What can we do to improve the aesthetics or resistance of a fabric? How can we enhance a textile? It depends on the fibers it's made of—we carry out different operations before and after the spinning process accordingly.
In order to dye, print, or apply finishes to the fabric, it's essential to perform the so-called “preparation operations.” We must remove impurities and anything that might hinder the application of dyes or finishes.
There are two types of impurities that can be found in fibers: natural ones, which come from the plant or animal itself, and added ones, which are introduced during the spinning process (gums, oils, etc.).
In plant-based fibers, we can perform a process called singeing, where protruding fibers (lint) are removed by bringing the fabric close to a flame. We can also desize (remove impurities we have added to the fabric) and scour (remove impurities that are not water-soluble). As mentioned in the fibers section, cotton can be mercerized to make the yarn shinier, improve dyeing, and swell the fibers, thus increasing strength.
On the other hand, animal-based fibers like wool or silk require the removal of grease and waxes using detergents and degumming agents before dyeing or weaving.
All fabrics made from natural fibers must be bleached before dyeing them in light or white colors (imagine we want a white or beige jute fabric—we must bleach it first, since jute’s natural color is brown).
We’ve all heard of “optical white,” which we can distinguish from “natural white” under UV light (the former glows, the latter doesn’t). Optical bleaching aims to enhance the degree of whiteness.
One major enhancement for textiles is dyeing. We can dye the fibers, the yarn, the fabric, or the finished garment. There are two main methods for this:
- Exhaustion dyeing: The textile material is immersed in dye until the dye is exhausted.
- Impregnation dyeing: The fabric is soaked with dye and then passed through two rollers to remove the excess. Finally, the fabric is washed.
Parameters such as pH, speed, temperature, and time influence the dyeing process. Dyeing depends on these and other variables, which is why dyeing defects are quite common. What are the most frequent issues? Unevenness, local stains, light spots, etc.
If we only want to color certain areas instead of the whole fabric, we use the printing technique.
What are the steps to achieve good printing?
- Prepare the fabric (mercerizing, bleaching, degreasing, etc.)
- Prepare the color paste to be used.
- Set up the machine and apply the color.
- Fix the color (via heat, steaming, or another method).
- Wash and carry out any steps required by the specific printing process.
To properly apply printing pastes, it's crucial to have the right viscosity. Otherwise, the design may not be defined correctly or may bleed through the fabric if it’s too liquid. This parameter can be measured using a viscometer.
We can print manually (each stencil in a frame), by machine (mold, rollers, screens), or digitally—always printing dark colors before lighter ones, as well as glitter, etc.
The main printing systems are:
- Direct printing: applying the paste directly to the fabric (the most common method).
- Discharge printing (colorless or colored): uses dischargeable dyes to create designs on dark fabrics.
- Resist printing: a resist paste is applied to block dye penetration, then the entire fabric is dyed.
- Sublimation or transfer printing: the design is first printed onto paper, then transferred to the fabric (usually polyester) using heat.
- Digital printing.
Thanks to printing, we can create textiles with flocking, inflatable effects, lamination, glitter, and more.
Finally, once the fabric is washed, bleached, and dyed or printed, we can apply chemical finishes (aprestos) and mechanical finishes.
Mechanical finishes apply heat, pressure, tension, etc., using machines designed for this purpose. Some mechanical finishes include: calendering (using tension, temperature, and humidity) to increase gloss or for ironing; embossing, where a design is engraved onto the fabric using pressure and heat; sanding, which gives a peach-skin effect; and raising, which increases the fabric’s fuzziness.
Chemical finishes (aprestos) improve specific properties of the fabric using chemical products. Common finishes include: water-repellent, antibacterial, flame-retardant, antifungal, UV-protective, and antistatic.
