Additives and colour management solutions for recycled polymers
based on an article by Lucia Buffoni, Marketing Manager Repi Group
At the NPE, Repi showcased their latest advancements in additives and colour management solutions tailored for thermoplastic polymers. Their range of additives, which facilitate the inclusion of increasing percentages of recycled polymers in final products, garnered substantial interest.
The portfolio includes aesthetics additives that correct off-shade raw materials such as toners, anti-oxidants or heat stabilisers, as well as performance aids such as intrinsic viscosity enhancers that make the recycled material mechanically valid for its purpose.
The company says that their anti yellow, optical brighteners and IV enhancers have represented over the years a valid aid to rPET recyclers and packaging converters. Such additives can be used at different stages of the rPET value chain, e.g., from recycling up to preform or tray manufacturing with no impact on processes, thus offering maximum flexibility even when there are variations in batches. The increasing demand for recycled percentages and the scarcity of food grade rPET flakes are presenting challenges related to quality and colour consistency between one batch and another. What both recyclers and converters particularly struggle to manage is the drop of L* of CieLab numbers while respectively recycling and moulding or extruding the final packaging.
While it is possible to correct off-shade rPET pellets with custom-made formulations that act both on the a* and on the b*, the darkening of material (precisely the drop of L*) is very difficult to avoid.
To address this, Repi introduced StabiPlus, a liquid additive that acts as a proactive stabiliser to prevent ageing and discolouration of rPET through multiple cycles. This additive can be used both at the recycling stage and directly by converters during packaging production. StabiPlus is claimed to preserve the intrinsic viscosity (IV) of rPET, maintaining its mechanical properties and broadening the sustainable use window of rPET.
Repi also showcased its IV enhancers, linear chain extenders that prevent cross-linking and increase rPET IV by over 0.05 dl/g. This enhancement is claimed to improve the top load performance of rPET bottles, making them comparable to those made from virgin PET.
Colour management system
A highlight of Repi’s participation at the show was the introduction of their colour management system (CMS), developed in collaboration with Krauss Maffei. The CMS, integral to Repi’s core business of liquid colours and additives for thermoplastic polymers, is claimed to meet the growing need for control and correction in processes using recycled polymers. It has shown good results in PET and rPET sheet extrusion processes, where it monitors colour consistency and provides feedback to dosing units. The system offers remote control capabilities for immediate intervention by Repi’s technical engineers, working in both transmission and reflection modes to handle coloured and transparent sheets with transparent additives.
The colour management system
In a live simulation at the show, virgin PP transparent preforms were injection moulded. These were then sent to a shredder, directly connected to an extruder producing rPP granules that were coloured blue by three Repi dosing units. The blue granules were conveyed to an injection moulding machine producing bottle openers, made of 100% recycled plastics.
In order to better simulate a real recycling closed loop, where the incoming material is often uneven in shade, a fourth Repi dosing unit was used to inject a “disturbing colour” into the extruder. The CMS worked to neutralise the off shade by varying the dosing of the three basic colours. This was possible thanks to a spectrophotometer that after reading the Lab* values of the resulting granules sent the correct input values to the three operating units that adjusted the dosage to the set tolerances.
