Polymers and fibres

What is a polymer

A large molecule composed of individual monomer units linked together

Example of monomer units

Vinyl chloride- makes vinyl chloride

Styrene- makes polystyrene

Glucose- makes up cellulose- has 100,000 monomer units

What does the n stand for in the polymer

The number of monomer units in your polymer (large number)

What is polymerisation

a process of reacting monomer molecules together in a chemical reaction to form polymer chains

Types of polymers- natural (biopolymers)- examples

Natural fibres, proteins and DNA

Types of polymers- semi-synthetic - examples

rayon fibres and cellophane

Types of polymers- synthetic - examples

PVC, polysterene, PTFE and nylon

Also kevlar- strongest synthetic fibre in world

What are co-polymers

Are extremely large molecules, are similar to normal polymers.

Have different limker monomer units

Examples of co-polymers

The rubber used in car tyres- styrene (25%) and 1,3-butadiene

What is the monomer and trade name for co-polymer used in food wrappimg and fibres

Vinyl chloride (20%) and vinyldene chloride (80%)

Saran

Monomer and trade name for co-polymer used in tyres and rubber articles

Styrene (25%) and 1,3-butadiene

Styrene-butadiene rubber (SBR)

Monomer and trade name for co-polymer used in adhesives and petrol hoses

Acrylonitrile 1,3- butadiene

Nitrile rubber

Monomer and trade name for c-polymer used in inner tubes

Isobutylene isoprene

Butyl rubber

What are monomers called that are organise themselves in a random fashion

Random copolymers

What are monomers called that organise themselves in an alternating fashion

Alternating co olymer

What are block polymers

When the monomers organise themselves into blocks

What is a graft co-polymer

This is when a long chain of a single monomer unit has branches/side chains of the other monomer unit grafted onto it

Interactions between polymer chains- branched polymers

Main chain that has brnaches

Are used in polyethylene- is low density and has a high degree of branching, means its flexible and can be cast into films

High density polyethylene- has a low degree of branching, less flexible and produces a stiffer plastic used in shampoo bottles

Interactions between polymer chains- cross linked

Have linear chains which are joined together by small vertical chains at random positions along the length of your main chain

used in poly(isoprene) rubber-used in inner tubes of bike wheels and epoxyresin (glue)

Interactions between polymer chains- linear

Chains are in a linear fashion and are found in plastics and nylon

Interactions between polymers- dendrimer

Only used for specialised polymers that have specifc uses taht yhave been engineered for this speciality e.g every single unit in a chain being branched

Different ways to synthesise polymers

Chain growth polymerisation

Cationic polymerisation

Anionic polymerisation

Step growth polymerisation

Classification of synthetic polymers- thermoplastics

• Hard at room temp (has a high glass transistion temperature)

• Soft and viscous at higher temperature- shaped and moulded

• Example- polysterene, polythelene, acrylonitile butadiene styrene (lego) and PET

Classification of synthetic polymers- thermosetting polymers

• when heated- produces an extensive 3 dimensional linkage, is highly cross-linked and solidifies into hard, insoluble mass

• cannot be reshaped or remoulded

• Example- bakelite and automobile

What is bakelite?

Reaction of phenol with formaldhyde- involves a loss of water and production of extensive 3 dimesnional linkages which produce a hard large molecule

Disadvantage of thermosetting polymers

They are inflexible, become brittle- plasticisers need to be added

Classification of synthetic polymers- elastomers

• Low glass transistion temperature

• Have ability to stretch and return to original shape- due to them having random coiled chains and can be stretched horizontally- stretch cannot be maintained due to the forces being london dispersion forces which are very weak and isnt many of them- returns to original shape

What are elastomers used for

Rubber and tyres

What are fibres?

• Thin threads of molton polymer that are extruded through a spinneret (small holes)

• Molten polymer is cooled and drawn out along the axis of the fibre to give it a tension strength

Importance of fibres

• Transfer and trace evidence found at crime scene

• Largest category of polymer evidence analysed by forensic chemists

• important in homicides, assault, sexual offences and hit and runs

What can fibres be classified into?

natural, semi-synthetic ans synthetic

The 3 categories in natural fibres

Animal source, pant source and mineral

What is cellulose

Natural large polymer

Made up of glucose monomer units held together by hydrogen bonds

Strong- gives strength to plants and wood

What fibres can cellulose make

Natural fibres- made up of 90% cellulose

Cellulose fibres

Other natural fibres- have different structures of cellulose in them to give them different properties

Cellulose known as a dicot fibre- what is this?

A fibre that comes from a plant with two seed leaves

Appearence of dicot fibres

Transparent, colourless and curved twisted fibres

Circular cross section and surface striations along length of the fibre

What is the seed fibre kapok?

Silky cotton like substance

Tiny cellulose tubes air sealed inside

Removed by hand, dried, sepearated and exported

Brittle and inelastic- cant be spun into a fabric

Can take on 30% of its weight in water and loses 10% around each month over 30 months-used for buoyancy aids

Appearence of kapok

Smooth hollow thin walled cylinders 2-3cm/10-35hm

Twisting and sharp bending and surface irregularities

Advantages of kapok

Can take on 30% of its weight in water and loses 10% around each month over 30 months-used for buoyancy aids

Non-toxic and non- allergenic

Used in life jackets, quilts etc- used as stuffing agent

What is the dicot fibre, flax (linen)

Skin/bast fibre- collected from the stem of the linen plant

High conc of cellulose in it- higher than in cotton

stronger than cotton

Appearence of flax (linen)

see slight thickenings of the transverse node shapes, I X V and Y

What is the dicot fibre, hemp

Comes from the cannabis plant

Two types- primary bast fibres (70%) and secondary bast fibres (30%)

Appearence of hemp under microscope

Colourless, transparent cylinders

Surface irregularities

Polygonal in cross section with surface striations

Types of hemp fibres- primary bast fibres

Make up 70% of hemp fibre production

One of the strongest natural fibres

Long and has high conc of cellulose, low lignin

Types of hemp- secodnary bast fibres

30% of hemp fibre production

Low cellulose content- not as strong as primary

Medium

High lignin

What is the dicot fibre, ramie

Long, glossy naturally white and silky appearence

Composed of cellulose

Extremely porous

Stromgest natural fibres

Greater strength when wet

Appearence of ramie

Nodelike ridges

Longitudinal striations

smooth surface

raised nodes

What is jute

1-4m long, soft and shiny fibres

White to brown

Spun into a harsh fibre containing cellulose and lignin- used for upholstery

Appearence of jute

Straight, smooth cylinder

Bundles of individual fibres with adhesions

What is the fruit fibre, coir ?

Composed of fibre bundles- these bundles are composed f dense aggrigate ribbon like fibres 1mm in length made from the core of the coconut

Are dried, hardened and spun- placed into floor mats, ropes and brushed

What are monocot fibres?

One seed leave

Hard fibres

Appearence of sisal, the monocot fibre under the microscope?

Transaparent, colourless to light yellowish tan cylinders

What is sisal?

A hard fibre

Used in cordage (ropes, floormats)

Can be put into a pulp and beaten within the inch of its life to produce sisal fabric- worn in hot countries

Disadvantages of sisal

The extensive beating and conversion from a hard fibre to soft fabric- is expensive

Appearence of monoct fibre, manilla?

Bundles of individual fibres

Polygonal to oval in shape

1mm in length and have rounded corners at end

What is the monocot fibre, manilla?

Used in ropes, cordage, brushes

Used in the pulp we use for paper

What is the animal fibre, silk?

Comes from the larvae of the silk worm

Protein fibre

Shiny fibre- has traingular prism like shape- can interact with light at different angles

strongest fibres- but strength decreases when wet

Used for bedding, parachutes etc

Appearence of silk under microscope

Pale yellow to brown/yellow fibres

Broad continious ribbons

Longitudonal striations

What is the seed fibre, cotton

Seed fibre- grow in seed pods of cotton pkant

When fibres are ready to be extracted- seed pods open and reveal cotton fibres

Short and weak- have to be spun into fabric to give them strength

90% cellulose

Appearence of cotton under microscopd

Thin threads with ribbon like shape that twist at regular intervals

Yellow white colour length around 2 inches

8 step process microscopic analysis of cotton fibres

What are semi- synthetic fibres

Chemically modified cellulose

How to make the semi synthetic fibre, rayon fibres?

• Extract the cellulose from wood pulp or cotton

• React this with a strong base (sodium hydroxide) and carbon disulphide- results in cellulose xanthate (viscose)

• Extrude this through a spinneret into a glass of sulphuric acid and sulphate salts- results in rayon filaments which are drawn out to form rayon fibres

What are rayon fibres

Long, smooth, highly reflective and shiny fibre

What are bicomponent fibres (synthetic fibres)

Have 2 differnt polymers

Are engineered for specifc purposes

Can organise themselves into a sheath and core design

Or organise themselves into a side by side design

What are the general characteristics of synthetic fibres

No surface characteristics, regular and uniform in shape

What is nylon

A step growth polymer

6- aminohexanoic acid

Uses- nylon stockings, carpets and seatbelts

What is kevlar

Strongest synthetic fibre

Their monomers are known as amides becuase they have a benzene rings

Hyrdrogen bonds network produced

Used in bullet proof vests