Nowadays, it’s hard to imagine a world without textiles. This applies in particular to the clothing that each of us wear every day. Clothes provide comfort and protection, and for a large group of people it is also an extremely important way to express their style and personality. Textile industry is often called one of the longest and most complex industrial chains. It consists of a large number of sub-sectors that cover the entire production cycle, starting with the production of raw materials (e.g. synthetic fibers), through semi-finished products (e.g. yarns and fabrics), to ready-to-use products such as carpets, clothing and textiles for industrial use.
Textile fibers are made of a huge amount of materials. Most of them are characterized by polymeric construction. The main raw materials for fiber production are:
- natural fibers – these are animal fibers (also called: protein fibers – e.g. silk, wool, hair), vegetable (cellulose fibers – e.g. flax, hemp, cotton, nettle) or mineral fibers, found in many natural minerals,
- artificial fibers – man-made fibers. These can be cellulose-based fibers (e.g. cellulose acetate) or synthetic polymers, e.g. nylon, polyacrylonitrile (anilana), polyester (elana) and polyurethane (lycra) fibers,
- recycled materials (so-called rPET) – these are materials from renewable natural resources, e.g. PLA (Polylactide), which is produced mainly from maize and is biodegradable, or cupro fibers, created as a result of precipitation of cellulose fibers in a copper bath.
The first process to which natural and artificial fibers are subjected to is spinning. Initially, the loose fibers pass through a series of different mechanical operations (loosening, mixing and carding) and then undergo proper spinning. This process can be divided into two basic types:
- woolen – is used to obtain yarns from natural fibers (wool) and compound yarns, which contain wool and synthetic fibers, e.g. polyester, polyacrylonitrile or polyamide,
- cotton – used for the production of cotton and mixed yarns composed of cotton fibers and other material, e.g. polyester, viscose or polyamide fibers.
The spinning process uses hardly degradable chemicals that are applied to fibers in an amount of 2 to 5% of mass substances. This facilitates the course of subsequent stages of the yarn making process. Mineral and silicone oils as well as aromatic hydrocarbons are most often used at this stage and are completely removed from the yarn during the final treatment. Yarn is used to produce two basic assortments of flat textile products, i.e. fabrics and knits.
In the case of fabrics, the first operation is bonding of the warps. It involves the application of special chemicals on the yarn, which increases its mechanical strength. This process is called sizing. The textile sizing agents can be based on polysaccharides (e.g. carboxymethylcellulose) or synthetic polymers such as polyacrylates. This is not the case with the knitting process. The yarn for knit fabric is specially prepared by applying slip preparations. These substances are intended to reduce the stress in the knitting process that results from the friction between the yarn and the guiding elements of the machine.
One of the products that can be used at the stage of sizing is Rokrysol JW20, which is an effective, synthetic sizing agent. It gives the yarn properties in accordance with the requirements ensuring further correct processing of the yarn into the fabric. Rokrysol JW20 is soluble in water in any ratio, which provides even application and coating of the yarn. After applying Rokrysol JW20, further stages of fabric processing (desizing, bleaching, dyeing or printing) take place more effectively. In the case of electrification of the yarn during processing, it is recommended to add the specialized anti-electrostatic preparation Rostat A to the sizing. This product almost completely eliminates the occurrence of static electricity, and also gives the fibers good slip properties. The product works well in the processes of preparation of textile raw materials as an addition to sizing of warps, preparation of raw materials after dyeing and final finishing of fabrics and knitted fabrics.
The next stage of processing of the textile raw material is further pre-treatment. Loose fibers, yarn, fabric and knitwear are bleached, dyed and refined. The selection and the order of the unit operations depends on the type of raw material and the form of the product (yarn, fabric or knitwear).
Preparation of cotton fiber products
The processing of cotton fibers and other cellulose fibers is very complex. It mainly uses processes such as tanning, desizing, mercerisation and bleaching.
The first process involves moving the raw material over the flame of the gas burner, thanks to which the elementary fibers are removed.
The next step is desizing. In the case of synthetic sizing, it is usually washed in a water bath with sodium carbonate along with wetting additives. The PCC Group offers a range of wetting agents that are perfectly suitable for use in the textile industry. The POLIkol (PEG) series is a polyoxyethylene glycol group that, due to its structure, has solubilizing, softening, lubricating, antistatic and moisturizing properties. Polyoxyethylene glycols are characterized by very good biodegradability. These are also safe and non-toxic substances, therefore they reduce the environmental harmfulness of water baths. ROKAnol IT product series are ethoxylated fatty alcohols that ensure proper wetting of the cleaned surface and dispersion of dirt particles, which affects the high performance in removing dirt from fabric/knitwear and hard surfaces. These products are perfect ingredients of alkaline and acidic detergents used for professional washing and industrial cleaning. In turn, ROKAnol NL products are used in pre-treatment of fibers. They can be used to remove oil stains from fabrics and knitted fabrics created during industrial knitting and weaving processes. ROKAnol NL products also improve bleaching efficiency, which directly affects the improvement of dye capillarity in dyeing processes.
The next process is mercerisation, which is designed to increase the strength of fibers and provide them with the appropriate gloss.
The last stage of the initial preparation of cotton fibers is whitening. It consists in discolouring the natural colour caused by impurities on coloured fibers (e.g. in the case of flax) that could not be removed by washing. An example of such chemical compound is sodium hypochlorite, which can be used for bleaching flax, hemp and cotton knitwear fabrics. Thanks to sodium hypochlorite, a very high degree of whiteness is obtained. In order to improve the efficiency of bleaching, chemical agents are used before the start of the process to neutralize the alkaline residues in the fibers (e.g. hydrochloric acid).
Treatment of wool products
Wool products also have to undergo a series of pre-treatments prior to carrying out the dyeing step. The basic processes to prepare them are carbonization, pre-washing and bleaching.
Carbonization aims to completely remove plant impurities. This process involves treating the wool fibers with a solution of sulfuric acid and then heating them to a temperature above 100°C. Damaged fibers are mechanically removed and the whole is neutralized with sodium acetate. After the carbonization is completed, a washing step follows in order to remove the substances from the fibers applied during spinning. Prewashing results in a high degree of wettability and absorbency of bleaching agents and dyes. The last stage is bleaching of the wool. Hydrogen peroxide is most commonly used in this process.
Products made of chemical fibers
Products made of synthetic fibers also require a number of operations, among which the most important are prewash and thermal stabilization.
As with natural fibers, prewash has the task of removing from the fibers the substances applied during spinning. In turn, thermal stabilization consists in heating products that are transported in the hot air environment through subsequent heating chambers. The thermal stabilization provides fabrics with shape stability in the final stages of manufacturing as well as during the use of products made of synthetic fibers.
Dyeing of textile products
Many textile products are dyed, such as loose fibers, yarns, fabrics, knitwear and even finished products. Two basic groups of dyeing methods can be distinguished: periodic and continuous, which also include semi-continuous methods.
Periodic methods consist in immersing a textile material in an aqueous solution of a dye for a specified period of time. Chemical auxiliaries are also added to the bath, which allows the dye molecules to migrate inside the fibers. After this process is completed, the bath is drained into the wastewater and the textile product is washed to remove chemicals.
The main element that distinguishes between continuous and periodic methods is the application of a dye by padding. In addition, in continuous methods, subsequent dyeing processes run continuously one after another, while in semi-continuous methods after padding, the process is interrupted and further stages are carried out as independent operations.
An example of a product that can act as a carrier in textile industry is Rokelan OPD. The product can be used as a carrier in the dyeing process of hydrophobic and polyester fibers, both pure and mixed. It ensures obtaining vivid colours regardless of their shade and intensity. Colourings using Rokelan OPD show good resistance to light. In addition, the use of this product guarantees high performance of the dye.
Chemical auxiliaries used for dyeing
Depending on the type of fibers, various additives are used to improve the dyeing process. In the case of cellulose fibers, where the baths take place in an alkaline environment, it is crucial to maintain the suitable pH of the bath. The most commonly used for this purpose is soda lye, i.e. an aqueous solution of sodium hydroxide (caustic soda).
Other additives used in the process of dyeing cellulose fibers are oxidizing agents (most often hydrogen peroxide is used here) and detergents that provide an effective course of the washing operation after dyeing. The Roksol series (PSWN, ICESOLDE PAN / 35L and AZR) is a group of effective washing and cleaning agents. These products can be used as agents for industrial washing of textile products. They dissolve very well in water and improve the effectiveness of dyeing through their penetrating properties. Roksol products allow the removal of a number of substances, such as natural fats, lubricants, synthetic waxes and sizing. Thanks to their low-foaming properties, they can be used in many technological processes on various types of apparatus without causing disturbances in their work.
In the case of wool fibers, where the dyeing process takes place in an acidic environment, sulfuric acid or acetic acid is used to provide a suitable pH for the bath. In addition, reducing agents (e.g., sodium thiosulphate) and leveling agents are also added to the solution, which are used to obtain uniform dyes.
In dyeing of synthetic fibers, a number of additives are also used. PES (polyester) fibers require the use of thickeners (e.g. polyacrylates) to limit dye migration during drying. PA (polyamide) fibers require strict pH control and for this purpose sulfuric or acetic acid is used. In addition, a number of levelling and dispersing agents are also used. The PCC Group offers a number of specialized products that can perform this function. The NNOC E dispersant is a product used in dyeing processes as a dispersing and equalising agent. It maintains sparingly soluble dyes in a homogeneous dispersion in colouring baths.
The textile printing process involves local dyeing to obtain a predetermined pattern. All types of fibers require proper preparation before printing. A previously prepared paste, which contains dyes or pigments, is applied to the textile substrate. Then, the already prepared fibers are subjected to a printing process, which can be performed by various methods (e.g. flat, rotational and spray film printing). After the process is completed, fixation takes place, otherwise called drying. The final stage is washing, thanks to which, non-fixed dye particles and various chemicals used to prepare the printing paste (such as dispersants or emulsifiers) are removed from the fibers. Ethoxylated nonylphenols, i.e. ROKAfenol products, work perfectly in this application. Their detergent, emulsifying and cleaning properties make them effective in supporting washing processes. ROKAfenol products can be used to clean different fibers, both wool and cotton, as well as chemical fibers, bristles and leather. Their resistance to high temperature and high concentration of electrolytes ensure the use in difficult conditions in the textile industry, for example in the process of washing wool and boiling cotton.
The last process that fibers are subjected to is chemical processing. Its aim is to give the products certain usable properties, e.g. waterproofness or limiting the tendency to crease. To prevent creasing of the materials, suitable crosslinking agents and softening additives are used.
In textile finishing processes, preparations such as Roksol AT2 and Roksol AZR can be used. These products make the textile products obtain a soft and pleasant touch. They have softening and antistatic properties, thanks to which they prevent electrification of fibers and facilitate their further processing. Roksol AZR also has emulsifying properties, thanks to which it supports the washing and spot cleaning process. The product is also characterized by good ability to penetrate the dye in the bath.
Hydrophobic (waterproof) finishes are obtained by adding suitable polymers to the surface of the fibers, which form a waterproof film. In addition, silicone and fluorocarbon agents are also used to improve them.
Textile market in the world
The estimated value of the global textile market is approximately USD 830 billion (data from the Grand View Research 2015 report) and this number is expected to increase in the coming years. The growing awareness of employers and employees regarding the provision of personal protective equipment and thus ensuring safety at work is one of the important drivers of this sector. In addition, the use of more and more modern fibers, such as kevlar, gives the opportunity to develop innovative products that create new applications in the clothing market. Another important aspect in the textile sector is the continuously observed fall in cotton prices in some markets (especially in India), mainly due to overproduction and high inventory levels in warehouses.