Emily Ng, Year 2 Research.
The ongoing environmental impacts of the textile industry are partially attributed to the exploited use of synthetic dyes. This project attempts to find ways for individuals who are uncertain on how to alleviate large-scale issues within the textile industry to dye fabric from skins of yellow onions and skins and pits of avocados. Cotton samples were scoured, pretreated with mordants and modifiers, dyed, and washed with a hotplate and magnetic stirrer. A serial dilution was then done to compare the absorbance values of the reserved washing liquid, with a higher absorbance value representing more colour loss. Mordants (Potassium Alum Sulfate and Gallnut) and modifiers (Vinegar and Salt) are said to have different wash fastness properties on naturally dyed fabric, but the data collected at this stage suggests that a pretreatment may not be necessary for food scrap dyed cotton to retain colour.
The textile industry is one of the world’s most polluting industries, and the use of chemical dyes is a contributing factor. Though less costly than their natural counterparts, they harm the health of the environment and human beings. When these dyes are released into the water, they decompose into harmful substances that disrupt the survival of aquatic and terrestrial organisms (Lellis et al. 2019). As well, over 60 million people work in this fast-growing industry and can experience dermatological and respiratory problems from long-term chemical exposure (Reports and Data 2019, Chowdhury 2018). This situation is alarming for the planet and its people as it is likely to worsen; by 2026, the compound annual growth rate of the textiles market is set to accelerate at 5.7 percent and the global dyes market to 10.13 Billion USD to satisfy the demand of the growing population (Reports and Data 2019).
To reduce the impact of textiles processing, this project explores the effectiveness of affordable non-toxic mordants and modifiers. Mordants, Potassium Alum Sulfate (Alum) and Gallnut, substances that bind dyes to fabric, and modifiers, Salt and Vinegar, substances that assist dyes to bond to fabric, were tested on cotton dyed from the skins of yellow onions and skins and pits of avocados (Griffin Dyeworks & Fiber Arts). The collected data informs a mordant or modifier’s wash fastness property, where good wash-fastness equates to a stronger mordant or modifier (Patwary 2013).
Similar works have compared the different behaviours of synthetic and natural mordants (Zinoth 2018, Mshelia and Zubairu 2015). Others have investigated the commercial viability of natural dyes and mordants as well as the allergic and toxic effects of synthetic dyes (Samanta 2009). There is conflicting information on the Internet regarding the effectiveness of mordants and modifiers, so this project explores, which, if any, mordants and/or modifiers better retain colour. It also explores whether a tannin process, Gallnut, is required to assist Alum in dyeing cellulose fibres (Maiwa Handprints Ltd). While helping alleviate pollution from the textile industry, extracting colour from food scraps could transform what is stereotypically considered waste into a resource.
Materials and Methods
Cutting Fabric: Cotton Handspun Handwoven Fabric (Maiwa Handprints Ltd) was cut into 24 7cm x 7.5cm samples.
Scouring Fabric: According to the Maiwa Guide to Natural Dyes, 10mL of Synthrapol and 20g of Soda Ash are used to scour 450g of cotton to ensure even dyeing. Due to conversion errors, 0.15mL of Synthrapol (Maiwa Handprints Ltd) and 2.25g of Soda Ash (Maiwa Handprints Ltd) were added to 750 mL of tap water to scour 15g of cotton for 1 hour. Scoured samples were then rinsed in cold tap water and dried flat in an unlit room.
Pretreating Scoured Fabric: Samples were hydrated in warm tap water before mordants or modifiers were applied in a stainless-steel saucepan. Mordants were applied according to the Maiwa Guide to Natural Dyes (Maiwa Handprints Ltd) and the modifiers were applied according to the All Natural Dyeing Guide (Jane 2016). 4 of the 24 samples were reserved as control.
Gallnut Only: 8 scoured samples were treated with 10% WOF (weight of fabric), equating to 0.5g of Gallnut Powder (Maiwa Handprints Ltd). It was stirred into 500mL of tap water once the water reached 75°C. The saucepan was placed on a trivet, with the 8 pieces of fabric soaking for 1 hour, lid covered. The samples were then divided into 2 groups: 4 were rinsed in cold water and left to dry flat in an unlit room. The other 4 samples were used to test if a tannin such as Gallnut is needed to pre-mordant cellulose fibre such as cotton, to bond better with Alum.
Alum and Gallnut: 4 Gallnut-treated samples were treated with 15% WOF, equating to 0.38g of Alum (Maiwa Handprints Ltd). It was stirred into 250mL of tap water once the water reached 75°C. The saucepan was placed on a trivet, with the 4 pieces of fabric soaking for 1 hour, lid covered. They were then rinsed in cold water and left to dry flat in an unlit room.
Alum Only: 4 scoured samples were treated with 15% WOF, equating to 0.38g of Potassium Alum (Maiwa Handprints Ltd). It was stirred into 250mL of tap water once the water reached 75°C. The saucepan was placed on a trivet, with the 4 pieces of fabric soaking for 1 hour, lid covered. They were then rinsed in cold water and left to dry flat in an unlit room.
Vinegar: 4 scoured samples were treated with Pure White Vinegar 5% Acetic Acid (No Name). The samples simmered in a 1:4 ratio of vinegar to water solution, equating to 187.5mL of water and 62.5mL of vinegar for 1 hour between 75-90°C. They were not rinsed before being dried flat in an unlit room.
Salt: 4 scoured samples were treated with Sea Salt (Assi Brand) with a 1:16 ratio of salt to water. 250mL of water and 15.6g of salt were heated until dissolved. This solution was remeasured to 250mL and heated along with the samples for 1 hour between 75-90°C. They were not rinsed before being dried flat in an unlit room.
Labelling Jars; Preparing Fabric: 6 glass jars were labelled for the onion-skin-dyed samples as Alum, Alum and Gallnut, Gallnut, Vinegar, Salt, and Control. 2 fabric samples were placed into each jar with 200mL of warm water to open up the fibres before the dyestuff was poured over. This procedure was repeated for the avocado-skin-and-pit-dyed samples.
Onion Skin Dyestuff: 2000mL of tap water and 30g of pre-rinsed onion skins were boiled down to 1000mL (time was not administered as volume depended on the power from outlet source). Filter paper (Whatman) filtered out impurities from the dyestuff. 2 dampened fabric samples were placed flat on the bottom of each jar before 100mL of dyestuff were poured over, and dyed for 24 hours.
Avocado Skin and Pit Dyestuff: Collected skins and pits of avocados were pre-rinsed to remove clinging flesh. 370g of pits, 140g of skin, and tap water were boiled; tap water was added and boiled down to concentrate solution until 600mL of filtered dyestuff remained. 2 dampened fabric samples were placed flat on the bottom of each jar before 85mL of dyestuff were poured over, and dyed for 24 hours.
Rinsing Fabric: Samples were removed from the jars into one of the six glass containers each with 200mL of cold tap water and were hand-stroked 30 times to remove loose particles. Excess water was shaken off before drying in an unlit room. Once dried, samples were stored in Zip-lock bags for 2 weeks to let the colour fully set in. This procedure was done for both the onion skin and avocado skin and pit samples. In preparation for the washing of samples, 12 pieces of dyed mordanted samples were reserved to show the original colour of dyed fabric while 12 pieces of mordanted fabric were washed consistently as explained in Figure 1.
Figure 1: 24 samples of scoured and pre-treated cotton were divided: 12 for Onion Skin Dyed Fabric and 12 for Avocado Skin and Pit Dyed Fabric. For each set, half were reserved to compare colour difference after washing.
Washing Fabric: Fabric samples were washed using a hot plate and a magnetic stirrer to mimic a washing machine. 75mL of distilled water was brought to 25°C in a 200mL beaker. A magnetic stirrer was then placed into the beaker along with one fabric sample for 2 minutes and 30 seconds at 100 rotations per minute, maintained at 20-40°C. Then, the beaker was removed from the hot plate and tweezers were used to shake off excess water before placing the washed sample onto a small glass Petri dish. The washing water was reserved into small jars to measure absorbance values using the WP-100Plus spectrophotometer (Walter). The samples were dried in a Central Scientific Oven (Cenco Instruments Corporation) for 1 hour at heat setting 2 and were washed another 2 times. The station was set up as shown in Figure 2.
Figure 2: Jars, beakers, and Petri dishes set-up before fabric was washed.
Data was collected after each sample was washed with distilled water to record colour loss and show the performance of different mordants or modifiers. Figures 3-6 show different ranges of hues and intensities of the dye on fabric samples qualitatively before and after washing.
Figure 3: Dried samples after soaking in onion skin dyestuff for 24 hours
Figure 4: Dried onion skin dyed samples after washing 3 times in water with hotplate and magnetic stirrer.
Figure 5: Dried samples after soaking in avocado skin and pit dyestuff for 24 hours.
Figure 6: Dried avocado skin and pit dyed samples after washing 3 times in water with hotplate and magnetic stirrer.
Quantitatively, a WP-100 Plus spectrophotometer was used to measure the colour loss of the fabric samples as absorbance values. The higher the absorbance values were, the more colour was considered to be washed out.
Onion skin: According to the absorbance values collected as seen in Table 1, the colour loss from all the samples ranged between 0.00AU to 0.02AU in the first wash. The absorbance values ranged between 0.33AU to 0.37AU for the second wash and 0.31AU to 0.33AU in the third wash. These values also can be seen in Figure 7 with respect to its serial dilution in Figure 8.
Table 1: Data collected from the three washes for onion skin dyed samples, with the wavelength set to 650nm on the spectrophotometer.
Figure 7: Onion skin dyed with 6 different pretreatments shown to have similar absorbance values after each wash.
Figure 8: Serial Dilution to compare the absorbance values after washing samples for onion skin dyed cotton.
Avocado skin and pit: According to the absorbance values collected as seen in Table 2, the colour loss from all the samples ranged between 0.28AU to 0.34AU in the first wash. The absorbance values ranged between -0.02AU to 0.00AU for the second wash. Values for the third wash were not collected. These values can also be seen in Figure 9 with respect to its serial dilution in Figure 10.
Table 2: Data collected from the two washes for avocado skin and pit dyed samples, with the wavelength set to 650nm on the spectrophotometer.
Figure 9: Onion skin dyed with 6 different pretreatments shown to have very similar absorbance values.
Figure 10: Serial Dilution used to compare absorbance values after washing samples for avocado skin and pit dyed cotton.
With larger absorbance values represent more colour loss, the current data suggest that no pretreatment is needed as absorbance value differences are slight.
These differences could stem from several reasons, given that when perceived by the naked eye, the colour of the washed fabric is more varied, as shown in Figure 3-6. The converted scouring ratios were slightly off from the Maiwa Guide to Natural Dyes, which could lead to uneven fabric dyeing. As well, the scoured fabric is normally placed directly into a pretreated solution or its dyeing medium (Maiwa Handprints Ltd). However, these samples were rehydrated and dried after each stage of scouring, pretreating, and dyeing instead, with a one-week gap in between. Moreover, fabric treated with salt or vinegar is typically placed into a dyeing medium immediately after mordanting. However, the samples had to be dried without being rinsed to keep the experiment as controlled as possible. As for the samples pretreated with Gallnut, though claimed to be a colourless tannin, they were tinted pink, which may have enhanced the pink and orange hue of the fabric unlike the other samples, which remained white after pretreatment. These shortcomings could have prevented the mordants and modifiers from acting as well as they could to reduce colour loss, while the washing procedure could have also led to more caveats.
The water temperature during the first wash of onion-skin-dyed samples was between 20-25°C, so the absorbance values are noted to be lower. After configuring the water temperature on the hot plate to get a consistent temperature for the remaining washes, the temperature increased, so there was more colour loss, which explains the spike in absorbance values from the first to the second wash of the onion-skin-dyed fabric as shown in Figure 7. The absorbance values collected in the second and third wash were close to the absorbance value of the undiluted dyestuff at 0.43AU as shown in Figure 8, which could indicate that the wavelength selected at 650nm may not have been ideal. The absorbance values for the avocado skin and pit washed samples could be seen to be much lower in Figure 9 because it produces a much lighter hue than onion skins. More so, leftover flesh from the skins and pits could have created a barrier, making it hard for water to penetrate quickly and have a lower colour loss compared to the undiluted dyestuff at 2.50AU as shown in Figure 10. While the hotplate and magnetic stirrer were used to mimic a controlled washing machine, the fabric’s position could differ depending on its interaction with the magnetic stirrer. The washed fabric samples were shaken to remove excess liquid before drying, but loose dyestuff particles could have dried onto the fabric, increasing the actual absorbance values when washed again. Lastly, the collected data zeroed or went below zero as early as the second wash for the avocado-skin-and-pit-dyed samples, so absorbance values from the third wash were not administered; these values suggest that the data was too dilute for reliable data collection.
Comparing the samples in Figure 3-6, it is likely that the initial amount of colour clinging onto the fabric and the hue produced varied, meaning darker colours do not necessarily equate to stronger mordants and modifiers. By eye, there are more obvious colour differences depending on the mordant or modifier, but the absorbance values were so similar, so more testing is needed to establish wash fastness properties.
Past studies have stated that natural
mordants and modifiers do not yield as strong colours as synthetic mordants
(Mshelia and Zubairu 2015, Samanta 2009), but the Kumar (2018) study showed
that non-synthetic mordants such as salt, vinegar, and potassium dichromate had
good wash fastness when mordanted onto cotton dyed from chosen leaves, tubers,
and flower plants at 600°C for one hour. Their study further supports the
idea that more research could be done to determine how to lower the
environmental impact of chemical dyes. Still, establishing how to best describe
wash fastness between mordants and modifiers is needed because natural dyes
create different shades when bonding with different substances. Future works
could research how much colour do the mordants and modifiers retain before the
fabric is washed. It could also expand on how pre-mordanting, mordanting in
dyeing medium, post-mordanting, and exposing fabric in a lit room could affect
the colour retained. We, individuals, cannot do much at the corporate level,
but debunking different sayings of which substances have better wash fastness could
provide us with the knowledge to support sustainable consumerism and green
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