Bühler sets new trends in PET sorting04/07/2008 More than 50 years ago, ICI used Bühler Sortex’s pioneering optical sorting techniques for the sorting of plastics. Over the years as technologies have advanced and environmental awareness increased, the use of recycled input materials has become important and the optical sorting of washed PET flakes is now a key process step in the PET bottle recycling loop. The removal of non-PET particles and coloured PET flakes delivers a high quality input material for subsequent recycling processes which in turn results in 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.
Andreas Christel, PET Recycling Product Manager at Bühler’s Thermal Processing Division believes that a further step towards a clear recycled PET is the application of optical sorting after thermal treatment of the PET flakes. “The thermal treatment may be a simple crystallisation 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.”
Faisal Baig, Product Marketing Professional at Bühler Sortex expands on their unique ability in this application “We believe that our SORTEX Z+ optical sorter offers the plastics industry an elegant solution that is by far the most efficient and cost effective while being exceptionally simple to operate and maintain.
“What makes our SORTEX Z+ unique is that it uses advanced cameras and PROfile shape recognition, enabling it to simultaneously identify reject material by shape as well as colour with exceptional accuracy so that the highest post-sort quality is achieved with the minimum number of passes.
“Unwanted colours and foreign material such as rubber, metal, paper, glass, wood, misshapes and ‘over longs’ are removed from a range of materials including PET, HDPE, PVC, uPVC, PVB, ABS, and other plastics in flake, granule or pellet form. “
The SORTEX Z+ which is available in various sizes and can sort between 0.5 and 6 tph of PET flakes is already being used intensively by several of the largest European companies that are heavily involved in rPET processing. The benefits they enjoy have aroused keen interest industry wide.