Are “pure cotton” clothes absolutely natural? Will chemical fiber clothes cause discomfort to the body?

When consumers choose clothing and textiles, material is one of the important deciding factors.

Common fibers for clothing and textiles can be divided into natural fibers and chemical fibers according to their sources.

Natural fibers provided the initial covering and cold-proof materials for human development, among which cotton fiber is one of the most important natural fibers. People living in the Indian subcontinent began to spin yarn with cotton fiber 5,000 years ago.

To this day, cotton clothing and textiles still play an important role in our daily lives. On the one hand, cotton fibers do have a particularly outstanding skin-friendly texture, soft feel, good moisture absorption and heat preservation properties. They are widely used in underwear, socks, coats, cotton clothes, quilts, towels, bed sheets and quilt covers and other products.

On the other hand, "pure cotton" enjoys a good reputation and is deeply trusted by everyone. This trust comes from the belief held by most consumers: cotton is a pure natural fiber, safe and harmless to the body. When it comes to chemical fibers, many consumers believe that chemical fibers contain a lot of chemical substances and will cause discomfort to the body.

Is this view correct?

Let me first state the conclusion. If we only consider the types of chemical substances that have been exposed to, then pure cotton is not "pure" at all. However, this evaluation method itself is unreasonable. As long as the textile products meet the corresponding national standards, whether they are pure cotton or chemical fibers, they are safe enough.

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Let’s talk about it in detail today.

Natural fibers are also exposed to a lot of chemicals

Spinning cotton right after it’s been picked? That’s impossible…

Many friends may have some misunderstandings about "pure natural". They think that pure cotton means freshly picked cotton is spun into yarn and woven into cloth. Sorry, if you really do this, the clothes will probably be rough, thick, hard and earthy. In short, they will definitely be uncomfortable and ugly to wear.

In fact, from the time cotton is picked to the time it finally becomes a soft and comfortable garment or textile, there is a very long and cumbersome processing chain in between. The typical processing steps usually include ginning - spinning - weaving - dyeing and finishing - cutting - sewing.

In this process, in order to present the final color and style, cotton fibers not only have to undergo multiple physical processing, but also inevitably multiple chemical treatments.

Depending on the needs of the process, cotton fibers will react with dozens of chemicals. Some chemicals will remain on the fibers and become important materials for the final textiles (such as dyes and coatings), while some chemicals are used to improve the processing conditions and will not react with the fibers or remain on the fibers (such as surfactants and finishing agents).

For example, mercerized cotton, which we often hear about, refers to cotton fabric that has been mercerized and is commonly used in shirts and T-shirts. The mercerization process refers to the use of the principle that cotton fibers undergo irreversible swelling in concentrated alkaline solutions to treat cotton yarn or cotton fabrics. Clothing made of cotton yarn or cotton fabrics that have been mercerized will have a silky luster and a soft feel.

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The printing and dyeing process gives textiles rich colors and patterns, and various dyes are used in the processing. Traditional plant dyeing uses natural dyes extracted from plants. With the full development of the chemical synthesis industry, chemical synthetic dyes have almost replaced traditional plant dyes because of their lower cost, more complete color spectrum, better dyeing and color fixation than plant dyes. Taking the use of vat dyes to dye pure cotton grey cloth as an example, the vat dye is reduced and dissolved into a leuco solution by insurance powder and caustic soda, and then adsorbed on the surface of cotton fibers, and then diffused into the fibers to complete the dyeing of the fibers, giving the fabric color.

The finishing process can improve the appearance and internal quality of textiles, enhance their performance or give them some special functions, and various finishing auxiliaries are also used in the processing process. Consumers often see iron-free cotton shirts, which are made of the fabric of the iron-free finishing process, and the finished garments are cross-linked with resin. The resin molecules form covalent cross-links with the cellulose molecules of the cotton fibers, improving the wrinkle resistance of the cotton fibers, thereby achieving the iron-free effect.

The above is just a brief introduction to the chemical treatment that cotton fibers or fabrics undergo during the mercerizing, dyeing, and finishing processes. During the entire textile processing process (especially dyeing, printing, and finishing), textiles are exposed to many other chemicals.

At this point, consumers may worry that after being treated with so many chemicals, will textile products become harmful to the body?

In fact, the national mandatory standard GB18401-2010 "National Basic Safety Technical Specifications for Textile Products" has made the most basic requirements for the safety of textile products. The national standard has strict requirements on the formaldehyde content, pH value, color fastness, odor, and degradable carcinogenic aromatic amine dyes of textile products to ensure that textile products are safe and harmless to the human body.

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Infant textile products should comply with the Class A requirements of the above standards, and products that come into direct contact with the skin should at least comply with the Class B requirements of the standards (if consumers are interested in this, they can refer to the specific content of the standard, which is public).

After reading this, you must have discovered that even if it is "pure cotton", it is exposed to a lot of chemical substances... But we have worn so many pure cotton clothes and they are all very safe. This is because qualified textiles have implemented national standards. So we really don't need to worry about the production process and the word "chemical". Just check whether the finished product meets the national standards. This also applies to chemical fiber products.

Chemical fiber, more efficient

Different from natural fibers, chemical fibers are a type of fibers produced by chemical methods. Chemical fibers have only a short history of over a hundred years, but they have large output and rich variety.

Compared to cotton fibers, which need to be planted in agriculture and have seeds harvested after a certain growth cycle before entering the subsequent industrial processing stage, the production of chemical fibers is more "direct" and enters the highly efficient industrial processing stage directly from the source.

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Take synthetic fibers, which have the largest output in the chemical fiber family, as an example. The source of synthetic fibers is petroleum. Petroleum is extracted and separated through layers of chemical systems to produce small molecule organic compounds needed to produce this type of fiber. The small molecule organic compounds are then synthesized into organic polymer compounds through addition polymerization or condensation polymerization, and then processed into fibers through various processes.

As for man-made fibers, which are also chemical fibers, natural polymer compounds or derivatives must be dissolved and purified before subsequent production and processing, which will not be elaborated here.

The emergence of chemical fibers has greatly enriched the variety and performance of textiles and clothing, and endowed the products with some functions and characteristics that are different from natural fiber materials. For example, the most notable feature of polyester is its poor hydrophilicity, which makes polyester fabrics easy to dry. Many high-quality quick-drying sportswear are made of ultra-fine polyester.

After the ultrafine fibers are woven into fabrics, the capillary siphon effect is formed between the fibers, which accelerates the evaporation of sweat on the fiber surface and keeps the human body dry and comfortable during exercise. Researchers have developed cotton-like polyester, which is a polyester with the advantages of cotton fibers and has significantly improved hydrophilicity; cashmere-like polyester is a polyester with wool fiber characteristics developed by drawing on the experience of cotton-like polyester. Its surface and cross-section are both honeycomb microporous structures, with a fineness close to cashmere, and has a soft and delicate feel like cashmere and good moisture absorption and breathability.

After the characteristics of natural fibers and chemical fibers are fully understood, people often use blending or interweaving processes in product development to combine the advantages of natural fibers and chemical fibers, thus achieving the effect of 1+1>2.

The most common example is polyester-cotton blended fabric, which is usually made of 65% polyester and 35% cotton fiber. The strength, wear resistance and shape retention of polyester-cotton blended fabric are better than those of pure cotton fabric, and at the same time, they have a certain degree of moisture absorption and soft feel. For example, traditional jeans are woven with pure cotton coarse yarn. Although they have good moisture absorption, they lack elasticity and have poor fit. Later, people developed a variety of fabrics suitable for jeans. For example, there is a kind of high-elastic denim that is a product of cotton yarn and spandex yarn. After interweaving with highly elastic spandex yarn (usually 3%-5%), you can get elastic denim fabric, which is close to the body and comfortable, and adds comfort on the basis of ensuring the special style of denim clothing.

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Natural fibers and chemical fibers each have their own advantages. Together, they weave a variety of clothing and textiles for us. Textile products that meet national standards are safe and reliable. Consumers can choose according to their actual needs when purchasing.

References:

[1] General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China, Administration of Standardization of the People's Republic of China. GB 18401—2010 National Basic Safety Technical Specification for Textile Products [S]. Beijing: National Standards Full Text Public System, 2011. https://openstd.samr.gov.cn/bzgk/gb/index

[2] Shi Yidong. Ecological Textiles and Environmentally Friendly Dyeing Auxiliary Agents[M]. Beijing: China Textile Press, 2014.

Author: Song Lidan, Consulting Engineer, Industrial Research Department, China Textile Construction Planning Institute

Review｜Zhang Jie, Chief Engineer of China Textile Construction Planning Institute

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