The effect of domestic laundry detergents on the light fastness of certain reactive dyes on 100% cotton

Abstract

This study presents findings on the effect of several domestic laundry detergents on the fastness to light of selected fiber reactive dyes applied to cotton. Cotton fabric dyed with commonly used reactive dyes were laundered with water only, several domestic detergents, and a laboratory-formulated neutral detergent, and then exposed to light for 2 h in the wet state. Exposures were repeated 15 times, equivalent to 30 h of exposure. Color loss and color difference were measured after 5, 10, and 15 wash cycles, and 10 h, 20 h, and 30 h of exposure. When the fabric was exposed to light wet, the color faded more rapidly than when it was exposed dry. The presence of an oxidizing bleach (sodium perborate or sodium percarbonate) in the detergent increased color loss during washing and wet exposure to light. Ultraviolet radiation from the light source, heat, moisture, alkali, and oxidizing bleach during exposure resulted in hydrolysis of the dye–fiber bond, causing dye desorption during washing and rinsing. The combination of ultraviolet radiation and oxidizing bleaches altered the chemistry of the dye and hence its shade. This was particularly evident on the black dye and one of the navy blue dyes.

Keywords

chemistry color detergents dyeing fastness materials

Consumers, retailers, and garment and fabric suppliers report instances of unacceptable color change and color loss with cotton and cotton-rich fabrics. Experience and anecdotal evidence suggest that the problem lies largely with navy blue and black pure cotton garments. The industry experience of the authors suggests that the cause of the color loss may be due to variations in laundry and drying practices. In Australia and New Zealand it is common practice to dry domestic laundry outside on a line; consequently, garments may be exposed to direct sunlight. Domestic washing conditions vary widely with time, temperature, detergent type, and concentration. Croud¹ investigated the influence of various washing powder formulations on dye fading and color loss. Some of these variations in washing have been known to influence the performance and behavior of a dye during the lifecycle of the garment. The desorption of dyes from cotton has been studied² and it was found that the presence of detergent, increased temperature, and higher pH accelerated the desorption of direct dyes. Lakhanpal,³ in his PhD thesis, investigated the wash-down effect of various dyes on cotton and its blends. In particular, he investigated the interaction of oxidative bleach-containing detergents and dyed textile substrates. Phillips and colleagues⁴ investigated ISO 105-C09, “Colour fastness to domestic and commercial laundering – oxidative bleach response using a non-phosphate reference detergent incorporating a low temperature bleach activator.” Their work showed that the presence of an oxidative bleach had a detrimental effect of the wash fastness of the dyes tested. Current tests for light fading do not provide data on the performance of dyes during domestic washing conditions and exposure to light during drying. Hence, the accepted reference standards of dye performance may not necessarily reflect performance under “real-life” use. Photofading of textile dyes has been reviewed,⁵ and a complex picture of the mechanisms relating to the fading of dyes is evident. The color of dyes arises from absorption of light in the visible region (i.e., 400–700 nm). The absorption of light raises the dye molecule to an electronically excited state. While in this state, the charge separation of the π electrons becomes greater and as such is more easily affected by moisture and detergent additives. Most dyes can be degraded by photo-oxidation via singlet oxygen, which may initiate dye destruction. Griffiths and Hawkins⁶ elucidated the photo-oxidative process of some azo dyes that showed the attack on the singlet oxygen was via an unsaturated hydroperoxide intermediate. Egerton,⁷ in his paper “Mechanism of Photodegradation of Textiles,” raises the hypothesis that hydrogen peroxide is formed on the wet fabric during exposure to light, particularly if the dye is of the sensitizing type.

The majority of 100% cotton and cotton-rich blends, particularly dark shades such as navy blue and black, are today dyed with reactive dyes. The bestselling reactive dye is C.I. Reactive Black 5,⁸ with current world production of more than 46,000 tons per annum. This dye is not only used in self-shades, but also in mixtures with other reactive dyes to produce specific products. C.I. Reactive Black 5 is a homo-bifunctional or double-anchor dye bis-β-sulphatoethersulphone, introduced in 1957 by Hoechst (DyStar) (Figure 1).⁸

Figure 1.

C.I. Reactive Black 5.

The two sulphone reactive groups give the dye relatively high fixation and, as such, good economy. It is widely used for the production of black and navy shades, but suffers from relatively poor fastness to light in all but the heaviest of depths. One of the advantages of the vinylsulphone structure is that it contains a masking group (OSO₃Na) attached to the two methyl groups. This masking group increases the dye’s resistance to hydrolysis during the early stages of the dyeing process, and is not removed or deactivated until alkali is added at the fixation stage. It is for this reason that the dyes can be prepared and sold in liquid form, which is a requirement for modern digital inkjet direct-to-fabric printing machines.⁹ C.I. Reactive Blue 222 is a bi-functional reactive dye based on monochlorotriazine together with a vinylsulphone reactive group; this dye is also included in our evaluation. No printed chemical constitution is available for this particular dyestuff.

Experimental

The fabric selected was a pure cotton single jersey, typically used for the manufacture of upper body garments and sportswear. It was supplied by Leading Textiles Pty., Ltd (Melbourne, Victoria, Australia).

The technical details of the fabric were:

Yarn type: rotor spun carded cotton – 1/24 tex.

Fabric mass per unit area: 178 g/m².

Fabric construction: single jersey, 11 wales/cm and 13 courses/cm.

The fabric was scoured and bleached at a liquor ratio of 10:1:

1.0 g/L commercial detergent mixture (Dyamul LFA – Yorkchem, Melbourne, Victoria, Australia).

1.0 g/Lsequestering agent (Seriquest CMA – Yorkchem) (methylphosphonate/polyacrylate type).

5.0 g/Lsodium hydroxide (solid).

5.0 g/Lhydrogen peroxide 50%.

Chemicals were added at a liquor temperature of 25℃ and the temperature raised to 98℃ at 3.0℃/min. The bath was held at 98℃ for 45 min before cooling to 60℃ at 3.0℃/min. The scoured and bleached fabric was given two rinses at 40℃, then neutralized to pH 6.4 using a 10% sulfuric acid solution. Finally, the fabric was rinsed in cold water prior to hydro-extraction, and dried in a relaxed state in a drying cabinet.

Dyestuffs selected were those typically used within the Australian industry, which are also used extensively within cotton-dyeing industries throughout Asia and the Indian subcontinent:

C.I. Reactive Blue 222, samples from two manufacturers.

C.I. Reactive Black 5 mixture.

Commercial navy blue dye based on C.I. Reactive Black 5.

The dyes were applied according to the method outlined below, using a Ahiba Turbomat machine at a liquor ratio of 8:1.

Dark blue mixture: 3.6%

C.I. Reactive Blue 222 (manufacturer 1): 3.6%

C.I. Reactive Blue 222 (manufacturer 2): 4.0% (the color strength of this dye was weaker than that from manufacturer 1.)

C.I. Reactive Black 5 mixture: 5.0%

Approximately 65–70 g of fabric was dyed at each dyeing. The fabric was wound onto a perforated cylinder through which the dye liquor was pumped. This method ensured level and consistent dyeing.

The dyeing procedure was as follows:

Set bath at 30℃ with 1.0 g/L Seriquest CMA (Yorkchem) and 70 g/L sodium chloride.

Circulate for 10 min, then add the dissolved dyestuff.

Raise the temperature to 60℃ at 2.0℃/min.

Add 20 g/L sodium carbonate in three portions at 10-min intervals. After the last addition of alkali dyeing is continued for a further 45 min. At the completion of dyeing the bath is cooled to 40℃.

The dyed fabric is given a thorough rinse with cold water by pumping water through the perforated cylinder and thence through the fabric, followed by neutralizing to pH 7.0 with acetic acid. Dyed fabrics were finally soaped at the boil with 1.0 g/L Dispersant 2000, a specialty product from Oxford Technologies (Melbourne, Victoria, Australia) based on sodium polyacrylate to remove unfixed and hydrolyzed dye.

Wash and exposure cycles

To simulate approximately 3–4 months of domestic laundering of a cotton garment, the dyed samples were washed 15 times then exposed to light in a wet condition for two hours after each wash using a 500 W mercury tungsten filament as specified in AS2001.4.21-2006.¹⁰ In order to ensure the MBTF lamp used gave the correct radiation emissions, a radiation profile of the lamp and sunlight at noon was carried out by the CSIRO Division of Polymer Science in Clayton, as shown in Figure 2. The lamp chosen was a 500 W Phillips high-pressure mercury lamp.

Figure 2.

Comparison of MBTF lamp against noon sunlight (y-axis-intensity-arbitrary units).

The resultant graph (Figure 2) compares closely with work carried out by Hindson and Southwell.¹¹ The initial intensity of light is low during the warm-up stage, and full intensity is reached after approximately 6 min. When compared to noon sunlight (500 nm), the MBTF lamp has a strong peak at around 550 nm. There is also a strong peak at 375 nm and a further peak at 400–410 nm, though not as strong as that at 375 nm. The spectrum differs to that of daylight as the radiation cuts out at about 300 nm and the peaks in the nearer ultraviolet (UV) between 350 nm and 375 nm occur at frequencies to which many dyestuffs are sensitive.⁶ The sensitivity of dyes to these frequencies can result in the rupture of the azo (–N=N–) link, as well as damage to the covalent bond that attaches the dyestuff to the cotton fiber. This may be aggravated by the presence of moisture and other chemicals present on the fabric. Unilever Research investigated “The Photofading Mechanism of Commercial Reactive Dyes on Cotton.”¹² They evaluated the effect of moisture on the rate of fading and found that in the range pH 3–8 wet fabric fades faster than dry. Large increases in the rate of fading were noted at pH 9.

During exposure the samples dried. The reflectance of the samples was measured and the color difference calculated after the 5th, 10th, and 15th cycle of washing and drying. The 15 wash and drying cycles as described above were carried out for each detergent and machine as shown in Table 1.

Table 1.

Detergent and machine type

Machine type	Detergent
Top loading	Typical detergent for top loading machines
Top loading	Formulated neutral detergent
Top loading	Water only
Front loading	Typical detergent for front loading machines

The volume of water used for a typical washload in each type of machine was carefully measured. This was necessary to determine the mass of domestic laundry detergent to be used in each case. Current standard washing fastness tests do not take into account the variability within domestic home laundry. For example, Australian Standard AS2001.4.15-2006 describes 24 test procedures, but all are similar to ISO 105, “Textiles – Tests for Colourfastness to Washing,” which is the international standard test method. None are truly representative of domestic practice.

In determining the quantity of detergent required for each type of machine, two machines were chosen: a Maytag top loading machine and a Hoover Zodiac 12 front loader. The liquor ratio was established for a 3.5 kg load of 100% cotton fabrics in each machine. The Maytag uses 75 liters for a large load and the Hoover Zodiac uses a standard 24.5 liters per washload. It was therefore determined that for the top loading machine a liquor ratio of 20:1 would be used. After a number of trials of various garments and weights, it was found that the liquor ratio in the front loading machine varied from 12.5:1 to 8:1; it was therefore decided to use a liquor ratio of 10:1.

Two commercial domestic home laundry detergents were chosen for the experimental work:

A formulated household detergent system recommended for top loading washing machines. No oxidizing bleaches were included in the formulation.

A widely used domestic detergent powder specially formulated for domestic front loading machines. This detergent system contained sodium perborate, an oxygen-generating bleaching and whitening additive that can affect the color fastness of the dyes.

A neutral-pH detergent was formulated as a reference with the following constituents:

15.85 g sodium dodecylbenzenesulphonate

2.90 g nonylphenolethoxylate, 10 mol ethylene oxide

3.50 g soap

77.75 g water

100.00 g total.

The composition and quantities of the neutral detergent were calculated from the European Colorfastness Establishment (ECE) reference detergent. Each of the commercial detergents was supplied with a measuring cup, and a level quantity of detergent in the measuring cup was weighed. The top loading detergent weighed 62.5 g, which would equate to 0.87 g/L for 72 liters or 1.3 g/L if only 50 liters of water were used. For the washing trial 1.0 g/L was considered a compromise. The front loading detergent had a greater bulk density and a level cup weighed 58.2 g. The nominal volume of water in the wash cycle of the Hoover Zodiac 12 machine was 24.2 liters. In this case a detergent concentration of 2.4 g/L was used for each wash cycle as this quantity was equivalent to the manufacturer’s recommendation of one scoop. The formulated neutral detergent was only evaluated as a top loading machine, and as such 1.0 g/L was used in the experiments.

Washing procedure

A complete set of four dyed samples were washed with each detergent in the Werner Mathis multipurpose dyeing machine, using the garment dyeing attachment. The machine speed was set to 12 rpm and the wash temperature to 45℃; liquor ratio was 20:1 for the top loading machine and 10:1 for the front loading machine. The pH values of the wash liquor and rinse liquor were taken as the machine drained. In the case of the top loading wash, a spray rinse was carried out at 27℃ equivalent to the volume of water used in the wash cycle, followed by a cold rinse for 10 min at 27℃. The Hoover Zodiac 12 machine uses five rinse cycles, each of 5 min. This system was applied and the pH at the end of each rinse was recorded during draining.

The washed fabrics were brought to an even moisture content of 83% by using a pair of squeeze rollers prior to exposure.

The dyed samples were then mounted for exposure, with the top and bottom of the sample covered so that only the marked area of the sample was exposed to the light (Figure 3).

Figure 3.

Samples mounted for exposure.

The surface temperature was measured using a black panel thermometer and was recorded as 73℃ ± 2.0℃. Samples were exposed for 2 h, then washed and exposed again for 2 h. This process was repeated until the sample had been washed five times and exposed for an equivalent of 10 h. During exposure the samples dried, simulating the drying of a washed sample on an outside line.

After exposure, the percentage color strengths of the samples were measured using the HunterLab ColorQUEST II Spectrophotometer (Leicestershire, UK). K/S values and the relative strengths between the exposed and unexposed areas were calculated using Premier Colorscan software (Premier Colorscan Instruments Private Ltd., Mumbai, India). Measurements were made under the following conditions: 10° observer, maximum wavelength 600 nm, and D65 light source. The relative percentage change in strength between the various washed samples were then compared to the reference sample that was unwashed and air-dried in the dark after dyeing and soaping.

Results and discussion

As several of the dyes used were not listed in the color index, thin layer chromatography (TLC) was carried out on the dyes selected in order to establish whether there were any peculiarities in their formulation. The TLC (Figure 4) shows that C.I. Reactive Black 5 is present in both the dark blue mixture as well as the Reactive Black mixture. The samples of C.I. Reactive Blue 222 from different manufacturers did not show the presence of C.I. Reactive Black 5; however, the C.I. Reactive Blue 222 from manufacturer 1 showed the presence of a red shading component. Depending on the conditions of manufacture, particularly at the coupling stage, C.I. Reactive Black 5 can vary in tone from reddish to bluish.⁷ For this reason, manufacturers add toning dyes; in this case, red and yellow dyes are included to produce a product of “standard” color.

Figure 4.

Thin layer chromatography of dyes used.

Dry fading

To provide a base standard for the impact of wet fading and washing, all the dyed fabrics were subjected to fading in the dry form without laundering (Australian Standard AS2001.4.21-2006).¹⁰ The loss in color strength of the dyed fabric was measured after 10 h, 20 h, and 30 h of exposure, as shown in Table 2.

Table 2.

Percentage color loss on dry exposure

	Number of hours of exposure
	10 h	20 h	30 h
5.0% Reactive Black mixture	13.8	14.5	16.8
3.6% Reactive Navy Blue mixture	11.3	9.5	9.8
3.6% C.I. Reactive Blue 222 (manufacturer 1)	9.0	10.4	12.6
4.0% C.I. Reactive Blue 222 (manufacturer 2)	9.7	13.6	16.1

From Table 2 it can be seen that the majority of color loss occurs within the first 10 h of exposure. In the case of C.I. Reactive Blue 222, dyes from both manufacturers exhibited a similar degree of fading after 10 h of exposure; however, the dye from manufacturer 2 lost 27% more color after 30 h of exposure. It would normally be assumed that dyes of the same C.I. number would have similar light fastness.

The pH of 1.0 g/L of each of the commercial detergents dissolved in deionized water was found to be 11.3. The pH of the wash cycle for the front loading machine was measured as pH 9.8, and that of the final rinse was found to be consistently 7.5. For the top loading machine the pH of the wash cycles were similar at pH 9.8, but the pH of the final single-rinse liquor following an intermediate spray rinse was 8.5. The pH of an aqueous extract (AS2001.3.1-1998) was determined after 15 wash cycles and found to be pH 7.7.

Significant color loss occurred during washing before exposure to light. The dyed samples were washed then dried in the dark prior to exposure. From Figure 5 it can be seen that in both cases the front loading detergent causes the most significant loss in strength of both versions of the blue dye. The dye from manufacturer 2 suffered the greatest loss in strength after 15 wash cycles when the front loading detergent was used.

Figure 5.

The percentage color loss on washing. (a) C.I. Reactive Blue 222, manufacturer 1; (b) C.I. Reactive Blue 222, manufacturer 2.

Figure 6 shows the difference between dry exposure and wet exposure when various detergents have been used. Color loss on dry exposure is only about 10%, whereas the front loading detergent has resulted in a strength loss of almost 35%. Both the top loading and neutral detergent behaved similarly.

Figure 6.

Comparison between wet and dry exposure, C.I. Reactive Blue 222 (manufacturer 1).

Figure 7 shows that the detergent has a significant effect on the degree of fading compared to dry fading. The degree of fading is significantly greater when the material is washed with a front loading detergent (purple bar) that contains an oxygen-generating salt such as sodium perborate or sodium percarbonate. The presence of moisture on the fabric during exposure increases the rate of fading (blue bar) compared to dry exposure (black bar). A visual example of this dye is shown in Figure 8.

Figure 7.

C.I. Reactive Black 5 mixture – comparison of wet fading against dry fading.

Figure 8.

Visual example of fading.

In the case of the navy blue mixture based on C.I. Reactive Black 5 (Figure 9), it is clear that the front loading detergent has a significant effect on the degree of color loss, shown here to be in excess of 40%. This is similar to the color loss for the black mixture.

Figure 9.

Navy blue based on C.I. Reactive Black 5 comparison of detergent action against dry fading.

Conclusion

The presence of detergent, higher temperatures, and higher pH can increase the desorption of dyes, particularly direct dyes. In the wet state, when the fabric is exposed to light and a peroxy compound is formed, increased photo fading will occur, particularly if the dye is sensitive to such conditions. If the dye–fiber covalent bond is ruptured, then the reactive dye behaves in a similar manner to direct dyes and can be desorbed from the fiber. It is therefore possible that the major cause of dye desorption, as well as an increase in fading when wet, is due to hydrolysis of the dye–fiber bond. Key initiators of dye–fiber bond hydrolysis are moisture, alkali, oxygen, UV radiation, and heat. It is possible that UV radiation during the drying stage catalyzes the breakdown of the dye–fiber bond, thus resulting in dye and hence color loss on subsequent washing. The process of dye–fiber bond hydrolysis can be ongoing as more dye–fiber bonds are broken.

This study strongly indicates that hydrolysis is a key factor in the ongoing rate of color loss and shade change as a result of laundering and drying during use.

The results suggest the following:

Dye loss can occur when washing in water only; this is most likely due to the presence of dissolved oxygen.

Dye loss increases if the detergent contains an oxygen-generating additive such as sodium perborate or sodium percarbonate.

Detergents increase the rate of color loss.

Different detergents have different effects on the rate of color loss.

Color loss can be activated by UV radiation.

Wet exposure to light increases the rate of dye–fiber bond hydrolysis.

This study has showed that navy and black cotton fabrics dyed with reactive dyes experience significant color change during domestic laundering and subsequent drying when exposed to light. Detergent formulation, in particular the presence of oxidizing bleaches in the formulation, and the structure of the dye both contribute to the degree of fading.

Footnotes

Declaration of conflicting interests

The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

References

Croud

. The influence of washing powder components on dye loss and dye fading. J Soc Dyers Colour 1996; 112: 117–117.

Rahimina A. The desorption of dyes from cotton. MPhil Thesis, University of Leeds, England, 1989.

Lakhanpal R. The interaction of oxidative-bleach containing detergents with dyed textile substrates. PhD Thesis, University of Manchester Institute of Science and Technology, England, 2000.

Phillips

Duncan

Jenkins

et al.

Development of a test to predict colour fading of cotton fabrics after multi-cycle laundering with a bleach-containing domestic detergent. Coloration Technology 1996; 112(10): 287–293.

Oakes

. Photofading of textile dyes. Rev Prog Color Relat Top 2001; 31: 21–28.

Griffiths

Hawkins

. Oxidation by singlet oxygen of arylazonaphthols exhibiting azo-hydrozone tautomerism. J Chem Soc, Perkin Trans 2 1977; 6: 747–747.

Egerton GS. Mechanism of photodegradation of textiles. In: Symposium on Photochemistry in Relation to Textiles. September 1949. Harrogate, UK: Soc. Dyers & Colourists.

Glover BJ. Reactive Black 5. In: SDCANZ International Symposium, Colouration. Christchurch, NZ, October 13–16, 2004.

Taylor

. Recent developments in reactive dyes. Rev Prog Color Relat Top 2000; 30: 93–100.

10.

AS2001.4.21-2006. Determination of colour fastness to light using an artificial light source (mercury vapour, tungsten filament, internally phosphor-coated lamp).

11.

Hindson

Southwell

. Mercury–tungsten fluorescent lamp for the fading assessment of textiles. Text I Ind 1974; 12: 42–42.

12.

Batchelor

Carr

Coleman

et al.

The photofading mechanism of commercial reactive dyes on cotton. Dyes Pigm 2003; 59(3): 269–275.