Additional Information: Scouring of silk
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1. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT
To prepare a silk yarn for dyeing and silk fabrics for dyeing and printing, it is necessary to partially or completely remove serecin, as well as natural oils and organic impurities. Depending on the percentage of sericin removed during scouring (sericin is present in raw silk in a ration between 20 and 25 %), the end-product is defined as unscoured (used only for shirts and suits), “souple” or degummed.
Scouring can be carried out either on the yarn or on the fabric. It is easier to remove serecin more evenly by performing the operation on the yarn itself. Nevertheless, the operation is generally carried out on the fabric, in order to exploit the protective action of this “natural size” against possible damage during weaving.
The scouring treatment can be carried out in a neutral, acid or alkaline solution, depending on the desired results. At the industrial level treatment in alkaline conditions is by far the most common. It is extremely important to control the temperature.
Scouring baths present a high total organic charge; the concentration of nitrogen organic components in particular is high.
“Unscoured” silk
The process to produce “unscoured” silk consists in removing from raw silk fabrics all residual substances from previous operations, with a minimal elimination of sericin (1 – 2 %), so that the fabric keeps the characteristic stiff-handle. The operation is carried out in a slightly alkaline bath at low temperature.
“Souple” silk
The process is carried out on werf yarns under acid conditions. The loss of weight is approximately 10%.
Degummed silk
This treatment is carried out on both yarns and fabrics and ensures a complete elimination of sericin, as well as substances in previous operations, without modifying the fibroin.
Hydrolytic degradation of the sericin protein macromolecule can be obtained by simply using soaps, by suing synthetic surfactants or mixtures of soapy and synthetic surfactants, by means of an enzymatic treatment, or by treating the silk in water at high temperatures and under pressure.
In the degumming process with soap, yarn and fabric are plunged into two baths (degumming baths). Each bath contains green soap at different concentrations. The treatment is followed by washing with ammonia and rinsing. The process temperature varies between 95 and 98°C. The soap concentration in the degumming bath varies between 10 – 15 g/l. On average the entire treatment lasts for 2 hours. It is possible to reuse exhausted baths after appropriate addition of soap.
Degumming with synthetic detergents implies the partial or total replacement of soap with synthetic non-ionic surfactants (e.g. ethoxylate fatty alcohol). It is also possible to combine a degumming treatment with an oxidizing or reducing bleaching and, in some cases, even with dyeing, thus improving water and energy saving. Generally, alkali and detergent mixtures are used at temperatures around 95 and 98°C. Such a treatment is suited to continuous processing.
Degumming under pressure at high temperature is a specific treatment essentially used to degum yarns. It is necessary to prepare an aqueous bath without surfactants and the temperature should be between 110 and 140°C. A post-treatment washing is required to eliminate substances used in previous processes.
2. NEW TECHNOLOGIES
- a) Changes in the process
No information is available.
- b) Changes in the heat supply system
No information is available.
- c) Changes in the energy distribution system
No information is available.
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