Effect of Bulk Water Content on colour of dyed fabric

A study on the effect of bulk water contentand drying temperature on the colour ofdyed cotton fabrics

Muthusamy Senthilkumara,* and Natarajan Selvakumarb

aDepartment of Textile Technology, PSG College of Technology, Coimbatore 641004, IndiaEmail: [email protected]

bDepartment of Textile Technology, Anna University Chennai, Chennai 600025, India

Received: 12 May 2010; Accepted: 6 October 2010

In the present study, the effect of various levels of bulk and free water content and its distribution on thecolour of cotton fabrics dyed with direct dyes and their combinations were analysed. Twill and plainstructures with two different parameters of fabric construction were chosen. The dyed samples wereadjusted to different levels of wet pick-up, with water ranging from 50% to 125% on the bone dry weightof the fabric (odwf) to achieve various levels of bulk water content. Further, the residual moisture contentof the samples was adjusted to 40–10% odwf by means of hot air drying at different temperatures toobtain different levels of free water content and its distribution. For the assessment of colour and itscomparison, the parameters RK ⁄ S and DE�ab values were used. In order to bring out the true effect ofmoisture distribution and fabric structure, normalisation of dye uptake in the fabric based on weight andarea were considered, respectively. The plain structures show a higher increase in colour than the twillstructures when the bulk water content increases. At the same time, the fabric structures do not play asignificant role, with increase in colour attributable to change in drying temperature. The findings revealthat the bulk water content, drying temperature and fabric geometry affects the colour of the fabricsignificantly.

IntroductionThe measurement of colour plays an important role in the

textile, paint and food industries. Colour is one of the

most fundamental aspects of textile design and

contributes greatly to the overall visual effect of a

finished fabric. Colour measurement and matching is a

vital process in ensuring that a standard colour is

achieved in all the production batches. The creation,

production and communication of colours are usually

dependent on subjective interpretations. The colour

perceived by an observer results from the interaction of a

light source with a sample and with the observer. Colour

perception starts with the interaction of light with an

object, which is then modified by the reflectance. Such

interactions not only depend on the amount of colorant

present, but are also influenced by other foreign matters,

such as moisture and its distribution and the chemical

additives that are present within the medium [1]. In the

case of textile materials, the moisture content and its

distribution varies with respect to the conditions adopted

in the water application systems, such as exposure to

humidity or spraying ⁄ dipping, and in the water removal

systems, such as mangling and oven drying. This in turn

leads to variations in the interaction of light with the

substrate, which affects its colour.

It is well known that when light falls on textile

materials, scattering takes place at the surface. The extent

of such scattering depends on the surface characteristics

of these materials. In addition to this, light also

undergoes diffusion through the material, resulting in

absorption and scattering within the material. Finally,

light comes out of the material as diffuse reflection,

which depends on the extent of surface and internal

scattering that takes place [2]. The internal scattering of

textile materials depends on the number of dye molecules

and the number of other molecules, which may be air,

water or chemical compounds, which are present in it.

While measuring colour, the medium of the material is

assumed to be the same as the medium of the light and

the incident light undergoes absorption, reflection and

transmission [3,4]. When a dyed textile material

undergoes transformation from the dry to wet state, it

results in reduction in reflectance because of change in

medium [5]. This drop in reflectance is attributable to

reduced light scattering. In the study by Lee et al. [6], it

was mentioned that the fabric with higher moisture

content appeared to be darker in colour than the fabric

with low moisture content.

In continuous dyeing, colour assessment can be carried

out after drying by reflectance measurement of the fabric

at the exit of the dyeing range. The performance of the

online colour measurement system depends on various

parameters, such as fabric speed, residual moisture

content and fabric temperature [7]. Textile fabrics can

carry moisture in the form of bound, free and bulk water.

The bound and free water content in the cotton fibre can

be as high as 19% on dry weight of fabric (odwf) [8] and

21% odwf [9], respectively. The water content above 40%

odwf will be present in the fabric as bulk water. A fabric

can hold up to approximately 80% odwf of water as bulk

water [10]. According to the percolation theory [11],

when water passes through randomly distributed paths in

a medium, there exists a percolation threshold, which

usually corresponds to critical water content (40% odwf

for cotton). Regardless of the rate of internal moisture

transfer, as long as the water content is less than the

doi: 10.1111/j.1478-4408.2011.00290.x

ª 2011 The Authors. Coloration Technology ª 2011 Society of Dyers and Colourists, Color. Technol., 127, 145–152 145

ColorationTechnology

Society of Dyers and Colourists

critical level, the surface will form discontinuous wet

patches during drying. Thus, the mass transfer decreases

and the drying rate falls with the surface water content

[12]. It is always useful to take into account the quantity

of moisture added and other processing parameters, such

as drying temperature, while assessing the colour of a

textile material from its wet colour [13,14].

In the textile industry, the most common approach is

an adaptation of the theory expressed by Kubelka and

Munk in 1931 [15]. This is a two-flux radiation transfer

theory that has been developed for optically

homogeneous substrates. However the textile material has

a definite structure, therefore it cannot be assumed to be

a homogeneous layer. As the theory also does not deal

with surface phenomena and the medium in which the

substrate is embedded, surface correction becomes

essential to minimise the inaccuracy. During the actual

processing, the dyed textile materials are in a wet state,

with different levels of moisture content, which has an

effect on their colour. The distribution of moisture during

drying under different conditions could also affect the

colour. In such a situation, correct colour communication

through the whole supply chain and colour reproduction

during dyeing becomes difficult. Studies have not been

carried out in the assessment of the colour of the textile

materials, taking bulk and free water content into

account. In this article, the above factors are considered

using different fabric structures dyed with direct dyes.

ExperimentalMaterials

In order to bring in the effect of fabric surface

characteristics, two different structures, namely plain and

twill, were considered. In both the structures, pick

density was varied to obtain different levels of effective

area of fabric surface.

Specifications of the fabrics used were:

– plain: (i) 24s · 20s, 74 ends per inch (EPI), 52 picks per

inch (PPI) and 140 g ⁄ m2 (P1) and: (ii) 24s · 20s, 74 EPI,

40 PPI and 113 g ⁄ m2 (P2);

– twill: (i) 24s · 20s, 74 EPI, 72 PPI and 181 g ⁄ m2 (T1)

and: (ii) 24s · 20s, 74 EPI, 60 PPI and 153 g ⁄ m2 (T2).

Three direct dyes, namely CI Direct Red 243, CI Direct

Yellow 106 and CI Direct Blue 85 supplied by DyStar

(USA), were used. Laboratory grade sodium chloride

(NaCl) and sodium carbonate (Na2CO3) were used in

dyeing of the fabrics.

Methods

Preparation of dyed samples

Dyes chosen were used individually and as a mixture

with different proportions for dyeing of the fabric

samples (Table 1). Dyed samples were produced with

0.5%, 2.0%, 3.5% and 5.0% shades and, for the

production of the above shades, sodium chloride

concentrations of 5, 10, 15 and 20 g ⁄ l were used,

respectively. A liquor to material ratio of 40:1 was used.

The material was introduced into a bath containing the

required quantity of dye and 0.1 g ⁄ l sodium carbonate at

50 �C. The temperature of the bath was gradually raised

to 95 �C and the dyeing was continued for 30 min. Over

this period, calculated quantities of salt were added at 5,

10 and 15 min. Immediately after completion of dyeing,

i.e. before washing, a small portion of fabric was removed

from the dyed samples for measuring their reflectance

after drying. Washing of dyed samples was carried out

with an alternate cold wash using running tap water for

5 min and soaping for 5 min. Finally, the samples were

thoroughly washed with running tap water. To ensure the

repeatability of the results, three samples were produced

for every set of conditions.

Determination of RK ⁄ S value

The values of the summative Kubelka-Munk function

(RK ⁄ S) of the fabric were calculated using the formula

given below from the reflectance value (R) at wavelengths

from 400 to 700 nm at an interval of 10 nm, measured

using a Datacolor 600 spectrophotometer (Datacolor,

USA):

XK=S

X700

k¼400

½ð1� RÞ2=ð2RÞ� ð1Þ

where K and S are absorption and scattering coefficients.

Determination of % dye uptake (D)

Dye uptake by the fabric was calculated using the

formula given below [16,17] and the values obtained are

given in Table 2:

D ¼ EðK2=K1Þ ð2Þ

where E is the % of dyebath exhaustion, K1 is the RK ⁄ Svalue of the dyed sample before washing and soaping in

the dry state and K2 is the RK ⁄ S value of the dyed sample

after soaping in the dry state.

E was calculated using the formula given below from

the absorbance value at kmax (Table 1) measured using an

ultraviolet–visible (UV–vis) spectrophotometer (Cary 3E;

Varian, USA):

E ¼ 100 ½1� ðA2=A1Þ� ð3Þ

where A1 and A2 are the initial and final absorbance

values of the dye solution, respectively.

Determination of colour difference (DE�ab) value

The colour difference (DE�ab) value of the fabric was

calculated using the formula given below [18]:

Table 1 Parts by weight of dyes used for dyeing

DirectRed 243

DirectYellow 106

DirectBlue 85

kmax for dyesolution (nm)

Code nameassigned todyed fabrics

1 0 0 516 R0 1 0 415 Y0 0 1 568 B1 1 0 506 RY0 1 1 570 YB1 0 1 545 RB1 1 1 556 RYB

Senthilkumar and Selvakumar Bulk water content and drying temperature on colour of cotton

146 ª 2011 The Authors. Coloration Technology ª 2011 Society of Dyers and Colourists, Color. Technol., 127, 145–152

DE�ab ¼ ½ðDL�Þ2 þ ðDa�Þ2 þ ðDb�Þ2�1=2

where DL* = L*sample – L*standard, Da* = a*sample –

a*standard, Db* = b*sample – b*standard, L* = 116(Y ⁄ Yn)1 ⁄ 3 –

16, a* = 500 [(X ⁄ Xn)1 ⁄ 3 – (Y ⁄ Yn)1 ⁄ 3] and b* equals

200[(Y ⁄ Yn)1 ⁄ 3 – (Z ⁄ Zn)1 ⁄ 3]

where, Xn, Yn, Zn are tristimulus values of reference

white and X, Y, Z are tristimulus values of the dyed

sample.

The X, Y and Z values of the fabric were calculated

from the reflectance value at an interval of 400–700 nm.

Determination of colour of the samples with different levels

of water content

One set of dyed samples was immersed in distilled water

for 5 min and their wet pick-up level was adjusted to

125%–50% odwf by a mangling (HVF; Mathis, USA)

technique to achieve different levels of bulk water

content. The sample conditioned at 65% relative

humidity (rh) was considered as the control sample in

analysing the effect of bulk water content on colour.

Another set of dyed samples was taken and their wet

pick-up was adjusted to 100% odwf. They were taken for

drying at 100 and 50 �C using a hot-air oven (Blue M

Electric Co., USA). The drying was carried out until the

fabrics reach a specific residual moisture content level.

The different levels considered were 10%, 20%, 30% and

40% odwf. The colour of these samples, expressed in

RK ⁄ S values, was determined following the method

explained above.

Results and DiscussionEffect of bulk water content on the colour of the fabric

In the earlier studies conducted [19–21], the focus was

on the analysis of the effect of a specific wet pick-up of

the sample on its colour. However, in the actual situation

of the present study, especially during the chemical

processing of the textile materials, and because the water

content in them varies, different levels of wet pick-up

were considered. Amongst the bound, free and bulk

water types present in the textile material, the bound and

free water contents remain the same at higher levels of

wet pick-up (in the present discussion, the term ‘bulk

water’ is used instead of ‘wet pick-up’). Taking into

account the bound water content of 19% odwf [8] and

free water content of 21% odwf [9] cited in the literature,

the bulk water content was calculated by subtracting the

above values from the wet pick-up levels. The values

obtained were 10%, 35%, 60% and 85% odwf for the wet

pick-up levels of 50%, 75%, 100% and 125% odwf,

respectively.

The colour strength (RK ⁄ S) of the twill fabric, T1, dyed

to different depths of shade and having various quantities

of bulk water content, is shown in Figure 1. This shows

that, for all dye combinations and depths of shade, the

colour strength of the fabrics increases with the increase

in bulk water content. At lower bulk water levels, the

increase in depth of colour of fabric should be attributed

to the occupation of water molecules in the free spaces

present in the material leading to different levels of water

to air combination. Further, when the bulk water content

increases, the surface water content of the fabric would

also increase. The colour strength of the fabric shows an

improvement as both the factors stated above further

reduce the scattering of light because of the change in

refractive index of the fabric medium. Fabrics T2, P1 and

P2 are also found to follow a similar trend.

Effect of drying temperature on the colour of fabric with

residual moisture content

The excess water present in the textile material is

removed after completion of the dyeing process either by

means of mangling or centrifuging. After centrifuging, the

textile materials still hold ca. 45% odwf moisture [22].

This residual moisture content in the fabric is removed

by means of drying. If the moisture content of the

material is high, the surface is covered with a continuous

layer of bulk water and evaporation initially takes place

mainly at the surface. As the moisture from the surface is

removed, moisture transfer from the interior would take

place by means of the capillary flow of free water through

voids. The rate of removal of such moisture is determined

by the external conditions, such as the temperature of hot

air and the humidity [23–25].

The effect of the drying temperature on the colour of

the dyed fabrics, dried to various residual moisture

contents, is presented. Figure 2 shows this effect in terms

of RK ⁄ S values for the twill fabric, T1, dyed with Direct

Red 243 to different percentages of shades. The colour of

the fabric decreases appreciably when the drying

temperature is raised from 50 to 100 �C for all

percentages of shades when the fabric is dried to obtain

Table 2 Calculated percentage dye uptake of fabrics

Dyedsamples % Shade

Twill Plain

T1 T2 P1 P2

R 0.5 82.79 83.31 81.67 82.172.0 72.78 74.97 79.19 78.003.5 70.34 70.38 72.30 71.495.0 67.32 66.91 70.88 69.14

Y 0.5 75.58 77.51 80.13 79.522.0 70.33 70.60 70.45 72.373.5 69.35 68.60 67.54 67.775.0 67.33 65.24 64.81 64.92

B 0.5 71.24 74.01 79.36 78.352.0 64.84 63.28 63.14 63.733.5 61.29 60.01 62.33 61.085.0 51.44 55.59 56.95 56.42

RY 0.5 78.87 80.57 81.32 81.012.0 71.75 72.90 74.87 76.563.5 70.98 69.16 68.81 69.885.0 66.35 65.65 67.19 66.31

YB 0.5 72.70 76.41 80.09 79.182.0 68.41 66.14 68.36 64.863.5 62.86 64.56 63.74 63.135.0 61.53 62.11 63.69 63.93

RB 0.5 74.08 77.55 81.30 79.202.0 66.52 68.21 67.55 66.903.5 64.57 64.80 66.12 65.935.0 58.08 57.16 59.32 59.20

RYB 0.5 77.84 76.82 80.85 81.042.0 68.68 70.38 73.44 70.513.5 64.24 65.97 66.28 65.835.0 59.50 60.52 61.23 62.72



40% and 30% residual moisture content. It shows that,

when a higher temperature is involved in drying to a

residual moisture content of 30% and above, free water

is also removed along with bulk water. This leads to an

uneven distribution of water in the material and results

in lower colour yield. Whereas, during drying at a lower

temperature, as it takes much longer to reach the above

residual moisture content levels, either removal of bulk

water alone (in the case of the 40% level) or bulk water

followed by free water (in the case of the 30% level)

takes place in a uniform manner and, hence, the results

appear darker. Furthermore, it is clear from Figure 2 that

drying of the fabric to 20 and 10% residual moisture

content does not have appreciable effect on its colour.

The magnitude of this effect can be seen from the higher

colour difference values (DE�ab) obtained for the samples

dried at these temperature for 40% and 30% residual

moisture content compared with 20% and 10% residual

moisture content (Table 3). The DE�ab values for 20% and

10% residual moisture content are much lower and well

within the accepted level for practical applications [18].

Hence, such lower residual moisture content attained

using any drying temperature is of no concern. This is

attributable to the water present in the material, which

is mostly in the bound state. In order to confirm the

explanation given above, a set of dyed samples (T1) were

prepared with 10% odwf moisture content by using

appropriate conditions (80% rh and 20 �C). Table 4

shows the colour of the above conditioned samples and

the DE�ab values calculated using the colour of the

samples dried at both 50 and 100 �C to 10% residual

moisture content. It can be inferred from the very low

DE�ab values obtained that the material dried to a residual

moisture content of 10% contains mostly bound water. It

is expected that, even for 20% residual moisture content,

most of the water in the material would be in the bound

state. The RK ⁄ S values of the other fabrics, T2, P1 and

P2, dyed with all other dyes, and their combinations,

also follow the same trend with respect to drying

temperature.

800

700

600

500

400

300∑K

/S v

alue

200

Bulk water content

100

Y RY R YB RYB RB B0

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

Figure 1 Effect of bulk water content on the depth of colour of twill fabric, T1

500

400

300

∑K

/S v

alue

200

100

050 °C 100 °C

M1 M2 M3 M4

50 °C 100 °C 50 °CDrying temperature

100 °C 50 °C 100 °C

Figure 2 Effect of drying temperature in achieving specific residual moisture content on the depth of colour of twill fabric, T1, dyedwith CI Direct Red 243. M1, M2, M3 and M4- Residual moisture content of 10%, 20%, 30% and 40% odwf respectively



Effect of water content on the colour of fabrics with

identical dye uptake

In order to bring out the true effect of various levels of

water content on the colour of the fabrics dyed with

various combinations of dyes, the RK ⁄ S value was

calculated for all fabrics at a particular dye uptake

(2 g ⁄ 100 g of fabric) using the experimentally measured

dye uptake (Table 2) and the corresponding RK ⁄ S values.

Figure 3 shows the percentage increase in RK ⁄ S value

for all combinations of dyes for fabric T1 with respect to

the sample conditioned at 65% rh and 20 �C when the

bulk water content increases from 10% to different

levels. The percentage increase in depth of colour as a

result of change in drying temperature from 100 to

50 �C at the different residual moisture contents of 40%–

10% for all combinations of dyes for fabric T1 is given

in Figure 4.

In both the cases, the fabrics dyed with CI Direct

Yellow 106 shows a higher percentage increase in depth

of colour compared with the fabrics dyed with other

dyes. This is attributable to the high luminosity factor of

this dye [18], which causes a large change in colour with

a change in water content. Samples dyed with CI Direct

Blue 85, or combinations of red and blue dye at various

bulk water content and residual moisture content levels,

exhibit a slightly lower percentage increase in RK ⁄ Svalues. This is because of the relatively lower reflectance

behaviour of blue dye [21]. Other fabrics examined were

also found to follow the same trend.

Effect of water content on the colour of fabric with

different structures

The effect of fabric structure on the change in colour of

the dyed samples with different levels of water content

was analysed by determining the RK ⁄ S value for a dye

uptake of 3 g ⁄ m2 of fabric. The projected dye uptake of

the fabrics for 1 m2 and the RK ⁄ S value of those fabrics

were used for that purpose.

Figure 5 shows the percentage increase in RK ⁄ S value

with respect to the samples conditioned at 65% rh, when

the bulk water content increased from 10% to different

levels, for all types of fabrics and for the dye Direct Red

243. The percentage increase in RK ⁄ S value varies

between 44.98% and 120.40% for different fabrics. It is

higher for plain fabrics when compared with twill fabrics.

The water-retaining capacity of the textile fabrics depends

on the pick density [10]. In the present study, the twill

fabrics have a higher pick density than the plain fabrics.

Because of the lower pick density, at any given bulk

water content, the plain fabrics will hold more water on

the surface compared with the twill fabrics. When this

fabric is taken for colour assessment, because of the

presence of a greater amount of surface water, scattering

of the reflected light is reduced, resulting in a higher

colour value. The increases in the RK ⁄ S value and the

Table 3 DE�ab values obtained for dyed T1 samples in the wetstate dried at 100 and 50 �C to different residual moisturecontents

Dyedsamples % Shade

DE�ab value

Residual moisture content

10% 20% 30% 40%

R 0.5 0.62 0.93 2.43 3.292.0 0.69 0.91 2.51 3.823.5 0.77 1.01 2.67 3.815.0 0.89 1.12 2.88 4.23

Y 0.5 0.82 1.13 3.11 4.342.0 0.79 1.11 3.24 4.543.5 0.91 1.32 3.83 4.665.0 0.97 1.35 4.19 5.01

B 0.5 0.54 0.91 1.37 2.512.0 0.61 0.96 1.31 2.693.5 0.67 0.89 1.41 2.815.0 0.71 1.02 1.33 3.03

RY 0.5 0.68 0.97 2.51 3.332.0 0.66 1.03 2.73 3.463.5 0.79 1.01 2.90 3.985.0 0.91 0.98 2.71 4.19

YB 0.5 0.78 1.02 2.42 3.452.0 0.93 1.12 2.73 3.313.5 0.83 0.99 2.53 3.735.0 0.96 1.08 2.90 4.43

RB 0.5 0.62 0.94 1.95 2.832.0 0.71 0.86 1.92 2.903.5 0.74 1.10 2.26 3.265.0 0.69 1.03 2.43 3.19

RYB 0.5 0.88 0.96 2.32 3.402.0 0.95 0.88 2.31 3.553.5 0.69 1.01 2.73 3.985.0 0.55 1.06 2.59 4.13

Table 4 DE�ab values obtained for dyed T1 samples in the drystate conditioned to 10% moisture content and the same dyedsamples in the wet state dried at 50 �C (A) ⁄ 100 �C (B) to 10%residual moisture content

Dyedsamples % Shade

DE�ab value

A B

R 0.5 0.10 0.222.0 0.06 0.313.5 0.09 0.265.0 0.11 0.30

Y 0.5 0.11 0.332.0 0.12 0.353.5 0.15 0.365.0 0.12 0.34

B 0.5 0.06 0.162.0 0.09 0.193.5 0.08 0.205.0 0.10 0.22

RY 0.5 0.11 0.232.0 0.13 0.293.5 0.12 0.245.0 0.10 0.28

YB 0.5 0.10 0.222.0 0.09 0.213.5 0.12 0.195.0 0.11 0.25

RB 0.5 0.09 0.192.0 0.12 0.233.5 0.13 0.265.0 0.11 0.21

RYB 0.5 0.11 0.252.0 0.13 0.293.5 0.10 0.315.0 0.14 0.36



depth of colour of the fabrics dyed with all other dyes

and their combinations were also found to follow a

similar trend.

The increase in RK ⁄ S value as a result of the change in

drying temperature from 100 to 50 �C for all types of

fabrics dyed with CI Direct Red 243 and containing

3 g ⁄ m2 of dye is given in Table 5. The table shows that,

for all the fabrics, the increase in depth of colour is

higher when the residual moisture content is above 20%.

Table 5 also shows that the difference in the increase in

RK ⁄ S value between twill and plain fabrics at any level of

residual moisture content falls between 0.01 and 5.25. As

this difference is very small, it can be said that that the

effect of the drying temperature on the colour value at

various moisture content levels on plain and twill

structures is almost same. The fabrics dyed with all other

dyes and their combinations were also found to follow

the same trend.

ConclusionsThe study clearly reveals that not only wetting, but also

the moisture distribution in the dyed fabrics and the

change in drying temperature from 100 to 50 �C have an

appreciable effect on the increase in depth of colour.

The depth of colour of the samples shows an increasing

trend when the bulk water content increases with

respect to the samples conditioned at 65% rh. The

difference, expressed by bothP

K ⁄ S and DE�ab, between

samples dried at 100 and 50 �C is higher when the

residual moisture content is raised to above 20%. Hence,

it is necessary to give due importance to the bulk water

content and its distribution and the temperature adopted

for drying, while measuring the colour of the dyed

cotton fabrics.

Further, this study reveals that the increase in depth of

colour as a result of the change in drying temperature is

235

215R Y B RY YB RB RYB

195

175

155

135

115

Incr

ease

in ∑

K/S

val

ue, %

95

75

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

10%

35%

60%

85%

Bulk water content

Figure 3 Effect of bulk water content on percentage increase in RK ⁄ S value of fabric T1 with a dye uptake of 2 g ⁄ 100 g

Incr

ease

in ∑

K/S

val

ue, %

DyesR

0

1

2

3

4

5

6

7

8

Y B RY YB RB

M1 M2 M3 M4

RYB

Figure 4 Effect of change in drying temperature from 100 to 50 �C on percentage increase in RK ⁄ S value of fabric T1 with a dye uptakeof 2 g ⁄ 100 g. M1, M2, M3 and M4- Residual moisture content of 10%, 20%, 30% and 40% odwf respectively



not appreciable up to 20% residual moisture content and

is substantial above this level. The fabric structures are

found to play an important role despite the same amount

of dye ⁄ unit area being present in them. The plain

structures show a higher increase in depth of colour than

the twill structures when the bulk water content

increases. At the same time, the fabric structures do not

play a significant role in the increase in colour

attributable to the change in drying temperature.

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Incr

ease

in ∑

K/S

val

ue, %

10%

M1 M2 M3 M4

T1 T2

P1 P240

50

60

70

80

90

100

110

120

130

35% 60% 85%Bulk water content

Figure 5 Effect of bulk water content on the depth of colour with various fabrics dyed with CI Direct Dye 243 with a dye uptake of3 g ⁄ m2. M1, M2, M3 and M4- Residual moisture content of 10%, 20%, 30% and 40% odwf respectively

Table 5 Effect of change in drying temperature from 100 to 50 �C on the depth of colour of various fabrics dyed with CI Direct Red 243with a dye uptake of 3 g ⁄ m2

Increase in RK ⁄ S value as a result of change in drying temperature from 100 to 50 �C

Residual moisture content

10% 20% 30% 40%

Twill Plain Difference Twill Plain Difference Twill Plain Difference Twill Plain Difference

1.06 (T1) 0.81 (P1) 0.25 2.81 (T1) 1.57 (P1) 1.24 12.54 (T1) 13.86 (P1) 1.32 19.51 (T1) 22.20 (P1) 2.690.94 (P2) 0.12 2.23 (P2) 0.58 14.52 (P2) 1.98 24.74 (P2) 5.23

0.95 (T2) 0.81 (P1) 0.14 2.77 (T2) 1.57 (P1) 1.20 12.36 (T2) 13.86 (P1) 1.50 19.49 (T2) 22.20 (P1) 2.710.94 (P2) 0.01 2.23 (P2) 0.54 14.52 (P2) 2.16 24.74 (P2) 5.25



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Effect of Bulk Water Content on colour of dyed fabric

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