Basic Technology of Plastics - Introduction to Polymeric Composites with Rice Hulls - page 25

is becoming widespread because plastics processors are taking advantage of the
additional factors of cheaper resins and shorter moulding cycles.
2.5 Recycling of Plastics
Recycled plastics also play a major part in the product manufacturing phase of
PCRH, so this subject is discussed here briefly and in detail later for the benefit
of the reader.
Recycling of plastics can be divided broadly into two major categories: industrial
and post-consumer recycling of plastic scrap. Industrial scrap is easy to recycle.
Many manufacturers recycle them on the factory floor and re-introduce into the
production line within the same company as a 'regrind' or sold to third parties as a
homogenous, reliable and uncontaminated source of resin. Post-consumer recycling of
plastic scrap requires the material to go through a complicated and time-consuming
operation before the material can be reclaimed. Bulk of the post-consumer plastic
waste comes from commercial, agricultural and municipal wastes. Municipal plastic
wastes consist primarily of packaging waste but also from appliances and electronic
equipment.
Post-consumer plastic wastes require collecting, handling, cleaning and size reduction
through shredding and grinding before they can be processed into a re-usable
form. The initial stage of the source and collection methods forms the most critical
aspects of a recycling operation. The demand for recycled plastics, generally in pellet
form, is increasing with rising costs of pure plastic resins. One may consider that
the demand for recycled materials from bottles (which probably forms the bulk of
plastic wastes in pure form) has the greatest demand from various manufacturing
sectors. Sometimes, the plastic wastes for collection at source may have different
grades separately but mostly they will be found in a mixed form, and they will need
extra effort to sort out before recycling can start. Some countries have identification
codes on the packages but even these may not help being lost in the mix. Separating
thermoplastic wastes from thermosets is important if one is to achieve quality recycled
material for re-processing. If it is difficult to identify a plastic waste then certain tests
(e.g., water floating test and burning test) can be employed. The problem of mixed
colours also arises, and it is best to recycle them separately as far as possible. Also, the
use of additives will help to enable one homogenous colour and, in some cases,
the manufacturers may ask for multi-coloured recycled material to produce somewhat
'psychedelic' finishes. In the production of PCRH, recycled plastic wastes can also
be used as the matrix.