Possibilities for imparting strength


In order to obtain strength in the yarn, which consists of individual fibers of relatively short length, the inherent strength of one fiber must be made wholly or partly transferable to another. In principle, there are two alternatives: adhesives and twist.

Total exploitation of the inherent strength of the fibers can be achieved only by using adhesives, as was done, for example, in the Twilo process. The adhesive effect can be produced by means of adhesive substances or adhesive fibers (polyvinyl-alcohol fibers). Since this process can be used only for a small market segment, twisting of the fiber strand remains the sole possibility for imparting strength, even for the future.

The extension of the fibers that arises during twisting leads, via the associated fiber tension, to increased pressure directed towards the yarn interior, i.e. to an increase in the frictional forces between the fibers and thus finally to the desired, immensely strong coherence of the body of the yarn (Fig. 57).

Fiber strands that are not held together by adhesives cannot completely exploit the inherent strength of the individual fibers.

Staple fiber yarns held together by twist have a degree of exploitation between 25% and 70% (normally 30-50%). Possibilities available for producing the required twist are  True twist (with reference to ring-spun yarn)true twist,  false twist and  self-twist (as in the Repco process).

Fig. 57 – Imparting strength to the yarn by twist