3.3.12.2 biodegradability + disposal of polymers

polyalkenes are what?

chemically inert (ie unreactive)

what is one problem with plastics?

most plastics are not quickly broken down by microbes + many not at all

explain why plastics cant be broken down by microbes

• addition polymers / polyalkenes are non-biodegradable

• this is due to the non-polar covalent bonds present between atoms in the polymer molecules

• as the C-C bonds aren’t polar, they are not susceptible to attack by nucleophiles + are therefore not easily hydrolysed

why do we need to reduced the amount of plastic we use or recycle it?

because buried plastic in landfill sites may take hundreds of years to decompose

how can addition polymers be recycled? give 2 ways

• they can be separated, washed + then melted down + remoulded by heating the polymer

• some polyalkenes eg poly(propene) are heated to a high temp that will break the polymer bonds + produce the monomers again → these can then be used to make new plastics

what forces must be overcome when melting an addition polymer?

Van der Waal’s forces between polymer molecules

explain why polyesters + polyamides are biodegradable

• the C-O or C-N bonds in the polymer chain are polar

• therefore δ⁺C can be attacked by nucleophiles/can be hydrolysed

because condensation polymers can be hydrolysed, what does this mean?

that they can be broken up + the constituent monomers are reformed

outline an advantage of condensation polymers than addition polymers eg polyalkenes

condensation polymers are biodegradable + so clearly constitute a smaller environmental hazard than addition polymers, whose chains are made up entirely of non-polar C-C bonds + which are therefore non-biodegradable

outline how condensation polymers are broken up

• the break up of these polymers is carried out in aqueous solution with a strong acid or strong base

• it can be classed as a hydrolysis reaction

outline the different ways addition are disposed

• as addition polymers are non-biodegradable, they are usually disposed of in landfill sites, along with other rubbish

• some may be melted down + remoulded

• poly(alkenes) can be burnt to produce carbon dioxide + water to produce energy, although carbon monoxide gas (toxic) + carbon (black soot) could also be produced if combustion is incomplete

give 2 advantages of recycling polymers

outline one disadvantage of recycling polymers