MATERIALS | THERMOFORMING
made of HIPS. Thermoformed cups showed no reduction in performance – and actually had several benefits compared to a PS cup, such as a higher top load, better haze and gloss, easier recyclability and 38% less weight. This helped to halve CO2 emissions, while saving around one- third on material costs per year. In a second trial – to replace PET – a similar sheet was compared with 0.4mm thick transparent A-PET sheet. Thermoformed cups had a 30% higher top load, slightly better haze and gloss, superior barrier properties and 38% less weight – with lower density. This helped to cut CO2 emissions by 55%, while saving around 8% on material costs per year. “This shows it is possible to convert to PP without changing machinery – and meeting brands’ sustainability targets,” said the presenters.
Foamed future Gabriella Sartori, marketing manager at Lyondell- Basell, presented details of the company’s new Moplen EP490H – a new PP grade for extruded foamed sheet. The heterophasic copolymer is designed specifically for foam applications. It is produced with a non-phthalate catalyst and is free of plasticis- ers and BPA. A complete foaming solution is available in combination with its Polybatch chemi- cal blowing agent masterbatches. Benefits include: high melt strength, for good foamability; good processability – with no gels; and high impact resistance for optimal food preservation. “Moplen EP490H has a high melt strength that enables the formation of a fine and uniformly dispersed cell structure,” she said. She claimed that the material has a lower density and higher foamability than “any conven- tional PP”. The process, using an annular die and physical foaming, claims to produce sheet with a density of 200 kg/m3
physical foaming (450 kg/m3
– compared with flat die/ ) and flat die/
chemical foaming (550 kg/m3
).
The subsequent thermoformed sheet can be used to make lightweight final products, she added. Other benefits include increased impact resist- ance and good dimensional stability, enhanced aesthetics (smooth surface) and easy recyclability. “The PP trays can be combined with PP lids of film for a monomaterial packaging design,” she said. “The typical chemical and temperature resistance of PP makes it suitable for washing systems.”
Light PET Delegates at an earlier Thin Wall Packaging event – held in the US – also heard of innovations in both polyester and PP. In a joint presentation, Kiefel and SML presented details of how C-PET can be used to create thin-wall packaging. C-PET can be used to replace PS and PP in food
packaging, having a heat resistance of 180-230 C. In addition, C-PET light is heat-resistant up to 100 C and can be processed in a single step. It is trans- parent and uses a patented tool technology. The speakers cited a C-PET light cup, which could be made using recyclate. It is suitable for steam sterilisation. The fact it can be made in a single step helps to raise output. C-PET light sheets combine virgin PET, skeleton
regrind and rPET from bottle flakes – as well as a nucleation accelerator and a colour-correction pigment. Critical attributes for processing include its intrinsic viscosity (IV) and crystallisation speed. The material’s properties are determined by the production process: because it undergoes both strain- and temperature-induced crystallisation as it cools, this helps to raise its physical properties (such as heat resistance). This is achieved by close control of process conditions – which also lead to precise sheet thickness and uniformity. The companies carried out optimisation trials on
more than 30 different formulations, testing around 30 tonnes for A-PET and PCR.
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