Indian Journal of Fibre & Textile Research Vol. 28, March 2003, pp. 76-85

Se]ective chemical pretreatments and post-treatments on microdenier po]yester fabric for improving surface depth of co]our

A K Samanta'

Textile Chemistry Section, Institute of Jute Technology, 35 Ballyguange Circular Road, Kolkata 700 019, India

and

o P Chattopadhya/, A Konar" & 0 N Sharma

The Technological Institute of Textile & Sciences, Bhiwani 127021, India

Received 2 November 200/; revised received alld accepted 5 February 2002

Polyester microdenier (0.8 dpl) and normal denier (~ 2dpl) multifilament fabrics have been subjected to pretreatment with different solvents and caustic soda prior to dyeing with disperse dye. The relative changes in their textile-related physico-chemical properties and structures have been evaluated by measuring weight loss, shrinkage, tensile strength , elongation, critical dissolution time and surface depth of colour in terms of K/S value. Among the th ree organic solvents (phenol, dimethyl formamide and nitrobenzene) used, the pretreatment with phenol shows some noticeable improvement in surface depth of colour without much affecting the above physical properties. The effect of treatment with 10% mixture of DMF-phenol (I : I) for 60 miil shows lesser weight loss but inferior balance of properties as compared to the treatment with 10% phenol or 10% DMF alone. Caustic soda pretreatment using 1-5% NaOH with 0.1-0.3% catalyst always shows higher weight loss in case of microdenier polyester fabric than that in case of normal denier polyester fabric. To achieve -15% weight reduction in microdenier polyester fabric , the optimum treatment conditions are: 5% NaOH , 0.1 % hexamethylene diamine,6O min treatment time and 90°C treatment temperature. Post-treatments with si licone and organo-modified silicone emulsion, having lower refractive index than that of the polyester fibre, are beneficial for improving surfac,~ depth of colour by 3.6 - 9% where amino-silicone emulsion shows the best results .

Keywords: Critical dissolution time, Di sperse dye, Dyeing, Microdenier fabric, Polyester fabric, Silicone emulsion

1 Introduction

In recent years, polyester microfilament fabrics have gai ned a great importance with increased popularity due to their numerous advantages' over normal denier(~ 2dpf) polyester fibre fabrics. The higher surface area of the microdenier fibre causes many difficulties/problems ' in its chemical processing like lighter appearance of depth of colour (higher dye requirement), non-uniform dyeing, and poor light and wash fastness. The higher surface area of microdenier fibre than that of normal denier fibre causes higher exposure of surface and lower dye concentration per specific surface area which ultimately result in poor light fastness and appearance of pale depth of colour.

3 To whom all the correspondence should oc addressed. Phone: 24765299; Fax: 0091 -033-24750996; E-mai l: ijt@caI2.vsnLneL in b Present address: Department of Textile Chemistry, M S Univer­sity of Baroda, Kala Bhavan, Vadodara 390001, India C Present address: Technical Department, Auro Textiles, Baddi , Solan 173 205, India

Weight reduction treatment using caustic soda on normal denier polyester fabric is an established and common process2

.3

. But, there is little information available on the effect of varying degree of caustic treatment on microdenier polyester fabric.

Extensive studies4. 'o have been made on solvent treatment of normal denier polyester multifilament yarns and its effect on dyeability. Weigmann et al. 5

investigated the effect of pretreatments with DMF solvent on fine structure of polyester. Bobeth6 studied the progressive swelling of continuous filament of polyester in phenol. Brennecke and Richer7 and Haga8

studied the swelling of polyester in various organic solvents. Ribnick et al.'} studied the interaction of 26 solvents with different textile fibres. Samanta et al.'o reported the selectiv~ solvent pretreatment of polyester yarn for achieving subsequent atmospheric dyeing. Samanta et at." also studied the effect of solvent mixture treatment to obtain dyeing uniformity and to homogenize physical/structural variation of textured polyester filaments induced in thermal

SAMANTA el 01.: MICRODENIER POLYESTER FABRIC 77

texturing process. But little or no study has been made on solvent swelling/pretreatment for microdenier polyester materials.

There are some studies1.l2-'4 on the problems and the suggested remedies of chemjcal processing of microdenier polyester fabrics. These are mainly related to preparatory chemical processing and selection of con'esponding machineries, proper after wash, selection of dyes, care in dyeing procedure, etc. The present work was, therefore, undertaken to study the caustic and solvent pretreatments of mkrodenier polyester multifilament yarn fabrics for improving their physical textile properties and dyeability. The effect of suitable finishing chemicals on shade depth of mkrodenier polyester fabrics has also been studied .

2 Materials and Methods 2.1 Materials

Plain weave fabrics of normal denier (2.14 dpf) polyester multifilament yarn (90 denier, 42 filaments and untwisted) both in warp and weft, and microdenier (0.80 dpf) polyester multifilament yarn (80 denier, 100 fi laments and untwisted) both in warp and weft were used.

Dimethyl formamide (DMF), phenol, nitrobenzene, trichloroethylene, sodium carbonate, sodium hydroxide (pallets), sodium hydrosulphite (hydrose), acetic acid, hydrochloric acid, cetyl-trimethyl ammonium bromide (CTAB), and hexamethylene diamine(HMDA), all of LR grade, and Nonidet-P-40 (non-ionic surfactant), Electrofix-LD liquid, silicone (polysiloxane) emulsion, Silicorel-TTSC (amino­modified polysiloxane), Finish-EP (epoxy-modified polysiloxane), and Finish-PUR (urethane-modified polysiloxane), all of textile finish grade, were used . Disperse Red B2B (CI Disperse Red 60) and the dispersing agent Setamol-WS [BASF (India) Ltd] were used for the study.

2.2 Methods 2.2.1 Scouring of Fabric

Scouring of fabrics was done by treating the fabrics in the solution (material-to-liquor ratio, 1:50) containing soda ash (4 gIL), caustic soda (l giL) and detergent (Nonidet-P-40) (2 giL) at 60° C for 30 min in a launder-O-meter.

2.2.2 Caustic Soda Pretreatment Scoured polyester fabric samples were treated

under relaxed conditions with selective doses (1-5 %) of aqueous caustic soda at 90° C for 60 min with two types of catalysts, viz. hexamethylene diamine (mild

catalyst) and cetyl-trimethyl ammonIUm bromide (strong catalyst) , maintaining the material-to-liquor ratio at 1 :50 in a launder-O-meter. The treated samples were washed initially with water and then with 0.1 % HCI (v/v) for 15 min at room temperature to neutralize any traces of alkali, if present. Finally , the samples were thoroughly washed with distilled water and then used for dyeing.

2.2.3 Solvent Pretreatment Scoured polyester fabric were treated under

relaxed conditions with different doses of aqueous DMF, aqueous phenol and nitrobenzene in trichloroethylene (TCE) separately for different durations at room temperature with a material-to­liquor ratio of 1 :50. The sol vent pretreated fabrics were then thoroughly washed with dilute acetic acid (0.5%, v/v) for DMF- treated samples, dilute caustic soda (0.1 %, w/v) for phenol-treated samples and TCE for nitrobenzene-treated samples. After final washing with water, the samples were air dried and then used for dyeing.

2.2.4 Dyeing The selective polyester fabric pieces were dyed with

disperse Red B2B dye in a laboratory HT-HP beaker dyeing machine following the standard dyeing proce­dure l5 with the following recipe: disperse dye, 0.5% (owf); dispersing agent, 0.5 gIL; Electrofix-LD liquid, 1 gIL; and acetic acid traces to maintain pH at 4.5 - 5.

Dyeing was started at 60°C and the temperature was raised to 130°C at the rate of 2°C/min . The dyeing was continued for another 40 min and then the content was cooled to 80°e. The disperse dyed polyester fabrics were then reduction cleared by treating with 2 gIL hydrbse and 2 gIL caustic soda at 60° C for 30 min. The fabric samples were finally washed and dried in air.

2.2.5 Application of Selective Finishing Chemicals Dyed polyester fabrics were padded with different

doses of selective finishing chemicals having low re­fractive indices than that of polyester fibre, squeezing to 100% expression in a laboratory padding mangle with two-dip two- nip application technique. The pad­ded fabrics were dried at 100°C for 10 min and cured at 150°C for 4 min in a laboratory stenter machine.

2.2.6 Measurement of Tensile Strength and Elongation Tensile strength and elongation behaviour of

control and treated fabrics were measured in a ZWICK 1445 Universal tensile testing machine using

78 INDIAN J. FIBRE TEXT. RES., MARCH 2003

small test specimen of the size 50 mm x 20 mm (ravelled-strip specimen), traverse speed 100 mlmin and pretension level 0.2 N (ref. 16) fo llowing the standard IS 1969-1968 method l7

. The average of 10 readings was taken to express the re levant properties for each sample.

2.2.7 Measurement of Bending Length

Fabric stiffness expressed by the bending length was measured as per the IS 6490-1971 (Cantilever T )1617. S' 'ff' . h est . uSll1g a asmlra Stl ness tes ter Wit a

specimen size of 200 mm x 25 mm. The average of 5 readings in each case was taken.

2.2.8 Measurement of Shrinkage

Area shrinkage of the fabric after each che mical trea tment was calcul ated by meas uring the difference in area of a g ive n segment of th e fab ri c before and after the treatment and ex press ing th at in percentage of initial area taken as pe r the standard procedure l7

.

The average of 5 readin gs was taken in each case.

2.2.9 Determination of Weight Loss Weight loss of fab ric was calculated by taking the

difference in weight of a g iven segment of oven-dried fabric before and after the treatment and then express ing that as a percentage of initial weight taken as per the standard procedure lH

• The average of 5 read ings was taken in each case.

2.2.10 Measu rement of Critical Dissolution Time

The yarns from both untreated and treated polyester fab ri cs were rave lled . Sing le loop of 11/4 inches diameter from s uch rave lled fi laments was fo rmed and hung from a s tainl ess stee l rod with a pretension load of 0.007 g/den. The filament ya rn in this fo rm was then di ssolved into 100% phe nol in a wider diameter test tube at 40°C and the time taken fo r the wei ght to fall do wn was reco rded by using a stop watch following the s tandard procedure l R

• T.he average of 5 readings was taken for each sample .

2.2.11 Measurement of Denier

To find out the change in count o f the yarn after so lvent swelling/causti c soda action with respect to the count of the parent yarn, the denier of both the fi lament yarns (normal denier and mi crodenier) ravelled from each treated and untreated fab ri cs was measured after removal of crimp with suitable pretension load (0.0016 g/den) using the standard procedure 19.

2.2.12 Determination of Surface Depth of Colour, Colour Strength and Related Parameters Surface colour value was estimated in terms of K/S

value (Kubelka-Munk Funct ionio using the following relationship:

(1- R).. max)2 K/ S=----

2R).. max

where K is the coeffic ient of absorption; S, the coefficient of scattering; R, the reflectance of

substrate; and A. max> the maximum absorbance wave length.

The KlS values of the dyed samples were obta ined from the Macbeth 2020 Plus reflectance spectrophotometer interphased with assoc iated colour measuring and computerized colour matching

softwares. The tota l co lour difference(llE), re lative colour s trength and dye uniformity were also obtained using the Macbeth CCM system with assoc iated softw are and fo ll owing relationships:

KIS va lue of pretreated sample

. (after dvein o ) Relative colou r strength (%)= • e X 100

KIS va lue of un treated sa mple

(a fter dyei ng)

I ? ? ) I'>E = V(I'>L)- + (I'>a) - + (M)-

where L is the lightness/ darkness; a, the redness/greenness; and b , the yellow ness/b lueness.

Dye uniformity = CY of KIS va lues

(measured at 10 diffe rent po ints of dyed fabric).

2.2.13 Assessment of Light Fastness

Li ght fastness of dyed po lyester fabri cs was assessed us ing a MBTF (Mercury Bulb Tungsten Filament Lamp, 500 Watts) microscal light fastness tester (fade-O-mete r) of Shirley Development Ltd, UK. A series of strips of dyed specimen was mounted a long with the e ight blue wool standard fabric strips on a cardboard . Strips of dyed polyester fabric samples were exposed to MBTF lamp by mounting them on the cardboard hanged to a metal frame of MBTF fade-O-mete r, where one fourth of each sample was covered by black paper and the remaining three fourths was kept open for exposure. The effec t of light on the co lour, i. e . fading behav iour, was examined by li fting the b lack cover from time to time a long with examining the fading of blue woo l standards. The light fastness of the specimen was assessed by the fading of blue woo l as per the standard IS 2454- 1967 procedure l7

.

SAMANTA el al.: MICRODENIER POLYESTER FABRIC 79

3 Results and Discussion 3.1 Effect of Organic Solvent Pretreatment on Fabric

Properties 3.1.1 Weight Loss, Shrinkage and Critical Dissolution Time

Table 1 shows that all the three solvents pretreatments cause 1.2 -2.3% weight loss for both polyester normal denier and microfibre fabrics. The weight loss is however slightly higher for polyester microfibre fabric than that for polyester normal denier fabric, ilTespective of the type of solvent used and it is lowest fo r 10% phenol pretreatment among the three solvents used for the comparable dose level; the weight loss increases with the increase in phenol concentration up to 20 %.

With the use of solvent pretreatment , the process ing o il , surface fini sh contents and surface oligomers are removed and little surface dissolution of the fibrous materi al occurs which causes reduction in weight of the material.

Shrinkage data (Table I) show that the polyester fabric on solvent pretreatment shrinks about 5.1 -10.2% for microdenier fabric and 4 .2 - 7.9% for normal denier polyester fabric. The extent of shrinkage is noticeably high in case of phenol and also the shrinkage increases linearly with the increase in phenol ' concentration. The shrinkage in case of pretreatment with 20% phenol is fo und to be as high as 10.2% for microdenier fabric and 7.9% fo r normal deni er polyester fabric. Pretreatments with 10% DMF and 10% nitrobenzene cause comparati vely lesser shrinkage. The observed shrinkage can be expl ained by the stress relaxation of the fibres in the fabric assembly, which is also fac ilitated by plasticization effect of the solvents.

The critical dissolution time (COT) va lue decreases with the increase in phenol concentration from 10% to 20%. Pretreatments with 10% DMF and 10% nitro­benzene show comparati vely less reduction in COT values. COT val ue indicates about the microstructure of the fibre in the fabric assembly. The drop in COT value is a clear indication of loosening of structural assembly of polymer/fibre by relaxation and deorientation of chains as well as increased localiza­tion of crystalline and non-crystalline regions, causing increased accessi bility of ex ternal agents as observed by Galil21. Higher COT value indicates higher density or crystallinity of the fibres. All the above effects are much predominant fo r polyester microdenier fabric than fo r normal denier polyester fabric .

3.1.2 Breaking strength, Elongation and Bending Length On solvent pretreatment, particul arl y in case of

phenol, there is an apparent increase in strength of

microdenier polyester fabric and thi s increase is almost equal to the concentration of phenol. Expectedly , the deori entation of polymer chain occurs due to the swelling action by solvent pretreatment which induces shrinkage of fil aments in fabric assembly. Thi s apparent increase in strength on solvent pretreatment of polyester fabrics (both normal denier and microdenier fil ament fabrics) is a resultant e ffect of two opposite factors, i.e. weight loss and shrinkage occurred simultaneously on solvent pretreatment, where the reduction in weight should reduce the strength while the shrinkage of fa bric should increase the fabric strength . Here, probably the shrinkage factor overcomes the weight loss facto r and therefore the fabric strength increases apparently to some extent. The resultant change in denier is depicted from denier values (Tablel).

There is a consistent increase in elongation on each solvent treatment, ilTespecti ve of the type and concentration of solvent used. The maximu m elongation is achieved in case of 20% phenol treatment. The increase in e longation is the clear manifestati on of observed shrinkage with ex pected deorientation of polymer chain and increased accessibility to ex ternal agents, as indi cated by the lowering of COT values.

The bending length results indicate the sti ffness (conversely softness or drape) of tex tile fabrics. The bending length increases to a small ex tent for each case of solvent treatment, irrespecti ve o f the solvent type and concentration, though the changes are very very small. This may be due to the removal of processing o il and surface finish contents.

3.1.3 Surface Depth of Colour,Colour Strength and Light Fastness

Table 1 shows that the surface colour strength (K/S value) increases for each case of solvent pretreatment followed by subsequent dyeing of both types of polyester fabric. Phenol pretreatment shows thi s effect to a higher ex tent as compared to DM F and nitrobenzene pretreatments. Pretreatment with 20% aqueous phenol shows 2 1 % increase in K/S value. For 10% DMF and 10% nitrobenzene pretreatments, the K/S values show 14% increase. Thus, it becomes ev ident that the solvent pretreatment, particularl y phenol pretreatment , increases the surface depth of colour to a measurable ex tent on subsequent dye ing of solvent pretreated polyester microdenier fabric. The solvent pretreatment is also li able to cause undesirable shrinkage and, to some extent, weight loss whi ch

00 0

Table 1 -Effect of solvent pretreatment on physical properties and subsequent dyeing behaviour of normal and microdenier polyester fabrics [Treatment time , 60 min ; Treatment temperature, 30± 2°C; and Dye, CI Di sperse Red 60 (0.5% shade) ]

Treatment Denier Weight Area Breaking Breaking Bending . Critical K/S Relative Total Light of loss shrinkage strength elonga- length dissolution value colour colour fastness

warp % % N/mm tion cm time strength, % difference rating yam % M;CIE

Untreated (Control)

Normal denier (90/42) 90.00 9.23 23.69 1.80 85 1.39 100 5 Microdenier (8011 00) 80.00 10.54 34.5 1.30 79 1.09 100 3-4

Treated with

10% Aqueous phenol Z 0

Normal denier 60 min 91.24 1.20 4.2 9.77 30.12 1.85 64 1.51 109.42 2.03 5 ;; 90 min 1.52 110.14 2.46 5 z

'-Microdenier 30min 1.27 li6.76 2.13 3-4 -n

60 min 81.35 1.33 5.1 10.96 38.37 1.40 58 1.29 116.56 1.47 3-4 0; 90 min 1.29 117.40 2.56 3-4 ::0

tTl overnight 1.29 11 8.5 1 1.51 3-4 -l

tTl 15% Aqueous phenol ><

:-l

Normal denier 91.49 1.97 7.1 10.04 35.70 1.90 51 1.53 110.87 0.95 5 ::0 tTl

Microdenier 81.56 2.05 8.6 11.81 41.53 1.45 39 1.30 119.24 1.22 3-4 en

20% Aqueous phenol 3: > ::0

Normal denier 92.06 2.02 7.9 11.37 38.76 1.95 43 1.55 112.32 2.19 5 n :r:

Microdenier 82.27 2.30 10.2 12.04 46.84 1.45 32 1.32 121.03 1.38 3-4 tv a a 10% Aqueous DM F w

Normal denier 90.66 1.79 3.5 9.81 26.82 1.85 72 1.40 101.45 0.39 5 Microdenier 80.71 1.92 4.1 10.97 35.45 1.35 64 1.20 110.09 0.83 3-4

10% Nitrobenzene in TeE

Norn1al denier 90.52 1.24 2.3 9.43 26.34 1.85 70 1.42 102.89 2.03 5 Microdenicr 80.57 1.56 2.7 10.66 35.67 1.35 60 L24 113.76 1.12 3-4

10% Aqueous mixture of DM Flphenol ( 1.- 1 )

Normal denier 90.43 0.75 1.9 9.30 24.79 1.85 78 1.41 102.17 1.00 5 Microdenier 80.62 0.78 2.1 10.57 35.04 1.35 70 1.22 112.36 0.49 3':'4

SAMANTA el al.: MICRODENIER POLYESTER FABRIC 81

again increases with the increase in phenol concentration. Hence, a compromise should be made between these two factors, i.e. increase in K/S value and increase in shrinkage with the increase in phenol concentration. Thus, the problem of apparent lighter look of the dyed polyester mjcrofibre fabric can be partly overcome to some extent by the pretreatment using 20% aqueous phenol solution in relaxed state before dyeing.

The increase in surface depth of colour, i.e. higher dye uptake, on solvent pretreatment followed by dyeing may be explained by the increased accessibility/diffusibility of disperse dyes onto solvent pretreated polyester fabrics as observed earlier in case of both normal polyester1o and nylon22 filament yarns. The solvent or swelling agent diffuses into fibre/polymer matrix and swells the fibre polymer in the fabric assembly associated with an expected increase in accessibility in non-crystalline zone due to better segregation of crystallites and non-crystallites as observed earlier by Galil21 and Warwicker23

.

Corresponding changes in K/S value in terms of relative colour strength percentage are also shown in Table 1.

The light fastness results show no noticeable change after these solvent pretreatment for both normal denier and microdenier polyester fabrics , irrespective of the type of solvent used.

3.2 Effect of Caustic Soda Pretreatment on Fabric Properties 3.2.1 Mild Catalyst (Hexamethylene diamine)

It is observed from Table 2 that 1-5% (lO-50g/L) pretreatment for 60 min at 90°C in the presence or absence of mild catalyst hexamethylene diamine (HMDA) shows 0.5-10.2% weight loss for normal denier polyester fabric and 1.27- 15 . 11 % weight loss for microdenier polyester fabric associated with 1-3.:5% area shrinkage for both the fabrics . There is also marginal reduction in elongation and marginal increase in COT values in case of pretreatment with 0.1 % HMDA and 1-5% caustic soda under the above conditions.

The observed weight loss is attributed to the sur­face saponification/hydrolysis of polyester by NaOH. The microdenier polyester fabric shows a higher amount of weight loss than normal denier fabric which may be attributed to the higher contact area of polymer surface with the alkali due to the higher spe­cific surface area of microdenier fibre fabric.

Breaking strength decreases for both 1 % and 5% concentrations of caustic soda at the same condition

of treatment but the effect is not so prominent due to the use of mild catalyst (HMDA). Thus, the physical properties of the normal denier or microdenier polyester fabrics do not change much on caustic pretreatment in the presence or absence of HMDA under the given set of conditions .

Thus, to achieve - 15% weight loss (desirable limit of weight reduction in normal denier polyester fabric for silky finish), treatment of polyester microdenier fabric using 5% NaOH in the presence of 0.1 % HMDA catalyst at 90°C for 60 min is recommended.

3.2.2 Strong Catalyst (Cetyl-trimethyl ammonium bromide) Table 2 shows that the weight loss increases

sharply for both 1 % and 5% caustic soda pretreatments with the increase in catalyst (CT AB ) concentration. For the treatment of 1 % CT AB along with 1 % caustic soda solution at 90°C for 60 min, the weight loss is as high as 25 % due to the increased hydrolysis of polyester in the presence of strong catalyst. Pretreatment with 5% NaOH at 90°C for 60 min in presence of 0.1% CTAB shows about 15% weight loss for normal denier polyester fabric and about 38.5% weight loss for microdenier polyester fabric. The weight loss in case of pretreatment with 1% CTAB and 5% NaOH under the same set of treatment conditions cannot be measured as both the mjcrodenier and normal denier fabrics disintegrate/degrade much at this condition.

In all the cases of NaOH treatment, the weight loss of microdenier polyester fabric is found to be much higher than that of normal denier polyester fabric under otherwise comparable conditions of treatment. The higher weight loss in case of microdenier polyester fabric is firstly because of the higher contact surface of the fabric and secondly the microfibres have more amorphous content24 and therefore are more susceptible to caustic attack. Such treatment with caustic soda along with controlled dose of CT AB distinctly improves the softness and feel of both types of polyester fabric which is indicated further from the reduction in bending length value after such treatments. The overall strength loss of the fabric due to the pretreatment is expectedly because of the increased weight loss and denier change predominating over shrinkage value in all the cases of NaOH treatment.

Table 2 further shows that for the treatment with 5% NaoH at 90°C for 60 min the weight loss increases rapidly with increase in CT AS concentration and above 0.3% catalyst concentration, the polyester fibre

00 tv

Table 2 -Effect of NaOH pretreatment (weight reduction) with or without catalyst on physical properties and subsequent dyeing behaviour of normal and microdenier polyester fabrics

[Treatment time, 60 min ; Treatment temperature, 90± 2°C; and Dye, CI Disperse Red 60 (0.5% shade)]

Treatment Denier of Weight Area Breaking Breaking Bending Critical K/S Relative colour Total colour warp yarn loss shrinkage strength elongation length dissolution value strength difference

% % Nlmm % cm time, s % t;E; CIE Untreated (Control)

Normal denier (90/42) 90 9.23 23.69 l.8 85 1.39 Microdenier (8011 00) 80 10.54 34.52 1.3 79 l.09

Treated with 1% NaOH 23.82 1.8 85 1.39 100 0.834 Normal denier 89.95 0.54 0.50 9.19 33.19 1.3 79 1.08 99.08 0.61 z Microdenier 79.80 1.27 0.50 10.45 0

J% NaOH + O.J% HMDA :; z

Normal denier 89.74 2.73 1.00 9.12 23.78 1.8 85 1.40 100.72 0.50 :---Microdenier 79.16 4.50 1.50 10.38 34.73 1.3 79 1.09 100 0.66 !l J% NaOH + 0.1% eTAB c:l

;0

Normal denier 88.24 4.49 2.00 9.04 23.22 1.75 86 1.39 100 0.88 rn Microdenier 77.81 7.01 2.00 10.06 35.65 1.20 81 l.08 99.08 0.52 -l rn 1% NaOH + 0.3% eTAB X

:-:l Normal denier 87.12 6.71 3.50 8.87 24.15 1.70 88 1.36 97.84 0.93 ;0

Microdenier 75.43 9.30 4.00 9.94 33.43 1.20 82 1.07 98.16 0.68 rn en

J% NaOH + 1% eTAB :s: Normal denier 84.30 12.37 4.00 8.29 24.36 1.60 89 1.35 97.12 1.19 » Microdenier 70.75 25.05 5.00 8.16 30.27 1.10 84 1.06 97.47 1.80 ;0

() 5% NaOH :r: Normal denier 88.19 6.66 3.00 9.07 23.49 1.70 86 1.38 99.28 0.35 IV

0

Microdenier 74.86 11 .26 3.50 9.55 30.27 1.20 82 1.08 99.08 0.76 0 VJ

5% NaOH + 0.1% HMDA Normal denier 85.38 10.20 3.00 8.17 22.52 1.60 89 1.37 98.56 0.90 Microdenier 72.14 15.11 3.50 9.33 28.48 1.10 83 1.08 99.08 0.64 5% NaOH + 0.1 % eTAB Normal denier 83.69 14.94 6.00 6.35 22.60 1.50 90 1.36 97.84 1.01 Mi crodenier 65.05 38.50 7.00 4.62 24.24 0.80 85 1.07 98.16 0.95 5% NaOH + 0.3% eTAB Normal denier 54.55 48 .17 8.00 2.94 28.63 1.00 92 Microdenier 60.20 Degrades 92 5% NaOH + 1% eTAB Normal denier Degrades Mi crodenier Degrades

SAMANTA ef a/.: MICRODENIER POLYESTER FABRIC 83

polymer gets damaged. On pretreatment with 1 % CT AB, the polyester fibre polymer starts disintegrat­ing and finally gets totally damaged. The fabric be­comes extremely soft when treated with 5% NaOH and 0.05% or 1 % CT AB at 90°C for 60 min which is also understood from the maximum reduction in bending length under the same condition. The mar­ginal increase in COT values indicates the effective increase in density after surface dissolution/hydrolysis of loosely held polymer chain on the surface, thereby decreasing the elongation . Higher weight loss due to high surface pol ymer hydrolysis/saponification is evi­dent in microdenier fabric due to the exposure of more surface area during the treatment.

3.2.3 Effect of Caustic Soda Pretreatment on Surface Depth of Colour

The K/S value or colour strength value is a quantitative measure of depth of shade i.e. surface depth of colour. It is observed from Table 2 that the colour strength of caustic pretreated and subsequent dyed polyester fabric changes very little and is found to decrease marg inally in most of the cases. However, the pretreatment with very low concentration (I %) of caustic soda in presence or absence of HMOA shows very marginal increase in K/S value. This may be due to the effect of so me finer surface rou ghness created because of the mild treatment which reduces the surface reflectance of dyed surface and hence the fabric apparently looks darker. But severe caustic treatment conditions with strong catalyst make the fibre more finer/smoother and delicate and hence the KIS value of subsequently dyed fabrics (both normal denier and microdenier) appears to be reduced marginally. Corresponding changes in surface depth of colour in terms of relative colour strength percentage are show n in Tab le 2.

3.3 Effect of Post-treatment on Colour Strength and Light Fastness

Table 3 shows that there is a measurable increase in surface depth of colour when se lective polymeric finishing agents, like silicone (po lys iloxane) emulsion, amino-modified polysiloxane, epoxy­modified polysiloxane and urethane- modified polysiloxane, are applied in different doses (0.5 -2% owf) to the normal and microdenier dyed polyester fabrics . Maximum increase in KJS value (-21 %) is observed for 2% application of amino­modified silicone emulsion. The use of epoxy­modified si I icone and urethan e· modifi ed si I icone on

dyed polyester fabrics (microdenier and normal denier) in different doses (0.5 - 2%) shows the maximum increase in K/S values at 1.5% and 0.5 % application level respectively . However, among the four different types of silicone emulsion used, the highest increase in surface depth of colour (K/S value) is found in case of 2% amino-modified silicone for both normal denier and microdenier fabrics. However, this increase in apparent surface depth of colour by use of organo-modified silicone emulsion is closer to but not equal, i.e. not capable of achieving the comparable shade depth achievable for the corresponding normal denier polyester fabric. Thi s increase in the apparent depth of colour by the use of above ordinary and modified silicone emulsions may be attributed to the following reason as depicted by Sandner25

. Polymeric medi a, like silicone and organo-modified silicone emulsions having lower refractive index (RIsi licone = 1.43) than that of polyester fabric (Rl pET = 1.65), deposited on the surface as a textile finish film reflect less light than unfinished dyed surface of polyester textiles and hence there is an apparent increase in surface depth of colour. Hence, the shade depth appears as darker.

With the increase in percentage level of am ino­silicone finish , the shade depth of dyed polyester textiles deepens, showing maximum at 2% application level as mentioned earlier. Optimum level for epoxy­modified silicone is reached at 1.5 % application level. Application of higher doses (1.5 % or 2% application level) of epoxy-modified silicone shows a further reduction in increased depth of shade, perhaps due to the higher level of smooth surface achieved by the higher application level, causing higher reflection of light in this case.

In case of polyurethane-modified silicone, the increase in surface depth of colour is maximum at minimum application level, i.e. the surface depth of colour reduces when the application level increases fro m 0.5% to 2%. This may be due to an increased masking effect of colour by the polymeric film of polyurethane-modified silicone. Hence, among the three types of silicone finishes, the application of 2% amino-modified silicone is recommended. Corresponding dye-uniformity data in terms of CV% of K/S values for above-said finishes is also shown in Table 3. The light fastness results show no noticeable change after these polymeric finishes; however, polyester microdenier fabric shows one grade lower

84 INDIAN 1. FIBR E TEXT. RES., MARCH 2003

Table 3 -Effect of differen t polymeric fini sh ing agents on surface depth of colour on dyed norma l denier and microdenier polyester fabric s

[Dye - C I Di sperse Red 60 (0.5% shade)]

Fini sh app lied and its KIS (avg.) % Inc rease in KIS doses

Normal Mi cro Normal Micro denie r denier denier denier

Nil (Control ) 1.39 1.09 2% silicone emul sion (Mi xture of 60:40 dimethyl and hydrogen 1.47 1.30 7.9 19.2 methyl polysiloxane)

Silicorel-TTSC (Am ino-mod ifi ed silicone em ul sion)

0.5 % 1.5 1 1.1 8.63 2.04 1.0 % 1.56 1.26 12.2 16. 19 1.5 % 1.56 1.25 12.2 15.33 2.0 % 1.6 1 1.32 15.8 2 1.1 0

Fini sh EP (Epoxy-mod ifi ed silicone emu lsion)

0.5 % 1.50 1.1 7 7.9 1 8.05 1.0 % 1.53 1.1 8 10.07 8.86 1.5% 1.56 1.2 1 12.2 10.96 2.0 % 1.52 1.1 6 9.35 7.27

Fini sh PUR (Polyurethane -mod ified silicone emul sion)

0.5 % 1.56 1.1 9 12.2 1.93 1.0% 1.52 1.1 4 9.35 1.64 1.5% 1.52 1.1 4 9.35 2.88 2.0% 1.53 1.1 5 10.07 1.07

light fastness than normal den ier polyester fabric, irrespective of the type of fini sh app li ed.

4 Conclusions 4.1 Treatment with 10 -20% aqueous solution of phe­nol at room temperature for 60 min on rnicrodenier polyester fab ric shows 12-2 1 % improvement in sur­face depth of colour, when subsequentl y dyed with disperse dye. The effect is much less pronounced in case of normal denier polyester fab ric than in case of microdenier polyester fabric . 4.2 Pretreatment with LO% DMF or LO% nitroben­zene or a mixture of LO% DM F-phenol (1 :1) shows lesser weight loss but inferior balance of fabric prop­erties and surface colour strength after dyei ng than that with 20% phenol treatment on both microdenier and normal denier polyester fabrics.

Dye uniformity Total colour di ffer- Li ght fastness (% C Y of KlS) ence /:,/;; C IE rating

Normal Micro Normal Micro Normal Mi cro denier denier den ier den ier deni er denier

1.73 2.01 5 3-4

2.36 0.82 5 3-4

1.25 1.72 1.77 4.20 5 3 - 4 2.38 2.6 1 1.78 3.86 5 3-4 2.97 1.28 2.24 4.40 5 3-4 2.44 2.40 2.30 4.38 5 3 - 4

1.76 2 .52 1.77 3.53 4-5 4 1.82 2.00 1.69 4 .22 4 - 5 4 2.58 1.44 1.93 4.05 4 - 5 4 0.83 1.84 1.08 4 .10 4-5 4

1.93 1.1 5 1.1 5 3.74 4-5 4 1.64 1.64 1.25 4.09 4-5 4 2.88 1.86 1.11 4 .04 4-5 4 1.07 2.1 1 1.29 3. 15 4-5 4

4.3 Treatment with 5% NaOH in presence of 0.1 % HMDA for 60 min at 90°C restricts/controls the weight loss of microdenier polyester fabric up to 15% leve l, a desirable limit for weight reduction treatment achievable using CT AB conventional catalyst on normal deni er polyester fabric . The use of conven­ti onal CT AB catalyst at the same dose level and com­parable conditions of treatment give 38.5% weight loss in microdeni er polyester fabric.

4.4 Like that in 20% phenol pretreatment, the equal level of increase in KlS value (-21 %) of di sperse dyed microdenier polyester fabric is achievable by post dyeing treatment with 2% amino-modified polysi lox­ane using pad-dry-cure technique without any sol­vent pretreatment. Epoxy-modified silicone and ure­thane-modi fied silicone finishes show, to some extent,

SAMANTA et al.: MICROD EN IER POLYESTER FABRIC 8S

lower increase in K/S value than that in case of 2% amino-modified polysiloxane. 4.5 Polyester mjcrodenier fabric shows one grade lower light fastness than that of normal denier polyes­ter fabric, irrespective of the type of solvent pretreat­ment and silicone-finish applied.

Acknowledgement

The authors are thankful to the Principal , Institute of Jute Technology (UT), Kolkata, for providing all supports to carry out a substantial part of this work at UT. Thanks are also due to the Director, TIT &S, Bhiwani, for all kinds of other support and to Mis Garden Silk Mills, Surat, for providing microdenier polyester fabrics.

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