Relationship between Properties and Structure of Viscose Rayon

In general, the fiber structures of various viscose fibers depend on the properties such as conditions of viscose, acid bath, stretching, regeneration and so forth. In the case of ordinary rayon, in which an acid bath offering high coagulative and regenerative powers is used, the major portion of fiber structure is determined in acid bath. For viscose fibers, however, in which a weak acid bath is employed, the regeneration and crystallization of fibers in acid bath are only carried out to a small extent and the fiber structure is not only dependent on acid bath conditions but also on the stretching and regeneration conditions. Consequently, a wide choice of fiber structures and properties is available by combining such factors such as viscose, acid bath, stretching and regeneration.

Under different stretching and regeneration conditions, the structure of viscose fiber in the same viscose and acid bath solution will vary clearly.
Following figure shows stained cross section of fibers from the same viscose and same acid bath under different stretching and regeneration conditions.

In above figure, all specimens are of viscose rayon fibers. As evident from specimen No. 1, fiber gives a thick outer layer by the core staining. In specimen No. 2 & 3, this layer gets thinner and in No. 4, it disappears showing total skin staining. Hence, the relationship between structure and properties was verified. It is evident that fiber structure as well as fiber properties greatly vary with stretching and regeneration conditions. Mechanical properties of these specimens were changed as structures were changed when a change in stretching and regeneration of fibers took place.

Specimen	1	2	3	4	5
Tenacity Wet (g/d)	4.0	4.2	4.5	4.2	3.2
Elongation Wet %	17	13	11	9	16
Knot Tenacity Conditioned (g/d)	3.0	2.3	1.7	1.1	1.9
Loop Tenacity Conditioned (g/d)	2.7	2.0	1.4	0.8	1.6
Degree of Drying %	91	75	46	33	23

 
There is a strong relationship between wet fibrillation properties and fibrillar structures of viscose fibers. The fibers having a thicker core-stainable layer in the outer part show little fibrillation while those having skin-stainable layer in the outer part show considerable fibrillation.
The following figure confirms the fact that those viscose fibers which have core-stainable layer in the outer part show little fibrillation while fibers having skin-stainable layer in the outer part show considerable fibrillation.

It is clear from figure that fibrillation (property of fiber) affects the structure of viscose rayon fibers.