Indian Journal of Fibre & Tex tile Research Vol 26, March-June 200 I, pp. 136-142

Ecofriendly dyeing of synthetic fibres

s 0 Oeshpandea

Sasmira's Institute of Man-made Textiles, Mumbai 400 025, Indi a

Synthetic fibres, including polyester, nylon and acrylic fibres , account for nearly 46% of the total world-wide fibre consu mption. Ecological consideration led to the significant developments in fib re production and their co louration techniques. Several new dyes and chemica ls have been introduced to reduce the pollution load in the d iluent. Recent developments in iron-based dyes and usc of vinyl sulphone dyes for nylon are reviewed.

Keywords : Acrylic, Banned dyes, Dye ing, Ecofriendly dyeing, Iron-based dyes, Nylon, Polyester. Vinyl sulphone dyes

1 Introduction During the last four decades, the tex tile industry

has witnessed phenomenal growth of synthetic fibres, many of which are being commonly used because of their affordability and excellent functionality. Natural fibres like cotton, wool and silk, which served mankind for many years, have been, to a greater extent, replaced by man-made fibres such as nylon , olefins and polyester. World-wide consumption of sy nthetic fibres constitutes 46% of the total textile fibre consumption 1 (42000 tones in 1996) as shown in Fig. I.

There are various factors that influence future fibre and fabric systems and their processing, such as less energy, less water requirement, less investment, etc. However, the environment-friendly production and processing of fibres and fabrics has gained greater significance today and it has brought about various changes in the production and processing techniques2

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In apparels, polyester has considerably gained over other fibres because of its better easy care characteristics and wrinkle resistance. One of the largest markets for polyester lies in the blends with cellulosics . The hi gh modulus and resilience of PET make polyester suitable as fillin g fibre for quilts, pillows and sleeping bags which can be laundered . Various innovative process ing techniques have produced polyester with comfort of cotton, soft warmth of wool and glamour of silk .

A combination of excellent wear resistance, retention of good appearance, low carpet cost and better dyeing properties make polyamide an ideal

a Phone : 49 18201/493535 1; Fax : 009 1-022-4930225; E-mail : sasmira @vsnl.com

materi al for carpet industry. It is also a principal material for women' s hosiery and certain stretch fabrics specially due to its low elastic modulus compared to that of polyester. Acryl ics have found wide use as wool replacement fibre in knitted apparel products, carpet and home furnishing.

Recent developments that have taken place in the dyeing of polyester, nylon and acrylic fibres , particularly in reference to ecological considerations, have been hi gh lighted in thi s paper.

2 Trends in Fibre Production Over the last seventy years, we have witnessed the

growth of synthetic fibres starting with the sy nthesis of nylon 66 in 1940s, polyester and acrylic in 1950s and olefin fibres in 1960s. Introduction of speciality fibres like Iycra spadex, which permitted us to manufacture first li ght-weight stretch fabrics for swi mwear, lingeri e and outwear, finds di stinctive position in the modern textile technology. Development of low-temperature polymerizati on in 1960 led to the in venti on of aromatic polyamides for high temperaturelfl ame-resistant texti les, VIZ. nomex

". ..c.-:='-="~ ......

/~ - - - - --~, ~-------- ...

54°/o/--'A -- ------~ ,--------- \ 1-- -- - - - - \

r----- I ,----- B I '- - -- I \___ ,46 0/0

,,- //

" ",/

-----"

Fig. I- World-wide fibre consu mplion [A-natu ral fibre s (Callan. rayon, wool and sil k). B-synlhet ic fibres (nylon, polyesler, acrylic, CIC)]

DESHPANDE: ECOFRIENDLY DYEING OF SYNTHETIC FIBRES 137

aramid. Similarly, high-tenacity and high-modulus fibres, like Kevlar aramid, were introduced. The following decades saw the development of modified engineered fibres like hydrophilic, low-pilling, f1ame­retardant, mass- coloured and si lk-like hollow polyester fibres; differential dyeing; antistatic, f1ame­retardant and mass-coloured nylon fibres; water­absorbent, low-pilling, f1ame- retardant, bicomponent and differential dyeable acrylic fibres; and several other multifunctional fibres.

In the recent years, the environmental consideration has led to the production of fibres that exhibit excellent new properties, such as recyclability and biodegradability. It is possible to recycle the polyester waste to ingredients and then back to new products through a process called methanolysi s effectively closing recycling loop. Recycling technologies for nylon are also advanced and waste carpets can be recycled. The conversion of acrylic fibres to ingredients and the subsequent recycling is not possible. Several other techniques have been developed for waste utili zation . Many current production processes use metal catalysts for polymerization that can be harmful to environment. In case of polyester, antimony and cobalt catalysts are being replaced with a new generation zeolite-based compounds which can reduce the waste considerabl/. A totally new field of genetic engi neering for the production of precision polymers, having multiple functionality including biodegradability, is emerging as a result of growing need of ecofriendly polymer fibres7

.

3 Polyester Dyeing When polyester was first introduced as textile

material, considerable difficulties were encountered in its dyeing due to the high crystallinity, hydrophobic nature and absence of chemically active groups in the fibre. Due to these reasons, the fibres could not be dyed with the dyestuffs generally used for dyeing cellulosic and protein fibres 2

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Di sperse dyes were initially developed for acetate fib re. However. with the introduction of polyester and other hydrophobic fibres, di sperse dyes became a large and pre-eminent group of dyes. To produce acceptable dyeing results, three innovative methods for application of these dyes on polyester and acetate fibres were developed. The three methods are: carrier dyei ng, high-temperature dyeing, and thermosol dyeing. The application of high-temperature dyeing method requires the active participation of machinery

designers and manufacturers, the foremost products of which were jet dyeing machines and thermosol units for continuous dyeing. Several innovations in polyester dyeing machinery included softflow, overflow and air-jet dyeing machines. Modifications in dyeing processes resu lted in reduced cycle time and less water, chemicals and energy consumption. This reduced the pollution load in the effluent.

Proper selection of dyes and chemicals is, therefore, vital to ach ieve environment-friendly polyester dyeing.

3.1 Selection of Dyes and Chemicals Many dyes and dye intermediates, compnSll1g

carcinogenic amines releasing groups, have been perceived as health hazardous. Dyes based on such amines (red li sted) interact with the body heat and skin perspiration, resulting in the fission of azo group(s) and formation of carcinogenic or allergic amines. Similarly, there are number of chemicals and textile auxiliary products used in preparatory and dyeing of polyester and other fibres which pose various environmental problems. Two possible alternatives to fill the void created by the banned dyes and chemicals are as follows:

• To experiment and identify dyes and chemicals from the existing ones which do not come under the preview of any ban and try them as alternatives or substitutes .

• To experiment and create new substitutes for the banned dyes and chemicals.

The following disperse dyes avail able in India (list not complete) are not banned and are safe for polyester dyeing ' 2:

CI Disperse Yellow 1,3,13.56,64 & 83 CI Disperse Violet 1,4,8,33,35,63 & 99 CI Disperse Red 1,4,5, 11 , I 3, 17,54,54: 1 ,60,73,

82,91,92,118,159 & 167:1 CI Disperse Orange 3,13,25,30,32,44 & 127 CI Disperse Blue 3,7,23 ,26,26: 1,3 1,35,56,72,

79,79: 1 ,83,87,94,109, 1 29, 149 & 183 CI Disperse Green 9 CI Disprse Brown 1 & 4: I CI Disperse Black 1 & 2

During polyester dyeing, chlorinated carriers should be avoided and the high BOD/COD acetic acid should be replaced by alternative products like Duracid. Safe disperse dyes with ecofriendly di spersing agents should be used.

138 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001

3.2 Evaluation of Ecofriendly Dyeing

An ecofriendly dyeing of polyester is evaluated for fastness properties (Table I) and heavy metal contents" (Table 2).

Polyester dyeing with safe disperse dye substitutes and other chemicals shows sati sfactory fastness properties (Table 1). Table 2 indicates the amount of heavy metal (s) leached out into synthetic sweat solution from dyed samples. The results show that the majority of the values of heavy metal contents of

polyester are within the eco-limits, except chromium content of polyester dyed with Disperse Orange 25 and Disperse Orange 61 and nickel content of polyester dyed with all five dyes.

3.3 Innovative Approach

Environmental requirements, related legislation and stricter eco-regulation in international marketing served as major driving force for innovations in both the dye manufacturing and dye application Industries.

Table 1- Banned disperse dyes and their alternatives with their fastness properties

Disperse dye c.1. No. Chemical Hue on polyester Fastness (ISO) to Status of dye (C. I.Generic) class of dye Light Washing Perspiration

(Medi um) (A lteration) (A lteration)

Yellow 7 26090 Disazo Reddish yellow 6 4.5 5 Banned Yellow 23 26070 Disazo Redd ish yellow 6.5 4.5 5 Alternative

Blue I 64500 Anthraquinone Greenish blue 4 4 .5 4.5 Banned Blue 364 NA Methine Bright greenish 3.5 5 5 Alternati ve Blue 367 NA Azo Greenish blue 7 5 5 Alternative

Red 151 NA Disazo Bright red 5 4.5 5 Banned Red 334 12225 Monoazo Bright red 5 5 5 Alternative

Red I 11110 Monoazo Red 4.5 5 5 Banned Red 94 NA Anthraquinone Bright red 7 4 .5 5 Alternati ve

Red 17 11210 Manoazo Red 4 4.5 5 Banned Red 94 NA Anthraquinone Bright red 7 4.5 5 Alternative

Blue 3 6 1505 Anthraquinone Bright blue 5 4 5 Banned Blue 23 61545 Alllhraquinone Bright blue 5 4.5 4.5 Alternati ve

Blue 7 62500 Anthraqu i none Greenish blue 4 4.5 5 Banned Blue 83 NA Anthraquinone Blue 6.5 5 5 Alternative

Blue 26 63305 Anthraquinone Blue 5 5 5 Banned Blue 3 1 64505 Anthraquinone Blue 4 5 4.5 Alternati ve

Yellow 56 NA Disazo Reddish yellow 6.6 4.5 5 Banned Yellow 86 NA Nitrodiphenyla Reddish yellow 7 5 5 Alternative

mine

Orange 53 NA Monoazo Bright reddish 5 5 5 Alternat ive

Table 2- Heavy metal content from sweat extracts of 5% dyed polyester

Dye Amount of heavy metal, mg/kg of fabric (C.I.Generic) Copper Z inc Nic kel Chromium

Disperse Blue 94 2.345 0 1.876 0 Di sperse Orange 25 1.815 1.834 3.176 0.908 Disperse Yellow 64 0.589 2.039 0.589 0 Disperse Orange 61 1.886 2.026 2.357 0.471 Disperse Red 92 0.897 1.555 1.346 0

Eco Limit (MST) 3.0 5.0 0.2 0. 1

DESHPANDE: ECOFRIENDLY DYEING OF SYNTHETIC FIBRES 139

Such innovative dye application methods for polyester and other fibres include the dyeing in supercritical carbon dioxide and the plasma treatment.

3.3.1 Dyeing in Supercritical Carbon Dioxide Joseph Jasper, Ciba and the research group of the

German North-West Textile Research Institute in Krofeld revealed a new method of dyeing from an environmentally safe solvent, supercritical carbon dioxide (SC02) 7.8 . The method was demonstrated at ITMA 1991.

The solvent SC02 shows ideal properties in that it is cheap, recyclable and extremely safe. The carbon dioxide used in such processes is obtained as byproduct from fermentation and ammonia synthesis and, therefore, does not add to pollution. The disadvantage of the process is the high pressure involved which requires special vessel engineering. How the gases and liquids are affected by the changes in pressure and temperature can be explained by the phase diagram (Fig. 2).

At critical point, if the gas is heated above its critical temperature it cannot be liquefied, however high is the applied pressure. In the case of carbon dioxide, the critical point is at 31 °C temperature and 7.3 Mpa pressure. Above the critical temperature, the gases retain the free mobility of the gaseous state but with the increase in pressure, density will increase toward that of a liquid. Such a highly compressed gas is termed as a supercritical fluid and these modulus combine the valuable properties of both liquid and gas. The fluid has remarkable penetration properties.

Two machines are currently available for dyeing polyester yarn in package form. A typical dyeing procedure7 invol ves the following steps:

• Set up the bath with goods and a charge of pure disperse dye.

100~-----------------------------.

C\l

~ 10

~ ~ If) If)

~ 1.0 0..

Solid Liquid __ Super critical :: Region

Critical point

o. 1 L.l_L~---1.----l--...J......-:::---''----:;BO -80 -40 0

° Temperature , C

Fig. 2- Phase diagram for carbon dioxide

• Run in SC02.

• Raise the temperature and pressure to 130°C and 30 Mpa.

• Gradually reduce the pressure to reduce the solubility of the dye in SC02.

• Recover the carbon dioxide

The method claims 100% dye uptake and eliminates the need for reduction clearing.

The following disperse dyes are found suitable for dyeing due to their solubility in SC02 (ref. 13 ):

3.3.2 Plasma Treatment Plasma includes ionized gases that contain ions,

electrons, radicals, excited molecules and atoms . These ionized gases are electrically neutral and are generated by electric discharge, high frequency electromagnetic oscillation, high energy radiations (such as a and X-rays) , etc.

Plasma technology finds application in a number of areas of textile processing. It improves dye uptake and adhesion to fabric lamination , and modifies fabric surface in such a manner that it becomes

. 14-25 Th · f I receptive . e most Important aspect 0 p asma treatment is that being non-aqueous and non-solvent based, it does not have any problem of effluent treatment and so it is more ecofriendly. Low­temperature plasma for textile finishing has commercially been exploited by some textile companies. Toray in Japan has developed both continuous and batch systems for polyester fabrics. The treatment is aimed at enhancement of the colour depth on polyester fabrics, especially black. It also imparts high hydrophilicity and other useful properties. Commercial manufacturers of plasma treatment equipment require high technology to generate uniform plasma over a large surface and a

140 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001

huge vol ume in reactor to maintain the vacuum. A plasma treatment machine for industrial application has been manufactured successfully in Russia

4 Nylon Dyeing Glass transition temperature of nylon 66 and nylon

6 in wet state being very low (below 20°C), the diffusion of dyes is easy in these fibres. Mainly, the acid, metal complex and disperse dyes are used for their coloration.

4.1 Selection of Dyes and Chemicals The main pollutants present in the nylon exhaust

dye liquor are unexhausted dye, acetic acid, dye fixing agents and heavy metallic compounds. Keeping in mind the red-listed and banned chemicals and dyes, their proper selection is vital for ecofreindly dyeing.

In place of acetic acid which is used for maintaining the pH in nylon dyeing, suitable substitute should be used. Even the use of formic acid in place of acetic acid can reduce biological oxygen demand (BOD) in the effluent. Leveling agents which contain chlorinated hydrocarbon or bleaching with active chlorine must be avoided to eli minate significant amount of AOX (activated carbon absorbable organo halogens) in the effluent. The dyes which are not carcinogenic, al lergic and sensitive to skin should be used . Azo dyes having such harmful properties are already banned. The following dyes available in India (list not complete) are safe for nylon dyeing l2

:

CIAcid Yellow 11,17,23,36,42,59,73,76,99,1 14, 132,244 & 45 Cl Acid Orange 7,lOA,74,80,82 & 86 CI Acid Red 1,14,18,35,37,52,70,88,183,194,195 & 219 CI Acid Blue 25,89,113 & 120 CI Acid Green 1,9 & 20 CI Acid Brown 45,48,345,348 & 349

CI Acid Black 1,21,24,26,52,58,61.63,64,77,164 & 235

4.2 Heavy Metal Contamination The presence of heavy metals in the effluent

obtained after nylon dyeing is very detrimental to operation of the waste treatment system. Apart from this, the eco-limits for the presence of traces of heavy metals on the madeups are a lso very low. Therefore, it is necessary to know the sources of contamination of heavy metals. It is observed that in addition to the known source of heavy metal contamination like mordant and premetallized dyes, the data published by American Dyestuff Manufacturers Institute (ADM!) show that traces of metals are expected to be present in various dye classes itself as given in Table 3 ( ref. 26 ).

4.3 Search for Safe Pre-metallized Dyes for Nylon There seems to be considerable scope to develop

iron and aluminum complexed dyes giv ing equivalent fas tness properties of conventional chromium and copper complexed dyes as viable environmental alternati ves26

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The National Textile Centre recently announced the synthesis of iron complexed formazon dyes by research chemists at North Carolina State University. Iron being a non-toxic metal, the dyes based on this chemistry are reported to have excellent light fastness on nylon and could replace the existing metal complex dyes. The use of iron salt in case of afterchroming of mordent dyes is also suggested . A representative example of 1:2 iron complex dye, developed by Clarient, is shown in Fig.3 (ref.32).

4.4 Nylon Dyeing with Vinylsu lphone Reactive Dyes Environment concerns regarding the use of

premetallized dyes have created new interest in possible use of reactive dyes for nylon dyeing. This can give deeper dyeing due to the double addition of

Table 3 - A verage metal content (ppm) in dye classes

Metal Dye class Aeid Basic Direct Disperse Fibre reactive Vat

Arsenic <I <I < I <I 1.4 <I Cadmium <I <I <I <I <I <I Chromium 9.0 2.5 3.0 3.0 24 83 Cobalt 3.2 <I <I <I <I <I Copper 79 33 35 45 71 110 Lead 37 6.0 28 37 52 6.0 Mercury < I 0.5 0.5 <I 0.5 1.0 Zinc <13 <32 8.0 3.0 4.0 4.0

DESHPANDE: ECOFRIENDLY DYEING OF SYNTHETIC FIBRES 141

R = S02NH(CH2)OMe

Fig. 3--lron complexed premetalli zed dye (Clarient)

Nylon-(CH2)6-NH2+ D-S02- CH=CH2

t Nylon - (CH2)6- NH -CH 2 - CH2- S02- D

t 0-50,- CH=CH,

Nylon - (CH2)6-N-CH2- CH2- S02- D

\ CH 2 - CH2- S02- D

Fig. 4-Double addition reaction of vinylsulphone reactive dye with nylon

Table 4-Extent to which dyes are lost in exhaust and wash liquor

Dye class Amount of dye di scharged in effluents, %

Direct 5 -20 Acid 7 - 20 Basic 2 - 3 Metal complex 2 - 5 Sulphur 30 - 40 Reactive 20 - 40 Disperse I - 20 Vat 5-20

vinylsulphone reactive dye molecules (Fig. 4). However, this is not possible with monochlorotriazine dyes2s .

In practice, a lower value of dye fixation is attainable due to the build up of negative charge from the sulphonate groups of fixed dye molecules, giving rise to strong repulsion effecLs. Thi s fact has invited

the attention of researchers to develop disperse vinylsulphone reactive dyes and cationic vinylsulphonic dyes in place of su lphonated dyes.

5 Acrylic Dyeing Acrylic fibres , which account for about 20% of

total world synthetic fibre production, show wool-like feel, bulking value, chemical inertness, and resistance to weathering, molds and bacteria. Du Pont produced first acrylic fibre on pilot plant scale in 1950 from 100% acrylonitrile which was extremely difficult to dye. Considerable amount of research work was carried out to develop fibre suitable for dyeing with different classes of dyes. This fibre received more attention than any other fibre, and the dyeing problems were solved by developing modified fibre and special type of dyes and retarders34

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5.1 Selection of Dyes and Chemicals As mentioned for polyester and nylon, the selection

of proper dyes and chemicals are of great importance for ecofriendly acrylic dyeing. One positive aspect of acrylic dyeing from ecological point of view is 90-97% exhaustion of cationic dyes on acrylc fibre. Table 4 shows the amount of dye discharged in the effluents after dyeing with various types of dyes.

The following dyes available in India (list not complete) are safe for acrylic dyeingl2.

CI Basic Yellow 2,11,13,25 & 28 Cl Basic Orange 22

Cl Basic Red 13,14,18,22 & 29 CI Basic Violet 7,14 & 16 CI Basic Blue I 3,54 & 146 CI Basic Brown 1 CI Black 36

To get the maximum exhaustion, which is important on acrylic fibre, proper selection of the dyeing technique after careful consideration of fibre saturation value, dye saturation factor and saturation factor of retarder is very important. Using dye saturation factor and fibre saturation value, it is possible to determine whether a particular dyeing recipe will cause over saturation of the fibre or not. Similarly, the saturation factor of the retardar, which is used for level dyeing, can also be considered in a similar manner to arrive at proper saturation limit of the dyeing. The fibre saturation values of certain acry lic fibres and the saturation factors of cationic dyes are given in Table 5. It is very important to dye

142 INDI AN J. FIBRE TEXT. RES ., MARCH-JUNE 2001

Table 5- Fibre saturation value and dye saturation fac tors

Fibre sa tu ration value Dye saturati on factor

Acribel : 2 .1 Astrazon Yellow GRL : 0.27 Acri lan 16 : 1.5 As trazon Red GTL :0.47 Acrylan 70 : 1.4 Besacryl Orange FL : 0.39 Cashmil on : 2.2 Besacryl Blue GL : 0 .2 1 Chem ifelon 3 1 :1.7 Max ilon Black Black NL :0.40 Courtell : 1.8 Remacryl Red BL : 0.33 Jaykrili c : 2.25 Kemkozl Blue B : 0.35 Dralon : 2 .1 Sandaxy l Br. Yellow : 0.50

B6GL OrIon 42 : 2.1 Sandoxy l Red BF : 0.38 OrIon 2 1 : 4.2 Seron Bllfe B : 0.21

Sykacryl Red B : 0 .34 Sykacryl Blue R : 0.22

acrylic fibres keeping in view the above technical data for the economy and less water pollution due to the less amount of dyes and chemicals in the effluent.

6 Conclusion Environmental consideration has great impact on

the production and colouration of synthetic fibres , namely polyester, nylon and acry lic fibres. It has led to the development of new fibre production, dyeing and processing techniques. Innovative ecofriendly methods li ke dyeing in supercri ti cal carbon dioxide and plasma treatments are emerging. The research work to develop new dyes, like iron complex dyes for nylon, and safe ecofriend ly chemicals for dyeing and processing of synthet ic fibres is in progress.

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