Regenerated Cellulose Fibres: Understanding Rayon, Viscose, Modal, Lyocell, Cupro, Acetate and Triacetate

In textile learning, some fibre names create repeated confusion. Rayon, viscose, modal, lyocell, cupro, acetate and triacetate are often placed together because all of them are connected with cellulose. However, they are not the same fibre. Some are regenerated cellulose fibres, while others are chemically modified cellulose-derived fibres.

This distinction is very important for students, merchandisers, buyers, designers and textile professionals. These fibres may look similar in fabric form because many of them are soft, smooth, lustrous and drapey. But their chemistry, manufacturing process, wet strength, absorbency, dyeing behaviour, heat behaviour and end uses can be quite different.

The purpose of this article is to explain the regenerated cellulose family in a simple but technically correct way.

Table of Contents

1. The Basic Family Tree
2. Why These Fibres Are Connected to Cellulose
3. Rayon
4. Viscose
5. Modal
6. Lyocell
7. Cupro
8. Acetate
9. Triacetate
10. Main Differences in One Table
11. Difference by Absorbency
12. Difference by Wet Strength
13. Difference by Drape and Handle
14. Difference by Dyeing Behaviour
15. Difference by Heat Behaviour
16. Practical Selection Guide
17. Sustainability Discussion
18. Simple Summary

1. The Basic Family Tree

The easiest way to understand these fibres is to divide them into two sub-families.

Sub-family	Fibres	Basic idea
Regenerated cellulose fibres	Viscose, Rayon, Modal, Lyocell, Cupro	Cellulose is dissolved and then regenerated back into fibre form.
Cellulose acetate fibres	Acetate, Triacetate	Cellulose is chemically modified by acetylation before being made into fibre.

Simple memory aid:

Viscose, Modal, Lyocell and Cupro are regenerated cellulose fibres.

Acetate and Triacetate are cellulose-derived, but chemically modified acetate fibres.

2. Why These Fibres Are Connected to Cellulose

Cellulose is the main structural material in plants. Cotton is almost pure cellulose. Wood pulp also contains cellulose and is commonly used as a raw material for many man-made cellulosic fibres.

However, cellulose cannot simply be melted like polyester or nylon. It does not behave like a normal thermoplastic polymer. Therefore, to convert cellulose into fibre form, textile chemists developed different chemical routes.

In regenerated cellulose fibres, cellulose is first converted into a soluble or spinnable form. It is then extruded through spinnerets and regenerated back into cellulose fibre. This is the broad logic behind viscose, modal, lyocell and cupro.

In acetate and triacetate, cellulose is chemically modified. Many of the hydroxyl groups in cellulose are converted into acetate groups. Because of this modification, acetate and triacetate behave differently from viscose or lyocell. They are less absorbent and more thermoplastic in nature.

3. Rayon

Rayon is the broadest and sometimes the most confusing term in this family. In many textile contexts, rayon means a man-made cellulosic fibre produced from natural cellulose, usually wood pulp or cotton linters.

However, rayon is not one single process. Different types of rayon can be made through different manufacturing routes. For example, viscose rayon is made by the viscose process, cupro rayon is made by the cuprammonium process, and lyocell is made by a solvent-spinning process.

In practical apparel language, rayon often means viscose, especially in commercial conversation. But technically, rayon is a broader term and viscose is one important type of rayon.

Term	Meaning
Rayon	Broad generic name for regenerated cellulose fibre, especially in American usage.
Viscose	The most common commercial type of rayon made by the viscose process.

Rayon fabrics are usually soft, absorbent, comfortable and drapey. Their main weakness is that many rayon fabrics, especially ordinary viscose, may lose strength when wet and may shrink or distort if not processed properly.

4. Viscose

Viscose is the most common regenerated cellulose fibre. It is made through the viscose process. In this process, cellulose is chemically treated, converted into a viscous spinning solution, extruded through spinnerets, and regenerated into fibre form.

Viscose is loved in apparel because it gives softness, drape and absorbency. It can imitate some aspects of silk-like fluidity at a much lower cost. In sarees, dresses, linings, scarves and women’s fashion fabrics, viscose is valued for its graceful fall.

Property of Viscose	Practical Meaning
Soft handle	Comfortable against skin.
Good drape	Fabric falls beautifully.
Good absorbency	Comfortable in warm weather.
Good dyeability	Takes colour well.
Silk-like appearance possible	Useful in fashion fabrics and dress materials.

However, ordinary viscose has some limitations. It generally has lower wet strength than modal and lyocell. It may crease easily and may shrink if not properly controlled during processing and finishing.

Limitation	Practical Issue
Lower wet strength	The fabric may become weaker when wet.
Creasing tendency	Garments may wrinkle easily.
Shrinkage risk	Requires proper finishing and garment care.
Poor resilience	May not spring back like synthetic fibres.

Practical note: Viscose is excellent where softness, absorbency and drape are more important than high wet strength or wrinkle resistance.

5. Modal

Modal is also a regenerated cellulose fibre, but it is generally considered an improved form compared with ordinary viscose. It is often described as a high wet-modulus rayon.

Wet modulus refers to the ability of a fibre to retain strength and shape under wet conditions. Ordinary viscose becomes much weaker when wet. Modal is engineered to perform better in wet conditions.

Feature	Viscose	Modal
Wet strength	Lower	Higher
Dimensional stability	Moderate to poor unless controlled	Better
Softness	Soft	Very soft
Drapability	Very good	Very good
Laundering performance	Needs care	Better than ordinary viscose
Common uses	Dresses, sarees, linings, fashionwear	Innerwear, T-shirts, loungewear, bedsheets, premium knits

Modal is popular in products where softness and repeated washing matter. Innerwear, sleepwear, T-shirts, loungewear and premium knitted fabrics often use modal because it gives a soft and smooth feel with better wet performance than ordinary viscose.

Simple explanation: Viscose gives beautiful drape. Modal gives drape plus better wet strength and softness.

6. Lyocell

Lyocell is another regenerated cellulose fibre, but its process is different from the viscose process. In lyocell production, cellulose is directly dissolved in a solvent system and then spun into fibre. It does not follow the traditional viscose xanthate route.

Lyocell is often associated with a more environmentally responsible image because the solvent system can be recovered and reused to a high degree in well-controlled production. However, sustainability always depends on the actual producer, pulp source, energy use and chemical recovery system.

Property of Lyocell	Practical Meaning
High dry and wet strength	Stronger than ordinary viscose.
Soft handle	Comfortable and pleasant against skin.
Good absorbency	Good moisture comfort.
Good drape	Suitable for shirts, dresses, trousers and fashionwear.
Fibrillation tendency	Can create peach-skin effect, but must be controlled.

The special point about lyocell is that it combines comfort and strength better than ordinary viscose. It is used in shirts, denim blends, dresses, trousers, bed linen, premium casualwear and drapey fashion fabrics.

Simple explanation: Lyocell is like a stronger, solvent-spun cousin of viscose with good comfort and drape.

7. Cupro

Cupro, also called cuprammonium rayon, is a regenerated cellulose fibre produced by dissolving cellulose in a cuprammonium solution and then regenerating it into fibre. Cotton linters have historically been an important cellulose source for cupro.

Cupro is known for its very smooth, fine and silk-like handle. It has excellent drape and is often used in lining fabrics, luxury dress materials, scarves, blouses and premium fashion fabrics.

Property of Cupro	Practical Meaning
Very fine filament possibility	Smooth and elegant fabrics can be produced.
Soft handle	Luxurious feel.
Excellent drape	Good for linings and flowing garments.
Good breathability	Comfortable in warm conditions.
Good dyeability	Attractive colour depth possible.

Compared with viscose, cupro often feels finer, smoother and more silk-like. However, it is less common than viscose, modal or lyocell in the general apparel market.

Simple explanation: Cupro is a regenerated cellulose fibre valued for a fine, smooth, silk-like handle.

8. Acetate

Acetate is different from viscose, modal, lyocell and cupro. It is not simply regenerated cellulose. It is a cellulose derivative.

In acetate fibre, cellulose is chemically reacted with acetylating agents to form cellulose acetate. This changes the chemical nature of cellulose. As a result, acetate does not behave exactly like regenerated cellulose fibres.

Acetate has a more thermoplastic and less absorbent character than viscose. It is valued for lustre, smoothness and drape, especially in linings, occasionwear, scarves, ties and decorative fabrics.

Property of Acetate	Practical Meaning
Silk-like lustre	Attractive in linings and occasionwear.
Good drape	Useful for flowing fabrics.
Lower absorbency than viscose	Dries faster but gives less moisture comfort.
Thermoplastic behaviour	Can be heat-shaped to some extent.
Heat and solvent sensitivity	Needs careful ironing and care.

Simple comparison: Viscose behaves more like absorbent cellulose. Acetate behaves more like a modified, lustrous, thermoplastic cellulose derivative.

9. Triacetate

Triacetate is closely related to acetate but has a higher degree of acetylation. In simple terms, more of the hydroxyl groups in cellulose are converted into acetate groups.

This higher acetylation gives triacetate better thermoplastic behaviour, better heat-setting ability and better pleat retention than ordinary acetate.

Property of Triacetate	Practical Meaning
Better heat-setting ability	Pleats and shapes can be retained.
Better dimensional stability than acetate	More stable in use and care.
Lower absorbency	Less moisture uptake than regenerated cellulose fibres.
Good wrinkle resistance	Useful for easy-care apparel.
Crisp handle possible	More structured than viscose.

Triacetate is useful in pleated garments, formalwear, dresses, linings and easy-care apparel where shape retention is important.

Simple explanation: Triacetate is a more highly modified acetate fibre with better heat-setting and pleat-retention behaviour.

10. Main Differences in One Table

Fibre	Chemical Nature	Process Idea	Main Strength	Main Weakness	Typical Use
Rayon	Broad regenerated cellulose term	Various regenerated cellulose routes	Soft, absorbent, drapey	Term can be confusing	General apparel
Viscose	Regenerated cellulose	Viscose process	Soft, absorbent, excellent drape	Lower wet strength, creasing	Dresses, sarees, linings, fashion fabrics
Modal	Regenerated cellulose	Modified viscose-type route	Better wet strength, very soft	Costlier than ordinary viscose	Innerwear, T-shirts, loungewear
Lyocell	Regenerated cellulose	Direct solvent spinning	High wet strength, soft, absorbent	Fibrillation if uncontrolled	Premium apparel, denim blends, shirts
Cupro	Regenerated cellulose	Cuprammonium route	Silk-like smoothness and drape	Less common, cost/process issues	Linings, scarves, luxury fabrics
Acetate	Cellulose acetate derivative	Acetylation and spinning	Lustre, drape, thermoplastic nature	Lower absorbency, heat/solvent sensitivity	Linings, occasionwear, scarves
Triacetate	More highly acetylated cellulose derivative	Higher acetylation	Heat-setting, pleat retention, stability	Low absorbency, synthetic-like handle	Pleated garments, formalwear, linings

11. Difference by Absorbency

The more the fibre remains chemically close to cellulose, the more absorbent it tends to be. Regenerated cellulose fibres such as viscose, modal, lyocell and cupro are generally more absorbent than acetate and triacetate.

Higher Absorbency	Lower Absorbency
Viscose, Modal, Lyocell, Cupro	Acetate, Triacetate

This difference comes from chemistry. Cellulose contains hydroxyl groups that attract moisture. In acetate and triacetate, many of these hydroxyl groups are chemically modified, so the fibre becomes less absorbent.

12. Difference by Wet Strength

Wet strength is one of the major differences among regenerated cellulose fibres. Ordinary viscose becomes weaker when wet. Modal and lyocell were developed partly to overcome this limitation.

Lower Wet Strength	Better Wet Strength
Ordinary viscose	Modal, Lyocell

This is why modal and lyocell are preferred in products that must withstand repeated washing, such as innerwear, T-shirts, loungewear, bedsheets and premium casualwear.

13. Difference by Drape and Handle

Many of these fibres are selected not only for their technical properties but also for their hand feel and fall. The difference in handle is very important in fashion and apparel merchandising.

Fibre	Handle Character
Viscose	Soft, fluid, heavy drape.
Modal	Very soft, smooth, slightly more stable.
Lyocell	Soft, smooth, stronger, sometimes peachy if fibrillated.
Cupro	Very smooth, silk-like, elegant drape.
Acetate	Lustrous, smooth, lining-like, less absorbent.
Triacetate	More crisp, stable and pleat-retaining.

For saree and apparel understanding, this is very useful. If the requirement is fall and fluidity, viscose works beautifully. If the requirement is premium softness and washing durability, modal or lyocell may be better. If the requirement is silk-like lining feel, cupro or acetate may be chosen. If pleat retention is important, triacetate becomes relevant.

14. Difference by Dyeing Behaviour

Dyeing behaviour is another major practical difference. Viscose, modal, lyocell and cupro behave more like cellulosic fibres in dyeing. Acetate and triacetate behave more like hydrophobic modified cellulose fibres.

Fibre	Dyeing Behaviour
Viscose	Dyes easily with dyes suitable for cellulosic fibres.
Modal	Similar to viscose, with good colour yield.
Lyocell	Good dyeability, but process must control fibrillation.
Cupro	Good dyeability and often rich shades.
Acetate	Usually dyed with disperse dyes.
Triacetate	Usually dyed with disperse dyes, often under different temperature conditions than acetate.

Important practical point: Viscose, modal, lyocell and cupro behave more like cellulosic fibres in dyeing, while acetate and triacetate are commonly dyed with disperse dyes.

15. Difference by Heat Behaviour

Regenerated cellulose fibres such as viscose, modal, lyocell and cupro are not thermoplastic in the way polyester, nylon, acetate or triacetate are. Acetate and triacetate show more thermoplastic behaviour because of chemical modification.

Fibre	Heat Behaviour
Viscose	Does not behave as a thermoplastic fibre.
Modal	Similar to regenerated cellulose.
Lyocell	Similar to regenerated cellulose.
Cupro	Similar to regenerated cellulose.
Acetate	Shows thermoplastic behaviour.
Triacetate	More thermoplastic and heat-settable than acetate.

This is why acetate and triacetate are useful for lustrous, pleated and shape-retaining fabrics, while viscose and lyocell are valued more for absorbency, comfort and drape.

16. Practical Selection Guide

From a buyer’s or merchandiser’s point of view, the fibre should be selected according to the expected product performance.

Requirement	Suitable Fibre Choice	Reason
Soft, fluid fall	Viscose	Excellent drape and absorbency.
Very soft washable knit	Modal	Softness with better wet strength.
Premium comfort with better strength	Lyocell	Good wet strength, comfort and drape.
Silk-like lining or luxury feel	Cupro	Fine, smooth, elegant drape.
Lustrous lining fabric	Acetate	Smooth lustre and drape.
Pleated or heat-set garment	Triacetate	Better heat-setting and pleat retention.

17. Sustainability Discussion

All man-made cellulosic fibres raise sustainability questions related to pulp sourcing, forest management, chemical use, water, energy and effluent control. However, their environmental profiles are not identical.

Conventional viscose has faced criticism because of chemical use and pollution risk when manufacturing is poorly controlled. Lyocell is often viewed more favourably because of its solvent-spinning route and high solvent recovery in responsible production systems.

However, it is not correct to say that one fibre name alone guarantees sustainability. A responsible fibre depends on the actual supply chain, certified pulp sourcing, closed-loop chemical recovery, energy management, effluent treatment and producer transparency.

Balanced sustainability statement: Lyocell generally has a better process reputation than conventional viscose, but sustainability depends on actual producer practices and supply-chain controls.

Important Numerical Properties of Regenerated Cellulose and Cellulose-Derived Fibres

In textile study, fibre properties are often discussed in words such as soft, strong, absorbent, drapey, lustrous or thermoplastic. However, for proper technical understanding, it is useful to compare these fibres through numerical properties also.

This article gives typical numerical ranges for important properties of regenerated cellulose and cellulose-derived fibres such as viscose rayon, modal, lyocell, cupro, acetate and triacetate.

Important note: These values should be treated as typical textile ranges, not absolute constants. Actual values can change according to fibre grade, denier, staple or filament form, drawing, spinning route, finishing, producer specification and test method.

Table of Contents

1. Key Numerical Properties
2. Quick Interpretation of the Properties
3. Useful Memory Numbers
4. What These Properties Mean in Practice
5. Important Caution While Comparing Fibre Data

1. Key Numerical Properties

Fibre	Density / Specific Gravity	Moisture Regain	Dry Tenacity	Wet Tenacity	Elongation at Break	Important Thermal Point
Viscose rayon	~1.50–1.53 g/cc	~11–13%	~1.5–2.5 g/denier; high-tenacity grade ~3–4.6 g/denier	~0.7–1.2 g/denier; high-tenacity grade ~1.9–3.0 g/denier	~15–30%; high-tenacity grade ~9–17%	Weakens and chars on heating; does not melt like thermoplastic fibres.
Modal	~1.50–1.52 g/cc	~11–13%	Commonly ~3.0–4.0 g/denier equivalent range	Retains wet strength better than ordinary viscose	~12–25%	Cellulosic fibre; does not melt like polyester or nylon.
Lyocell / Tencel-type lyocell	~1.50–1.52 g/cc	~11–13%; often cited around 11.5%	~38–42 cN/tex, roughly ~4.3–4.8 g/denier	~34–38 cN/tex, roughly ~3.9–4.3 g/denier	Dry ~11–16%; wet ~16–18%	Cellulosic fibre; no true melting point; decomposes or chars.
Cupro / cuprammonium rayon	~1.50–1.54 g/cc	~11–12.5%	~1.7–2.3 g/denier	~0.9–2.5 g/denier, depending on grade and source	~10–17% dry	Cellulosic fibre; chars or decomposes rather than melting.
Acetate / secondary acetate	~1.30–1.32 g/cc	~6.5%	~9.7–11.5 cN/tex, roughly ~1.1–1.3 g/denier	Lower than dry; often around ~0.8–1.0 g/denier	Dry ~23–30%; wet ~35–45%	Thermoplastic; softening/melting often around ~230°C range.
Triacetate	~1.30–1.32 g/cc	~2.5–3.5%	~1.1–1.4 g/denier	~0.7–0.8 g/denier	Dry ~25–35%; wet ~30–40%	More heat-settable than acetate; often cited near ~300°C melting/softening range.

2. Quick Interpretation of the Properties

Property	Highest / Best Among These	Practical Meaning
Highest wet strength	Lyocell, then Modal	Better for repeated washing, stronger wet processing and more durable laundering.
Highest drape / fluid fall	Viscose, Cupro, Lyocell	Good for sarees, dresses, linings, scarves and flowing garments.
Most silk-like smoothness	Cupro, then Lyocell / Acetate	Good for luxury handle, lining feel and elegant fall.
Highest absorbency	Viscose, Modal, Lyocell, Cupro	Comfortable, breathable and suitable for cellulosic dyeing routes.
Lowest absorbency	Triacetate, then Acetate	Quicker drying, more thermoplastic and more synthetic-like in behaviour.
Best heat-setting / pleat retention	Triacetate, then Acetate	Useful for pleats, shape retention and formalwear.
Weakest when wet	Ordinary viscose	Needs care during washing, dyeing, wet processing and finishing.
Most thermoplastic behaviour	Triacetate and Acetate	Can soften or shape with heat; care needed in ironing and pressing.

3. Useful Memory Numbers

For teaching, merchandising or quick textile revision, the following memory numbers are helpful.

Fibre	Memory Number
Viscose	Moisture regain ~11–13%; wet strength may fall to roughly half of dry strength.
Modal	Moisture regain ~11–13%; better wet strength than ordinary viscose.
Lyocell	Moisture regain ~11.5%; dry tenacity around 40 cN/tex; wet tenacity remains high.
Cupro	Moisture regain ~11%; dry tenacity ~1.7–2.3 g/denier.
Acetate	Moisture regain ~6.5%; density ~1.3 g/cc.
Triacetate	Moisture regain ~3.5%; density ~1.3 g/cc; better heat-setting than acetate.

4. What These Properties Mean in Practice

4.1 Moisture Regain

Moisture regain tells us how much moisture a fibre absorbs from the atmosphere under standard conditions. Viscose, modal, lyocell and cupro have higher moisture regain because they remain closer to cellulose in chemical behaviour.

Acetate and triacetate have lower moisture regain because cellulose has been chemically modified by acetylation. This reduces the number of free hydroxyl groups available to attract moisture.

Practical meaning: Higher moisture regain generally improves moisture comfort and dyeability, but it may also increase swelling, shrinkage or wet-processing sensitivity.

4.2 Dry and Wet Tenacity

Tenacity is fibre strength expressed relative to fineness. Dry tenacity tells us fibre strength in dry condition, while wet tenacity tells us strength when the fibre is wet.

Ordinary viscose has a major weakness: its wet tenacity is much lower than its dry tenacity. Modal and lyocell perform better in wet condition. Lyocell is especially strong among regenerated cellulose fibres.

Practical meaning: Better wet strength is important for repeated washing, wet processing, dyeing, garment laundering and long-term durability.

4.3 Elongation at Break

Elongation at break tells us how much a fibre can stretch before breaking. Acetate and triacetate generally show higher elongation than ordinary regenerated cellulose fibres, but they are not elastic fibres like elastane.

In regenerated cellulose fibres, elongation contributes to processing behaviour, fabric flexibility and resistance to sudden stress, but recovery may still be limited compared with true elastic fibres.

4.4 Density

Density affects fabric weight and feel. Viscose, modal, lyocell and cupro have density around 1.50 g/cc. Acetate and triacetate are lighter, with density around 1.30 g/cc.

Practical meaning: For the same fibre volume, acetate and triacetate may feel lighter than regenerated cellulose fibres such as viscose or lyocell.

4.5 Thermal Behaviour

Regenerated cellulose fibres such as viscose, modal, lyocell and cupro do not melt like polyester or nylon. They degrade, char or decompose on strong heating.

Acetate and triacetate behave differently. They show thermoplastic behaviour and can soften with heat. Triacetate is more heat-settable than acetate and is therefore useful for pleated or shape-retaining garments.

Conclusion

The regenerated cellulose family is best understood by looking at both origin and process. Viscose, modal, lyocell and cupro begin with cellulose and are regenerated into fibre form through different chemical routes. They retain many cellulose-like qualities such as absorbency, comfort and dyeability, but differ in strength, softness, stability and production method.

Acetate and triacetate also begin with cellulose, but they are chemically modified into cellulose acetate fibres. Because of this, they are less absorbent, more thermoplastic and more suitable for lustrous, lining-like, pleated or shape-retaining fabrics.

Thus, these fibres should not be treated as identical. They belong to a related family, but each fibre has its own identity, behaviour and best use. For textile professionals, this distinction is important because the correct fibre choice affects fabric handle, comfort, dyeing, finishing, garment performance and consumer satisfaction.

General Disclaimer

This article is intended for textile education and general understanding. Fibre properties may vary depending on manufacturer, fibre grade, yarn structure, fabric construction, dyeing, finishing and garment care conditions. For technical specifications, testing standards and commercial decisions, readers should refer to supplier data sheets, relevant textile standards and laboratory test results.

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What is the difference of Modal from Viscose

What Is the Difference Between Modal and Viscose?

Modal is often described casually as “better viscose” or “a softer form of rayon.” That statement is partly correct, but it is not complete enough for a textile student, merchandiser or quality professional.

Both viscose and modal belong to the family of regenerated cellulose fibres. Both begin with cellulose, generally obtained from wood pulp, and both are manufactured by dissolving cellulose and regenerating it again into fibre form. Therefore, the difference is not that viscose is synthetic and modal is natural. Both are man-made cellulosic fibres.

The real difference lies in wet strength, wet modulus, dimensional stability, and behaviour during use and washing. Modal was developed to overcome some of the important limitations of ordinary viscose, especially its weakness and deformability in wet condition.

Simple answer: Viscose is a regenerated cellulose fibre known for softness, absorbency, drape and affordability. Modal is a modified high-wet-modulus regenerated cellulose fibre designed to retain better strength and shape when wet.

Table of Contents

1. What Is Viscose?
2. What Is Modal?
3. Is Modal a Brand Name or a Generic Fibre Name?
4. Why Was Modal Developed?
5. The Main Technical Difference: Wet Modulus
6. Modal vs Viscose: Comparison Table
7. Is Modal Stronger Than Viscose?
8. Why Does Modal Feel Soft?
9. Can Modal Be Blended With Other Fibres?
10. Is Modern Viscose Now Identical to Modal?
11. Is Modal More Sustainable Than Viscose?
12. Practical Meaning for Merchandisers
13. Common Misunderstandings
14. Final Summary
15. Sources

1. What Is Viscose?

Viscose is one of the most widely used man-made cellulosic fibres. It is popular because it gives a soft feel, good absorbency, attractive drape and comfort similar to natural cellulosic fibres such as cotton.

In fabric form, viscose can look elegant and flow beautifully. That is why it is widely used in dresses, sarees, kurtas, scarves, linings, tops, printed fabrics and many other fashion products.

However, ordinary viscose has one important weakness: it loses a significant part of its strength when wet. When viscose fabric is wet, the fibre becomes more sensitive to stretching, distortion and dimensional change. This is why viscose garments often require careful washing, gentle squeezing and controlled drying.

The key limitation of viscose is not softness. Viscose is soft. The limitation is its wet mechanical behaviour.

2. What Is Modal?

Modal is also a regenerated cellulose fibre, but it should not be treated as ordinary viscose with a fashionable name. Technically, modal is a high-wet-modulus regenerated cellulose fibre.

The phrase “high wet modulus” is very important. In simple terms, modulus refers to the resistance of a fibre to extension under load. A low-modulus fibre stretches more easily, while a higher-modulus fibre resists stretching better.

When we say high wet modulus, we mean that the fibre resists stretching and deformation better when it is wet. This is the central reason modal behaves better during washing, wet processing and repeated use.

In a simplified form, the idea of modulus can be represented as:

\[ \text{Modulus} = \frac{\text{Stress}}{\text{Strain}} \]

In practical textile language, a fibre with higher wet modulus will resist deformation better in wet condition. Modal is valued because it gives the comfort of regenerated cellulose while improving one of the biggest weaknesses of ordinary viscose.

3. Is Modal a Brand Name or a Generic Fibre Name?

Modal is a generic fibre name. It is not a company-specific name in the way that a trademark or brand name is company-specific.

This clarification is important because many consumers know modal through commercial names such as TENCEL™ Modal or LENZING™ Modal. In such cases, TENCEL™ or LENZING™ is the brand or company identifier, while modal is the generic fibre type.

Generic fibre name	Brand or company example
Modal	TENCEL™ Modal, LENZING™ Modal
Lyocell	TENCEL™ Lyocell
Viscose	LENZING™ ECOVERO™ Viscose
Polyester	Trevira, Dacron and other branded forms

Therefore, it is better to say that Lenzing is a major producer of branded modal fibres, not that modal itself belongs exclusively to Lenzing.

4. Why Was Modal Developed?

Ordinary viscose has many advantages. It is soft, absorbent, comfortable, drapey and dyeable. But it also has important limitations: lower wet strength, easy stretching in wet condition, poorer dimensional stability, and a greater need for care during laundering.

Modal was developed to improve these limitations. It gives the softness and absorbency of regenerated cellulose, but with better wet strength and better shape retention.

This makes modal especially suitable for garments that are worn close to the body and washed frequently, such as innerwear, T-shirts, tops, loungewear, nightwear, babywear and soft knitted fabrics.

5. The Main Technical Difference: Wet Modulus

The most important difference between modal and ordinary viscose is wet modulus. Ordinary viscose has a relatively low initial modulus. It can stretch under comparatively low load, especially in wet condition.

Modal has a higher wet modulus. This means it resists stretching better when wet. The result is better dimensional stability, better laundering behaviour and better resistance to wet deformation.

This does not mean that modal is indestructible. It is still a cellulosic fibre. Its performance also depends on fibre quality, yarn quality, fabric construction, dyeing, finishing and garment care. But compared with ordinary viscose, modal is designed to perform better under wet conditions.

6. Modal vs Viscose: Comparison Table

Property	Ordinary Viscose	Modal
Fibre family	Regenerated cellulose	Regenerated cellulose
Generic status	Generic fibre name	Generic fibre name
Process family	Viscose process	Modified viscose-route process
Wet strength	Lower	Higher
Wet modulus	Lower	Higher
Stretching when wet	More likely	Less likely
Shape retention	Comparatively weaker	Better
Shrinkage control	Needs more care	Generally better
Handle	Soft, smooth and drapey	Soft, smooth and often silkier
Dyeability	Good	Good
Absorbency	Good	Good to very good
Common uses	Dresses, sarees, tops, linings and scarves	Innerwear, T-shirts, loungewear, tops and blends
Main advantage	Drape, comfort and affordability	Wet strength, softness and dimensional stability
Main limitation	Weakness and deformation in wet condition	Usually costlier than ordinary viscose

7. Is Modal Stronger Than Viscose?

Modal is generally stronger than ordinary viscose, especially in wet condition. This is the most meaningful performance difference between the two fibres.

In dry condition, the actual strength depends on the fibre specification, yarn count, spinning method, fabric construction and finishing. But when wet, ordinary viscose loses strength more noticeably. Modal was specifically developed to reduce this weakness.

For example, a modal-rich knitted fabric used in innerwear or loungewear can give softness while maintaining better shape over repeated washing. A similar fabric made from ordinary viscose may feel soft but can be more vulnerable to stretching, distortion or poor recovery.

8. Why Does Modal Feel Soft?

Modal fibres are known for their smooth, soft and pleasant touch. This softness comes from the fibre’s cellulosic nature, smooth surface, fine fibre structure and good moisture absorption.

Modal is often compared with cotton and mercerised cotton because it can give a smooth and comfortable handle. It may also show good lustre, softness and drape depending on the fibre, yarn, fabric construction and finishing.

However, fibre name alone does not guarantee luxury. A poorly made modal fabric can still perform badly, and a well-made viscose fabric can still look and feel excellent. Final fabric feel depends on fibre quality, yarn count, twist level, knitting or weaving structure, GSM, dyeing, finishing, blending ratio and garment construction.

9. Can Modal Be Blended With Other Fibres?

Modal can be blended with many textile fibres, including cotton, polyester, wool, silk, elastane and other regenerated cellulose fibres. Common blends include modal-cotton, modal-elastane, modal-polyester, modal-viscose, modal-lyocell, modal-wool and modal-silk.

Blending is done to balance comfort, cost, strength, stretch, appearance, moisture behaviour and garment performance. For example, modal with elastane is popular in innerwear and loungewear because modal gives softness and absorbency, while elastane gives stretch and recovery.

10. Is Modern Viscose Now Identical to Modal?

No. Modern viscose has certainly improved. Producers now make better-quality viscose fibres with improved uniformity, better process control, improved sustainability claims and better wet-processing behaviour.

However, modern viscose does not automatically become modal. Modal has a specific fibre definition based on high wet modulus and high breaking strength. Unless a regenerated cellulose fibre meets the modal specification, it remains viscose or another appropriate generic category.

Correct statement: Modern viscose may be improved, but it is not identical to modal. Modal remains a separate high-wet-modulus regenerated cellulose fibre category.

11. Is Modal More Sustainable Than Viscose?

This question needs careful handling. Modal is often marketed as a more sustainable fibre, especially when it is made from responsibly sourced wood and produced by companies with good chemical recovery systems.

But it is not correct to make a blanket statement that modal is sustainable and viscose is not. Both modal and viscose are man-made cellulosic fibres. Their environmental impact depends on wood or pulp sourcing, forest certification, chemical management, carbon disulfide control, water use, energy use, wastewater treatment, producer transparency and supply-chain traceability.

A better statement is: modal can be a better-performing regenerated cellulose fibre, but its sustainability depends on sourcing, manufacturing practices, chemical recovery and certification.

12. Practical Meaning for Merchandisers

For merchandisers, modal should not be treated only as a fancy word on a label. It has practical implications for quality, garment performance and customer expectation.

When buying modal fabrics or garments, check the blend percentage first. Is the fabric 100% modal, modal-cotton, modal-elastane or only a small percentage of modal? A garment with a small modal percentage should not be described as if its entire behaviour is determined by modal.

Next, check the fabric construction. A modal single jersey, modal rib, modal interlock, modal woven fabric and modal blend fabric will all behave differently. GSM, yarn count, twist, loop length, finishing and garment construction can change performance significantly.

Ask for dimensional stability after washing, pilling performance, colour fastness to washing, rubbing and perspiration, and stretch recovery if elastane is present. If sustainability is claimed, ask for traceability and certification rather than relying only on the fibre name.

13. Common Misunderstandings

Misunderstanding 1: Modal is natural, viscose is synthetic.

This is not correct. Both are regenerated cellulose fibres. They begin from natural cellulose but are chemically processed and manufactured into fibre form.

Misunderstanding 2: Modal is only a brand name.

This is not correct. Modal is a generic fibre name. Some companies sell branded modal fibres, but modal itself is not company-specific.

Misunderstanding 3: Modal and viscose are now the same because modern viscose has improved.

This is not correct. Modern viscose may be better than older viscose, but modal remains a separate high-wet-modulus fibre category.

Misunderstanding 4: Modal never shrinks or pills.

This is not correct. Modal generally has better dimensional stability than ordinary viscose, but shrinkage and pilling depend on yarn, fabric construction, finishing, washing and garment care.

Misunderstanding 5: Modal is always sustainable.

Not necessarily. Sustainability depends on pulp sourcing, chemical recovery, manufacturing process, certification and traceability.

14. Final Summary

Viscose and modal are both regenerated cellulose fibres, but modal is a more advanced high-wet-modulus fibre designed to improve the wet strength and dimensional stability limitations of ordinary viscose.

Viscose is soft, absorbent, drapey and affordable, but it becomes weaker when wet. Modal retains better strength and resists stretching better in wet condition. This makes modal more suitable for garments that require softness along with repeated washing performance, such as innerwear, loungewear, T-shirts, tops and soft knitted apparel.

The best short explanation is: modal is not a completely different fibre family from viscose. It is a high-wet-modulus regenerated cellulose fibre developed to perform better than ordinary viscose, especially when wet.

One-line takeaway: Modal is a stronger, more wet-stable regenerated cellulose fibre, while viscose is the broader conventional regenerated cellulose fibre category.

Related Reading on Fibre Properties, Blends and Textile Testing

• How to Determine Fibre Composition in Blended Fabrics
• Determination of Linear Density of Textile Fibres: Understanding Fibre Fineness
• Mercerization: The Midas Touch That Makes Cotton Shine
• Why Combed Cotton is Better Than Carded Cotton

Sources

1. ISO 2076:2010. Textiles — Man-made fibres — Generic names. International Organization for Standardization.
2. BISFA. Terminology of Man-made Fibres. International Bureau for the Standardization of Man-made Fibres, 2017.
3. Textile Exchange. Modal. Textile Exchange Glossary.
4. Textile Exchange. Viscose. Textile Exchange Glossary.
5. Lenzing Group. Fiber Technologies: Explore Lenzing's Production Processes.

General Disclaimer

This article is intended for educational and general textile knowledge purposes only. Fibre behaviour can vary depending on producer, fibre specification, yarn quality, fabric construction, dyeing, finishing, garment processing and washing method. For commercial decisions, laboratory test reports, supplier technical data sheets and recognised national or international standards should be consulted.

Learning about Viscose, Modal and Tencel

The production process of the three fibers has been convered elsewhere in the blog. Here I would like to discuss some of the properties useful for fabric buyers for comparison.

In dry state viscose is only slight weaker than cotton. However, in the wet state, the strength is about 38% that of cotton. That makes it a very tricky fiber to blend with cotton and subsequent dyeing with cotton. The fabric undergoes changes in shape when wet processing.

Also strength of cotton increases when wet- being 1.14 times that in dry state. However, for viscose it is about 0.5 times that in dry state. This necesssitates that the viscose should be dry cleaned rather than ordinarily washed.

Modal's strength is comparable to cotton in dry state. In wet state, it is about 78% of the cotton strength. For Tencel, it is much more than cotton both in dry and wet state.

A table comparing the properties of the three is given below:

The above table represents three fibers from Birla. VSF is the first generation viscose. Modal is second generation and Tencel is the third generation viscose.

This Link describes the precautions to be followed in viscose processing.

Thanks for your attention. Did you find the information you were looking for ? Please leave a comment. Do you need to know more ? Please suggest a topic in the comments.

Fiber Identification - Burning Test- Man-made Fibers

Viscose Rayon 

All viscose including High Wet Modulus scorch and ignite quickly when brought near the flame. Like cotton they burn quickly with yellow flame when in the flame. When removed from the flame they continue to burn. There is no afterglow unlike cotton. The smell is that of burning paper. They leave a light gray and feathery ash.

Acetate Rayon  ( And Triacetate Rayon)

When brought near the flame, it fuses away from flame turning black. When in the flame, it flames quickly. The fabric puckers, sputters and melts. It drips like burning tar. When removed from the flame, it continues to burn and melt. It smells like vinegar. It leaves a brittle hard, irregular black ash which is difficult to crush.

Nylon 

Image via Wikipedia

Nylon fuses and shrinks away from the flame when brought near the flame. In flame, it burns slowly without melting. When removed from flame the flame diminishes and tends to die out. It has somewhat pungent odor. It leaves a hard, round, tough and gray bead.

Aramid  ( Nomex)

When brought near the flame, it shrinks away from the flame. When in the flames it puckers and chars. When removed from flame, it extinguishes by itself. It has no smell and it leaves a hard black bead.

Polyester  

Image via Wikipedia

Polyester fuses and shrinks away from flame. When in flame, it burns slowly with melting. When removed from the flame, it burns with difficulty. It has slightly sweetish smell. It leaves a hard round brittle, black bead.

Acrylics 

Orlon, Acrilan and Creslan and Zefran fuse and melt away from Flame when brought near the flame. When in flame Orlon flames rapidly. The fiber puckers, sputters and melts. Acrilan flames rapidly and melts. Creslan flames and melts and Zefran sputters slightly and flames. When removed flame all of acrylics continue to burn and melt. Orlon has a slightly burning meat-like smell. Acrilan has a buring steak smell. Creslan has sharp sweet smell and Zefran has a turmeric like smell. Orlon, Acrilan and Cresla have hard, brittle and irregular black bead. Zefran has irregular black ash that can be crushed easily.

Modacrylics

Verel and SEF fuse and shrink away from the flame when approached near a flame. When in flame, Verel burns very slowly with melting. SEF shrinks, melts and smolders. When removed from flames, all modacrylics are self extinguishing. Verel has a gunpower smell whereas SEF has a sharp sweet smell. Verel leaves a hard and irregular black bead whereas SEF leaves a hard and irregular black bead.

Spandax 

Fuses but doesn’t shrinks away from the flame when approached near the flame. When in flame, it burns with melting. It has an acrid smell. It leaves a soft, fluffy black bead.

Now that you've finished reading this post, what are you going do? You should go join the Forum.

How to Identify Constituent Fibre Percentage in a Blend-1

How to Identify Constituent Fibre Percentage in a Textile Blend

Textile fabrics are often made from blends of two or more fibres. A polyester-cotton shirt, a polyester-viscose fabric, or a cotton-viscose blend may look like a single material to the eye, but its behaviour during dyeing, finishing, washing, shrinkage, comfort, strength, and costing depends heavily on the actual fibre composition.

For this reason, textile laboratories use quantitative fibre analysis to determine how much of each fibre is present in a blend. In simple terms, one fibre component is dissolved using a suitable chemical reagent, while the undissolved residue is filtered, washed, dried, and weighed. From the change in weight, the percentage of each fibre can be calculated.

Table of Contents

• Why Fibre Percentage Identification Matters
• Basic Principle of Chemical Fibre Analysis
• General Precautions Before Testing
• Polyester/Cotton or Polyester/Viscose Blend
• Cotton/Viscose Blend
• Polyester/Cotton/Viscose Blend
• Quick Calculation Table
• Practical Points to Remember
• Related Reading
• Sources
• General Disclaimer

Visual 1: A simple schematic showing a blended textile sample, selective chemical dissolution, filtration, residue drying, and final weighing.

Why Fibre Percentage Identification Matters

Knowing the fibre composition of a textile blend is important for production, merchandising, dyeing, quality control, costing, product labeling, and customer communication. A fabric declared as polyester-cotton, for example, may behave very differently depending on whether the blend is 65:35, 80:20, or 50:50.

Polyester and cotton also require different dyeing and finishing approaches. Polyester is hydrophobic and is commonly dyed with disperse dyes, while cotton is hydrophilic and is commonly processed with dye classes suitable for cellulosic fibres. Viscose is also cellulose-based, but it has different wet strength and chemical behaviour compared with cotton.

Basic Principle of Chemical Fibre Analysis

The basic principle of quantitative chemical analysis is selective dissolution. A known weight of the blended sample is treated with a reagent that dissolves one component while leaving the other component mainly unaffected. The remaining fibre residue is then separated, washed, neutralised if required, dried, cooled, and weighed.

The percentage of the undissolved fibre can be calculated as:

\[ \text{Percentage of residue fibre} = \frac{\text{Dry weight of residue}}{\text{Original dry weight of sample}} \times 100 \]

The dissolved fibre percentage can then be calculated as:

\[ \text{Percentage of dissolved fibre} = 100 - \text{Percentage of residue fibre} \]

In actual laboratory practice, correction factors may be required because the fibre remaining as residue may still lose a small amount of weight during chemical treatment. These correction factors should be applied according to the relevant standard method or laboratory procedure.

General Precautions Before Testing

Before quantitative analysis, the fibres present in the blend should first be identified by suitable qualitative methods such as microscopic examination, burning behaviour, solubility behaviour, or other standard fibre identification methods. Quantitative analysis should not be started blindly on a completely unknown sample.

The sample should also be free from non-fibrous material such as size, oil, wax, dirt, resin, finishing chemicals, coatings, or other additives. These substances can affect the sample weight and may lead to incorrect percentage calculation. If present, they should be removed by a suitable pre-treatment method before chemical analysis.

1. Polyester/Cotton or Polyester/Viscose Blend

In a polyester/cotton or polyester/viscose blend, the cellulosic component can be dissolved using sulphuric acid under controlled conditions, while polyester remains as the residue. Cotton and viscose are cellulose-based fibres, whereas polyester is more resistant to this treatment.

Method

1. Take approximately 0.5 to 1.0 gram of the blend sample and weigh it accurately.
2. Place the sample in a clean flask and add 75% by weight sulphuric acid.
3. Maintain a material-to-liquor ratio of about 1:200 so that the sample is properly immersed.
4. Keep the flask in a water bath for about one hour at approximately \(50 \pm 5^\circ C\).
5. Filter the contents carefully. The residue left on the filter is polyester.
6. Wash the polyester residue thoroughly with water and neutralise it using dilute ammonia solution.
7. Dry the residue at approximately \(110^\circ C\), cool it in a desiccator, and weigh it accurately.

The dried residue gives the polyester content. The remaining percentage represents the cellulosic component, either cotton or viscose depending on the original blend.

Calculation

\[ \text{Polyester %} = \frac{\text{Dry weight of polyester residue}}{\text{Original dry weight of sample}} \times 100 \]

\[ \text{Cotton or Viscose %} = 100 - \text{Polyester %} \]

Example

If the original dry sample weight is 1.000 gram and the final dry polyester residue is 0.650 gram, then:

\[ \text{Polyester %} = \frac{0.650}{1.000} \times 100 = 65% \]

\[ \text{Cotton or Viscose %} = 100 - 65 = 35% \]

Therefore, the blend is approximately 65% polyester and 35% cotton or viscose.

Visual 2: Flow diagram for polyester/cotton or polyester/viscose analysis, showing cellulosic dissolution and polyester residue calculation.

2. Cotton/Viscose Blend

Cotton and viscose are both cellulose-based fibres, but their chemical behaviour is not identical. Viscose is regenerated cellulose and is generally more easily attacked by certain reagents than cotton. In this method, viscose dissolves and cotton remains as the residue.

Method

1. Take approximately 0.5 to 1.0 gram of accurately weighed sample.
2. Place the sample in a flask and add 60% by weight sulphuric acid.
3. Maintain a material-to-liquor ratio of about 1:100.
4. Stir the solution mechanically for about 30 minutes.
5. During this treatment, viscose dissolves and cotton remains.
6. Filter the cotton residue and wash it thoroughly with water.
7. Neutralise the residue with dilute ammonium hydroxide solution, wash again, dry, cool, and weigh.

A correction factor is important in this method because cotton may lose some weight during the treatment. A commonly used correction mentioned for this process is about 5% weight loss for cotton. Therefore, the observed cotton residue weight should be corrected before calculating the final blend percentage.

Calculation With Cotton Correction

If cotton loses approximately 5% during the process, the corrected cotton weight can be calculated as:

\[ \text{Corrected cotton weight} = \frac{\text{Observed cotton residue weight}}{0.95} \]

Then:

\[ \text{Corrected cotton %} = \frac{\text{Corrected cotton weight}}{\text{Original dry sample weight}} \times 100 \]

\[ \text{Viscose %} = 100 - \text{Corrected cotton %} \]

Example

Suppose the original dry sample weight is 1.000 gram and the observed cotton residue after drying is 0.475 gram. The corrected cotton weight is:

\[ \frac{0.475}{0.95} = 0.500 \text{ gram} \]

Therefore:

\[ \text{Cotton %} = \frac{0.500}{1.000} \times 100 = 50% \]

\[ \text{Viscose %} = 100 - 50 = 50% \]

After applying the correction factor, the blend is approximately 50% cotton and 50% viscose.

3. Polyester/Cotton/Viscose Blend

A polyester/cotton/viscose blend contains one synthetic fibre and two cellulosic fibres. The analysis is done in stages. First, viscose is dissolved using 60% sulphuric acid. The remaining fibres are cotton and polyester. Then cotton is dissolved using stronger sulphuric acid, leaving polyester as the final residue.

This step-by-step separation allows the three components to be estimated separately. The first weight loss gives viscose, the final residue gives polyester, and cotton can be calculated by difference.

Method

1. Take an accurately weighed dry sample of the polyester/cotton/viscose blend.
2. Treat the sample with 60% by weight sulphuric acid. Viscose dissolves under this treatment.
3. Filter, wash, dry, cool, and weigh the remaining cotton and polyester residue.
4. Treat this residue with 75% sulphuric acid. Cotton dissolves under this treatment.
5. Filter the final residue carefully. Wash thoroughly, neutralise if required, dry, cool, and weigh.
6. The final residue is polyester. Cotton is calculated by difference after accounting for viscose and polyester.

Calculation

Let:

\[ W_0 = \text{Original dry sample weight} \]

\[ W_1 = \text{Dry weight after dissolving viscose} \]

\[ W_2 = \text{Final dry polyester residue} \]

Then:

\[ \text{Viscose %} = \frac{W_0 - W_1}{W_0} \times 100 \]

\[ \text{Polyester %} = \frac{W_2}{W_0} \times 100 \]

\[ \text{Cotton %} = 100 - \text{Viscose %} - \text{Polyester %} \]

Example

Suppose the original dry sample weight is 1.000 gram, the dry weight after dissolving viscose is 0.700 gram, and the final polyester residue is 0.400 gram. The blend percentages are calculated as follows:

\[ \text{Viscose %} = \frac{1.000 - 0.700}{1.000} \times 100 = 30% \]

\[ \text{Polyester %} = \frac{0.400}{1.000} \times 100 = 40% \]

\[ \text{Cotton %} = 100 - 30 - 40 = 30% \]

Therefore, the blend is approximately 40% polyester, 30% cotton, and 30% viscose.

Visual 3: Three-stage analysis chart for polyester/cotton/viscose blend, showing viscose removal, cotton removal, and polyester residue.

Quick Calculation Table

Blend	First Dissolved Component	Residue Obtained	Main Calculation
Polyester/Cotton	Cotton	Polyester	Polyester % = residue weight ÷ original weight × 100
Polyester/Viscose	Viscose	Polyester	Polyester % = residue weight ÷ original weight × 100
Cotton/Viscose	Viscose	Cotton	Corrected cotton weight may be required before percentage calculation
Polyester/Cotton/Viscose	Viscose first, cotton second	Polyester final residue	Viscose by first loss, polyester by final residue, cotton by difference

Practical Points to Remember

The accuracy of fibre percentage analysis depends on careful sampling, accurate weighing, complete dissolution, complete washing, correct neutralisation, and proper drying. Even a small error in drying or weighing can affect the final percentage, especially when the sample weight is small.

Chemical analysis is different from a simple burning test. A burning test can help identify the probable fibre type, but it cannot reliably provide the percentage of each fibre in a blend. For blend percentage, controlled quantitative analysis is required.

Correction factors should not be ignored. The fibre left as residue may still lose a small amount of weight during the chemical process. If a standard method prescribes a correction factor, it should be applied before reporting the final blend composition.

Related Reading on Fibre Identification and Textile Testing

• How to Identify Constituent Fibre Percentage in a Blend-2
• Fiber Identification - Burning Test- Man-made Fibers
• Distinguishing Linen from Cotton
• Regenerated Cellulose Fibres: Understanding Rayon, Viscose, Modal, Lyocell, Cupro, Acetate and Triacetate

Sources

1. ISO 1833-1:2020. Textiles — Quantitative chemical analysis — Part 1: General principles of testing. International Organization for Standardization. https://www.iso.org/standard/74881.html
2. Bureau of Indian Standards. IS 3416:1988 / IS 3416 Part 1: Method for quantitative chemical analysis of binary mixtures of polyester fibres with cotton or regenerated cellulose. https://law.resource.org/pub/in/bis/S12/is.3416.1988.pdf
3. Bureau of Indian Standards. IS 3416-1:1988 Amendment: Sulphuric acid method for polyester with cotton or regenerated cellulose. https://law.resource.org/pub/in/bis/S12/is.3416.1.1988.pdf
4. Japan Customs. Textile Analysis: Natural or Chemical Fiber? https://www.customs.go.jp/ccl/e_etc/3.htm
5. AATCC. Textile Research, Test Methods, and Standards Development. https://www.aatcc.org/

General Disclaimer

This article is intended for textile learning and general technical understanding. It is not a substitute for an accredited laboratory test report, official standard method, or professional chemical safety training. The procedures mentioned involve strong chemicals such as sulphuric acid and should be performed only by trained personnel in a properly equipped laboratory with suitable safety precautions, ventilation, neutralising arrangements, and personal protective equipment.

Properties of Viscose Rayon

Properties of Viscose Rayon

Moisture Absorption

It absorbs more moisture than cotton. Moisture Content of Coton is 6% at 70 deg F and 65% RH, and for Viscose Rayon it is 13% under the same conditions.

Tensile Strength

The Tensile Strength of the fibre is less when the fibre is wet than when dry. 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.

Elasticity

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, whule high tenacity rayon has only 9-17% elongation at break.

Density

The density of Viscose rayon is 1.53 g/cc. Rayon filaments are available in three densities: 1.5, 3.0 and 4.5

Action of Heat and Light

At 300 deg F or more, VR loses its strength and begins to decompose at 350-400 deg F. Prolonged exposure to sunlight also weakens the fibre due to moisture and ultraviolet light of the sunlight.

Chemical Properties

Viscose rayon consists of cellulose of lower DP than cotton cellulose. Also amorphous region of Viscose rayon is present to a greater extent, therefore, Viscose rayon reacts faster than cotton with chemicals. Acids like H2SO4 HCL breaks the cellulose to hydrocellulose. Oxidising agents like Na(OCl)2, Bleaching powder, K2Cr2O7, KMnO4- form oxycellulose. Cold acid solutions for a short time do not attack viscose rayon.

Action of Solvents

Textile solvents can be used on Viscose rayon without any deteriorating effect. 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 ( moulds, mildew, fungus, bacteria) affect the colour, strength, dyeing properties and lustre of rayon. Clean and dry viscose rayon is rarely attacked by moulds and mildew.

Longitudinal View

The longitudinal view of these fibres show many striations running parallel to the long axis of the fibre. The cross section of viscose has striated periphery, having many sharp indentations, and cross sectional contours vary from circular and oval to ribbon-like forms.

Manufacturing Process of Viscose Rayon

Viscose Rayon

It is a regenerated cellulosic fibre and cellulose is the raw material for producing this man made fibre.

The raw material is obtained from a special variety of wood called spruce.

Manufacturing Process

a. Purification of Cellulose:

The manufacture of viscose rayon starts with the purification of cellulose. Spruce trees are cut into timber. Their barks are removed and cut into pieces measuring 7/8" x 1/2" x 1/4". These pieces are treated with a solution of calcium bisulphite and cooked with steam under pressure for about 14 hours.
The cellulosic component of the wood is unaffected by this treatment, but the cementing material called lignin, which is present in the wood, is converted into its sulphonated compound which is soluble in water. This can be washed off, thereby purifying the remaining cellulose. This cellulose is treated with excess of water. After this it is treated with a bleaching agent (sod hypochlorite) and finally converted into paper boards or sheets. This is called wood pulp, which is normally purchased by the manufacturers of viscose rayon.

b. Conditioning of Wood Pulp:
The pulp sheets are cut by a guillotine to the required dimension and are kept in a special room. Air moves freely among the divisors by means of ventilatorys, the temperature is maintained at 30 deg celcius. In this way the desired moisture content can be had.

c. Steeping Process:
The conditioned wood pulp sheets are treated with caustic soda solution ( about 17.5%). It is called mercerising or steeping. The high DP cellulose (1000) is converted into soda cellulose. The sheets are allowed to soak (steep0 until they become dark brown in colour. This takes about 1-14 hours. The caustic soda solution is drained off and sheets are pressed to squeeze out excess caustic soda solution. 100 kg of sulphite pulp gives about 310 kg of soda cellulose.

4. Shredding or cutting process:
The wet, soft sheets of soda cellulose are passed through a shredding machine which cuts them into small bits. In 2-3 hours the sheets are broken into fine crumbs.

5. Ageing Process:
To obtain almost ideal solution of cellulose, the soda cellulose is stored in small galvanised drums for about 48 hours at 28 deg C. This process is called ageing process.The ageing process is essential. During This process, the DP od soda cellulose is decreased from 1000 to about 300 by oxygen present in the air, contained in the drum.

6. Churning Process or Xanthation:
After ageing, the crumbs of soda cellulose are transferred to rotating, air tight, hexagonal churners or mixers. Carbon disulphide ( 10% of the weight of the crumbs) is added to the mixer and churned together for 3 hours by rotating the mixers at a slow speed of 2 rev per minutes. Sodium cellulose xanthate is formed during this process and the colors of the product changes from white to reddish orange.

7. Mixing or dissolving Process:
The orange product i.e. sod.cell.xanthate is in the form of small balls. These fall into a mixer called dissover which is provided with a stirrer. A dilute solution of caustic soda is added, and the contents are stirred for 4-5 hours and at the same time, the dissovler is cooled. The sod.cell.xan. dissovles to give a clear brown thick liquor, similar to honey. This is called 'viscose' and it contains about 6.5% caustic soda and 7.5% cellulose.

8. Ripening Process:
This viscose solution requires to be ripened to give a solution having best spinning qualities. Ripening is carried by storing the viscose solution for 4-5 days at 10 to 18 deg. The viscosity of the solution first decreases and then rises to its original value. The ripened solutoin is filtered carefully and is now ready for spinning to produce viscose rayon filaments.

9. Spinning Process:

The viscose solution is forced through a spinnerette, having many fine holes ( 0.05-0.1mm) diameter. The spinnerette is submerged into a solution containing the following chemicals.
10% --> sulphuric acid, 18%- Sod sulphate, 1% - Zinc sulphate, 2% glucose, 69% water.

The spinning solution is kept at 40-45 deg celcius.

Sodium sulphate precipitates the dissoved sod. cell.xanthate. Sulphuric Acid converts xanthate into cellulose, carbon disulphide and sod. sulphate. the glucose is supposed to give softness and pliability to the filaments whereas zinc sulphate gives added strength.

The quality of viscose rayon filament formed depends upon:

1. The temperature of the spinning bath
2. The composition of the spinning bath.
3. The speed of coagulation
4. The period of immersion of the filament in the spinning bath.
5. The speed of spinning.
6. The stretch imparted to the filaments.

As a number of filaments emerge from the spinnerette, they are taken together to an eye at the surface of the spinning bath and then guided to two rollers from where they are wound on to a spindle.