Recycling, selection and design

Recycling issues

• Recyclable

• Biodegradable

Recyclable

After having completed its life cycle in one component

• can be reprocessed

• can re-enter materials cycle, can be reused in another component

biodegradable

by interactions with the environment, the material deteriorates and returns to same state in which it existed prior to processing

Metals

• Most experience corrosion and are biodegradable

• Some metals are toxic and when landfilled present health hazards

• alloys of most metals are recyclable

• but may not be feasible to recycle all alloys

• Quality tends to diminish with each cycle

Aluminium alloys

• very corrosion resistant and therefore non-biodegradable

• not easily corroded so can be fully reclaimed

• low ratio of energy required to refine recycled aluminium relative to primary prod.

• primary sources of recycled aluminium: used beverage cans and scrapped automobiles

glass

• consumed in the greatest quantities

• does not decompose so is not biodegradable

• land fill mainly consists of glass

• salvaged glass must be recycled by colour, tyoe and composition

advantage of glass

more rapid and increased production rates

• reduction in pollutant emissions

plastics

Most plastics aren’t biodegradable, but those that are are expensive to produce. Some are combustible without toxic emissions so may be disposed by burning (incineration)

• their value and quality decreases with each cycle

• presence of fillers makes recycling difficult

Thermoplastic polymers

• can be most reclaimed and recycled

• as they are reformed upon heating

• sorting by type and colour

Rubbers

• when vulcanised, they are thermoset

• So chemical recycling is difficult as form doesn’t change when ehated

• Contain fillers so difficult to recycle

• ground and adhesive added to create place mats or rubber toys

• rubber tyres are main scrap and are used for industrial applications

• dirty emissions

Recyclable alternatives to rubber

• thermoplastic elastomers: easily reshaped

• production energy requirements are lower than thermoset

• as vulcanisation is not required

Composite

• difficult to recycle as multi-phase and mixed on fine scale

• tech developed to recycle polymer-matrix composites

steps of recycling polymer-matrix composites

1) shredding and grinding

2) used as filler material that is blended with polymer

3) molding

• other processes allow to separate the fibers and matrix materials

• matrix may be turned into gas, sometimes recovered as monomer

• they will have short fibers as a result of the grinding

• so lower mechanical strength