Unit 2 - Lecture 10 Topic 2

Question 1

What forms does rayon come in?

Answer 1

Regenerated or precipitated cellulose is “rayon”, but where that fibre has been made by a viscose process, this would be called “viscose” or “viscose rayon”. In a modified viscose process for high wet modulus, this creates “modal” or “modal rayon”. In a solvent extrusion process, where no chemical intermediates are formed, “lyocell” or “lyocell rayon” is created.

Question 2

How is cellulose involved in rayon?

Answer 2

Rayon fibres are 100% regenerated cellulose. Cellulose (wood pulp) is dissolved, possibly chemically altered and regenerated (or precipitated) into cellulose again.

Question 3

How does rayon react to water?

Answer 3

Rayon is hydrophilic (water-loving). Generally, the weak fibres tend to be weaker when wet (unlike natural cellulosic fibres), however modal rayon can be similar in strength as cotton. Water is attracted to the –OH groups in viscose and it has high amorphous regions.

Question 4

Does viscose rayon have high or low degrees of polymerization?

Answer 4

Short, between ~250-700.

Question 5

Does viscose rayon have high or low crystalline properties?

Answer 5

Low.

Question 6

Is viscose rayon orientated?

Answer 6

It is not well oriented with the fibre axis.

Question 7

What are the surface features of viscose rayon?

Answer 7

It has lengthwise striations and a serrated cross-sectional shape.

Question 8

How does the cross-sectional shape of viscose rayon form?

Answer 8

Serrated cross-sectional shape occurs as the solvent evaporates after wet-spinning and the fibre partially collapses.

Question 9

Is rayon used in filament or staple lengths?

Answer 9

Both!

Question 10

What is the tensile strength of viscose and why?

Answer 10

It has low tensile strength that is even lower when wet. This is because there are relatively few polymers to support the load due to it’s low orientation and low proportion of crystalline areas therefore less H-bonding capability.

Question 11

What is the elongation property of viscose like?

Answer 11

It has high elongation at break. Polymers can easily slip past each other so the fibre elongates with a small pulling force.

Question 12

What is the elastic recovery of viscose?

Answer 12

It has poor elastic recovery. Viscose fabrics tend to wrinkle and stretch easily because H-bonds will break and reform in new positions and there is easy slippage of the H- bonds which contributes to stretching.

Question 13

How does viscose bode with static electricity?

Answer 13

Viscose does not build up static electricity due to the good moisture absorption.

Question 14

Why are viscose fibres soft and easily bent?

Answer 14

Due to amorphous regions and the polymers are not aligned well enough to form many strong H-bonds.

Question 15

What is the resiliency of viscose like?

Answer 15

Viscose easily wrinkles as H-bonds are broken when bent, compressed and formed in new positions as with cotton and linen.

Question 16

What are the lustre and drape properties of viscose?

Answer 16

Viscose can have high lustre as it is a manufactured fibre with a manufactured fibre shape. It can also be made duller by adding finishes and drapes well.

Question 17

Modal rayon:

Answer 17

This is a modification of normal viscose rayon. It goes by other names like ‘high wet modulus (HWM) rayon’, and ‘polynosic’. The fibrils are manufactured into the structure and it has a rounder cross section than viscose rayon.

Question 18

What is the durability of modal rayon?

Answer 18

It has higher strength than viscose because of it’s higher DP and more crystalline structure.

Question 19

What are the absorption and stiffness properties of modal?

Answer 19

It is slightly less absorbent than viscose rayon and stiffer than viscose, but softer than cotton.

Question 20

What is the dimensional stability and fibre blend use of modal?

Answer 20

Modal has a better dimensional stability than viscose and is often blended with other fibres as it has a higher modulus than viscose (eg, cotton, nylon, polyester).

Question 21

Why is lyocell environmentally friendly?

Answer 21

The creation of lyocell is an environmentally friendly process because only one solvent is used which is recycled. There are managed forests for producing lyocell. It is a wet-spun regenerated cellulosic fibre.

Question 22

What are the microscopic physical features of lyocell?

Answer 22

Lyocell has smooth surfaces and round cross sections.

Question 23

How crystalline is lyocell?

Answer 23

More crystalline than viscose & modal.

Question 24

What is Lyocell’s trademark name?

Answer 24

Tencel.

Question 25

What is the durability of lyocell like?

Answer 25

Lyocell has high strength because fibrillation occurs, particularly under wet abrasion.

Question 26

What are the absorbency properties of lyocell?

Answer 26

Lyocell is absorbent because of it’s OH groups.

Question 27

Why does lyocell appear fuzzy?

Answer 27

Fuzzy appearance can occur due to fibrillation.

Question 28

Rayon from bamboo:

Answer 28

Proprietary method or viscose process used to spin bamboo into rayon. Natural bamboo fibre is a bast fibre.

Question 29

Acetate:

Answer 29

Originated in Europe in the early 20th century, acetate is the first thermoplastic (heat sensitive) fibre that melted under a hot iron.

Question 30

What is the microscopic structure of acetate?

Answer 30

It has a striated surface with a lobed cross-section.

Question 31

What are the degrees of polymerisation for acetate?

Answer 31

Low, between ~250-300.

Question 32

What is the orientation and crystalline properties of acetate?

Answer 32

Acetate is poorly oriented and highly amorphous.

Question 33

Is acetate used in filament or staple form? What is it used for?

Answer 33

Acetate is typically used in its filament form. Common applications of acetate are lining fabrics for dresses, suits or coats and draperies.

Question 34

What is the strength, elongation, resilience, and elastic recovery of acetate?

Answer 34

Acetate has low strength, high elongation, poor resiliency and poor elastic recovery.

Question 35

Why is acetate soft?

Answer 35

Because of it’s low modulus.

Question 36

What is the absorbency of acetate?

Answer 36

Acetate is less hydrophilic than rayon because it has fewer –OH groups. It has about the same moisture regain as cotton.

Question 37

Is acetate light weight?

Answer 37

Yes!

Question 38

What is the lustre and resiliency of acetate like?

Answer 38

Fabrics typically have high lustre (unless a delusterant agent has been used) with moderate resiliency. Acetate wrinkles easily and is prone to wrinkling after laundering which can be difficult to iron out the wrinkles.