Sustainable Textile Dyes (Part 2)

BULETIN TEKSTIL.COM/ Jakarta – Sustainable textile dyes (Part 1) examined the history, origins, and categorization of colors, particularly natural dyes in textiles. Another name for employing natural dyes as textile dyes is sustainable textile dyes. On this occasion, we will cover how to obtain dyes, the varied chemical compositions of dyes, and the application of dyes in industry.

Figure 1: Natural dyes used on textiles

Essentially, natural pigments/dyes may be isolated from plants by extracting plant components with a solvent that matches the polarity of the material to be removed. Natural dyes may be extracted from various plant components using water as a solvent at high or low temperatures. A color change will occur if the water used is polluted with minerals such as iron. To avoid discoloration, use distilled or deionized water. The solution is then heated to boiling (98-100° C) for heat-sensitive dyes (typically colours from flowers) and sustained for 1-2 hours depending on the extracted dyes.

Extraction is the separation of a substance from a mixture using a suitable solvent. When an equilibrium was attained between the concentrations of the chemicals in the solvent and the concentrations in the plant cells, the extraction process was terminated. Filtration separates the solvent from the sample after the extraction procedure. Among the different extraction procedures used to acquire natural colors are:

1. It is advised that flavonoids group substances be extracted in an acidic environment because acids can denature plant cell walls, allowing anthocyanin pigments to depart the cells and preventing flavonoids from oxidizing. Anthocyanins extract effectively in acidic solvents, particularly tartaric acid.
2.  The indigo dye was extracted from tilapia leaves by hydrolysis for 24 hours using an acid catalyst. The hydrolysis process products are separated into filtrate and raffinate. The filtrate was then oxidized for 12 hours using an aerator. The use of 0.01 M sulfuric acid as a catalyst in this manner results in high indigo hues.

Content of Chemical Compounds

Natural dyes derived from plants can be red, yellow, blue, brown, or black, depending on the kind and section of the plant and how it is acquired. Plants create around 2000 pigments. Furthermore, dyes produced from many plants can be categorized as medicines, and some of them have antimicrobial action. Natural dye molecules are made up of unsaturated organic compounds, chromophores as color carriers such as azo groups, nitroso, nitro, and carbonyl groups, and auxochromes as color and fiber binders such as cations and anions.

Natural chemical compounds which are yellow-orange-red pigments are carotenoids. Important carotenoid groups include carotenes (ß-carotene (C40H56) and lycopene (C40H56)); xanthophyl (canthaxanthin (C40H52O2), zeaxanthin (C40H56O2), and lutein (C40H56O2)), and capsanthin (C40H56O3). ß-carotene is an orange-yellow pigment, while lycopene is a pigment that can give a red color. Xanthophyl is an oxygen carotene, can give an orange-yellow color. Lutein is also a very common carotenoid, more green-yellow in color. The yellow-orange color of annatto comes from the outer layer of the Bixa orellana seed, this color is a combination of carotenoids, bixin and nor-bixin.

Flavonoids are a diverse group of polyphenolic compounds contributing to the yellow color of horticultural products, more than 4000 unique flavonoid structures have been identified from 53 plant sources. Based on differences in molecular structure, flavonoids are grouped into six different main classes namely flavonols, flavanones, flavones, isoflavones, flavonols, and anthocyanidins. Important pigments from flavones are apigenin, kaempferol, quercetin, myricetin, luteolin, tricin, izoramnetin. Quercetin is one of the most important flavonoids, having the molecular formula C15H10O7. Luteolin is a yellow compound, also a flavonoid, with the molecular formula C15H10O6.

Anthocyanidins are included in the class of very colorful flavonoids. Anthocyanins are glycosides of the anthocyanidins which are a class of phenolics giving them a blue-red-orange purple color. Tannins are classified into hydrolyzable tannins (pyrogallol tannins) and condensed tannins (cathecol).

Condensed tannins known as proanthocyanidins are polymers consisting of 2 to 50 (or more) flavonoid units joined by carbon-carbon bonds, which are not susceptible to hydrolysis. Hydrolyzable tannins (pyrogallol) and condensed tannins (cathecol) or flavonoid tannins come from the flavonol group; can be used as a skin tanner. Each gives a brownish yellow and reddish brown.

Tetrapyrolle is chlorophyll which is a green pigment used by all plants for photosynthesis to take place. Use as a colorant is limited, because of the lability of magnesium and the associated discoloration that occurs. Anthracenes contain several well-known dyes. The largest group best known for their use are the anthraquinones (quinones), because they give them their intense color. Anthraquinone dyes require a mordant (complex metal ion) for the fabric dyeing process.

Betacyanin (betalains) is a red pigment, obtained from red beet (Beta vulgaris) extract. Beetroot extract contains red, yellow and also bluish-red pigments depending on the betanin content, stable at a high pH range. Used for food coloring such as beverages, confectionery and dairy products. Indigo blue is obtained from dry leaf extract of Indigofera spp, which contains indican glucosides or isatan B or Indigotin. Heating tea leaves in a wet environment and an acidic atmosphere, can cause changes in chlorophyll compounds to pheophytin, and the color changes to brownish green.

Figure 2 – Beets

Industrial Applications

1.Textile industry

Many traditional batik and weaving craftsmen are familiar with plants that can be used to dye textile materials; some of them are indigo leaves (Indigofera sp.), soga high bark (Ceriops candolleana arn), tegeran wood (Cudraina javanensis), turmeric (Curcuma sp.), tea (Camelia sp.), noni root (Morinda citrifolia), soga jambal bark (Pelthophorum ferruginum), kesumba (Bixa orellana) and guava leaves (Psidiumguajava).

So that the resulting textile colors are not easily faded and brilliant, then in the dyeing process it is necessary to add a material that can function as a mordant or fixator (binder) of dyes. Fixation materials need to be selected from materials that are environmentally friendly and non-toxic so that they do not become a problem for the environment. Binders that are often used in the batik industry include: citron, lime, vinegar, saltpeter, borax, alum, rock sugar, palm sugar, tunjung, prussi, drops, lime water, tape, klutuk bananas, klutuk guava leaves.

Making cotton cloth with natural dyes from mangosteen rind extract (without or with lime, alum or tunjung fixation), jackfruit bark extract (with tunjung fixation) and kesumba seed extract (with tunjung or alum fixation), mango leaf extract (with alum fixation), can provide good fastness on batik fabrics.

Figure 3 – Batik Products

2. Food industry

Natural coloring agents commonly used as food additives include: annatto extract, red beetroot, canthaxanthin, carotene, Dactylopuis coccus extract, cottonseed, grape skin extract, fruit and vegetable juices, Tagetes extract, carrot oil, corn endosperm oil, paprika and paprika oleoresin, riboflavin, turmeric, turmeric oleoresin, xanthophylls (flavoxanthins, rubiaxanthins, zeaxanthin), and chlorophyll.

Annato has been used as a food coloring agent for more than 200 years, to color various food and dairy products, especially cheese. The yellow-orange color of Annatto comes from the outer layer of the tropical seeds of the Bixaorellana tree; The content of carotenoids, bixin, and norbixin will give a yellow-orange appearance.

The most commonly used pigment in the food industry is beta carotene which is obtained from some microalgae and cyanobacteria. Canthaxanthin is an orange-pink to dark red pigment including carotenoids used to color cheese (dairy products), confectionery/candy, fish and meat products, fruit products, drinks, snacks/snacks, beer and wine. However, under EU regulations canthaxanthin is not considered a food additive. Lutein is a more yellowish-green carotenoid, and is not allowed as a food coloring in the United States except for coloring poultry/chicken foodstuffs.

Figure 4 – Sources of natural dyes for food

3. Pharmaceutical industry

Natural dyes also play an important role in human health because they contain several biologically active compounds, have a number of pharmacological properties such as strong antioxidant, antimutagenic, anti-inflammatory and antiarthritic effects. Carotenoids can act as biological antioxidants, protecting cells and tissues from damage by free radicals and free oxygen and also as a source of antitumor. Grape seed extract is a major source of a group of powerful antioxidants, also bio-colours are used to color tablets/pills and tonics.

4. Cosmetic Industry

Dyes derived from plants such as Bixa orellana and Lithospermum erythrorhizon serve as natural dye sources for coloring lipsticks and eye shadow liners. Anthocyanin pigment powder from rose petals 4 days post-cut, has the best pigment quality. Rose flower anthocyanin pigments 2-4% are more effective in contributing reddish and yellowish colors (yellowness) to body lotion cosmetics. Polyphenol pigments from areca seeds (Areca catechu L.) contain catechins, epicatechins, leukocyanidins and complex flavonoids which can give a red-yellow color to transparent soap products.

Figure 5 – Natural coloring for lipstick

5. Craft Industry

Craft items that use cellulose or natural fibers can be colored with natural dyes which can be used to dye fabrics made from natural fibers. Luteolin is one of the yellow coloring compounds, which produces glitter (vibrant) and light fastness, used in the gold dyeing process. Coloring of non-textile natural fibers such as; agel, pineapple fiber, hati rattan and bamboo shreds using natural dyes from gambir, giving it a reddish brown color. When using cocoa pod shells it gives a brown color, while palm shells and seaweed give it a gray brown color.

6. Leather Tanning Industry

Tannins extracted from walnut shells, eucalyptus bark, turmeric rhizomes and tea leaves are often used for tanning leather. The use of these materials is still limited to the small-scale leather tanning industry, while large-scale industries use chrome tanners. The tannins extracted from Gambir leaves mostly consist of flavonol monomers such as catechins, epicatechins and alkaloids. Several studies have reported that coloring leather using natural dyes of the type carminic acid and laccaic acid at a concentration of 5%, immersion time of 100 minutes produces skin with a stable red color while natural dyes from monascorubrin and betanine produce poor light fastness, so they are not suitable for coloring.

(Red B-Teks/Agung )

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