Extrusion is a complex process that requires heavy investments and which obliges to large production runs.This injection approach to add specific properties into the polymer offers permanent durability. The polymer chain is modified by integrating those new additives that are fixed to it. Thus, resistance to washing for the new properties will last as long as the fiber itself. However, on the counter side, physical behavior of the fiber will change too. For example, the addition of fluorocarbons into the polymer to give flame retardant properties to the fiber will lower its tenacity and melting point.
Each time a polymer is modified, more delicate it is to process this polymer in subsequent operations as texturing for instance.The most popular use for inserting properties into polymers is coloration, called “solution dyed”. Nowadays, other functionalities are possible as antibacterials or optical brighteners.
This is the most common method to finish fabrics today. The principle is to add a chemical solution onto a woven or a knitted piece of fabric while in the finishing process. In fact, that would be the last part of applying finishes, after dyeing but before heat setting.
The principle of application is to add a chemical solution into the finishing bath while fabrics are circulating through. This fabric will absorb a predetermined quantity that is controlled by means of adjusting speed of the rolling fabric and by the concentration of the functional agent into the aqueous solution.
We can easily picture that this method of finishing is relatively simple and flexible. By the fact that the finisher is already treating his fabrics, he has this opportunity either to add another step, either to apply simultaneously new additives to bring new functionalities to the final product.
