doi: 10.1111/j.1478-4408.2010.00251.
Modification of polyester fabric by
chemical ⁄ thermal treatment to improve
Coloration
dyeing ability
Technology
Wafaa M Raslan,a,*Ahmed Bendak,a Eid M Khalilb and Thanaa
Fawzia
a
National Research Centre, Textile Research Division, El-Tahrir st., Dokki,
Cairo 12311, Egypt
Email: wafaa_raslan@hotmail.com
Society of Dyers and Colourists
b
Faculty of Science, Helwan University, Cairo, Egypt
Received: 30 December 2009; Accepted: 27 April 2010
Attempts were made to enhance the dyeability of polyester fabric by thermal treatment or combined
chemical ⁄ thermal treatment in hot air or in steam, either slack or under load. Ethanolamine, hydrazine
hydrate, ethylene glycol and a benzophenone derivative were applied to the fabric by padding technique
prior to the thermal treatment. The dyeability of polyester fabric was found to be improved at nearly
boiling without using carriers and ⁄ or high-temperature ⁄ high-pressure techniques. The rate of dyeing of
chemically ⁄ thermally treated polyester fabric was found to increase. Differential thermal analysis of the
polyester samples was interpreted in terms of dyeability improvement. The glass transition temperature
of the treated fabric was found to decrease compared with the untreated one, resulting in an
enhancement in the dyeability of polyester fabric with disperse dye.
Introduction as well as the depth of dye molecules penetrated inside
the fibre structure.
Polyester fibres are dyed with disperse dyes. The dyeing
is carried out at high temperature ⁄ high pressure or by
using carriers at 100 C. Carriers cause the fibres to swell Experimental
[1]. Heat treatment of polyester fibres can lead to Materials
variations in the absorption behaviour. These variations White polyester fabric (78 dtex and 34 filaments),
appear in dyeing properties, in iodine sorption, as well as provided by the Misr Spinning Co. (Egypt), was soaped at
swellability of the fibres [2]. The effect of heat treatment 40 C for 30 min, thoroughly washed and air-dried at
in the presence of a nonionic surfactant on some selected room temperature. Chemicals and reagents of pure grade
properties of polyester fabric is studied over the (laboratory grade) were used, such as ethanolamine,
temperature range 180–220 C. The moisture-related hydrazine hydrate, ethylene glycol, acetic acid and 2-
properties of surfactant ⁄ heat-treated polyester are greatly hydroxy-4-methoxybenzophenone supplied from Aldrich.
improved. The uptake of disperse dyes by heat-set Commercial dyestuffs supplied from Bayer, namely CI
polyester was found to be temperature dependent [3–6]. Disperse Red 60 (kmax = 525) and CI Disperse Yellow 72
The effect of heat setting at different temperatures and (kmax = 445), were used in this study.
draw ratios on the diffusion of disperse dyes in polyester
was studied [7]. The diffusion is controlled by the Treatments
mobility of polymer chain segments, which can be Thermal treatment was carried out in a closed oven at
indicated by measurements of the glass transition various temperatures (160 and 180 C) for 15 min in slack
temperature (Tg). Both the diffusivity and dye-saturation conditions or under a defined load (3 kg ⁄ m2). Steam
values depend on the difference between the dyeing treatment was carried out at 100 C for a further 15 min in
temperatures and glass–transition temperature. The a steamer device (AMPs20; R. B. Electronic & Engineering
physical characteristics of polyester fibres, such as Pvt. Ltd, India) at the Central Service Laboratory, National
solubility and dye absorption, are related to the Research Centre, Egypt. Other samples were chemically
orientation and crystallinity of the fibres [8,9]. treated with various concentrations (5–20 ml ⁄ l) of
In this work, the aim was to perform a systematic hydrazine hydrate, ethanolamine, ethylene glycol and
investigation on the thermal and ⁄ or combined 2-hydroxy-4-methoxybenzophenone solutions by padding
chemical ⁄ thermal treatment of polyester through variation technique to a wet pick-up of 100%. The chemically
of the treatment conditions. Work was extended to study pretreated samples were thermally treated at 160 C for
the influences of these treatments on the dyeability 15 min in hot air under slack conditions.
behaviour of polyester fibre at boiling without using
carriers. The changes induced in the properties of the Dyeing procedure
polyester fibres are evaluated through measurements of Polyester samples were exhaust dyed in an aqueous bath
the colour intensity, the rate of dyeing (tan a), containing disperse dye and 1 g ⁄ l dispersing agent.
swellability, roughness and differential thermal analysis, Dyeing was performed at 100 C for different time
ª 2010 The Authors. Journal compilation ª 2010 Society of Dyers and Colourists, Color. Technol., 126, 231–236 231
Raslan et al. Modification of polyester fabric
intervals (15–60 min). The acidity of the bath was 6
adjusted to pH 4.5 with acetic acid. Both thermally and
chemically ⁄ thermally treated polyester fabrics with 5
hydrazine hydrate, ethanolamine, ethylene glycol and a
benzophenone derivative were subjected to dyeing in 4
comparison with the untreated sample. After dyeing, the
polyester samples were thoroughly washed several times
K/S
3
and dried under ambient conditions [10].
2
Colour measurement
Spectral reflectance measurements of the dyed fabric 1
were carried out using a recording filter
spectrophotometer. The colour strength, expressed as K ⁄ S
0
values of the dyed samples, was determined by applying 0 10 20 30 40 50 60 70
the Kubellka–Munk equation [11]. Dyeing time, min
Figure 1 Dependence of the colour intensity of thermally treated
Swellability polyester fabrics at different temperatures on the dyeing time
The swelling can be expressed in terms of the increase in [treatment: hot air, slack, 15 min, 4—4 untreated, m—m 160 C,
diameter according to Eqn 1 [12]: — 180 C; dyeing: CI Disperse Red 60 (0.5% owf), 100 C,
pH 4.5, liquor to goods ratio 100:1]
D2 D1 temperature may be attributed to increased accessibility
%SD ¼ 100 ð1Þ
D1 as a result of decreased orientation and to formation of
voids and cracks as shown in our previous work [13].
where SD is the transverse diameter swelling, D1 the Hence, the modified polyester exhibited enhanced colour
diameter of the sample before swelling (lm) and D2 the intensity upon dyeing.
diameter of the sample after swelling (lm). Figure 2 shows the dependence of colour intensity on
the time of dyeing in relation to the thermal treatment
Differential thermal analysis media. The thermal treatment of polyester fabric in steam
Differential thermal analysis (DTA) was carried out using at 100 C displays the highest colour intensity, while the
a thermal analyser 7 series (Perkin Elmer, USA). Fibres thermal treatment in hot air (slack or under load of
were cut into fine pieces of ca. 200 mesh in size. 3 kg ⁄ m2) gives a lower effect on the enhancement of
Approximately 25–40 mg of the cut fibres were polyester dyeability. This may be attributable to the
sandwiched between two layers of calcined alumina in swelling effect of steam and increasing of the disorder in
the sample holder. The rate of heating was adjusted to the fine structure of the fibre [12].
15 C ⁄ min. Thermographs were recorded from 5 to
350 C under normal atmospheric conditions. Chemical ⁄ thermal treatment
Swellability
Table 1 shows the diameters of the untreated and treated
Results and Discussion
polyester fibres with various chemical compounds, as
Temperature, time and media of treatment well as the corresponding percentage swellability. It can
Polyester samples were thermally treated in hot air for
15 min under slack conditions or under load (3 kg ⁄ m2) at 5
temperatures of 160 and 180 C. The treated samples, 4.5
along with the untreated one, were dyed as described in
4
the Experimental section. The extent of dyeing is
expressed as colour intensity. 3.5
Figure 1 shows the dependence of the colour intensity 3
of the thermally treated polyester fabric at different
K/S
2.5
temperatures on the time of dyeing. It is observed that the
treated samples at 180 C exhaust a higher amount of 2
dye. The dyeing of the treated sample at 160 C is in the 1.5
midway position. The increase in the colour intensity at
1
high temperature may be because of the change in fibre
crystallinity as reported elsewhere [7,13]. The glass 0.5
transition temperature (Tg) of polyester fabric was found 0
0 10 20 30 40 50 60 70
to decrease from 72 C for the untreated sample to 69 C
Dyeing time, min
for the thermally treated sample. This leads to increasing
the chain mobility and a more open structure Figure 2 Dependence of the colour intensity of thermally treated
subsequently being formed, which may cause easier polyester fabric on the time of dyeing in relation to the media of
treatment [treatment: hot air, 160 C, 15 min, ·—· untreated,
penetration of the dye molecule, leading to a large
4—4 load 3 kg ⁄ m2, m—m slack, •—• steam at 100 C; dyeing:
increase in the colour intensity. Also, the increase in the CI Disperse Red 60 (0.5% owf), 100 C, pH 4.5, liquor to goods
colour intensity with increasing the thermal treatment ratio 100:1]
232 ª 2010 The Authors. Journal compilation ª 2010 Society of Dyers and Colourists, Color. Technol., 126, 231–236
Raslan et al. Modification of polyester fabric
Table 1 Effect of chemical ⁄ thermal treatmenta,b on the 14
swellability of polyester fabrics
12
Increase in
Diameter Swellability cross-section 10
Polyester sample (lm) (%) area (%)
8
K/S
Untreated 11.0
Treated with: 6
Ethanolamine 11.4 3.6 7.4
2-Hydroxy-4-methoxy 11.8 7.2 15.0
benzophenone 4
Ethylene glycol 12.0 9.0 19.0
Hydrazine hydrate 12.8 16 35.5 2
a Chemical treatment: 1.5% (v ⁄ v), padding, pick-up 100% 0
b Thermal treatment: hot air, slack, 160 C, 15 min
0 10 20 30 40 50 60 70
Dyeing time, min
Figure 4 Dependence of the colour intensity of
be seen that hydrazine hydrate treatment was found to be ethanolamine ⁄ thermally treated polyester fabric on the dyeing
more effective in enhancing the swelling properties of time [treatment: 160 C, 15 min, hot air, ·—· untreated, + — +
polyester fabric than ethylene glycol, 2-hydroxy-4- slack thermally treated, 4—4 5 ml ⁄ l, m—m 10 ml ⁄ l, —
15 ml ⁄ l, •—• 20 ml ⁄ l; dyeing CI Disperse Red 60 (1.0% owf),
methoxy benzophenone and ethanolamine. The more the 100 C, pH 4.5, liquor to goods ratio 100:1]
swelling effect by the chemical compound, the more the
dye uptake of the fibre [12].
causing a loss in weight. The used concentrations
Hydrazine hydrate (5–20 ml ⁄ l = 0.5–2% v ⁄ v) of hydrazine hydrate solutions
Polyester fabric was treated with hydrazine hydrate led to an increase in the fibre cross-sectional area as well
solutions of various concentrations (5–20 ml ⁄ l) by as its swellability (Table 1) and do not cause a noticeable
padding technique (pick-up 100%) and then thermally loss in weight of polyester fibres. Applying the padding
treated at 160 C for 15 min. Figure 3 shows the technique in the treatment may decrease the consumption
dependence of the attained colour intensity of the dyed of chemicals as well as reducing the pollution impact,
pretreated polyester fabric on the dyeing time in relation besides enhancing the fibre dyeability and decreasing the
to the hydrazine hydrate concentrations. It can be seen setting temperature of the polyester fabric.
that the colour intensity of the dyed pretreated polyester
fabric increases with an increase in the concentration of Ethanolamine
hydrazine hydrate. Treatment of polyester fabrics with Figure 4 shows the dependence of the colour intensity of
hydrazine hydrate before thermal treatment attains a the dyed pretreated polyester fabrics on the dyeing time
noticeable enhancement in its dyeability. As previously when using various concentrations of ethanolamine. It
reported [14], relatively smaller amines, such as can be seen that the colour intensity of the dyed
hydrazine, swell the less ordered regions of the fibre and pretreated polyester fabrics increases with an increase in
its high concentrated solutions (above 40%) may attack the concentration of ethanolamine from 5 to 20 ml ⁄ l.
the ester linkage in the molecular chain, effectively Treatment of polyester fabric with ethanolamine leads
to an increase in the swellability of polyester (Table 1)
and a decrease in the glass transition temperature
14 (Table 2) of the fibres. Aminolysis have been previously
studied [15] in relation to the change in the fine structure
12 and morphology of polyester fibres. The amine
10
Table 2 Glass transition, crystallinity and melting temperatures
of polyester fabric
8
K/S
Polyester samples Tg (C) Tc (C) Tm (C)
6
4 Untreated 72 166 260
Treated with hot air under:
Load (3 kg ⁄ m2) 70.0 157 259
2
Slack 69.4 153 259
Treated with steam 69.0 153 258
0 Chemically ⁄ thermally treateda,b with:
0 10 20 30 40 50 60 70
Dyeing time, min Ethanolamine 70 155 258
2-hydroxy-4-methoxy benzophenone 63.0 159 257
Figure 3 Dyeability of hydrazine hydrate ⁄ thermally treated Ethylene glycol 69.8 164 258
polyester fabrics [treatment: 160 C, 15 min, hot air, ·—· Hydrazine hydrate 63.0 152 257
untreated, + — + slack thermally treated, 4—4 5 ml ⁄ l, m—m
10 ml ⁄ l, — 15 ml ⁄ l, •—• 20 ml ⁄ l; dyeing: CI Disperse Red 60 a Chemical treatment: 1.5% (v ⁄ v), padding, pick-up 100%
(1.0% owf), 100 C, pH 4.5, liquor to goods ratio 100:1] b Thermal treatment: hot air, slack, 160 C, 15 min
ª 2010 The Authors. Journal compilation ª 2010 Society of Dyers and Colourists, Color. Technol., 126, 231–236 233
Raslan et al. Modification of polyester fabric
12 12
10
10
8
8
K/S
6
K/S
6
4
4
2
2 0
0 10 20 30 40 50 60 70
Dyeing time, min
0
0 10 20 30 40 50 60 70 Figure 6 Dependence of the colour intensity of 2-hydroxy-4-
Dyeing time, min methoxybenzophenone ⁄ thermally treated polyester fabric on the
dyeing time [treatment: 160 C, 15 min, hot air, ·—· untreated,
Figure 5 Dependence of the colour intensity of ethylene + — + slack thermally treated, 4—4 5 ml ⁄ l, m—m 10 ml ⁄ l,
glycol ⁄ thermally treated polyester fabric on the dyeing time — 15 ml ⁄ l, •—• 20 ml ⁄ l; dyeing: CI Disperse Red 71 (1.0%
[treatment: 160 C, 15 min, hot air, ·—· untreated, + — + slack owf), 100 C, pH 4.5, liquor to goods ratio 100:1]
thermally treated, 4—4 5 ml ⁄ l, m—m 10 ml ⁄ l, — 15 ml ⁄ l,
•—• 20 ml ⁄ l; dyeing: CI Disperse Red 60 (1.0% owf), 100 C, penetration of the dye molecules inside the fibre easier
pH 4.5, liquor to goods ratio 100:1]
and lead to increasing the dye uptake and consequently
the colour strength.
concentrations used in our work affect fibre swellability In a separate experiment, high-temperature ⁄ high-
and polymeric chain mobility and do not cause loss in pressure (HT ⁄ HP) dyeing is tried for selected samples.
weight. The dyeing was performed in an HT ⁄ HP Sample Dyeing
Machine from HLL (India). The dyeing process was
Ethylene glycol carried out at 130 C and maintained for a period of
Polyester fabric was treated with various concentrations 30 min. It was found that the colour strengths (K ⁄ S) for
of ethylene glycol (5–20 ml ⁄ l) by padding technique and the polyester fabric treated with hydrazine hydrate,
then squeezed to 100% pick-up, followed by thermal ethanolamine and ethylene glycol followed by thermal
treatment in hot air at 160 C for 15 min. Figure 5 shows treatment are 9.9, 8.8 and 8.2, respectively, compared
the effect of chemical ⁄ thermal treatment of polyester with 6.8 for the untreated one when dyeing with CI
fabrics with ethylene glycol on the colour intensity Disperse Red 60. This increase in the colour intensity of
attained from dyeing with disperse dye at boiling point. the treated polyester when dyeing using the HT ⁄ HP
The ethylene glycol ⁄ thermally treated polyester fabric technique may be reflected by a saving of energy and
attains greater colour intensity upon dyeing than the time in dyeing process.
untreated one and ⁄ or when thermally treated in hot air. It
is also noticed that the increase of the concentration of Kinetic investigation
ethylene glycol leads to an increase in the colour Figure 7 illustrates the relation between the colour
intensity of polyester fabrics. The swelling effect of intensity of the hydrazine hydrate ⁄ thermally treated
ethylene glycol (Table 1) and the reorientation of the polyester fabric and the square root of the dyeing time at
amorphous regions as a result of chemical ⁄ thermal 100 C. Straight lines are given. The slope of the straight
treatment may create more voids accessible to dye line as indicated by tan a, where a is the degree of
molecules [14]. inclination of the straight line [16,17], attained 0.1407,
0.1637 and 0.2817 for the untreated, thermally treated at
Benzophenone derivative 160 C and hydrazine hydrate ⁄ thermally treated polyester
Polyester fabrics were treated with a benzophenone fabrics, respectively. It can be seen that the rates of
derivative using various concentrations (5–20 ml ⁄ l) by the dyeing of the treated polyester thermally or
padding technique then thermally treated at 160 C for chemically ⁄ thermally were significantly increased at a
15 min. The treated fabric is dyed with CI Disperse Yellow dyeing temperature of 100 C using CI Disperse Red 60.
72. Figure 6 shows the dependence of the colour intensity Hydrazine hydrate ⁄ thermal treatment was found to be
of chemically ⁄ thermally treated polyester fabric on the more effective in increasing the rate of dyeing of the
concentration of 2-hydroxy-4-methoxybenzophenone in polyester fabric with disperse dye than the thermal
relation to dyeing time. The colour intensity of the treated treatment alone.
polyester fabric increases by increasing the concentration
of benzophenone derivative. Treatment with 2-hydroxy-4- Surface roughness
methoxybenzophenone results in remarkable cracks on The Surfacorder Surface Roughness Measuring
the polyester surface, as shown in our previous work [13], Instrument SE 1700a (Japan) was used for measuring
in addition to its swelling effect (Table 1). That may make polyester fabric surface roughness properties. The results
234 ª 2010 The Authors. Journal compilation ª 2010 Society of Dyers and Colourists, Color. Technol., 126, 231–236
Raslan et al. Modification of polyester fabric
16 (a)
Untreated
14 y = 0.2817x
Thermally treated
R 2 = 0.9875
Hydrazine hydrate treated
12
10
y = 0.1637x
K/S
8 R 2 = 0.9886
4 y = 0.1407x
R 2 = 0.9894
2
0
0 10 20 30 40 50 60
Square root of dyeing time
Figure 7 Rate of dyeing (tan a) of untreated and
hydrazine ⁄ thermally treated polyester fabric
were found to be 27.6 lm for the hydrazine
hydrate ⁄ thermally treated polyester sample compared
with 27.4 lm for the untreated one. The rougher surface
(b)
of the treated sample may be as a result of the induced
changes and formation of cracks on the fibre surface after
treatment, as reported elsewhere [13]. The slight increase
in surface roughness of the polyester may be reflected by
enhancing its dyeability because of an increase in the
diffusion of dye molecules inside the fibre.
Differential thermal analysis
The application of DTA for characterisation of the
thermal degradation of synthetic fibres has been studied
[18]. The melting behaviour and the thermodynamic
functions, such as melting point, heat of fusion and (c)
degree of crystallinity, can be determined by this
technique [19]. Melting and glass transition temperatures
have a fundamental effect on the properties of the fibres.
Table 2 inferred that the glass transition, crystallisation
and melting temperatures exhibit values of 72, 166 and
260 C, respectively, for untreated polyester fibres. There
is a decrease in Tg and Tc for the treated polyester fabric.
It can be seen that Tg depends on the type of treatment.
The polyester fabrics treated with steam have a lower Tg
value than those thermally treated in hot air under slack
conditions. The chemical ⁄ thermal treatment of polyester
fabrics with various chemicals such as ethanolamine,
Figure 8 Cross sections of polyester fabrics: (a) untreated and
hydrazine hydrate, ethylene glycol and 2-hydroxy-4-
dyed; (b) steam treated (treatment: 100 C, 15 min, slack); (c)
methoxybenzophenone causes a decrease in the glass hydrazine hydrate ⁄ thermally treated (treatment: 1.5% v ⁄ v
transition temperature. The polyester fabric treated with hydrazine hydrate, 160 C, 15 min [all dyeings: CI Disperse Red
2-hydroxy-4-methoxybenzophenone and hydrazine 60 (1.0% owf), 100 C, 60 min, pH 4.5, liquor to goods ratio
1:100]
hydrate has the same value of Tg (63 C) as compared
with 72 C for the untreated one (Table 2). A decrease in
the glass transition temperature led to a segmental
polyester fabrics increases because of the effect of steam
movement of polymeric chains in the fibres. Also, a lower
and hydrazine hydrate treatments (Table 3). This holds
glass transition temperature promotes softness of
true with the results in Table 2, whereas the glass
polyester and thus disperse dye molecules can penetrate
transition temperature of the treated samples decreased.
easily [20].
Cross-section microscopy Conclusions
Microscopic graphs of cross sections of untreated fabric, The changes in the dyeing behaviour of polyester fibres
fabric thermally treated with steam and a hydrazine because of thermal and ⁄ or chemical ⁄ thermal treatments
hydrate ⁄ thermally treated sample are shown in Figure 8. were comparatively studied via evaluation of the colour
It can be seen that the depth of the disperse dye intensity, DTA and the depth of dye inside the fibre. The
molecules inside the interior structures of the pretreated dyeability of the treated fabric with disperse dye was
ª 2010 The Authors. Journal compilation ª 2010 Society of Dyers and Colourists, Color. Technol., 126, 231–236 235
Raslan et al. Modification of polyester fabric
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49 (1960) 153.
Untreated polyester 28.4 6. J Andrissen and J V Soest, Textilveredlung, 3 (1968) 618.
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Hydrazine hydrate (1.5% v ⁄ v) ⁄ thermally 46.5 12 (1968) 2491.
treated polyester 8. A Seves, B Focher, L Vicini and G Prati, Tinctroria, 70
(1973) 34.
9. J O Warwicker, J.S.D.C., 88 (1972) 142.
a Dyeing: CI Disperse Red 60 conc., 1% owf; 100 C, 60 min, pH 4.5,
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11. D Judd and M Wyszecki, Colour in Business, Science and
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temperature of the treated fabric with steam and the 15. G S Mischra and B L Deapura, Ind. J. Text. Res., 15 (1990)
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72 to 69–63 C. Increasing the depth of dye inside the 16. U Mayer, W Ender and A Wurz, Milliand Textilber., 47
interior structure of the fibres may overcome the ring (1966) 653.
17. U Mayer, M Brock, H Fleischer and H Pastor, Milliand
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236 ª 2010 The Authors. Journal compilation ª 2010 Society of Dyers and Colourists, Color. Technol., 126, 231–236
