Before threads can be woven into fabric, they must be "sized," a process that adds a strengthening and smoothing coating to the thread.Sizing of the warp yarn is essential to reduce breakage of the yarn and thus production stops on the weaving machine. On the weaving machine, the warp yarns are subjected to several types of actions i.e. cyclic strain, flexing, abrasion at various loom parts and inter yarn friction.
Sizing -- the dipping-in-a-hot-chemical-bath stage of the traditional textile process -- allows threads to withstand all the friction and stretching and straining of weaving. The size that soaks into the threads during this process is a solution of starch or PVA (polyvinyl alcohol) -- compounds that coat the threads for lubrication, smooth down any stray fibers, and strengthen the threads.The sizing of spun yarns: With special reference to the specification, preparation and use of size mixings
Different types of water soluble polymers called textile sizing agents/chemicals such as modified starch, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), acrylates are used to protect the yarn. Also wax is added to reduce the abrasiveness of the warp yarns. The sizing agents may be classified into two categories,
1.Natural Sizing agents such as starch and its derivatives , cellulose and its derivatives and protein based sizing agents.
2.Synthetic Sizing Agents such as polyacrylates ,modified polyesters ,poly vinyl alcohol based and styrol/maleic acid copolymers.
Sizing: Materials, methods & machines
On sizing machines, warp thread material is supplied either from a warp beam or from several thread beams with simultaneous take-off. The warp threads may be pre-wetted and impregnated with sizing liquor in a second immersion bath. The threads then pass through combs that separate them and prevent them from gluing together. The parallel threads are then dried on cylinders, rewound and fed to the loom or knitting machine in this form.
Basic requirements for any sizing operation is an even size application over the entire warp. But also the perfect thread tension and the right degree of drying of the warp have a direct impact in the quality of the fabric.
The materials used in sizing: Their chemical and physical properties, and simple methods for their technical analysis and valuation; a course of lectures ... at he Manchester School of Technology
The purpose of a desizing process is to remove sizes that have been attached to warp yarns during a weaving process. Prior to the desizing process, therefore, the size analysis should be performed in order to set desizing conditions suitable for the sizes.
Different methods of desizing are: A desizing method is selected on the basis of analysis of size , type of fabric , eco friendliness , ease of removal , cost of desizing and effluent treatment.
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