Chemicals are present in all parts of textile processing. This part will walk you through the production steps – from fibre to finished garment – and give you an idea of the kind of chemicals that are used.
All textiles are made up of fibres that are arranged in different ways to create the desired strength, durability, appearance and texture. The fibres can be of countless origins, but can be grouped into four main categories. Natural fibres, with the exception of silk, have a relatively short fibre length, measured in centimetres. Silk and man-made fibres have on the other hand very long fibre lengths (filaments) ranging from hundreds of metres to kilometres long.
Plant fibres consists of cellulosic material, normally derived from cotton, linen, hemp or bamboo, but more or less any plant with extractable cellulose can be used. Cotton is by far the most commonly used plant fibre and the cultivation of cotton is enormously resource-intensive, with high inputs of water, pesticides, insecticides and fertilisers leaving a large toxic footprint where grown, if not cultivated organically or under specific sustainable conditions.
pesticides, insecticides, fertilisers
Animal fibres consist of proteins. Wool and silk are the most commonly used fibres from this group, but the wool can come from a number of different animals. In order to make animals grow faster and produce higher yields of wool, pesticides and insecticides are used to prevent disease. Dipping is a common practice to control parasites in sheep farming, making use of both organic phosphates as well as synthetic pyrethroid. After the wool fibres have been sheared they are treated with chemicals during the scouring and washing process.
pesticides, insecticides, scouring chemicals
Man-made fibres such as viscose (rayon) or lyocell are based on cellulosic raw material, normally from wood pulp. They are heavily treated with chemicals before the new fibre is spun. The whole process of producing fibres from wood pulp is very resource-intensive, involving the use of several hazardous substances.
acids, bases, process chemicals
Synthetic fibres are made from monomers sourced from fossil oil feedstocks, which are subsequently polymerised into different fibres. Given all the possible monomers that can be made from a synthetic feedstock, the possible combinations are endless. However the most common synthetic fibre is polyester, followed by polyamide, polyacrylic and aramide. Depending on the monomer used to produce the fibre, an endless number of chemicals may be used in the process. For some of the synthetic fibres such as polyester, dyeing can be accomplished already when the fibre is manufactured.
petroleum-based feedstock, dyes, pigments, catalysts, stabilizers
When the fibre has been harvested or produced the next step is to spin the fibres into a yarn. It is easy to believe that this step, which is a mechanical one, uses no chemicals. But in order to increase the strength of the fibre, increase fibre cohesion and reduce friction during the spinning process, spinning oils are added.
The core of textile manufacture is fabric production. Fabrics can be created in many different ways, the most common being weaving, knitting or through production of non-woven fabrics. To prevent the yarn from breaking during these processes, it is important to strengthen the yarn and reduce friction. Sizing chemicals and lubricants are therefore added.
solvents, adhesives, binders
Pre-treatment processes can be carried out with fibres, yarns or fabrics. It enables subsequent processing of the material, which needs to be prepared to accept dyes and functional chemicals. This is done in a multi-step process. Exactly which steps the fabric goes through depends on the type, or blend of fibre, and how it will be treated afterwards. In some cases pre-treated fabrics are manufactured for later garment dyeing.
The most common steps involving chemicals for a fabric are:
- Washing, general cleaning of the fabric following previous steps and treatments.
- De-sizing removes the sizing chemicals from the warp yarns in the woven fabric.
- Scouring removes fatty waxes and greases from natural fibres, cotton seed and husk.
detergents, bases, solvents
- Bleaching makes the fibres whiter and facilitates the dyeing process. It also makes the fibres more absorbent.
- Mercerizing makes cellulosic fibres swell and and get stronger, more lustrous and a greater capacity to accept dye. By doing so one can reduce the amount of dyes needed.
- Carbonizing removes vegetable residues such as seed pods from the wool.
Dyeing and printing
During dyeing and printing both hazardous chemicals and dyestuffs are used. Dyes used for dyeing, can also be used for printing, but must then undergo the same fixation and washings steps as after the dyeing process. The most common way to print a fabric in full width is to use pigment prints, where the pigments stick to a surface using polymeric resin or a binder. No washing processes are needed. For garment printing , plastisol printing is very common. The PVC-based paste often contains hazardous chemicals, such as phthalates, but there are also alternatives based on acrylate or polyurethane.
Dyeing can take place in several steps when processing the textile. It can be done when spinning the synthetic or man-made fibres, as loose natural or regenerated fibers and in the form of yarns or fabrics. Garment dyeing is also common.
For fiber blends, two types of dyed fibres can be spunned together e.g. viscose and wool.
Full-width printing is carried out on pre-treated fabrics, but it is also possible to put a print on a garment or manufactured textile product by screen or transfer printing. Digital printing is another method.
There are other printing techniques as discharge and resist print using dyes and chemicals. This includes washing to get rid of surplus dyes and residues.
pigments, dyes, binders and polymeric resin (acrylates, PVC, PUR), plasticisers
This step of the process is all about adding special technical properties or an aesthetic appeal to the finished fabric. Depending on the properties desired, such as flame retardance, enhanced water resistance, antibacterial treatment, protective coatings or specific fashion treatments, a diverse range of chemicals are used. Some examples are given below.
- Handle modification
Softeners (polyetylen, quartenary ammonium compounds, silicones, polyurethanes)
Stiffeners (starches resins, polyvinylacetat, polyvinylalcohol)
- Crease resistance (anti-wrinkling, easy care)
different types of resins, often formaldehyde based
- Antistatic treatment
cationic softeners, polyglycols
- Antibacterial/anti-odor treatment
biocides as silver, triclosane
- Water repellance
water repellents based on waxes, silicones, fluorocarbons
- Oil/soil repellance
oil/soil repellents based on fluorocabons
- Flame retardance
flame retardants (halogenated, phosphor based)
- (Protective) coatings
Acrylates, polyurethanes, silcones, PVC with plasticisers
- Laminated films and membranes
in the material layers: Different types of polymers (polyurethane, POLYTETRAFLUORETHYLENE, modified polyester)
in adhesives: Different types of polymers such as polyurethane based, and thermoplastic polymers
- Garment treatments for fashion
Potassium permanganate, sodium hypochlorite, calcium hypochlorite, sodium hydro sulphite, potassium dichromate, formaldehyde resins, cationic softeners, cationic silicone softeners
Manufacturing, transport, sales and retail
When the fabric has the desired colour and properties, it is made into finished products such as sweaters, jeans, shoes or other special items like carpets, furniture or car seats. This step includes processes such as cutting, sewing and the addition of buttons and zippers, for example. In some cases dyeing and printing of the finished garments, with the fabric only pre-treated, occurs at this step. In garment dyeing there are a lot of dyestuff and chemicals used (showed in step 5). Some times dyestuff with quite bad wash permanence are chosen to give the clothing in fashion a worn out look. For garment printing, Plastisol prints (PVC) are very common, but there are other types available for example based on acrylate or polyurethane.
- Transport preparation, which includes protection from mould during transportation and storage, mostly using biocides.
Dimethyl fumarate, ethylene oxide, methylbromide, 1,2 dichloroethane, phospine, dichloromethane, sulfuryl fluoride
A range of chemicals is normally used in most steps of the production process to assist the tasks of other chemicals. Such general auxiliaries include: