Has it ever happened to you, while you were shopping, that you touched a piece of clothing to feel the quality of the fabric?
I’m sure the answer is yes, which is hardly surprising since innumerable types of fabric are available to us, each of with its own tactile qualities. We all come into contact with numerous fabrics every day, not only in our personal clothing, but also when using them in the most diverse applications. The end product which most of us see is the result of complex industrial processes, which generally include the following main sequence of steps: production of the fibres, arrangement of the fibres into yarns, generation of the raw fabric material, and processing the fabric to make the finished product. Each step in the production process demands precise control of ambient air humidity to maintain the quality and workability of the product.
The fibres, which are intrinsically hygroscopic, may be natural (cotton, linen), animal or synthetic (nylon, polyester, glass fibre, acetate, rayon or aramid). The latter are produced using a perforated die to extrude the raw material. The fibres produced in this way are then treated to improve their properties in relation to the type of material. Nylon, polyester and glass fibre are subjected to the melt-spun method, which cools the melted polymer to increase its strength. Acetate fibres, on the other hand, are heated to evaporate their solvent content in the dry-spun method. Finally, rayon and aramid fibres are solidified in a fluid bath, using the wet-spun method. Once the various types of fibres have been obtained, they are wound together to produce the yarn, which may be of a single type or a mixture of different fibres, depending on the desired characteristics. The yarn is then sent to the next phases of production, which consist in making the fabric and using it to make the finished product.
- The speed of the production machinery, the hygroscopic nature of the material and the continual friction between the machines and the product can cause slow downs, jams and breakage of the yarn due to electrostatic discharges and the process dust blocking the machinery. The optimal humidity for many steps in the process is 50% to 60%, with peak values of 87% for particular cotton processes.
- Once the finished product has been made, it is often decorated by printing – itself a process which is strongly affected by ambient humidity. Humidity control is therefore crucial, and two technologies are currently available for increasing the water content of the air: isothermal humidification, which injects vapour (intrinsically hygienic) into the air, and adiabatic humidification, which atomizes water into minuscule droplets. These droplets are absorbed by the air increasing its specific humidity while also partially abating internal thermal loads, thus reducing the need for air conditioning (1 liter of evaporated water provides 690W of cooling power).
Both technologies, isothermal and adiabatic, are supported by numerous commercial products, which are suited for humidifying both ducted air and ambient air.
Relative humidity is a critical factor in ensuring uninterrupted production and maintaining the quality of the finished textile product. The tight delivery times and highly customised production demanded by the modern market require production which is both efficient and operating at full capacity to maximise profit and customer satisfaction. Precise control of relative humidity reduces electrostatic discharges and the generation of process dust, and maintains the structural characteristics of the yarn, thus preventing breakages.
