Sizing, or dressing, agents are compounds that form a film around the yarn or individual fibres, increasing weight, crispness, and lustre. Sizing substances, including starches, gelatin, glue, casein, and clay, are frequently applied to cottons and are not permanent.
Weighting, in the processing of silk, involves the application of metallic salts to add body and weight. The process is not permanent but can be repeated.
Also called felting or milling, fulling is a process that increases the thickness and compactness of wool by subjecting it to moisture, heat, friction, and pressure until shrinkage of 10 to 25 percent is achieved. Shrinkage occurs in both the warp and weft, producing a smooth, tightly finished fabric that may be so compact that it resembles felt.
Making fabrics softer and sometimes also increasing absorbency involves the addition of such agents as dextrin, glycerin, sulfonated oils, sulfated tallow, and sulfated alcohols.
Finishes improving performance
The performance of fabrics in use has been greatly improved by the development of processes to control shrinkage, new resin finishes, and new heat-sensitive synthetic fibres.
Shrinkage control processes are applied by compressive shrinkage, resin treatment, or heat-setting. Compressive, or relaxation, shrinkage is applied to cotton and to certain cotton blends to reduce the stretching they experience during weaving and other processing. The fabric is dampened and dried in a relaxed state, eliminating tensions and distortions. The number of warp and weft yarns per square inch is increased, contributing greater durability, and fabrics treated by this method are usually smooth and have soft lustre. The process involves spraying the fabric with water and then pressing the fabric against a steam-heated cylinder covered with a thick blanket of woollen felt or rubber. The manufacturer is often required to specify the residual shrinkage, or percentage of shrinkage, that may still occur after the preshrinking process.
Rayons and rayon blends may be stabilized by the use of resins, which impregnate the fibre. Such fabrics may also be stabilized by employing acetals to produce cross-linking, a chemical reaction. Such synthetics as polyesters and nylons, which are heat sensitive, are usually permanently stabilized by heat-setting during finishing.
Shrinkage of wools is frequently controlled by treatment with chlorine, partially destroying the scales that occur on wool fibres and thus increasing resistance to the natural tendency of wool to felt. Other methods employ coating with resins that attach to the scales in order to discourage felting shrinkage.
Durable press fabrics have such characteristics as shape retention, permanent pleating and creasing, permanently smooth seams, and the ability to shed wrinkles, and thus retain a fresh appearance without ironing. Such fabrics may be safely washed and dried by machine. These useful characteristics are imparted by a curing process. Depending upon composition and desired results, fabrics may be precured, a process in which a chemical resin is added, the fabric is dried and cured (baked), and heat is applied by pressing after garment construction; or fabrics may be postcured, a process in which resin is added, the fabric is dried, made into a garment, pressed, and then cured.
Wash-and-wear was an early durable press process employing chemical treatment and curing of fabrics; at least light ironing was required to restore appearance. Later, however, processes were developed that allowed such fabrics to regain smoothness after home machine washing at moderate temperature, followed by tumble drying.
Crease, or wrinkle, resistance is frequently achieved by application of a synthetic resin, such as melamine or epoxy.
Soil release finishes facilitate removal of waterborne and oil stains from fabrics such as polyester and cotton blends and fabrics treated for durable press, which usually show some resistance to stain removal by normal cleaning processes. Other finishes have been developed that give fabrics resistance to water and oil stains.
The accumulation of static electricity in such synthetic fibres as nylon, polyesters, and acrylics produces clinging, which may be reduced by application of permanent antistatic agents during processing. Consumers can partially reduce static electricity by adding commercial fabric softeners during laundering.
Antibacterial and antifungus finishes
Antibacterial finishes are germicides applied to fabrics to prevent odours produced by bacterial decomposition, such as perspiration odours, and also to reduce the possibility of infection by contact with contaminated textiles. Fabrics may also be treated with germicides to prevent mildew, a parasitic fungus that may grow on fabrics that are not thoroughly dried. Both mildew and rot, another form of decay, may also be controlled by treatment with resins
Waterproofing and water repellence
Waterproofing is a process applied to such items as raincoats and umbrellas, closing the pores of the fabric by application of such substances as insoluble metallic compounds, paraffin, bituminous materials, and drying oils. Water-repellent finishes are surface finishes imparting some degree of resistance to water but are more comfortable to wear because the fabric pores remain open. Such finishes include wax and resin mixtures, aluminum salts, silicones, and fluorochemicals.
Flameproof, fireproof, and fire-resistant finishes
Flameproof fabrics are able to withstand exposure to flame or high temperature. This is achieved by application of various finishes, depending upon the fabric treated, that cause burning to stop as soon as the source of heat is removed. Fireproofing is achieved by the application of a finish that will cut off the oxygen supply around the flame. Fire-resistant finishes cause fabrics to resist the spread of flame.