Fiber Science

Fiber Science is the study of the formation, structure, and properties of fibers on micro to macroscopic levels.

The study of fibrous materials and their use in a variety of conventional and non-conventional applications.

Type of fibers

1- Manmade/Manufactured

a)- Synthetic ( Nylon, polyester, acrylic)

b)- Regenerated ( Rayon)

2- Natural Fibers

a)- Cellulosic origin

b)- Protein origin

Fiber Length

Length of fiber ClassUnit of

measurement Appearance

Long Filament fibers Yards/meters

Short Short fibers Inches/centimeters

Classification of fibers on the basis of length

Fiber Applications

Home Textile

Technical Applications

Apparel

Apparel Applications

Home Textiles

Technical Textiles

Fiber Science

Properties of fibers

1-Physical Properties

2-Chemical Properties

3-Mechanical Properties

Fiber Science

Physical Properties of fibers

Length

Fineness

Crimp

Maturity

Toughness

Elongation

Lusture etc.

Fiber Science

Mechanical Properties of fibers

Strength

Elasticity

Extensibility

Rigidity

Fiber Science

C) Chemical Properties

Solubility in aqueous salt

Solubility in organic salt

Chemical composition

Chemical structure of synthetic fibers

Monomers Vs Polymers

Synthetic Fibers

Monomer Vs Polymer

(Polyethylene terephthalate (PET)

Synthetic Fibers

Nylon 6 is synthesized by polymerization of caprolactam

caprolactam Nylon 6

Synthetic Fibers

Polyester is formed by Poly-condensation of PET monomer

Synthetic Fibers

In PET fibres, the molecules are mainly arranged in fiber, film and in package form

Flax

Cotton

Silk

Wool

Cashmere and Mohair

Synthetic Fibers

• Rayon –1st artificial fiber from wood

• Acetate – artificial from wood (satin)

• Nylon –1st synthetic fiber• Olefin – synthetic (carpet)

• Acrylic – synthetic wool• Polyester – most common syn.• Specialty fibers – Kevlar, Spandex

Rayon

Acetate

Nylon

Olefin and Acrylic

Polyester

Manufactured fibers

Manufactured (MF) fibers (formerly termed “man-made”) are formedfrom a suitable raw material as a thick, sticky liquid, which is “spun”or extruded through spinneret holes, forming streams that aresolidified into fibers

The raw material for MF fibers may be itself a natural substance, or itmay be synthetic (synthesized from basic chemical units), but it isconverted into textile fibers by a manufacturing process

While there are MF fibers made of natural rubber (as well as ofsynthetic rubber), there is no such thing as a natural rubber fiber.Similarly, Tencel lyocell is not a natural fiber; it is an MF fiber made ofa natural material, cellulose

Textile fibers are made up of molecules, these fiber molecules are called polymers.

The Unit of polymer is called monomer ( mono-one: mer-part)

At molecular level, polymer is extremely long and linear whereas monomer is very small

Monomers are usually reactive whereas polymers tend to be unreactive

This causes the monomers to join end to end to form a polymer called polymerization

Polymerization

Length of polymer is most important. All fibers, both natural and man made have long to extremely long polymer lengths

Measuring length of polymer is complicated yet not impossible

Degree of polymerization (DP) is therefore calculated

Degree of Polymerization=

Average molecular weight of polymer

Molecular weight of the repeating unit in the polymer

• 5000 DP for cotton means 5000 repeating units (cellobiose)

• Polymerization of natural polymers are not known

• Polymerization of synthetic polymer is categorized into

a. Addition Polymerization

a. Condensation Polymerization

a)- Addition Polymerization

Monomers add or join end to end without liberating any by product on polymerization.

Some fibers which consist of addition polymerization are acrylic, modacrylic, polyethylene, polypropylene etc.

b) Condensation Polymerization

In this process monomers join end to end and liberate a by product

This product is a simple compound, e-g water, ammonia, hydrogen chloride

Some fibers consisting of condensation polymerization are elastomeric, nylon and polymers.

• Polymers of cotton, acetate, flax, silk, triacetate, viscose andother regenerated fibers and wool don’t fit into aboveclassification because not enough is yet known about theirpolymers and synthesis

Types of polymers

1-Homopolymer ( Same or one kind of polymer)

2-Copolymer ( Two or more different polymers)

Copolymers are further divided into

i. Alternating copolymer

ii. Block Polymer

iii. Graft Polymer

iv. Random polymer

Types of Polymer

Homopolymer Homos is “same” or one kind of polymer

Nylon, vinyl chloride, polypropylene

The lack of branches in its structure

allows the polymer chains to pack closely

together, resulting in a dense, highly

crystalline material of high strength and

moderate stiffness.

500,000 atomic units for High Density

Polyethylene

Copolymer

Polymerized from two or more monomers

• Silk is composed of 16 different amino acids

• Wool is composed of 20 different amino acids

Copolymers are sub categorized into four groups

A thermoplastic resin produced by the

copolymerization of styrene and maleic

anhydride

A rigid, heat-resistant, and chemical-resistant

plastic, it is used in automobile parts, small

appliances, and food-service trays

most of the copolymers contain about 5 to 20

percent maleic anhydride, depending on the

application, and some grades also contain

small amounts of butadiene for better impact

resistance.

Alternating copolymer

41

Copolymers can be used to tailor functionality or generate

new behaviors.

Block copolymer, example:

Poly(styrene)-block-poly(butadiene)

Random copolymer, example:

Poly(styrene-ran-butadiene)

Graft copolymer,

example:

Poly(styrene)-graft-

poly(butadiene)

42

Combs, brushes and ladders give you ways to stiffen a polymer.

43

Rod like polymers are used for very high strength, liquid crystals, efficient viscosification

S

N

S

N

* *n

Rodlike because of helix

Rodlike because of linear backbone

Crystalline and amorphous

regions

Crystalline regions provide

strength and amorphous regions

provide stretch

Amorphous and crystalline regions

(a) Linear structure; thermoplastics such

as acrylics, nylons, polyethylene, and

polyvinyl chloride have linear structures.

(b) Branched structure, such as

polyethylene.

(c) Crosslinked structure; many rubbers

and elastomers have this structure.

(d) Network structure, is highly cross-

linked; examples include thermosetting

plastics such as epoxies and phenolics.

Possible arrangement of monomers in a polymer

Chemical Bonds

The basic nature and reactivity of the fiber can be derived bythe type of chemical bond that holds the polymers together

A chemical bond is an attraction between atoms that allowsthe formation of chemical substances that contain two or moreatoms

The bond is caused by the electromagnetic force attractionbetween opposite charges, either between electrons and nuclei,or as the result of a dipole attraction

Classification of Bonds

Chemical bond can be broadly classified as follows

• Intra-polymer bonds

• Inter-polymer bonds

Intra-polymer Bonding

• Bonds holding the atoms together to make up the fibre polymer is

called intra-polymer bonding.

• Textile fibre polymers are mainly organic compounds, expect some

natural mineral and man-made inorganic fibres.

• They are predominantly composed of carbon and hydrogen atoms,

with some oxygen, nitrogen, chlorine and/or fluorine atoms.

• In general, single covalent bonds join the atoms forming the polymer

Intra-polymer Bonds

The major bonds that are used for intermolecular bonding are as follow

• Covalent bonds

• Amide or peptide group

• Benzene ring

• Ether linkages

• Ester groups

• Hydroxyl group

• Nitrile group

Covalent bonds

Covalent bonding is a common type of bonding, in which theelectro negativity difference between the bonded atoms is smallor nonexistent.

Their bond energy or bond strength is between 330 and 420kilojoules

The amide or peptide group:

In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group (R-C=O) linked to a nitrogen atom (N).

When present in nylon polymers it is called the amide group.

It is also present in silk, wool, mohair and all other animal or protein fibres and then it is called peptide group

Benzene rings

They are sometimes referred to as the aromatic radical.

It is a hexagon shaped molecule composed of mainly carbon and hydrogen

Ether linkages

• The ether linkages may be found in polymers such as cellulose, elastomeric, ester-cellulose and polyesters.

• It exists between carbon and oxygen atoms.

• Ethers are chemically unreactive. One reason for this is the great chemical stability of the carbon-oxygen linkages found in every ether molecule.

Ester groups

• They are formed by replacing the hydrogen of an acid with an organic radical.

• In fibre polymers they are usually the reactions between:

a. A carboxyl group (-COOH), also called carboxylic acid

b. A hydroxyl group (-OH)

Inter polymer bonds

• In basic senses these bonds are responsible for holding the polymers together for the formation of a fibre.

• The major bonds used for interpolymer bonding are as follows,

Van der Waals forces

Hydrogen bonds

Salt linkages

Van der Waals forces:

They are weak forces which exist in the interpolymer forces of attraction when the atoms come close to one another.

They are formed between atoms along the length of adjacent polymers when these are less than 0.3 nm apart but no closer than about 0.2 nm.

They occur between all fibre polymer system and their bond energy in 8.4 KJ.

Hydrogen bonds

They are formed between hydrogen and oxygen atoms, and hydrogen and nitrogen atoms on adjacent polymers when these are less than 0.5 nm apart.

They occur within the natural polymers, regenerated cellulose polymers, nylon polymers, polyvinyl alcohol, polyester polymers, protein and secondary cellulose acetate fibres.

Their bond energy is 20.9 KJ

The hydrogen bonds are mainly responsible for the tenacity and the elastic-plastic nature of the natural, regenerated cellulose, nylon, PVA and protein fibres

Salt linkages

• They are formed between the carboxyl radical on one polymer and the positively charged amino group on an adjacent polymer.

• They exist mainly in the protein and nylon fibre polymers.

• Their bond energy is 54.4 KJ.

• They are responsible for the attraction of the water molecules and they too contribute to the strength of the fibre.

• The presence of salt linkages is necessary for dye absorption