Densification can be carried out with heat (thermal densification), or without heat (cold compaction).
Cold compactioninvolves crushing and compacting EPS by machine. The compacted materials are extruded into a solid ‘log’. The log is cut to length to fit onto a pellet. It is usual for the compactedEPSto be stored on-site until 5 to 20 metric tones are available, as this makes transport and distribution more cost-effective. The more densely compacted theEPSis, the better, since a higher weight of EPS can be loaded for transport and a higher price per tone may be paid by the recycler. Cold compaction can reduce EPS volume down to one-fortieth of the original.
Thermal densification involves breaking up and meltingEPSinside a controlled-temperature chamber. The temperature is controlled to allow the EPS to melt without burning. This collapses the expanded foam cells, enabling it then to be recycled into other products. Higher compaction ratios (up to 95% volume reduction) can be achieved using higher temperatures but the end product has fewer recycling options and is most suited to incineration with energy recovery or disposal to landfill. The melting process could also generating some odor and on-and-off operation of the machine can be a big waste of energy and time because of cooling and re-heating of the machine.
