PETpla.net Insider 09 / 2019

MATERIALS / RECYCLING PET planet Insider Vol. 19 No. 09/19 www.petpla.net 39 Consistent preform wall thicknesses for large-volume containers Optimising with nanoparticles by Gabriele Kosmehl In a joint project, the Institut für Kunststofftechnik (IKT) in Stuttgart, Germany, Fricke und Mallah Microwave Technology GmbH and Spritzguß Müller GmbH are researching the manufacturing of plastic containers with volumes greater than 30 l in stretch blow moulding procedures. PETplanet talked to Head of the IKT Institut für Kunststofftechnik, Prof. Christian Bonten and his academic co-worker in processing technology, Ms Laura Klis, MSc, about the results that they are hoping for from nanoscale fillers as regards improved wall thickness homogeneity of the parts due to an adjusted warming process using microwave radiation. The objective of a new project by the IKT and two partner companies is to design thick-walled preforms in such a way that, from the very start, consistent heating takes place before the stretch blowing process and a consistent result can be generated. “In the stretch blowing process for large-volume containers, even greater challenges must be overcome that relate to the warming process with infrared (IR) emitters,” explains Laura Klis. “Preforms with inconsistent wall thicknesses sometimes aren´t heated homogeneously by IR radiation. This might cause a polymer film tear in the tool or poor mechanical properties of the end product.” Therefore, Head of Institute Prof. Bonten’s team is working on opti- mising the materials and is planning to compound special fillers into the plastic before using it in the injection moulding process. By means of the special and well distributed fillers, the preforms are warmed, not using tradi- tional IR but microwave energy. “The fillers work as small hot spots in the material and allow for a homog- enous warming,” explains Klis. During the research project, which is scheduled to last three years, dif- ferent materials are to be tested with different filler types and filler contents. Besides PET with and without a pro- portion of rPET, bio-based and biode- gradable plastics like PLA will also be used. As the compounds need to be well suited for warming with semicon- ductor-based microwave techniques, the decision was made to use carbon- based fillers. “Carbon nanotubes or graphene are very small and – if well distributed - have a great surface to volume relation, ,” says Prof. Bonten. “Precisely in relation to PET, this offers the advantage that they can also be used even in transparent containers.” Good results are expected even from a filler content of around two per- cent by weight. “We will certainly also be testing less expensive fillers such as magnetite or carbon black, which might allow costwise to use even ten percent by weight. Perhaps we may also be able to generate the best results with particle mixes – ultimately, we will find it out in large-scale tests,” says Klis confidently. Expertise in tool construction and injection moulding comes from Spritzguß Müller GmbH. There, work is currently in progress on the construc- tion of an injection moulding tool and ultimately, the optimised preforms will also be stretch blow moulded there. An (optical) retail-typical microwave is used as a cavity for microwave irradiation. Project partner Fricke und Mallah Microwave Technology GmbH is con- tributing to the innovative microwave source. Their technology enables to generate microwave radiation no longer by magnetrons, but by semi- conductors. Hence, scientists at IKT are expecting a higher effieciency in heat input, better controllability, and focussing of the heat sources, which is supposed to result in a more homogenous warming than in the IR procedure. The extent to which micro- waves will lead to shorter heating times compared to IR and therefore to gains in energy efficiency could be a welcome additional finding of the project. www.ikt.uni-stuttgart.de MATERIALS The semi-conductor-based microwave radiation is generated by a generator.