Mechanical & Chemical Finishing of Silk Fabric

The wash and wear performance of silk fabric is increasingly important, and appropriate softeners, elastomers and synthetic resins must be used to meet the requirements; the functional finishing of silk, such as stain resistance and flame retardancy, is the focus of the functional finishing of silk fabrics; another important area of ​​finishing is antibacterial finishing that can maintain hygiene and freshness. The improvement of the feel and appearance of silk fabrics is mainly achieved through mechanical finishing, and the functional finishing is achieved through chemical finishing.

Mechanical Finishing

• Calendering: Calendering can improve the feel and appearance of the fabric. Generally, cold calendering is used for silk fabrics, and the fabric can get a soft hand. Common calendering equipment is Palmer or Felt calender, which is mainly used for smooth plain crepe fabrics and twill serge fabrics, such as poplin and damask.
• Steaming: Steaming can give silk fabric dimensional stability, eliminate fabric wrinkles, and make the fabric feel smooth. In the relaxed state, the fabric is treated with superheated steam along the less hard felt. At present, the batch steaming machine is mainly used, and the continuous calender with felt is also used.
• Tentering: At the same time, the tentering allows the silk fabric to be dried by hot air and stretches the fabric to the set width. At the same time, through the combined effect of heat or heat and other factors, the fabric can be given the required hand feel. In the early days, silk finishing mainly used a calender for drying fabrics with hot air. Now, due to the use of various elastomers and resins, an oven with a temperature of up to 150°C is required.
• Filling: Filling finishing can improve the optical appearance of silk fabrics. Silk is very sensitive to the mechanical friction of various finishing processes. Even if the best preventive measures are taken, the silk fabric may still be scratched. In order to improve the optical appearance of the scratched part, it is necessary to apply a fine oil film to the fabric evenly. Both sides, so that the scratches are not easy to see, thereby improving the appearance of the fabric. In the early days, only the problematic fabric parts were manually stuffed and lined. Now, the equipment is used to evenly distribute the oil on several oil feed rollers, and a fine oil film is evenly coated on the entire fabric.
• Kneading: Kneading and finishing is mainly to give the fabric a soft feel, especially when the calendering effect is insufficient. At present, the scraper kneading machine is mostly used, and the fabric passes over the edge of the inclined scraper to complete the kneading and finishing.
• Pre-shrinking: Using a horizontal steamer or pre-shrinking machine to pre-shrink the silk fabric can make the fabric shrink and relax.

Chemical Finishing

• Weight gain: due to the removal of sericin, the silk will lose 20%~50% weight after degumming. The weight gain of silk fabric can make up for the lost weight, and at the same time give the fabric a fuller, fluffy feel and better filling performance, and improve the fabric The drapability of the fabric gives the fabric better wash and wear performance. There are three ways to gain weight: plant weight gain, mineral weight gain, and graft weight gain (polymer weight gain). The most advanced method at present is to use polymer “grafting” to gain weight. This method increases weight. Heavy processing becomes very easy. Grafting weight gain methods mainly use methacrylic acid amine and ammonium persulfate to treat silk fabrics, which can improve the dyeing performance of silk fabrics while gaining weight. However, there are still advantages to grafting finishing before or after dyeing. At the same time, the method of grafting to increase the weight still needs to be further industrialized, and only a few manufacturers, such as the hank manufacturers for silk ties, adopt this method of weight increase.
• Softness: In order to obtain long-lasting softness of silk fabrics, chemical softeners must be used. Commonly used long-lasting softeners are organic softeners and silicone softeners, including oils, waxes and fats; cationic-mainly some imidazoles Phospholines, ethoxylated fatty amines; anions-stearic acid, acid, palmitic acid and fatty alcohols and other sulfates or sulfonates; non-ionic-long-chain alcohols, acids, glycerol, oils and waxes Polyethylene glycol, polyethoxyester; silicone emulsion-polydimethylsiloxane, polymethylhydrogensiloxane, amino silicon, etc.; polyethylene emulsion. The current trend is to use organic silicon epoxy derivatives, which can impart softness, crepe resistance and anti-yellowing properties to fabrics.
• Antistatic: The silk can be grafted with monomers to improve the static accumulation performance, so as to reduce the amount of static electricity accumulated on the silk fabric. There are two main antistatic agents, one is the static eliminator, whose function is mainly to improve the moisture absorption of the fabric It can be used to finish the silk fabric with a specific water-soluble vinyl monomer and a specific acid, or deposit specific metal particles on the fabric, or use a metallic silver coating, which can produce static elimination effects; the other is an antistatic agent, Its principle of action is to impart antistatic properties to the fabric by reducing the friction between fibers and between fiber and metal. Generally, specific alkaline lubricants such as metal oil and butyl stearate are used. Anti-wrinkle: Compared with synthetic fibers, silk has a poorer easy-care performance, so it is necessary to carry out good crease recovery (CR) finishing on silk to improve its dimensional stability and crease recovery after washing. The existing anti-wrinkle finishing agents include cross-linking agents, urea-formaldehyde pre-condensation for weight gain, dimethylol dihydroxy ethylene urea to increase dry and wet wrinkle recovery performance, silicone, acrylate softener and catalyst. In addition, other anti-wrinkle agents that can improve the dry and wet CR, tear strength, elasticity and weight gain of silk fabrics include various N-methylol derivatives of nitrogen-containing compounds and other finishing agents.
• Waterproof and oil-repellent: The principle of waterproof and oil-repellent finishing is to reduce the surface energy of silk fabrics in the air, so as to block oil stains or oily stains. The most commonly used surface finishing agent for fabrics is Teflon, and other important water-repellent agents are , Aluminum compound used alone or together with soap, wax dispersant, etc. When natural silk is grafted with steam of hexafluoropropylene, vinyl fluoride, vinyl chloride and acrylonitrile, it is waterproof, oil repellent, resistant to mineral acid and light. Stability will be improved.
• Flame-retardant: Silk is self-extinguishing. This performance is imparted by polyhalogen acid reaction products with ring cores, such as chlorsaccharic acid and thiourea, but it still cannot safely pass the “vertical flame test”, so flame retardancy is required tidy. Titanium hexachloride, titanium tetrachloride and zirconium chloride can impart good flame retardancy to fabrics. Non-ionic complexes of zirconium, titanium or tungsten can also be used as flame retardant finishing agents for silk fabrics. In addition, specific phosphorus-containing compounds can also be used Improve the flame retardancy of silk fabrics, and the crepe resistance and shrinkage properties have also been improved.
• Antibacterial: Antibacterial finishing has become more and more popular in the finishing of silk fabrics. The main method is to use rolling, dipping or spraying to treat the fabrics. The finishing liquid includes N-(2,2-dichloroethylene) salicylic. Amide, 0.01%~0.25% solution, salicylanilide, dodecyltrimethylamine chloride, etc. Phenolic compounds are widely used because they are moderately active and can be deposited on the surface of the fabric in the form of an emulsion to compound into a polymer film .
• Light resistance: The chemical sensitivity of silk to light has always been one of the biggest obstacles to the application of silk. This is caused by ultraviolet radiation, which means that plants exposed to the sun will absorb ultraviolet rays. Because the light stability of silk affects the job It is very important. Therefore, it is necessary to finish silk fabrics to prevent free radiation. At present, UV absorbers or light stabilizers are mainly used to finish silk fabrics, such as phenyl ester and salicylate. The development still needs further research.

New Finishing Types

• Aromatic finishing: Aromatic finishing can prevent the fabric from producing odor after long-term use, make the clothing emit a fresh smell, and give the fabric softness. It is especially suitable for towels, napkins, casual wear, etc.
• Cooling finishing: These finishing agents can be applied to the fabric to give the human body a cool feeling, and can react with the human body’s chemical substances to make the human body feel cool. These finishing agents can contain fragrances and give the human body a sense of freshness.
• Heat-resistant finishing: This kind of finishing agent can make the fabric have heat-resistance, and the fabric has heat-retaining property due to the porosity and infrared radiation of the fabric.
• Hydrophilic finishing: Hydrophilic finishing agents can give fabrics good moisture absorption and softness, and the fabrics can be treated by rolling-drying or dipping processes.