Polymers

What are polymers?

Molecules made from repeating monomers which link through polymerisation

What is the definition of a natural polymer?

made from plants and animals

renewble and biodegradable

What is the definition of a synthetic polymer?

lightweight, flexible, corrosion resistant

made from petrochemicals

What are examples of natural polymers?

abudant

starch, cellulose, proteins and dna

Why is wood used as a natural polymer?

abundant and versatile

made from cellulose

What are the properties of cellulose when used as a polymer?

cellulose fibres held by hydrogen bonds

strong but vulnerable to moisture

What are properties of wood?

strong in grain direction

limited to the size of the tree

rotting fire and beetles will destroy

What are pros and cons of wood?

renewable

deforestation - loss of habitats

burning releases carbon dioxide

What are natural fibres?

• wool and cotton

• fibres spun into clothes and dyed

  • soft absorbant and durable

What is the chemical structure of cellulose?

glucose monomers linked with beta 1-4 glycosidic bonds

What are general properties of polymers?

insulating - electric and thermal

impact absorbing and flexible

lightweight and corrosion resistant

can be colourd

easily formed, worked and bonded

composites

What are properties of synthetic polymers?

• petrochemicals

• durable

• lightweigt

• corrosion resistant

  • non biodegradable

Why are polmers good for packaging?

keeps food fresh for longer

Why are polymers good for electronics?

ligth and strong

Why are polymers good for construction?

weather protection and support

What are thermoplastics?

• soften at high temperatures and can be reshaped repeatidly

  • solidify when cool but with further heating can be reshaped

What is a thermosetting polymer?

sets permanently when heated as forms rigid cross links which cant be removed with further heating

What is carbon in terms of a polymer backbone?

• carbon forms 4 strong bonds with either itself or other atoms

  • ensures the stability of the polymer chain

How is crude oil formed?

• remains of small marine atoms and plants are buried deep beneath the sea bed

• high pressure and no oxygen causes them to be converted into hydrocarbons

  • liquid and gas crude oil is trappeed in porous rock strata beneath the impervious layer

How is crude oil located?

localisation in countries with large amounts of non renewable resources

north sea, usa

transported in raw form in bulk carriies to industrialised countries

What are enviromental risks of oil exploiation/ crude oil?

sea pollution

explosions in refineries

green houe gases and global warming

What are the economic risks of oil exploitation/ crudue oil

resources in politically sensitive regions

using a valuble resource as fuel

What is the purpose of fractional distillation?

seperate hydrocarbons based on boiling points

what is the fractional distillation process?

oil is heated so components are vapourised

there is a temperature gradiend, hotter at the bottom cooler at the top

longer chains have higher boiling points so condense lower down the coloumn

shorter the chain the higher it condenses

What is the order of components collected from fractional distillation?

• refiner gas

• petrol

• kerosene

• diesel

• fuel oil

  • lubrication oil

What is the purpose of catalytic cracking?

treats the fractions further

the longer chains are less valuble so it cracks them into smaller monomers which e.g. essential to make polymers

What is the process of catalytic cracking?

heated to vapourise using super heated steam

vapours mix with a catalyyst

bonds vibrate to the extent that they break forming smaller molecules

monomers are seperated again through fractional distilation

Why use a catalyst in catalytic cracking?

speed up the reaction

reaction happens at lower temperature

lower energy consumption

What are the advantages of catalytic cracking?

• higher yield for desired monomers

• lower operating temperature saving energy

  • catalst e.g. zeolite can be recycled

what monomers are used in the petrochemical industry?

• ethene which is mostly produced by cracking

• ethene reacts with molecules in catalytic reaction producing monomers

  • most monomers made through petrochemicals

What is chain growth polymerisation?

monomers are added one at a time to increase the chain length

What is the process of chain growth polymerisation?

1. initiation - free radical species is generated by adding a catalyst. radical attacks the monomer at the start of the chain

2. propegation — chain grows one monomer at a time to the active end

   1. termination - chain stops growing when radicals collide and neutralise each other creating a stable polymer

What is the process of step growth polymerisation - nylon?

• no initiation required, monomers join directly anywhere along the chain and join through condensation reactions

  • monomers have reactive units

• termination happens when the chain ends join

How does chain length affect polymer properties?

• longer the chain the more it tangles and the more bonds

• increased strength and melting point

How do intermolecular forces affect polymer proeprties?

more van der waals and hydrogen bonds the higher the melting point, ridgitity and strength

How does branching affect polymers?

the more branches, the lower the melting point and density

as can’t pack together closly

How does cross linking affect polymer properties?

the more cross links the higher the strength and density

more chemical bonds

How do you impact test polymers?

• different mass pendulums swing unntil the polymer breaks

• polymer mounted in a grip

  • the stronger and more impact resistant the poymer, the greater force required

How do you pressure test a polymer?

• subjected to very hihh internal pressures to hilight any weekness

How do you tensile test polymers?

stretched under different loads and their peformance recorded

Why do you stress crack polymers?

evaluating stress at sharp corners to see vulnerabilities to cracks and ability to resist cracks

What is extrustion of polymers?

• beads are melted and forced into a die

• shape off die determines product

  • fibres and rods

What is blow moulding?

• parison goes intothe mould

• end sealed when mould closes

• air forces plastic near melting point into the shape of the mould

  • bottles

what is injection moulding?

• molten plastic forced into mould under pressure

• mould is in 2 halves which are seperated to reveale cast

• foaming agents can be added for strength / sponge

  • washing machines

How do you make thin plastic sheets?

pressurised plastic tube is heated and blows like a baloon

sausage is drawn up a tower where its cooled and collapses

edges are trimmed forming 2 layers of thin plastic sheets

Polymers and their non biodegradability?

• plastic lasts for years and ends in landfill or oceans

  • use biodegradable polymers, reduce polymer use and improve recycling

Polymers and toxic by products?

• combusion of polymers releaes oxides green house gases

  • inciderate under controlled conditions

Plastics and difficulty recycling?

• most items are made from mixed plastics whih are hard to recycle

  • simplify types of plastics used, more advanced recycling

Phthalates and plastics?

• feminise fish and men

  • switch to safer alternatives, regulate their use

Mercury and plastics?

• mercury released by chlorine contaminating ecosyystems and causing mercury poisoning

  • switch to membrane cll technology