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Fundamental structure features of yarn



i)Volumetric density, ii) fibersegment length  between points of entanglement, and iii) mobility of the fiber segments between points entanglement. These three structural features and the variety of yarns are necessary to understand the basis for differences in yarn performance.Volumetric density in yarn is dependent on fiber compactness, the packing density of fiber or filament in the cross section of the yarn in a relaxed state. A great deal of air or empty spaces is contained in all yarns, but staple and textured filaments yarn tends to contain most. A yarn can be considered dimensionally stable if the fiber packing density is approximately the same in the relaxed state and low level of stress. The variation of packing density is also important in relation to aesthetics and yarn quality.
The average fiber segment length between points of entanglement within a yarn structure is sometimes referred as fiber modulus length. In most yarn structures in which twist is the basic mechanism of entanglement, the average fiber or filament segment length between points of entanglement is related to twist geometry. The orientation of the fiber segment length between points of entanglement with respect to the yarn axis is important also.
The mobility or freedom of movement and direction of movement of fiber segments relative to other fibers and fiber segments in the structure plays a major role in yarn performance as well. Especially important is the lateral movement of fiber segment near the yarn surface on abrasion, snagging, pilling, hand, etc in fabric structures. Yarn structures that have minimum degree of fiber segment mobility both longitudinally (in the direction of the yarn axis) and cross-sectionals (in the direction normal to the yarn axis) are considered to be dimensionally stable.

If one were to probe various types of yarn with a pin and with the aid of low-power magnification, a qualitative feeling could be gotten for some of the afro-mentioned yarn structural features, such as, fiber segment length and mobility. Microscopy would be necessary to observe the orientation of fiber segments and fiber packing density. However, adequate technique is necessary to fully characterize the intrinsic fiber contiguity in yarn, especially the internal fiber entanglement.
Yarn structural features depend mainly on the properties of the constituent fibers or filaments and the inherent characteristics of the processing systems .Excluding generic-related parameters (such as fiber friction, modulus, resilience, extensibility, and elasticity) the fiber properties of greatest importance are length, fineness, crimp, and cross-sectional shape. The inherent characteristics of the processing system are fiber orientation and entanglement. Fiber orientation refers to the position of the fiber or filament segment in relation to the yarn axis and, in general, the degree of linearity of the fibers or filaments in a yarn. Fiber entanglement, as used here, relates to both the nature of entanglement and the frequency or the degree of entanglement.

A comparison of the structural features in various types of yarn and some factors affecting the structural features is given in table
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