Study Unit 2.2 Fibre Formation

Question 1

What can be considered a starting material in Manufactured cellulosic fibres

Answer 1

Manufactured cellulosic fibres have cellulose, as found in wood or cotton pulp, as a starting material.

Question 2

What would enable cellulose to be spun?

Answer 2

It must first be dissolved

Question 3

Name 4 ways to spun cellulose

Answer 3

viscose
cuprammonium
acetate
lyocell processes.

Question 4

What can be considered a starting material in Manufactured non- cellulosic fibres?

Answer 4

Manufactured non-cellulosic fibres have monomers derived mainly from petroleum as starting materials.

Question 5

The fibre-forming materials are made in two steps:

Answer 5

1. Synthesis of reactive precursors (monomers).
2. Coupling of thousands of monomers to form macromolecules (polymers). Two different types of polymerisation reactions, namely addition and condensation, are used to form the polymers.

Question 6

How are addition polymers formed?

Answer 6

When two, usually identical, reactive monomers are directly coupled to form the polymer, without a by-product, addition polymers are formed.

Question 7

Addition polymers include :

Answer 7

polyacrylics and polypropylene.

Question 8

Condensation polymers are made by:

Answer 8

are made by coupling two, usually different, reactive monomers, with the elimination of a small by-product (usually water). Condensation polymers include polyester and polyamides.

Question 9

Block copolymers are made by:

Answer 9

Block copolymers are made by pre-forming reactive monomers into blocks and then polymerising them, usually by condensation reactions.
Block copolymer fibres include elastomeric fibres.

Question 10

Spinning processes

Answer 10

Forcing polymers in a liquid state through a spinneret produces manufactured fibres.
The spinneret is similar, in principle, to a bathroom showerhead.
It may have anything from 350 to over 5000 holes.
The polymers are solid in their initial state and must be converted to a fluid state, usually by melting or dissolving in a solvent, before being extruded through the spinneret. Once the liquid leaves the spinneret, it solidifies again.

Question 11

Define filaments

Answer 11

The continuous strands of manufactured fibres

Question 12

There are four main methods of spinning filaments:

Answer 12

wet, dry, melt and gel spinning.

Question 13

Wet spinning

Answer 13

Wet spinning is the oldest process.
It is used for fibre-forming polymers that have been dissolved in a solvent.
The spinnerets are submerged in a chemical bath and as the filaments emerge they precipitate from solution and solidify (coagulate).
Because the solution is extruded directly into the precipitating liquid, this process for making fibres is called wet spinning.
Fibres produced by this process include rayon, acrylic, modacrylic, aramid and spandex.

Question 14

Dry spinning

Answer 14

Dry spinning is also used for fibre-forming polymers that have been dissolved in a solvent.
However, evaporating the solvent in a stream of air or inert gas allows solidification to occur.
The filaments do not come in contact with a precipitating liquid, eliminating the need for drying and easing solvent recovery.
This process may be used for the production of acetate, triacetate, acrylic, modacrylic and spandex fibres.

Question 15

Melt spinning

Answer 15

In melt spinning, the fibre-forming polymer is melted for extrusion through the spinneret and then cools to directly solidify.
This process is used for the production of nylon, polyester and polyolefin fibres.

Question 16

Gel spinning

Answer 16

Gel spinning is a special process used to obtain high strength or other special fibre properties.
The polymer is not in a true liquid state during extrusion. The process can also be described as dry-wet spinning, since the filaments first pass through air and then are cooled further in a liquid bath.
Gel spinning produces some high-strength polyethylene and aramid fibres.

Question 17

Drawing and orientation

Answer 17

While extruded filaments are solidifying, or in some cases even after they have hardened, the filaments may be drawn out (stretched) between rollers to impart strength.
Drawing pulls the molecular chains together and orients them along the fibre axis, creating a considerably stronger fibre.
Spinneret size and drawing conditions determine the final filament diameter.