Production of PET-Flakes. Processing steps for better quality
Valery Beketov, sales manager of Siegfried Schumacher GmbH, distributor of Herbold Meckesheim GmbH (Germany) equipment in Russia
Report points PET-flakes made out of PET bottles have become an important raw material for some polyester processing industries. Fiber mills, manufacturers of thermoforming sheet, producers of strappings purchase important amounts of PET-flakes to replace high priced virgin resin. But the economic interest is not often meeting the quality requirements of the industries. The use is limited by flakes being not clean and pure enough. Costly additonal sorting or pelletizing is needed. Sometimes only second class products can be made out of the flakes. Bottle to bottle use or food contact must be limited to a very short percentage of high quality flakes produced world wide. This lecture tries to show some steps to flake quality improvement and hopes to open your eyes for even more profitable use of this secondary raw material in the future. 1. The basic treatment. 2. How to remove paper. 2.1. Air sifting. 2.2. Wet grinding with friction washer. 2.3. Two step size reduction with air sifting in between. 3. How to remove foreign plastics. 3.1. Before size reduction: - by hand sorting, the most simple way and – in countries without high labour cost – the most economic way; - hand sorting under black light makes it easier to see PVC bottles and to do better hand sorting; - electronic detection by NIR camera and automatic sorting by air jets, the most economic way in high labour cost countries. This method needs very efficient debaling before, 100% of the bottles must be individual, no remainings of the bales are allowed. 3.2After size reduction: - the swim sink-tank, that is already part of the basic system removes polyolefines from the plastics that are heavier than water; - a hydrocyclone does the same job but more efficient if higher throughputs (2 t/hr and more) are requested; - electronic detection and automatic sorting of the flakes at the end of the line, - very costly method. 4. How to remove residual film and fibres. 5. How to remove glue.