Chapter 8) Polymers and Society

8) Polynomers and Society

Polynomers

  • are what form plastics and synthetic fibers

  • long chains formed from simpler molecules called monomers

  • monomers undergo many types of reactions to link together and become a polymer

→ natural: occur in plants and animals made of cellulose or proteins - polymer in plants and cellulose and starch formed by condensation polymerisation - polymers in animals are proteins and formed by condensation polymerisation → synthetic: made from raw materials from fossil fuels or biomass

Addition Polymerisation (one monomer)

  • the monomers must be alkenes (double bonds)

  • the double bond is broken which allows from addition of the next monomer unit

Condensation Polymerisation (two different monomers)

  • polymers that are formed through a condensation reaction where molecules (monomers) join together, losing small molecules as byproducts (often water)

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Thermoplastic

  • Thermoplastic and thermosoftening plastics can be reheated, remolded and cooled

  • formed by an addition reaction

Thermoset

  • Thermosetting plastics cannot be remolded, they do not melt, they char

  • Formed by a condensation reaction

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Polymer Selection

Affected by:

Choice of Monomer

  • an addition polymer requires monomers with carbon carbon double bonds

  • the monomers can be the same they can be different

  • a condensation polymer has a small molecule be eliminated in the polymerisation reaction

Degree of Branching

  • two types of polyethylene: Low density (LDPE) and high density (HDPE)

  • each are polyethylene but are produces under different condition to have different properties and uses

  • LDPE is produces under high pressure (20,000psi) and moderate temperature (200C)

  • HDPE is produces under low pressure (200psi) and lower temperature (150C)

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Degree of Crystallinity

  • defined as how regularly aligned (ordered) the polymer chains are - the more ordered the higher the degree of crystallinity

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Length of polymer chain Addition of plasticisers Other Additives

  • Plasticisers: soften and increase flexibility

  • UV stabilisers: absorb UV rays to prevent polymer breakdown

  • flame retardants: reduce the likelihood of polymers burning

  • Dyes: add colour and/or patterns

Catergorising and Recycling

  • Different codes (triangle symbols) on the bottom of plastic items identify the type of plastic it is made from

Plastics and Bioplastic

  • Polymers can be made from non-renewable (from fossil fuels) or renewable (bioplastics from biomass) resources

  • Using bioplastics helps the environment with:

→ reduction of use of fossil fuels

→ closer to carbon neutrality

Environmental Impact

  • does not change the physical properties of the polymer

Degradability

The capacity of the material to be broken down into smaller and smaller fragments

Biodegradability

The capacity of the material to be broken down into simple molecules (carbon dioxide and water)

  • All plastic is degradable/biodegradable depending on time frame

Recyclable

  • The capacity of the material to be converted into new materials and objects

  • takes place at specialised recycling facility

  • not all polymers can be recycled

Circular Economy

  • Recycling options include mechanical, chemical and organic

Mechanical Recycling

  • collected, cleaned and sorted

  • shredded and pelletised

  • then used to produce new products

Chemical Recycling

  • cleaned, cleaned and osrted

  • treated chemically to its molecular building blocks

  • reactions such as hydrogenation (applying hydrogen and heat), pyrolysis (heating without oxygen) producing hydrocarbons

Organic Recycling

  • bioplastics are collected, cleaned and sorted

  • composted in a special facility