone: DMF(I : I) 60 14.89 10.86 4.42 5.33 1.85 1.68 0.55 0.87 5 3-4

Acetone: DMF(l :2) 60 14.94 11 .07 4.76 7.37 1.68 1.51 0.82 1.19 5 3-4

Acetone: DMF( 1:3) 60 15 .85 10.49 11.1 5 1.74 1.84 2.36 1.0 I 0.49 5 3-4

Xylene: DMF(3: I) 60 15.95 10.80 11.85 4.75 1.16 2.28 0.60 0.43 5 3-4

Xylene: DMF(2: I) 60 16.54 12.75 15 .99 23.67 2.27 1.82 0.96 1.13 5 3-4

Xylene: DMF( I: I) 60 15 .96 10.85 11.92 5.23 1.99 1.67 0.31 0.87 5 3-4

Xylene: DMF( I :2) 60 17.27 13.68 21. 11 32.69 2.50 1.49 0.74 1.57 5 3-4

Xylene: DMF( 1:3) 60 16.06 13.58 12.62 31.72 2. 18 1.58 2.5 1 0.70 5 3-4

ND--Normal denier; and MD--Microdenier

(single and mixed) disperse dyed normal denier and microdenier polyester fabrics is significantly higher than that of corresponding control fabric.

In case of single solvent, the surface colour strength increases with the increase in treatment time for all the three single solvents used. However, almost maximum per cent increase in surface colour strength is obtained even after only 60 min solvent pretreatment of mkrodenier polyester fabric. Xylene pretreatment for 120 min shows the highest increase in surface colour strength for both polyester microdenier (22.31 %) and normal denier (18.02%) fabrics.

It is clearly observed that per cent increase in KlS value for mixed solvent pretreated polyester microdenier and normal denier fabrics is maximum for 2: I acetone/DMF and 1:2 xy lene/DMF mixtures. For normal denier polyester fabric, the per cent increase in KlS values ranges from 4.42 to 11 .85 in case of acetone/DMF mixture and from 11 .85 to 21. 11 111 case of xylene/DMF mixture. The

corresponding value for mjcrodenier polyester fabric ranges from 1.74% to 2 1.53% in case of acetonelDMF mixture and from 4.75% to 32.69% in case of xy lene/DMF mixture.

Thus, it is evident that the solvent pretreatment increases the surface depth of colour to a measurable extent on subsequent disperse dyeing of solvent pretreated polyester microdenier fabric. Hence, the problem of apparent lighter look of the dyed polyester micmfibre fabric can be partly overcome to some extent by solvent pretreatment.

The increase in surface depth of colour may be explained by the increased dye accessibi lity in polymeric mass by the swelling action of solvents coupled with the structural changes and plasticizing effect of each solvent used. The swell ing agent diffuses into polymer matrix and swells the polymer, causing increased access ibility of non-crystalline zone for better segregation of crystallites and non­crystall ites which is also reported earlier by Warwicker et al. 15

SAMANTA et al.: MICR ODEN IER POLY ESTER FABR IC 319

The maximum improvement in shade depth at the above specified ratios of two mixed solvents may be due to the fact that the resultant solubil ity parameter of mixed solvents is close to the total solubil ity parameter of polyester fibre.

The dye uniformity , i.e. uniformity of shade depth in terms of CY% of KlS values, varies from a mjnimum of 0.96 to a maximum of 2.62 for all the solvents pretreated dyed polyester normal denier and microdenier fabrics . Table 3 shows that the dye uniformity is improved (CY% of KIS values decreases) in solvent pretreated polyester microdenier fabric. Structural homogenization38

, removal of 0ligomers39

, plasticizing effect and action as carrier by retained solvents7 in the pretreatment process and selection40 of suitable category of disperse dyes and choice of proper dyeing cycle 1.40 in dyeing of microdenier polyester fabric may be considered as the main responsible factors for this. However, there is no consistent trend or significant improvement in CY% of KIS values for both the single and mixed solvents

pretreated normal denier polyester fabric. Corresponding total colour difference (L,E) values

for all the so lvent pretreated dyed polyester normal denier and microdenier fabric samples are shown in Tab le 3 . No improvement is observed in standard light fastness rating for solvent pretreated and subsequently disperse dyed normal denier and microdenier polyester fabrics, irrespect ive of the type of solvent used.

3.4 ElTect of Dye Bath Additives on Light Fastness and Dyeing Behaviour of Microdenier Polyester Fabric

Tab le 4 shows the effect of se lective UY absorber and antioxidant (applied in dye bath ) on light fastness and average KlS values of dyed microdenier polyester fabric after being exposed to light for different durations. It is observed that the addition of di fferent doses of UY absorber and antioxidant compounds in the dye bath increases the light fastness rating of dyed microdenier polyester samples by \-1 .5 grade or it remains unchanged, depending on the type of

Table 4 - Effect of additives (U V absorber / antioxidant) in dye bath on light fastness properties of microdenier polyes ter fabric

r Dye-Foron Rubine S-2GFLI (2 % shade) I

Additive, % Average KJS values for different durations of fading Light fastness (owf) Oh 20 h 40 h 80 h 160 h 320 h rating

Nil (Control) 10.3 1 10.20 10.06 9.28 3-4

Sod ium azide 0.5 10AO 10.35 10.2 1 9.78 9.38 4 1.0 lOA I 10.36 10.24 9.80 9.39 4 1.5 10.53 IOA8 10.37 9.90 9.46 4 2.0 10.62 10.57 IOA5 9.98 9.56 4

Benzophenone 0.5 10.52 10.50 10A I 10.3 1 9.88 9A7 5 1.0 10.9 1 10.82 10.80 10.69 10.26 9.83 5 1.5 11.0 I 10.98 10.90 10.8 1 10.38 9.93 5 2.0 11 .54 11 .52 II A4 11 .35 10.88 10AO 5

1,2,3-Benzotriazole 0.5 11.20 I I. I 6 11 .02 10.80 10.08 4 1.0 11.35 11.30 11.19 10.97 10.23 4 1.5 11.67 11.62 11.49 11.30 10.50 4 2.0 11.70 11.65 11.54 11.33 10.54 4

Methyl ethyl ketone 0·.5 10.59 10.56 IOA5 10.27 9.85 9.56 4-5 1.0 10.62 10.59 IOA8 10.30 9.88 9.58 4-5 1.5 10.64 10.60 10.52 10.34 9.92 9.60 4-5 2.0 10.74 10.71 10.60 IOA2 10.00 9.67 4-5

LTDP 0.5 IOA9 IOA3 10.28 9.76 9A4 3-4 1.0 10.95 10.88 10.74 10.19 9.87 3-4 1.5 11 .05 10.98 10.85 10.30 9.97 3-4 2.0 11.12 11.05 10.9 1 10.36 10.00 4

320 INDIAN J. FIBR E TEXT. RES., SEPTEMB ER 2003

Table 5 - Effect of additives (UV absorber / antiox idant) in dye bath on dyei ng behaviour of microdenier polyester fabric

r Dye- Foron Rubine S·2GFLI (2% shade) 1

Additi ve. % Average Increase Dye Total (owf) KIS in KIS uniformi ty colour

va lue va lue (CV % of difference % KIS) (6E)

Nil 10.31 2.93 (Contro l)

Sodium az ide 0.5 10.40 0 .87 2 .27 3.95 1.0 10.41 0.97 2.56 3.78 1.5 10.53 2. 13 2.89 3. 11 2.0 10.62 3.00 2.04 3.37

Benzophenone 0.5 10.32 2.04 2.93 3.60 1.0 10.91 5.82 3.2 1 3.80 1.5 11.01 6.79 2.85 3.67 2.0 11.54 11.93 3.35 3.50

1,2,3- Benzo-triazole 0.5 11.20 8.63 2.43 3.83 1.0 11.35 10.09 2.67 3.26 1.5 11.67 13.19 3.89 3.73 2.0 11.70 13.48 2.02 3.76

Methyl ethy l ketone 0.5 10.59 2.7 1 2.09 3.54 1.0 10.62 3.00 3.83 3.96 1.5 10.64 3.20 2.50 3.53 2.0 10.74 4. 17 2.96 3.03

LTDP 0.5 10.49 1.75 3.71 3.45 1.0 10.95 6 .21 1.93 3.68 1.5 11.05 7. 17 2. 11 3.20 2.0 11.1 2 7.86 2 .44 3.69

compound used . The improvement in light fastness rating· is max imum in case of benzophenone and methyl ethyl ketone (UY absorber) even at a very low dose level (0.5%) . In case of sodium azide and 1,2,3-benzotriazole, a little improvement in the light

fastness is observed, irrespective of the d.ose level. But, almost no improvement is observed in case of L TOP (antioxidant) .

The stability of disperse colour towards fading under MBTF light fastness tester is found to be the highest in case of benozophenone and methyl ethyl ketone among all the fou r UY absorbers used . The stab ility increases marginally with the increase in dose from 0.5% to 2%.

Table 5 shows the effect of dye bath additives (UY absorber and antioxidant) on dyeing behaviour of mjcrodenier polyester fabric . 1,2,3-benzotriazole

shows some improvement in depth of colour (KIS value) , whereas other dye bath additives show littl e improvement in surface colour strength, dye uniformity and total colour difference ( 6£).

4 Conclusions 4.1 Pretreatment of both normal denier and microden­ier polyester fabrics with selective organic solvents increases shrinkage, weight loss, moisture regain, den ier, breaking elongation, surface depth of colour and dye uniformity but decreases the critical d issolu­tion time, indicating the increased access ibility of ex­ternal agents towards the fibre. 4.2 Among the three different si ngle solvents used, the pretreatment with xylene gives a better balance of the property parameters of both the polyester microdenier and normal denier fabrics at room temperature for 60 min treatment. At these conditions, the xy lene pre­treatment and subsequent disperse dyeing of microden­ier polyester fabric show the highest improvement in surface depth of colour (2 1-22%) with reduction in CY% of KlS values, indicating the better dye uniform­ity as compared to other single solvents used. 4.3 The use of selective proportion of acetone/ OMF(2:1) and xylene/ OMF ( 1:2 and 1:3) in so lvent mixture shows very good improvement in surface depth of colour. xy lene/ OMF ( 1 :2) mi xture gives the highest KlS value (surface depth of colour) among all the single and mixed solvents used. 4.4 Among all the UY absorbers and anti oxidants applied in dye bath for microdenier polyester fabric, benzophenone and methyl ethyl ketone show the no­ticeable improvement in light fastness.

Acknowledgement T he authors are thankful to Prof. Prabir Ray,

Principal, Institute of lute Technology, Kolkata, for all necessary support. They are also thankful to M/s Garden Silk Mill s, Surat, fo r suppl ying mi crodenier polyester fabric .

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