Structure and Properties of Viscose Rayon Fibers
The structure of rayon fiber is generally that of smooth, inelastic filaments like glass rods. However, different processes, additives and finishes can vary the physical appearance and structure of viscose rayon.
Figure 1: Microscopic view of Viscose Rayon Fiber
Chemical formula of viscose rayon obtained by reacting cellulose with alkali and carbon disulphide CS2 is as follows:
Figure 2: Chemical Formula of Viscose Rayon.
Different kind of fibers can be identified by their microscopic appearance better, than their physical appearance. When viscose rayon is viewed under microscopic lens:
Figure 3: Longitudinal and Cross-Sectional view of Viscose Rayon Fibers.
The longitudinal appearance of regular viscose rayon exhibits uniform diameter and interior parallel lines called striations.
In cross section view, viscose fiber shows highly irregular or serrated edges.
Properties of Viscose Rayon
Rayon as a fabric is soft and comfortable. It drapes well which is why it is highly sought after as an apparel fabric. Most characteristics are variable depending on processing, additives and other finishing treatments and fabric construction.
It absorbs more moisture than cotton. Moisture Content of Cotton is 6% at 70F whereas for Viscose Rayon, it is 13% under the same conditions.
The Tensile Strength of the fiber is greater when the fiber is dry as compared to its wet state. Because of this, it stretches and shrinks more than cotton. It is 1.5-2.4 gpd in the dry state and 0.7-1.2 gpd in the wet state. For high tenacity variety the values are 3-4.6 gpd and 1.9 to 3.0 gpd respectively.
The elasticity of Viscose Rayon is less than 2-3%. This is very important in handling viscose yarns during weaving, stentering etc. when sudden tensions are applied.
Elongation at Break
Ordinary Viscose rayon has 15-30% elongation at break, while high tenacity rayon has only 9-17% elongation at break.
The density of Viscose rayon is 1.53 g/cm3. Rayon filaments are available in three densities: 1.5, 3.0 and 4.5.
Action of Heat and Light
At 300o F or more, Viscose Rayon loses its strength and begins to decompose at 350-400o F. Prolonged exposure to sunlight also weakens the fiber due to moisture and ultraviolet light of the sunlight.
Rayon is the most absorbent of all cellulosic fibers, even more so than cotton or linen. Rayon absorbs perspiration and allows it to evaporate away from skin which makes it an excellent summer fabric. Its high absorbency equally applies to dyes as well giving them deep and thick colors.
Its abrasion resistance is very low thanks to the inelasticity of rayon. It is easily damaged by scraping.
Tenacity of viscose rayon is 2.4-3.2 gpd.
Moisture regain is 11-13%.
Action of Acids
The resistance of regenerated cellulose rayon's to acids is generally less than that of cotton. Organic acids can be safely used in 1 to 2 percent concentration without injury to the fiber. Inorganic acids such as hydrochloric & nitric can be used in surprisingly strong concentrations provided the temperatures are not too high and the treatment is brief. At high temperatures and concentrations all acid will destroy or carbonize regenerated rayons. In short, it is damaged by strong acids, but it is moderate with weak acids.
Action of Bases
Viscose rayon has a good resistance to weak alkalis but strong alkalis can harm theses fibers thoroughly.
Action of Dry Heat
Viscose Rayon, under the influence of heat as well as light, shows rapid loss in strength. Degradation of cellulose is lower in the absence of oxygen. Continued heating in the absence of oxygen leads to deterioration of the cellulose.
Action of Solvents
Textile solvents can be used on Viscose rayon without any deteriorating effect. For example, Viscose rayon dissolves in cuprammonium hydroxide solution.
Effect of Iron
Contact with iron in the form of ferrous hydroxide weakens viscose rayon yarns. Therefore, staining, marking or touching of rayon to iron or iron surface should be avoided.
Action of Microorganisms
Microorganisms (molds, mildew, fungus, bacteria) affect the color, strength, dyeing properties and luster of rayon. Clean and dry viscose rayon is rarely attacked by mildew.
Relationship between Structure and Properties 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.
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.
Manufacturing of Viscose Rayon Fibers
Rayon fiber made from "viscose process" is called Viscose Rayon. Viscose Rayon is the oldest commercial manmade fiber. Viscose Rayon is a manufactured fiber composed of regenerated cellulose. Out of all the fibers produced, rayon is the most perplexing to consumers.
Polycarbonate Polymers: History, Synthesis, Properties, Pros and Cones, and Applications
Polycarbonate polymers (PC) have carbonate groups in their chemical structures. They are basically a type if thermoplastic polymers. These polymers are strong and tough materials and are easily thermoformed and molded, so they have a wide use in engineering applications. They are also widely used in many other wide range applications i.e. electronic, data storage, construction, aircraft etc.
Why do fabrics shrink? Shrinkage in Fabrics!
During the manufacturing process of fabric or we call it fabric processing, fabric comes in lot of tension and stretches when it moves from one machine to another which causes stretching in fabric structure and when this tension is removed, and fabric is relaxed it tends to get back in its original structure causing shrinkage.
Worsted Yarn Manufacturing Process
A fine smooth yarn spun from combed long staple wool. Worsted yarns are more tightly twisted than the bulkier woolen yarns. The soft, heavy yarn is strong and durable and is often used for sweaters. Worsted yarns are also used for fine dress fabrics and suit materials.