Fiber tenacity and fiber elongation


The higher the required yarn tenacity the higher the inherent strength of the fibers used must be. However, in order to achieve stable spinning conditions a sufficiently high number of fibers must be available in the yarn cross-section in addition to adequate fiber tenacity (see  Fiber count).
Yarn blends of cotton and polyester are increasingly being used to manufacture rotor-spun yarns featuring particularly high tenacity and where the end product permits this. It is apparent from the fiber tenacity values of different types of fiber shown in Table 11 that PES fibers display approx. twice the tenacity of cotton fibers. The higher tenacity of these yarns results both in more stable delivery behavior in weaving preparation and on weaving and knitting machines and also in higher fabric strength (weaves, knits) and thus improved properties in use.
However, when considering fiber properties, fiber tenacity should not be viewed in isolation. Fiber elongation is at least as important. Only the product of fiber tenacity and fiber elongation, i.e. the work capacity, enables a meaningful statement to be made regarding the further processing behavior of the fibers and yarns in the spinning process.

The material utilization of fiber tenacity in the rotor yarn is between 40 and 60%, depending on yarn count, and is thus some 15 - 25% less than that of ring-spun yarns. Fig. 70 shows the linear relationship between fiber tenacity (B) and yarn tenacity (A) in cN/tex.

Table 11 – Breaking strength (cN/tex) of natural and man-made fibers

Fig. 70 – Relationship between fiber tenacity (B) and yarn tenacity (A) in cN/tex