- 30 April 2008 -
Thermal treatment enhances optical sorting

Buhler Sortex Ltd has made improvements to its optical sorting process for selecting materials in plastics recycling by adding a thermal treatment step before the optical sorting operation. The thermal treatment may be a simple crystallization step over a few minutes or a drying or even solid state polycondensation step under air, vacuum or nitrogen over a few hours. Due either to the former bottle content or incorporated additives, some PET flakes tend to discolour much more than others during thermal treatment. Sorting this small percentage of discoloured flakes out of the material stream will improve the colour quality of subsequently recycled products significantly. The rejected flakes can then be used for less colour sensitive applications like coloured sheet or straps.

The importance of using recycled materials in the PET recycling loop continues to grow. Consequently, there is a need to remove non-PET particles and coloured PET flakes to deliver a high quality input material for subsequent recycling processes. This leads to recycled bottles or films with better colour, fibres with less breakage, reduced product loss from melt filtration, longer screen lives and generally improved processing conditions.

Buhler Sortex Ltd.; www.buhlersortex.com