PETpla.net Insider 06+07 / 2014

MATERIAL / RECYCLING 27 PET planet insider Vol. 15 No. 06+07/14 www.petpla.net 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 Cielab. An additional aim is to influence and balance the level of grey (L value) and green, so to improve the value “a” coordinates Cielab. The key to obtaining successful for- mulations 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 production of rPET chips. A further issue is how not to inter- fere and modify process parameters while working, even with high vacuum levels. The anti-yellow additives line has seen its number of formulations approved and used in all injection and extrusion processes and in the various PET recycling technologies, where a number of issues related to the vacuum and the sensitivity of the filtration and cleaning 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%. The active collaboration with leading equipment manufacturers and end users allow Repi to play an important role glob- ally in this specific field. To illustrate the behaviour of the company’s anti- yellow additives, graphs 1 and 2 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 reac- tion takes place, the chain extender is physically bonded into the main PET backbone. The reaction can continue to 100%, according to the temperature and the residence time available and the chain extender cannot be released from the polymer. The link estab- lished between the PET and the chain extender is stronger than the ester bond and is not subject to further hydrolytic scission. 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 preforms, this additive helps to improve the physical and mechanical character- istics of the final product. In PET sheet extrusion, it enables a better thickness distribution, as well as an optimisation of the process para- meters (pressure in the melting pump increases significantly). Calenders will get less dirty, substantially reducing the need for cleaning. Graph 3 shows the improved mechanical properties achieved by using the additive in the production of PET bottles. Graph 4 shows time saving in reaching even a better IV level in the SSP process. www.repi.com Graph 1: Remap AY performance on PET sheets Graph 2: Remap AY performance on rPET chips in a standard PET recycling process Graph 3: Top load results on the same shape of bottle with and without Remap IVE Graph 4: Time vs. IV (dl/g) in a standard SSP process with and without Remap IVE