fashion and cotton
People often believe that natural fibres are associated with environmental responsibility. However, this is not always the case. Take for example cotton, one of the most used natural fibres. Even though only 2% of the world’s agricultural land is used for the production of cotton, this single crop is responsible for 24% of global insecticide use. The association between cotton and natural and thus, sustainable fibres, is therefore not correct. To understand the full impact of textiles, it’s not enough to look only at fibre content. More factors need to be taken into account, such as the production process and the wet-processing (dying, printing or finishing of textiles) that a material goes through.
In addition to this, the last stages of a garment’s life cycle also prove to be very challenging for the environment. 80% of textiles end up in landfill or are incinerated rather than recycled. And even if textiles are recycled, it often results in value loss through applications, such as insulation material and mattress stuffing. This loss of value in the recycling processes is also called downcycling. The opposite of this, upcycling, is much more befitting of a circular economy. But upcycling, which means maintaining or improving the value of the resources is almost never done. Currently, less than 1% of textiles are recycled back into textiles for the fashion industry. This proves there is still a large challenge in improving the end-of-life strategy of textiles.
When you take a closer look at textiles and their components, you quickly realize you have to learn more about fibre compositions. A fibre is a morphological term for materials characterized by their fineness, flexibility and length. The most obvious way to distinguish fibres is to separate them into two categories: natural fibres and man-made fibres. Man-made fibres can be further separated into petroleum-based polymers (also called synthetic fibres) and cellulose-based or biobased fibres. The synthetic fibres, such as polyester, polyamide and elastane take up the lion share of the market with roughly 60%, whereas the cellulose-based cotton fibres represent 35% of the market share. According to The Fiber Year, in 2014 other cellulose-based fibres like viscose, lyocell, wool, silk, flax and synthetic fibres from bio-based raw materials had a market share of around 5%. So, as polyester and cotton are the most frequently used fibres in the textile industry, Paulien Harmsen MSc, expertise Leader Biomass Fractionation, Wageningen Food & Biobased Research, will focus on the advantages and disadvantages of both fibres in textile applications, as well as recycling processes.
Cotton - the most popular natural fibre, accounting for 90% of all natural fibres used by man. Cotton is by far the most used natural fibre for textiles. Annual production volume of conventional cotton is 23 million tonnes, which is around 23% of the total textile fibre volume. We should cherish cotton fibres, as there is no substitute. Cotton is the seed hair of the cotton plant. After harvesting, the raw cotton fibres contain around 90% cellulose, a polymer of glucose molecules. After the purification processes, the fibre contains 99% cellulose and has become hydrophilic, which means water loving.
For comparison, other fibre crops have a much lower cellulose content after harvesting 70% for hemp and flax and 40% for lignocellulosic crops, such as Miscanthus and bamboo. cotton is unique as it is almost pure cellulose.
Cotton fibres have a hollow opening in the middle, called the lumen, that runs the length of the fibre. When the boll opens and the fibre dries in the sun, the lumen collapses. This causes the fibre to twist and form so-called convolutions. These convolutions differentiate cotton fibres from all other forms of seed hair fibres and are partially responsible for many of cotton’s unique characteristics. Cotton is comfortable, breathable and soft, making it very pleasant to wear. Cotton fibres are strong, but they are even 10-20% stronger when wet, which is a unique property Other advantages of cotton are the resistance to high pH and most organic solvents, and good affinity for dyes.
Disadvantages of cotton are the tendency to wrinkle and that cotton is not resistant to acids and cellulose-degrading enzymes and mildew.
The strength of the cotton fibre is influenced by three things.
degree of polymerization or DP (which is the length of the cellulose molecule in the cotton fibre)
the molecular arrangement of these cellulose molecules in the cotton fibre. The higher the DP, the stronger the cotton fibre length of the cotton fibre itself.
Cotton fibre is a staple fibre, a fibre of relatively short length Application of cotton fibres is mainly based on the length of this staple fibre. We distinguish here three categories: long-staple fibres, medium-staple fibres and short-staple fibres.
Long-staple fibres are about 30-40 mm long and are of the highest quality.They are only limitedly available.
Medium-staple fibres are about 25-33 mm long and are plentiful and standard.
Short-staple fibres are about 10-25 mm long, which is too short for textile processing and so they are usually not used in textiles.
degree of polymerization, molecular arrangement of cellulose molecules and length of the cotton fibre are all things that influence the strength of cotton fibres. This does not hold for the resistance to high pH. Though the resistance to high pH is indeed a characteristic of the cotton fibre, it does not improve its strength.
Cotton can be mechanically recycled via cutting and shredding of 100% cotton fabrics. However, the resulting fibres are shorter than original cotton fibres and cannot be used to produce yarns of the same quality, unless combined with other virgin fibres. Mechanical recycling of cotton therefore leads to fibres of inferior quality and is regarded as downcycling. Cotton can also be chemically recycled. This is done through different chemical processes where the cellulose is dissolved to a cellulose pulp. Fibres made from this pulp are called regenerated cellulose fibres. Examples are viscose and lyocell. Regenerated cellulose fibres have totally different properties than conventional cotton and are not a replacement for cotton. Cotton is a strong fibre and becomes even stronger when wet, whereas viscose is not so strong and becomes weaker when wet.So only original cotton fibres display the special properties And every processing or recycling step leads to lower qualities or to a different type of textile fibre.
Production of cotton cannot be enlarged, and we should value much more the cotton that is available now.
Because cotton is a natural product and because of the way it is designed and manufactured into clothing, it has many advantages, such as its ability to control moisture, insulate, provide comfort and it is also hypoallergenic, weatherproof and is a durable fabric.
Life cycle of polyester
there is a chance that you wear recycled PET bottles, Have you ever thought of the materials you wear on your skin?
fleece, is one of the most famous polyester based fabric. But nowadays the majority of the fabrics contain polyester. polyester is very popular in fashion, why? its not natural?
so we ought to look at circular alternatives and the challenges that come with them. Polyesters are synthetic polymers, long chains built of small molecules like monomers, like a beaded necklace. The term polyester is a generic name for polymers containing ester-linkages in the polymeric chain. The most widely used polyester is PET or polyethylene terephthalate. PET is produced from the monomers ethylene glycol, a dialcohol, and terephthalic acid, a diacid. These monomers are mainly made from petrochemical resources, but the dialcohol can also be produced from renewable resources. After the production of PET the polymer is formed into granules, ready to be processed. PET is a thermoplast, which means that it melts when heated and becomes solid again upon cooling. For this reason, you can process PET by melt spinning and drawing. Melt spinning is the simplest extrusion process, because we do not need any solvents. This makes it the preferred method for all polymers that can melt without thermal degradation. PET granules are fed into an extruder and processed at 280-290 °C to produce smooth, round-shaped filaments, which are fibres of indefinite length.
PET can be recycled by mechanical and chemical methods. For mechanical recycling you make use of the fact that PET is a thermoplast and can be melted and spun to fibre again. Best results are obtained when materials made of 100% PET are recycled, as the presence of contaminants will result in inferior products. Today there are textiles on the market labelled as ‘recycled polyester’, produced by mechanical recycling of PET bottles.
However, textile PET is of lower quality than bottle PET and cannot be mechanically recycled. Then, chemical recycling is an option, which means that the polymer is broken down into its building blocks, the monomers ethylene glycol and terephthalic acid, from which new polymers can be made. As a result, chemically recycled PET has the same properties as virgin PET and has superior technical properties compared to mechanically recycled PET.
Several characteristics have made PET-fibre the main synthetic fibre used in textiles and apparel. This is because PET-fibres are strong, durable and stretchable, easy to wash, dry and use. Due to the composition, PET fibres are rather inert, stable in wet and dry conditions, resistant to chemicals and mildew, all weather resistant and cannot be damaged by sunlight. PET is easy to blend with other textile fibres and cheap when produced from petrochemical resources.
The main disadvantage of polyester is that it is uncomfortable on bare skin due to low moisture absorption and poor vapour transmission. It is a hydrophobic fibre, so it dislikes water, resulting in static electricity issues. Additionally, it sheds microfibres during wearing and washing, and these microfibres are not biodegradable.
So, what are the other options for reducing the use of petrochemical PET in our textiles, besides consuming fewer clothes?
The monomers of PET could in theory both be replaced by a biobased alternative, so-called drop-ins. Ethylene glycol can be produced from renewable materials to produce partially biobased PET, but for terephthalic acid this is not so easy. Another route is the development of totally new types of biobased polyesters. For example, polylactic acid or PLA is the largest biobased polyester and one of the most attractive examples of a fully biobased material with no petrochemical counterpart. In many properties it resembles PET but one major difference is the thermal stability, as PLA melts between 120-175 °C, whereas PET melts around 260 °C. So you can image what happens when you iron a PLA shirt! we cannot ignore the use of polyester in the fashion industry. Properties like strength and water repellence cannot be matched by natural polymers.
In the end we need biobased polyesters that are fully recyclable.
the differentiation between natural and man-made fibres is very important. Raw materials that form the basis of several synthetic fibres are for example coal, crude oil and natural gas. These fossil fuels are needed in order to develop synthetic fibres such as polyamide, polyester and polyurethane. Synthetic fibres, which take up roughly 60% of the market base, base their existence on fossil fuels and therefore deplete the available stock of non-renewable resources. In addition, synthetic fibres are manufactured from plastics and need to be shaped into fibres with the use of heat. Whereas natural fibres cotton, wool, silk and flax are naturally shaped like a fibre when harvested. These however have large impact through, among others, farming, pesticide- and water use and treatment of the fibre to prepare it for textiles. So, unfortunately both cellulose and synthetic fibres have a significant impact during their manufacturing process.
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