PETpla.net Insider 04 / 2019

MATERIALS / RECYCLING PET planet Insider Vol. 20 No. 04/19 www.petpla.net 38 dirt accumulate at molecule radi- cals on the rough surface resulting in a yellowing of flakes after thermal treatment. Since less alkali is neces- sary and soilings are emulsified by applying Tubiwash cleaning additives, extrusion filters are less contaminated (time and material saving) and PET flakes appear brighter. (Fig.3) Cleaning additive - further support Wherever hardening agents (lime) are dragged into an alkaline wet process deposits can reach machine parts such as heat exchangers which reduces the energy transmission. Due to the special composition most of the Tubiwash additives contain lime inhibi- tors to minimise lime deposits. Some PET recyclers are obliged to minimise the total dissolved solids con- centration in their waste water. There- fore a cleaning with less alkali is pre- ferred to reduce the ions in the water and a cleaning additive is welcome. Cleaning additive and alkali – the perfect combination Alkali has a certain cleaning effect and additionally cleaning additives can significantly improve the effect due to their cleaning and emulsifying power. Therefore a cleaning additive such as Tubiwash can be useful and valuable in PET recycling processes to fulfill also future requirements. www.cht.com The perfect combination for cleaning PET flakes - Sustainable and efficient process aids for PET bottle and tray recycling Cleaning additive and alkali CHT Group has supported the mechanical PET recycling process worldwide by focusing on efficient auxiliaries for quality improvements and process optimisations. As the actual recycling market is changing, the requirements on the cleaning process are also becoming different. Fig 3: PET flakes after roasting (220 °C, 30min) cleaned with NaOH (left) / NaOH + Tubiwash (right) Besides the rising demand for high quality recycled material, the increas- ing deterioration of input material (more non-food) quality requires an efficient cleaning that meets the high- est quality demands. The cleaning is usually done with an alkaline liquor, based on caustic soda and a cleaning additive. What are the different roles of the liquor components and why the usage of a cleaning additive is abso- lutely worthwhile? Improvement of the recyclate quality Adhesive removal The adhesive removal can be an important factor in recycling pro- cess, depending on the input material. Therefore a high cleaning temperature (70-90°C) as well as alkaline salts and cleaning additives are used to remove the melt adhesives. The amount of alkali is limited because of a reduced friction among each flake resulting in a decreasing adhesive removal (fig. 1). The cleaning additive from Tubiwash range however increases the adhesive removal (fig. 2). Removing of organic substances Depending on the input mate- rial PET bottles and trays can con- tain oily and fatty substances. Alkalis degrade the native oils and fats into smaller molecules (alkaline hydrolyses / saponification). The cleaning addi- tive Tubiwash removes them from the recyclate surface and emulsifies the molecules. Thus the emulsified organic substances cannot deposit on the PET flakes or the machine anymore. Improvement of flakes appearance Remaining substances on PET flakes often become yellowish after a thermal treatment (i.e. extrusion). Therefore removing soilings as well as taking away adhesives and organic substances are the main goals of the aqueous cleaning stage. Due to alkali the PET surface becomes consider- ably rougher (saponification) which supports the cleaning. On the other hand high amounts of alkali in combi- nation with high treatment times and high temperatures cause a reduced brightness of the flakes. Oxygen and Fig 1: Dependency of adhesive removal on alkali and cleaning additive Fig. 2: Flakes incl. adhesive A cleaned at 70 °C with H 2 O / NaOH (25mS/cm) / NaOH + Tubiwash (right) Recycling Special