Recycling techniques of polyolefins from plastic wastes

Disposing of plastic wastes to landfill is becoming undesirable due to legislation pressures,
rising costs and the poor biodegradability of commonly used polymers. In addition,
incineration meets with strong societal opposition. Therefore, recycling either mechanical or
chemical, seems to be the only route of plastic wastes management towards sustainability.
Polyolefins, mainly polyethylene (LDPE or HDPE) and polypropylene (PP) are a major type of
thermoplastic used throughout the world in a wide variety of applications. In Western Europe
alone approximately 22 million tones of these polymers are consumed each year,
representing an amount of 56% of the total thermoplastics.
In the present investigation the recycling of LDPE, HDPE and PP was examined using two
different methods: the dissolution/reprecipitation and pyrolysis. The first belongs to the
mechanical recycling techniques while the second to the chemical/feedstock recycling. During
the first technique the polymer can be separated and recycled using a solvent/non-solvent
system. For this purpose different solvents/non-solvents were examined at different weight
percent amounts and temperatures using either model polymers as raw material or
commercial waste products (packaging film, bags, pipes and food retail products). At all
different experimental conditions and for all samples examined the polymer recovery was
always greater than 90%. The quality of the recycled polymer was examined using FTIR and
DSC. Furthermore, pyrolysis of LDPE, HDPE and PP was investigated with or without the use
of an acid FCC catalyst. Experiments were carried out in a laboratory fixed bed reactor. The
gaseous product was analyzed using GC, while the liquid with GC-MS. A small gaseous and
a large liquid fraction were obtained from all polymers. Analysis of the derived gases and oils
showed that pyrolysis products were hydrocarbons consisting of a series of alkanes and
alkenes, with a great potential to be recycled back into the petrochemical industry as a
feedstock for the production of new plastics or refined fuels.