Indian Journal of Fibre & Textile Research

Vol. 38, June 2013, pp. 202-206

Optimization of polyester printing with

disperse dye nanoparticles

H Osman1,a

& M Khairy2

1Textile Printing, Dyeing & Finishing Deptartment,

Faculty of Applied Arts, Benha University, Benha, Egypt 2Chemistry Department, Faculty of Science,

Benha University, Benha, Egypt

Received 13 April 2012; revised received and

accepted 25 July 2012

A nanoparticle size disperse dye treated with ultrasound has

been applied on polyester fabric without using a carrier. Various

dyeing and process parameters used are studied in detail, such as

K/S values, dye particle size, dye exposure to ultrasound waves,

printing paste pH, steaming conditions of prints, morphological

study using SEM and TEM of dye particles and fastness

properties of the prints. The use of nanosized dye particles

enormously improves the colour depth of the prints without the

addition of extra chemicals to the printing paste.

Keywords: Ball miller, Dye nanoparticles, Fastness properties,

Polyester fabric, Printing, Ultrasound waves

A disperse dye is defined as a substantially water

insoluble dye having an affinity for one or more

hydrophobic fibres1. Disperse dyes are essentially non-

ionic dyes2, they are the most commonly employed

dyes in the textile industry to colour synthetic fibers

such as polyester, acrylic and acetate3. Disperse dyes

have extremely low water solubility and for application

from this medium, they must be milled to a very low

particle size and dispersed in water using a surfactant

(dispersing agent)4 or else a carrier must be added

during textile coloration.

The actual mechanism by which a carrier used in

dyeing accelerates textile coloration has been widely

debated. Polyester fibres absorb the carrier and swell.

This swelling can impede liquor flow in packaging

causing unlevelness. The overall effect leads to

lowering of the polymer glass transition temperature

(Tg), thus promoting polymer chain movements and

creating free volume. This speeds up diffusion of the

dye into the fibres. Alternatively, the carrier may form

a liquid film around the surface of the fibre in which

the dye is very soluble, thus increasing the rate of

transfer into the fibre5.

Power ultrasound (US) can enhance a wide variety

of chemical and physical processes; mainly due to

the phenomenon known as cavitations in a liquid

medium that is the growth and explosive collapse of

microscopic bubbles. Sudden and explosive collapse

of these bubbles can generate hot spots6, i.e. localized

high temperature, high pressure, shock waves and

severe shear forces capable of breaking chemical

bonds. Many efforts have been made explore this

technique in the textile coloration as it is a major

wet process, which consumes much energy and

water and releases large effluent to the environment.

Improvements observed in ultrasound assisted coloration

processes are generally attributed to cavitations

phenomena7 and, as a consequence, other mechanical

and chemical effects are as shown below:

• Dispersion (breaking up of aggregates with high

relative molecular mass);

• Degassing (explussion of dissolved or entrapped

air from fibre capillaries);

• Diffusion (accelerating the rate of diffusion of dye

inside the fibre);

• Intense agitation of the liquid;

• Destruction of the diffusion layer at dye/fibre

interfaces;

• Generation of free radicals; and

• Dilation of polymeric amorphous regions.

In the present work, 100% polyester fabric is

printed using a disperse dye having nanosized

particles. The dye is milled and treated with

ultrasound for different durations in order to obtain

tiny dye particles able to disperse in the printing paste

without adding a dispersing agent, since the size of

nanoparticles is small enough to diffuse into the

hydrophobic fibres properly.

All materials used were of analytical grade. The

100% plain weave polyester fabric of 185 g/m2,

purchased from El-Mahalla El Kobra, Egypt, was

used. The disperse dye Dianix Yellow-Brown HRSL-

SE 150, supplied and manufactured by Dystar Textile

Farben, Germany, was used. A thickening agent (an

acrylic synthetic polymer of low concentration),

having the commercial name Alcoprit PTF, supplied

—————— aCorresponding author.

E-mail: m.shawkey.2006@gmail.com

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203

and manufactured by Ciba Speciality Chemicals,

Switzerland, was used.

Preparation of Dye Nanoparticles

The disperse dye was ground using an energy Ball

Mill with a speed of 50 cycles/min. The dye powder

was sealed in a hardened steel vial (AISI 44°C

stainless steel) using hardened steel balls of 6 mm

diameter. Milling was performed using a ball :

powder mass ratio of 4:1. The dye was milled at

different intervals, such as 4, 6, 9 and 25 days. After

each milling interval, the particle size of the resulted

dye powder was measured. The smallest particle size

of 23 nm chosen to be used in the present study was

obtained from milling the dye powder for 25 days.

Two stock solutions were prepared using the

milled nanoparticle dye powder of 1% and 3%,

where 1 and 3 g of dye powder was dispersed in

99 and 97 mL of distilled water respectively. Each

dispersion was irradiated with ultrasound waves (720

kHz) and stirred at 80 °C for different periods of time,

such as 4, 6 and 8 h.

Printing Procedure

To investigate each factor, two printing pastes were

prepared for each parameter containing the two

different dye concentrations. The printing paste has

the following recipe:

Stock dye solution : 300 mL

Alcoprint PTF thickener : 50 g

Water : X mL

Total weight of paste : 1000 g

The pH was adjusted at 6 using sodium dihydrogen

phosphate. The printing paste was applied to fabric

through flat screen printing technique and then

samples were left to dry at room temperature. Fixation

of dye was carried out with two methods, namely

steaming at 130 °C for 30 min and thermofixation at

140 °C for 10 min to determine the optimal fixation

method that results in best K/S values. The samples

were finally washed off using a 2g/L non-ionic

detergent (Sera Wash M-RK) at a liquor ratio of 1:50.

Soaping was carried out at 60 °C for 10 min.

Effect of Ultrasonic Irradiation and Particle Size

The two stock solutions, having a different

nanoparticle dye concentration, are exposed to

ultrasound irradiation for 4, 6 and 8h respectively.

The K/S values of the prints, both steamed and

thermofixed, are given in Fig. 1.

It is obvious that ultrasound treatment of both stock

dye solutions has a great influence on the colour yield

of the printed polyester fabrics. To determine the best

dye fixation method, steaming and thermofixation are

applied on the prints separately using both dye

concentrations. For steamed prints, optimum K/S

enhancement reaches 85.4% and 53.9 % for polyester

prints with 1% and 3 % stock solutions respectively

compared with the untreated dye solution with

ultrasound waves. These great results are due to the

fact that ultrasound enhances the dye molecule's

diffusion into the fibres8,9

. Also, ultrasound has a

significant effect on the reduction of particle size of

the disperse dye10,11

.

On the other hand, the figure shows that

thermafixation has a negative influence on the K/S

values of the prints. These results show that

thermofixation in the absence of a carrier fixes only

50-70 % dye while in the steaming process, steam

condenses on the cold fabric, raising its temperature

to 100 °C and swelling the thickener film. The

condensed water is largely evaporated again during

the exposure to steam but the thickener is not bount

into the fabric as in dry fixation, subsequently handle

of the fabric becomes softer. The absorption capacity

(build-up) increases in proportion to the steam

pressure and corresponding temperature. The colour

depth obtained at high pressures cannot be obtained

by using longer times at lower pressures. Figure 1

shows that steaming is the best method for dye

fixation and subsequently, it is chosen to be applied in

the proceeding work.

Printing Paste pH

Disperse dyes are sensitive to alkalis and so

polyester is generally dyed under acidic condition12

.

Sodium dihydrogen phosphate is recommended

Fig. 1—Effect of ultrasound exposure duration on K/S values of

steamed and thermofixed polyester prints

INDIAN J FIBRE TEXT. RES., JUNE 2013

204

because, unlike some organic acids, it has no

corrosive effect on nickel screens and is compatible

with natural thickeners. Figure 2 illustrates the effect

of printing paste pH using the nanotreated dye with

ultrasound exposure for 8 h on the K/S of polyester

fabrics. The printing process is carried out using

two stock dye solutions having 1% and 3% disperse

dye concentrations printed on polyester fabric and

followed by steaming at 130°C for 30min. The best

K/S values are obtained for both stock dye solutions at

pH 6. It means that the use of a nanoparticle disperse

dye enables the dye to penetrate the fibres more easily

at more neutral pH value.

Steaming Conditions It is well established that with saturated steam at

100° C the fixation is incomplete unless a carrier is

used. Also, the colour depth obtained at high pressures

cannot be obtained by using longer times at lower

pressures13

. Fibres of the most common polyester are

quite crystalline, very hydrophobic and have no ionic

groups. Hot water does not swell them and large

dye molecules (that have lower diffusion coefficients)

do not easily penetrate into the fibre interior.

For the samples used in this study, the effect of

steaming temperature and time on the K/S of polyester

fabrics printed with disperse dye nanoparticles of the

two different concentrations is investigated and the

data is plotted in Fig. 3.

It is observed that the best K/S values are obtained

by increasing both steaming temperature and time that

reach their maximum values on steaming at 130 °C

for 40 min. Despite that, steaming for 30 min is

chosen as the best steaming time since a small K/S

difference is observed on steaming for longer durations.

It is also noted that these results are considered

satisfying since no carrier is added to the printing

paste and are referred to both the nanosize of dye

particles as well the as ultrasound treatment of dye.

SEM and TEM Studies

The surface morphology, structure and particle size

of dye samples milled at different durations prior to

their exposure to ultrasound are shown in Figs 4 & 5.

Figure 4 shows the SEM images of dye particles

which have different shapes like breaking dishes

shape, spherical shape and tiny sprinkled dots. The

TEM micrographs of the samples milled at 9 and 25

days compared with the unmilled sample are shown in

Fig. 5. The micrographs indicate uniform spherical

dye nanoparticles. The micrographs also indicate that

an average size of the nanosized dispersed dyes is

200–23 nm in diameter. It is found that, the particle

size decreases as the period of grinding increases. The

difference in particle size after grinding is referred to

their dissociation due to the impact of shear forces

that act on dye particles in the ball mill that converts

gradually the particle size from 200 nm (before

milling) to 60nm (after 9 days of milling) and 23 nm

(after 25 days of milling).

Fig. 2—Effect of printing paste pH on the colour strength of

polyester prints

Fig. 3—Effect of steaming temperature (a) and time (b) on K/S of

polyester prints

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205

Fastness Properties

The durability of printing on polyester fabrics with disperse dye nanoparticles with and without exposure to ultrasound waves (using overall optimum conditions) is evaluated in terms of washing, perspiration, rubbing, light, tensile strength (tenacity and elongation) (Table 1).

Table 1 shows negligible differences in properties on comparing printing polyester fabrics using disperse dye nanoparticles with or without pretreatment with ultrasound waves.

Fig. 4—SEM images of disperse dye (a) before milling, and after

(b) 4 days, (c) 6 days, (d) 9 days, and (e) 25 days of milling

Table 1—Properties of polyester fabrics printed with disperse dye nanoparitcles (exposed to ultrasound waves for 8 h) using overall

optimum conditions

Perspiration Wash

fastness Acidic Alkaline

Rub

fastness

Tensile strength Sample

St. Alt. St. Alt. St. Alt. Dry Wet

Light

fastness

Tenacity, kg Elongation, %

Untreated

1% dye

4-5

5

4

4

4

4

3-4

4

6

124

40

3% dye 4-5 5 4 4 4f 4 3-4 4 6 118 36

Treated

1% dye

4-5

4-5

4-5

4

4-5

4

4

4-5

6

120

33

3% dye 4-5 4 4-5 4 4-5 4 3-4 4 5-6 122 45

Fig. 5—Representative TEM images of disperse dye (a) before

milling, and after (b) 9 days, and (c) 25 days of milling

INDIAN J FIBRE TEXT. RES., JUNE 2013

206

In this study, a disperse dye is ground to a nanosize

of 23 nm and is exposed afterwards to ultrasound

treatment, in the form of a solution of two dye

concentrations for 8 h. The nanoparticle suspension

is directly added to the stock thickener and printed

on a polyester substrate. All measurements as well

as various parameters affecting dye fixation are

investigated. The results indicate that grinding and

ultrasound exposure of the dye results in minimizing

particle size which facilitates dye penetration in the

hydrophobic substrate. This result is obtained without

the incorporation of a carrier in the printing paste

and only pH is adjusted at 6. Steaming at 130° C

for 30min used for dye fixation of the prints show

very good fastness properties and no differences can

be observed from prints of untreated dye with

ultrasound. SEM measurement illustrates the effect of

grinding on dye particle size.

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