Engineering approach to textile structure | Textile properties developed by drawing of man made fiber

ENGINEERING APPROACH TO TEXTILE STRUCTURES

Man-made fibers must be drawn to orient their constituent molecules into an orderly arrangement parallel to the fiber axis, and this leads to higher tenacity. The greater the draw ratio, the greater the degree of molecular orientation (i.e. crystallization), and  higher the fiber tenacity. Most man-made fibers must be drawn to some degree to give them adequate tenacity to fit them for commercial applications, but that having been said, there is still room for producing a range of fibers of different tenacities from the same material to suit different end-use. For example, engineering uses require fibers of higher tenacity than normally needed for apparel fabrics or carpets.

If one uses the analogy of yarn in which fiber are parallel to one another (Staple fiber yarns) and those in which fibers are very much crumpled and distorted (textured yarns) , it is not difficult to see why drawn, and therefore strong fibers with good molecular orientation are much less extensible than un drawn fibers with little molecular orientation. In fact, as tenacity increases due to drawing, extensibility decreases.  This means that Young’s modulus for the fiber increases and the fibers becomes stiffer; this will have an effect on the aesthetic properties of fabrics made from the fibers, such as handle, softness, drape and also on weaving property.

The length of the molecules also affects the fiber tenacity, and the means of modifying tensile properties vary a great deal from one fiber material to another. In wet spinning, the constitution of the coagulating bath may be modified to slow down the rate of polymer formation – conditions of formation affect molecular orientation; in melt spinning some drawing may take place in the spinning bath; in other cases it takes place after wards; in other cases again it takes place in hot liquid baths.. In the case of melt spinning drawing may be done cold, as in the case of nylon or hot spinning hot spinning drawing may be done cold, as in the case of polyesters. It may take place in one stage, but in some cases it is done in two stages, and these factors all affect the manner and degree of molecular orientation.

Polypropylene crystallizes so rapidly that un drawn filaments are highly crystalline.. In this, it is different from other fibers that are melt spun, and the production of this fiber is very sensitive to spinning conditions; the ability to control these conditions can be used to produce fibers of engineering and textile-end uses with a wide range of crystallinity and physical properties.