BODYING of FIBERS, YARNS AND FABRICS
Post 149 -by Gautam Shah
Fibers, yarns and fabrics have poor bulk or lose the bulk during various treatments, are re-bodied by many different substances. Bodying is also possible without any substantive material application. Certain heat and water treatments shrink the materials, increasing the bulk, whereas mechanical (physical) manipulations also increase the apparent bulk.
Bodying is required to control the next process. Fibers (like silk) are bulked to aid re-spinning or handling before the end stage like stitching, packing and presentation or use of the material. Bodying has strong effect on the suppleness (fall of curtains, drapes, crease lines) and tactile feel of the material. It also affects the thermal management (through heat exchange and moisture movement). For curtains-drapery fabrics the bulking governs the diffusion of view across, ‘modelling’ of the objects, diffraction of light, masking and strength. For furnishing fabrics and floor spreads the bulk, suppleness, direction of texture, electrical behaviour, moisture absorption, dust and body scale retention, and micro air movements over the surface are important, and these are endowed by nature of such treatments.
Some of the prime techniques of bulking fibers, yarns and fabrics are manipulative in nature like: leave behind impurities, lints, staple fibers etc. by reduced carding, etc., mixing of different fibers before spinning, co-spinning (with coarser fibers), twisting, mixed fibre weaving (with mixed for warp-wefts), employing fabric formation techniques like weaving, knitting, shrinking, perma-crease setting, singeing etc.
Another method of bodying is to add some form of gum or size (simply starch), in the form of starch, gelatin, or resin or a combination of these with lubricating substances such as oils or wax. Some are temporary materials and are removed during laundering. Cheap cotton or rayon fabrics are often heavily starched for stiffness which after laundering may become quite limp. Fabrics like organdy are permanently stiffened cottons. The application of a carefully controlled acid solution causes the surface of the yarn to become softened and a gelatin like. An after wash in cold water causes the gelatinous outer surface to harden forming a permanently stiffened exterior.
Raw silk contains, from 25 to 30 percent of its weight in sericin or gum. And when the fiber is cleaned this substance is removed. Silks may be weighted both to enable the producer to regain some of the loss in fiber weight and to add greater body to fabrics. The silk fabric is first placed in an acid solution of stannic chloride (a chloride of tin). The fiber is allowed to absorb the substance, it is then washed, placed into a solution of sodium phosphate and then is washed again. During this process, an insoluble compound (tin phosphate) is formed within the fiber, and the weight and body of the fiber is increased. A further treatment with sodium silicate solution forms another chemical compound. The silk fiber can hold considerably more than its own weight of this added chemical weighting. Heavily weighted silks may have very poor abrasion resistance and eventually will break from their own weight. Any silk labelled pure dye Silk may not contain more than 10 percent of weighting, or 15 percent for black fabrics. If heavily weighted silks are burned, a skeleton of the metallic compound in the shape of the woven fabric is left behind.
Wool fabrics are fulled to give the fabric a more compact structure. In a type of pre-shrinking, fabrics are subjected to moisture, heat, soap, and pressure. This causes the yarn to shrink and to lie closer together and gives the fabric a denser structure. Wool cloth may be given more or less fulling, depending upon the desired characteristics of the resultant fabrics. Melton cloth, for example is one of the most heavily fulled wool fabrics and has a dense, felt like texture.