PETpla.net Insider 06 / 2016

MATERIAL / RECYCLING 17 PET planet insider Vol. 17 No. 06/16 www.petpla.net Aesthetics and performance through Advanced Additives Revaluation to recycled PET The use of recycled material in PET preform and sheet pro- duction is growing rapidly and gaining an ever larger market share. The aesthetic features of the final product, which can be liable to degrade using rPET, often do not satisfy cus- tomer specifications. Recycled PET is generally character- ised by a yellowish shade and a lower and irregular Intrinsic Viscosity, which influences the mechanical properties of the final package. Cielab. An additional aim is to influ- ence and balance the level of grey (L value) and green, so to improve the value “a” coordinates Cielab. The key to obtaining success- ful formulations of Anti Yellow is the extensive knowhow on the different processes involved. These differ in the case of the injection of preforms, the extrusion of sheets, and the produc- tion of rPET chips). A further issue is how not to interfere and modify pro- cess parameters while working, even with high vacuum levels. The Anti Yellow additives line developed by Repi has seen its number of formula- tions approved and used not only in all injection and extrusion processes, but also in the various PET recycling technologies, where a number of issues related to the vacuum and the sensitivity of the filtration and clean- ing, require special attention. The very low addition rates in use have also required the optimisation of the dosing systems: Repi claims that their dosing units on the market today can guarantee a constant dosage to an accuracy of 0.004%. To illustrate the behaviour of the company’s Anti Yellow additives, the graphs show lab values on two main applications, PET sheet and rPET resin. High performance additives Among the high performing addi- tives by Repi, an interesting role is also played by the “no cross link” Intrinsic Viscosity Enhancer (IVE), added during the processing in order to improve the molecular weight (MW) and the mechanical properties. After the reaction takes place, the chain extender is physically bonded into the main PET backbone. The reac- tion can continue to 100%, according to the temperature and the residence time available and the chain extender cannot be released from the poly- mer. The link established between the PET and the chain extender is stronger than the ester bond and is not subject to further hydrolytic scis- sion. The molecular weight (MW) and the mechanical properties increase accordingly. The chain linearity reduces the risk of creating gels. In the production of rPET resin and pre- forms, this additive helps to improve the physical and mechanical charac- teristics of the final product. In PET sheet extrusion, it enables a better thickness distribution, as well as an optimisation of the process param- eters (pressure in the melting pump increases significantly). Calenders will get less dirty, substantially reducing the need for cleaning. www.repi.com Special additives are required in PET performs, in the production of rPET resin as well as in the extrusion of PET sheets. Repi, global supplier of high performing liquid colours and special additives began working on rPET in 2007. The result has been a series of advanced additives able to correct the shade and to improve IV parameters of rPET, whatever the end-product is. Today a variety of innovative solutions is undergoing constant improvement for each specific family of products made from rPET. This is in parallel with the on-going develop- ments in recycling technologies and the introduction of different grades of rPET, whose use is growing, in percentage terms, relative to the total quantity of resin. The principal rea- sons are firstly to improve the aes- thetics and secondly to increase the performance of the final product, be it for PET preforms, PET sheet or rPET resin. Anti Yellow additives Repi‘s Anti Yellow additives are formulated so to be able to modify the main required parameter, namely to correct the yellowish shade with an action on the value of “b” coordinates RECYCLING S P E C I A L Effect of Remap AY on rPET chips 100% 50% 0% -50% -100% REMAP AY@0,03% none REMAP AY 00015@0,03% Performance PET sheets db dL da REMAP AY @0,005% none REMAP AY 00090@0,005% Performance on R-PET resin 100% 50% 0% -50% -100% dL da db