MATERIALS / RECYCLING PETplanet Insider Vol. 24 No. 01+02/23 www.petpla.net 24 During Holland Colours interviews both the converters and brand owners seem to agree that a yellowish off-colour is not accepted by the average consumer because it is associated with spoilt product. Other aspects related to rPET quality are Intrinsic Viscosity (IV), absence of black spots and haze. Different solutions to retain rPET value It is a given that high quality, transparent rPET is scarce and prohibitively expensive to come by. There are several options being worked on to address the problem of limited availability of high quality rPET. Most of these are clearly described in the Design for Recycling Guidelines by the various recycling platforms and associations. A solution that has already been implemented on a wide scale is to use completely clear packaging. Eliminating colour in packaging will ensure that the value is retained. Reason being that packaging materials are predominantly separated in two recycling streams, i.e. clear and coloured. Mixing and reprocessing various colours, even transparent versions, results in a lower quality output. As stated before the discolouration of clear rPET is due to multiple heat cycles in combination with residual component traces. Another solution has been to use closed loops in the recycling process. For example, large brand owners own a stake in deposit return systems for PET bottles. This helps to ensure the quality of the PET bottles being collected and it allows them to standardise a significant portion of the PET collected for the recycling. This can help in some ways, but inevitably, after multiple heat cycles the same undesirable discolouration issues might arise. A technical solution to the undesirable yellowish discolouration is colour neutralisation. Using opposite colourants allows for a wider colour range of rPET to be used, which of course means that while the total amount of rPET stays the same, more of the available rPET can now be utilised. How does colour neutralisation work? What are the different product forms and what are their pros and cons? An undesirable colour cast can be neutralised by means of adding an opposite colourant in the melt processing step, among others the extrusion and injection moulding process. The melt processing step could take place at a recycling facility but also at a (packaging) converter. By addition of the right amount of opposite colourant the rPET will be as close to virgin PET as possible from a colouristic point of view. However, depending on the starting value of the input material, the L-value will always be affected. Monochromatic colour wheel The different forms These concentrates are available in various product forms, depending on the type of carrier used, liquid or solid. A liquid concentrate allows for a low dosing rate also called let down rate (LDR). It’s easy to control and dispersed effectively in the target plastic. However it might have some stability issues with functional colourants or additives settling out. Furthermore some housekeeping challenges might occur when spilled. A solid concentrate or masterbatch might be based on a wax or polymer and allows for cleaner and easier handling and depending on the type of carrier material either disperses very easily or requires somewhat more melt mixing shear. The colourant, carrier material and LDR of a formulation can be tailored to specific needs. Seeing as there is a trend towards 100% rPET, a wax based solid masterbatch might be preferred. From a sustainability perspective, a nonpetroleum, non-food source based wax based solid masterbatch is an option which helps in the goal towards 100% rPET. Also regulatory requirements in relation to the end-use have to be considered in the composition of the concentrate or masterbatch. The optimal specific product form depends on several factors like the needs and production setup. www.hollandcolours.com “Opposite colourants used for optimising rPET colour are preferably pre-dispersed and encapsulated in a carrier material resulting in a concentrate or masterbatch allowing for economical and effi cient dosing and dispersion in the fi nal product. This solution off ers enormous fl exibility and can help create a reliable and consistent stream of high quality rPET that matches customer needs. These solutions are paramount in order to meet global sustainability needs.” Raymond Jongman, EMEIA Sales Manager, Holland Colours
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