Influence of Household Washing on the Colorimetric Properties of Intrinsically Natural Organic Cotton Fabrics

ABSTRACT

This research aimed to examine how household washing influences the colorimetric characteristics of natural colored organic cotton (NaCOC) fabrics. The colorimetric properties of (NaCOC) fabrics were assessed both before and after undergoing washing for up to 30 cycles. The findings indicated that washing significantly influenced the colorimetric properties of naturally dyed cotton fabrics, as evidenced by changes in lightness and saturation. The most significant difference in color between the two samples was observed after the initial wash, highlighting the reduction in both parameters, lightness and saturation, after this first washing. Between the second and fifth washes, there are notable differences in these parameters. However, from the fifth wash, the variation in color difference was minimal. Additionally, the FTIR-ATR analysis of the extracts in petroleum ether and subsequently in ethanol of the NaCOC fabrics, before and after home washing, in conjunction with a comparison with shrinkage, demonstrated that the latter process was accountable for the darkening of the sample.

摘要

本研究旨在检验家用洗涤如何影响天然彩色有机棉（NaCOC）织物的比色特性. （NaCOC）织物的比色性能在洗涤前和洗涤后进行了长达30个循环的评估. 研究结果表明，洗涤显著影响天然染色棉织物的比色性能，明度和饱和度的变化就是明证. 两个样品之间最显著的颜色差异是在初次洗涤后观察到的，这突出了第一次洗涤后亮度和饱和度这两个参数的降低. 在第二次和第五次洗涤之间，这些参数存在显著差异. 然而，从第五次洗涤开始，色差的变化最小. 此外，在家庭洗涤前后，对NaCOC织物的石油醚提取物和随后的乙醇提取物进行FTIR-ATR分析，并与收缩率进行比较，表明后一个过程是样品变暗的原因.

KEYWORDS:

• Natural colored cotton
• colorimetric
• color changes
• household washing

关键词:

• 天然彩色棉
• 比色法
• 颜色变化
• household washing家庭洗涤

Introduction

Cotton, the most vital natural fiber, is utilized by nearly every individual worldwide on a daily basis. Supporting the livelihoods of approximately 250 million people, it stands as one of the foremost fiber crops cultivated in over 80 countries. While being a renewable natural resource, responsible management of cotton is imperative. Natural colored cotton, characterized by its pigmented fibers in shades of green, brown and red, is available commercially in brown and green hues (Dickerson, Lane, and Rodriguez 1999). Previous research on natural colored organic cotton (Crews and Hustvedt 2005; Dickerson, Lane, and Rodriguez 1999; Frydrych 2007; Hua et al. 2007; Kang and Epps 2008; Khan et al. 2010) can be categorized into three distinct groups: cellulose synthesis and genetic diversity (Dickerson, Lane, and Rodriguez 1999; Hua et al. 2007), pigment migration, color variations and property changes (Crews and Hustvedt 2005; Frydrych 2007; Kang and Epps 2008) and performance after repeated laundering (Hua et al. 2007).

Evidence from archeological findings suggests that naturally colored cotton has been utilized for at least 2500 years. However, the use of this type of cotton gradually declined due to its lower fiber quality and lower yields compared to white cotton, resulting in reduced profitability (Cardoso et al. 2011). In recent times, there has been a resurgence of interest in naturally pigmented cotton, driven by growing ecological concerns. This renewed interest has also led to an increase in the market share of naturally colored organic cotton (NaCOC). The textile and fashion industries are particularly drawn to NaCOC because it eliminates the need for dyeing, thereby reducing environmental pollution (Frydrych 2007; Hua et al. 2007; Khan et al. 2010).

The dyeing process results in an excessive amount of effluent, which is not only expensive but also requires immediate action to minimize its harmful effects. In order to prevent this action, recent studies have been conducted proposing more sustainable processes for dyeing cotton with tannin derivatives (Rahman Liman et al. 2021; Tauhidul Islam et al. 2021, 2022). Another way to prevent the action of dye is to avoid it. Therefore, the increasing environmental concerns have prompted different nations, including Israel, the United States and Brazil, to enhance their endeavors in creating strains with vibrant colors (Demir et al. 2011; Ma, Luo, et al. 2016). These new strains are characterized by improved fiber properties and a wide range of natural colors that exhibit desirable fastness, aligning with modern spinning and finishing techniques (Chen and Yokochi 2000). Spinning and finishing processes are essential in transforming raw cotton into marketable goods. Cellulose, which constitutes approximately 90–95% of cotton fibers, is the primary component, while non-cellulosic elements like waxes and salts make up the remaining percentage. Waxes play a crucial role in facilitating spinning; however, they need to be eliminated through appropriate chemical treatments (Chae, Lee, and Cho 2011). Typically, wet alkali treatments (scouring) involving various caustic solutions are employed to remove non-cellulosic constituents and the addition of wetting agents enhances the absorption properties of cotton fibers (de Morais Teixeira et al. 2010).

Naturally pigmented cotton and conventional white cotton can be compared in various aspects. The dissimilarities between them do not solely arise from their color variations. Their chemical compositions, structures and certain other characteristics exhibit remarkable similarities. Nevertheless, there exist fundamental disparities between the two types of cotton (Ma, Luo, et al. 2016).

The definitive identification of the specific constituents of the pigments present in colored cotton remains an ongoing challenge. Numerous research studies have been conducted to determine the composition and properties of the natural pigments found in colored cotton. It has been discovered that the brown coloration observed in colored cotton fibers is attributed to the presence of tannin vacuoles within the lumen of the fiber cells. Conversely, the green coloration in green-colored cotton primarily originates from caffeic acid, a derivative of cinnamic acid, which is predominantly found in the suberin layer. Importantly, the quantity of pigments is more prominent in brown cotton compared to green cotton. This difference in pigment types serves as one of the justifications for selecting brown cotton fabrics in the current study (Matusiak et al. 2007), which aims to investigate the impact of household washing on the color variation of cotton fabric.

Fabrics produced with NaCOC cotton offer several benefits, one of which is their absence of agrochemicals and chemicals used in the dyeing process. This makes them highly suitable for individuals with multiple chemical sensitivity and skin hypersensitivity. In this study, we have specifically examined the impact of domestic washing with a gentle soap on the colorimetric properties of the fabric. It is well known that the color of this type of cotton intensifies with washing and our analysis has focused on this intriguing characteristic.

Experimental part

Material

This study uses NaCOC, grown in Brazil, supplied by the Spanish company “Organic Cotton Colors (OCC)” (Organic cotton Colours). For the realization of the yarn used in this study, the following cotton varieties of this company have been used: Topaz, Light ruby, Dark ruby and Raw (white) cottons. Characteristics of the corresponding varieties are included in Table 1.

Table 1. Characteristics of the NaCOC fibers used.

Sample	SCI	MIC	MAT	UHM (mm)	UL (%)	SF (%)	STR (g/tex)	ELG (%)
Topaz	84	4.23	0.84	26.67	79.5	9.5	25.0	8.6
Light ruby	-	4.26	0.84	20.50	78.8	11.9	19.6	9.9
Dark ruby	-	4.15	0.84	21.01	79.2	12.0	21.7	9.0
White Raw	99	3.76	0.84	25.73	78.0	10.3	26.3	7.0

Were:

- SCI: Spinning Consistency Index. It is a parameter for predicting the spinnability of the fibers. In general, the higher the index, the higher the yarn strength and the better the overall fiber spinnability.

- MIC: Micronaire Index. The pressure drop is measured by passing air through the fibers.

- MAT: Maturity index. It indicates the degree of cell wall thickness within a cotton sample. The HVI Maturity Index correlates very well to the AFIS Maturity Ratio and the microscopy reference method (cross-sectional analysis).

- UHML: Upper Half Mean Length. It is the mean length by the number of fibers and corresponds to the classer’s staple length and the AFIS Upper Quartile Length by weight.

- UL%: Uniformity Index. It expresses the ratio of the Mean Length to the Upper Half Mean Length. It is an indication of the distribution of fiber length within the fibrogram.

- SF%: Short Fiber Index. Indicates the number of fibers in percent less than 12.7 mm in length. It correlates very well to the AFIS Short Fiber Content by weight (SFC).

- STR: Bundle strength. Is the breaking strength of the cotton fibers in grams per tex.

- ELG: Elongation. It is a measurement of increase in the length of the cotton test piece, expressed in %, as a result of the application of a load.

With these fibers, the Spanish company OCC made a mixture in equal parts of the four cottons described in Table 1 and proceeded to carry out a combed spinning process (opening, cleaning, carding, drawing, combing, drawing and finally roving machine). Ring spinning was carried out on a PINTER machine model Merlin spa 1803, under the conditions indicated in Table 2, that includes the characteristics of the yarn obtained.

Table 2. Spinning conditions and characteristics of the yarn obtained.

Type of ring spinning machine	PINTER model Merlin spa1803
Roving count (ktex)	0.600
Yarn count (tex)	29,5
Twist (t/m)	705
Linear spinning speed	16.65 m/min
Revolutions per minute of the spindle	7,500 rpm
Ring diameter	42 mm
Type of traveller	Bräcker 2DR

In the present study, the fabric employed is made up of a conventional cotton warp and a NaCOC weft. These components were woven using an air-jet Dornier loom and a Staübli Jacquard machine. The fabric is constructed in a five satin pattern, with a density of 38.4 yarn/cm (2/30 Nm) for the warp and 19 pics/cm (2/34 Nm) for the weft. The areal density is 314 g/m². Its width measures 146 cm. No other treatment has been applied to the fabric.

Washing

The Fox Fibre® Colorganic® detergent has been used in this work. This laundry detergent is specifically designed for washing delicate fabrics. It is formulated with a blend of cleaning agents, surfactants and grease solvents to effectively remove dirt and stains without damaging the fibers. The soap used in this detergent is carefully selected to control foam and maintain a regular pH level. Additionally, natural organic acids and additives are included to ensure the integrity of the fibers is maintained throughout the washing process. This detergent has not environmental impact on aquatic life and it is fast and complete biodegradable.

The cotton fabrics were subjected to washing in a conventional household washing machine (FAGOR, F2810) under typical Spanish household conditions, which included a temperature of 40°C, a duration of 1 hour, 15 ml of Fox Fibre® Colorganic® detergent and a water hardness of 400 mg CaCO₃/L. The pH of the detergent at the concentration used in household washing is 9. Fabric specimens measuring 170 × 150 cm were utilized and underwent 1 to 30 washes under the aforementioned conditions. After each wash, the samples were dried in a Frommer model dry 92 tumble dryer and then conditioned in a standard climate of 20°C and 60% RH for 24 hours.

Characterization

The CIEL*a*b* coordinates and UPF were utilized to measure the optical parameters, which were then correlated with the number of washes and the shrinkage of the samples. UPF was also related with the weight per surface unit and thickness.

The color of the samples was assessed using a GRETAGMACBETH COLOR I7 equipment, following the ISO 105-J03 standard (Textiles — Tests for colour fastness — Part J03: Calculation of colour differences 2009), with D65 illuminant and a ten-degree observer. To determine the color differences between each washed fabric and the original, the parameter ∆E_ab* was employed (Eq. 1):

(1) $\mathrm{\Delta }{{\mathit{E}}_{\mathit{ab}}}^{\ast }=\sqrt{{\left(\mathrm{\Delta }{\mathit{L}}^{\ast }\right)}^2+{\left(\mathrm{\Delta }{\mathit{a}}^{\ast }\right)}^2+{\left(\mathrm{\Delta }{\mathit{b}}^{\ast }\right)}^2}$(1)

were L*, a* and b* are the lightness, green–red coordinate and blue-yellow coordinate, respectively, in the CIEL*a*b* space.

The Ultraviolet Protection Factor (UPF) of the fabrics was determined by the in vitro method using an Ultraviolet Transmittance Analyser UV1000F (Labsphere) and according to Standard AS/NZ 4399: 1996 (Gies et al. 2017).

The UPF of each specimen is calculated as follows:

(2) $\mathit{UPF}=\mathit{\hspace{0.17em}}\frac{{\int }_{280}^{400}{S}_{\lambda }{E}_{\lambda }\mathrm{\Delta \lambda }}{{\int }_{280}^{400}{S}_{\lambda }{E}_{\lambda }{T}_{\lambda }\mathrm{\Delta \lambda }}$(2)

where:

${\mathrm{E}}_{\mathit{\lambda }}$CIE relative erythemal spectral effectiveness,

${\mathrm{S}}_{\mathit{\lambda }}$ solar spectral irradiance,

${\mathrm{T}}_{\mathit{\lambda }}$ spectral transmittance of the fabric,

Δ$\mathit{\lambda }$ wavelength step in nm,

$\mathit{\lambda }$ wavelength in nm.

The weight per surface unit, g/m², of the fabrics was determined according to ASTM D3776 (ASTM D3776) and thickness was assessed through the ISO 5084 standard (ISO 5084)

The shrinkage of the fabrics after laundering was determined according to ISO 3759:2011 (ISO 3759). The extraction of waxes and pigments was conducted using a soxhlet apparatus. A duplicate of 10 g of the sample was subjected to petroleum ether in the soxhlet for a duration of 4 hours. The resulting petroleum ether was then evaporated to obtain a yellowish and transparent oily residue. The extracted cotton was dried at room temperature and subjected to another 4 hours treatment in the soxhlet apparatus, this time with ethanol 95%. This treatment facilitated the extraction of pigments that are soluble in polar solvents (Ma, Hussain, et al. 2016).

Following the evaporation of the petroleum ether and ethanol, the residues collected were dried and analyzed using Fourier Transform Infrared Analysis-Attenuated Total Reflection (FTIR-ATR). A Nicolet 6700 FTIR spectrometer (Thermo Scientific, Waltham, MA, USA) with a SmartOrbit Diamond ATR accessory was used to determine the spectra of the extracts. Thirty-two scans were competed in the 400–4000 cm⁻¹ range, at a spectral resolution of 2 cm⁻¹.

Results

Figure 1 illustrates the appearance of the samples obtained after each washing cycle. The upper part of the figure displays the scanner images of the actual samples, while the lower part represents the simulated RGB colors derived from the CIEL*a*b* results (https://www.nixsensor.com/free-colour-converter/).

Figure 1. Pictures of fabric samples in function of the number of washes. (up: scanner of the real samples; down: simulated colors based on L*a*b* results).

Figures 2–4 contain the results of L*, a* and b*, respectively, obtained from the colorimetric determinations of each sample. L* corresponds to brightness of the sample, a* corresponds to a* axis (green-red) and b* corresponds to b* axis (yellow-blue) in the CIEL*a*b* space.

Figure 2. Evolution of L* in function of the number of washes.

Figure 3. Evolution of a* in function of the number of washes.

Figure 4. Evolution of b* in function of the number of washes.

Contrary to what typically occurs in industrially dyed cottons, the color of the samples becomes darker with each wash, as evidenced by the decrease in the lightness (L*) of the samples with the number of washes (Figure 2).

The initial washing produces the greatest loss of brightness, with the slope of lightness loss of 2.33 L* units/wash. Lightness decreases further during subsequent washes, where the lightness loss rate is 0.38 L* units/wash and then again between five and thirty washes, with a lightness loss rate of 0.04 L* units/wash.

The change in a* value in relation to the number of washes is depicted in Figure 3. Initially, there is a decrease in a* value which indicates a loss of red color. However, after five washes, this decrease becomes minimal or non-existent. Therefore, some amount of red color is lost during the first few washes.

The relationship between the number of washes and the evolution of the b* parameter is depicted in Figure 4. The b* parameter ranges from yellow (+b*) to blue (-b*). A positive value of b* indicates the presence of yellow color in this parameter, which linearly diminishes with each home washing.

Consequently, the substrates experience a loss of the red and yellow colors, which are essential components of the brown color. To gain a more comprehensive understanding of the significance behind the decrease in both a* and b*, we will delve into the definition of chroma or saturation (C*) within the CIEL*C*h* color space. This color space, similar to CIEL*a*b* but utilizing cylindrical coordinates instead of rectangular coordinates, is preferred by certain professionals in the industry due to its strong correlation with human color perception.

(3) $C^{\ast }=\sqrt{\mathit{a}{\ast }^2+\mathit{b}{\ast }^2}$(3)

After completing the relevant calculations and plotting C* as a function of the number of washes (Figure 5), it becomes clear that there is a linear decrease in saturation with each subsequent wash. However, visually the intensity of the remaining colors increases, leading to a decrease in luminosity.

Figure 5. Evolution of C* in function of the number of washes.

Finally, ΔE*_ab corresponds to CIEL*a*b* color differences, all of them between washed and unwashed fabric (reference). The change in color difference, ΔE*_ab, as the number of washes increases, is depicted by three distinct lines with different slopes, as shown in Figure 6. The first line corresponds to the color change caused by the initial wash. This represents the most significant difference in color between the two samples (ΔE*_ab = 2.34) and can be attributed to the removal of dirt and waxes, as well as the pronounced effect on pigments under the washing conditions. In the second range (y = 0.3878× + 2.0517; R² = 0.966), which spans from one to five washes, there is a notable decrease in the rate of color change (from 2.34 units per wash in the first range to 0.39 units per wash in the second range). This indicates that there is some activity or influence on the substrate that leads to a significant change in color difference, although not as substantial as in the first wash. Finally, from five to thirty washes, although there is still a color change, the variation in color differences is minimal, with a velocity of color change of 0.06 units per wash (y = 0.0581× + 3.7; R² = 0.896).

Figure 6. Color difference between ΔEab in function of the number of washes.

Upon comparing the color differences between a sample and its preceding one, it is evident that the first wash causes a substantial change in color (ΔE*_ab = 2.33), aligning with the previously mentioned notable color loss. Nevertheless, the average color variation among the subsequent samples (compared to their respective previous samples) remains relatively stable (ΔE*_ab $\approx$ 0.53 units/wash) and is challenging to perceive with the human eye. However, these differences become significant when the cumulative impact of minor color variations after each wash is considered. When we merge the initial samples, following one wash, five washes and thirty washes, into a unified figure (Figure 7), it becomes evident that the visual disparities are already noticeable.

Figure 7. Comparison between the color of original sample and samples washed 1, 5 and 30 times.

To further comprehend the underlying causes of this color change, which results in reduced luminosity and diminished red and yellow hues, several parameters will be examined.

As depicted by Figure 8, it is evident that a significant amount of color is lost during the initial washes. However, the color of the fabric shows a marked increase during this stage, in contrast to the higher color intensity observed in the washing water. This paradoxical finding may be explained by two competing phenomena that could be occurring concurrently. The first of these mechanisms includes the removal of waxes, dirt and largely polar solvent-soluble pigments during the first wash. The second phenomenon involves the shrinkage of the cotton fabric during washing, which induces an increase in coloration.

Figure 8. Wastewater of the four first washes.

In order to gain a better understanding of what happens to pigments during the initial wash, samples of Dark ruby cotton, which is known for being the darkest cotton, were subjected to the same washing conditions as previously described in order to assess the removal of washes and pigments in the first wash. Following conditioning, the original and washed cotton samples were extracted using petroleum ether and subsequently with 95% ethanol, as outlined in the characterization section.

Upon evaporation of the petroleum ether, a transparent oily residue, representing the cotton waxes, was obtained and characterized using ATR-FTIR (Figure 9). It can be inferred from the obtained spectra that they correspond to waxes and its analysis revealed no significant differences between the original and washed samples. This indicates that the washing process does not have a significant impact on the composition of the waxes.

Figure 9. ATR spectra of the petroleum ether extraction for original cotton (blue) and washed ruby cotton {red).

Following the extraction with petroleum ether, the extraction with 95% ethanol is carried out on the same yarn. After this last extraction, the extracts were subjected to evaporation and concentration. The resulting residue was then analyzed using ATR-FTIR, as depicted in Figure 10.

Figure 10. ATR spectra of the ethanol extraction for original cotton (blue) and washed ruby cotton (red).

The two spectra acquired are notably dissimilar and while this method’s ability to identify them is limited, it is evident that the ethanol-extracted substance (polar solvent-soluble pigments) varies between the two specimens examined. Thus, it has been established that the washing process results in the loss of pigments that are detectable in the washing water. Nevertheless, the extract’s evaporation and measurement indicate that it is less than 1%.

After providing a rationale for the loss of pigments in the fabric, the cause behind the darker appearance of the fabrics, despite the minor loss of pigments, will be determined. It is widely acknowledged that cotton undergoes shrinkage during the washing process. Therefore, this study aims to explore the relationship between fabric shrinkage and its impact on color. The changes in dimensional stability, specifically in the warp (COT, conventional cotton) and weft (NaCOC) directions are visually depicted in Figure 11. Notably, there is a significant shrinkage of 8.3% and 5.3% in the warp and weft directions, respectively, after the initial wash. Consequently, the substantial increase in darkness observed in the fabric samples after the first wash can be attributed to this considerable initial shrinkage.

Figure 11. Shrinkage in the warp (COT) and weft (NaCOC) directions in function of the number of washes.

After the initial significant reduction in the size of the sample, two distinct responses occur. The first one takes place between one and five washes, during which the fabric experiences a 0.35% increase in shrinkage in both directions. Although this increase is less significant than the initial decrease, it is still greater than the final response. In the final response, the shrinkage increases linearly with the number of washes at a rate of 0.12% (R² = 0.943) in the warp direction and 0.08% (R² = 0.991) in the weft direction.

Figure 12 examines the relationship between the luminosity of the fabric, L*, and the shrinkage. It reveals a strong linear correlation between the decrease in luminosity and the increase in shrinkage.

Figure 12. Variation of L* with shrinkage.

However, it should be noted that there is no correlation between the decrease in red (a*) and yellow (b*) values and the shrinkage of the fabric. This implies that the observed color change in the fabrics is actually a result of the fabric’s brightness being altered due to shrinkage during the washing process.

In Table 3, the changes in UV-A, UV-B and UPF (Ultraviolet Protection Factor) are presented in relation to the number of washes. It is clear that there has been a notable rise in UPF during the first five washes. The UPF value has increased from 281 to 412 within two washes and, subsequently, it stabilizes at a relatively consistent fluctuating level between 450 and 540. This finding confirms that the most significant impact and alterations occur during the first five washes.

Table 3. Evolution of UPF, areal density and thickness of the samples in function of the number of washes.

Washes	0	1	2	3	4	5	10	15	20	25	30
UVA (%)	0.31	0.21	0.20	0.17	0.17	0.19	0.18	0.16	0.17	0.16	0.17
UVB (%)	0.37	0.27	0.26	0.23	0.23	0.23	0.23	0.23	0.21	0.21	0.24
UPF	281	402	412	473	474	499	453	479	541	530	445
Weight per m^2 (g/m^2)	314	345	352	355	357	357	363	366	369	365	373
Thickness (μm)	7.23	8.93	8.90	8.87	9.23	9.10	9.37	9.37	9.67	9.27	9.70

It is well known that the relationship between the UPF (Ultraviolet Protection Factor) of a fabric and its color can vary depending on several factors, including the type of fiber, the thickness of the fabric, the fabric design and the dyeing method. Thus, in the substrates studied, only two parameters can affect: the thickness of the fabric and the color (related to the type of dyeing in general terms).

Regarding the thickness of the fabric, in general, the denser the fabric, the higher its ability to block UV rays. Thicker fabrics may have a higher UPF regardless of color. Algaba (Algaba, Pepió, and Riva 2008) established that the weight per surface unit and thickness of the fabrics are structural parameters that are strongly correlated with UPF. An increase in any of these parameters leads to an increase in UPF. To examine this phenomenon, the values of areal density and fabric thickness have also been included in Table 3. It can be observed that both parameters increase with the number of washes, which is a response to the shrinkage of the fabrics that occurs during washing. Hence, it is evident that the UV protection of the fabrics examined is significantly impacted by shrinkage.

On the other hand, the color of the fabric can affect its ability to block UV rays to some extent. Riva (Riva et al. 2009) concluded that the diffuse transmission of ultraviolet radiation through fabrics decreases as the color intensity of the fabrics increases. As transmission decreases, the UPF increases with the intensity of the dye. In fact, dark colors tend to absorb more UV radiation than light colors, which can result in a slightly lower UPF for dark fabrics. However, this difference is usually relatively small and may be insignificant compared to other factors such as fiber type and fabric thickness. In this study, the decrease in brightness should result in a decrease in UPF. However, as this does not happen, it once again confirms that the shrinkage that occurs, especially in the first wash, is the driver of the darkening phenomenon that takes place during washes and in the increase of the UPF protection.

Conclusions

The impact of home washing on the colorimetric properties of naturally colored organic cotton (NaCOC) fabrics has been investigated, revealing that washing can have a substantial effect on the visual characteristics of these textiles, particularly in terms of lightness and saturation. The initial wash is found to be the most influential in terms of color modification, although subsequent washes up to the fifth also exhibit a noticeable impact. During the first wash, two simultaneous phenomena occur. Firstly, the pigments present in NaCOC are extracted and transferred to the wash water, resulting in a reduction in the saturation components, a* and b*, of the CIEL*a*b* coordinates. Secondly, the fabric undergoes shrinkage, leading to a darkening of the color. Considering the overall behavior, it can be inferred that the darkening of the fabric due to shrinkage is more significant than the loss of pigments, making it the dominant phenomenon in household washing. Furthermore, this shrinkage also contributes to a significant increase in the fabric’s ultraviolet protection factor (UPF).

Highlights

Innovation and Impact: This study introduces an approach to the field of sustainable textiles, focusing on the influence of domestic laundering on the colorimetric attributes of natural colored organic cotton (NaCOC) fabrics. Understanding how natural organic cotton materials react to routine domestic laundering is crucial for sustainable fashion and the textile industry.

Methodological Details: This article provides a detailed description of the experimental process, which includes fabric preparation, laundering, shrinkage and colorimetric analysis. The comprehensive nature of the methodology enhances the reliability of the study and allows for replication of the results.

Analytical Depth: This study conducted a thorough quantitative analysis of the color change of NaCOC fabrics, after repeated laundering cycles, relating these phenomena with the losses of pigments after each wash and with the shrinkage of the fabrics, providing important insights into the relationship among those variables. The inclusion of quantitative data and visual representations adds a level of scientific precision to this research.

Illustrative Elements: This study includes informative visual content, such as charts and images, to visually demonstrate the changes in color and lightness that occur in NaCOC) fabrics after domestic washing. These illustrative components are integral in clarifying the findings of this study.

Sustainability Implications: The findings of this study are crucial for promoting sustainable textile practices, as they shed light on the behavior of naturally colored cotton fabrics when subjected to domestic laundering. Understanding these characteristics is essential for advocating sustainable and environment-friendly textile options.

Acknowledgments

The authors would like to express their gratitude to Mr. Francisco José Barahona, Mr. Oliver García, Mrs. Montserrat Guerrero, Mr. Ferran Parés and Mrs. Zurine Ramírez for their assistance in the experimental work.

Disclosure statement

No potential conflict of interest was reported by the author(s).