D3.5: Monomaterial Packaging Design

This report is prepared in alignment with EU STOPP deliverable D3.5, Monomaterial packaging development to facilitate recyclability of flexible plastic food packaging. Flexible films have a major share in food packaging industry for safety and shelf life. The EU Packaging and Packaging Waste Regulation (PPWR) mandates all packaging to be recyclable by 2030. The state-of-the-art multifunctional films such as Polyethylene Terephthalate – Polyethylene – Polypropylene (PET-PE, PET-PP) impose various sorting and recycling challenges. PP offers good physical and aesthetic properties, outstanding barrier for water vapour but limited Oxygen barrier which is critical for food shelf life. The PPWR and supporting design for recycling (DfR) standard EN 18120-7 (CEN-2026) enforce all flexible PP-PE as monomaterial without Oxygen barrier PET layer in the material composition. The RecyClass protocol on Recyclability Evaluation defines PP monomaterial films to be 90% composed of PP with maximum thickness of 250 µm. The EN 18120-7 guidelines prohibit use of barrier coating such as aluminium foil. Additives which do not impede recycling and reuse can be compounded with PP at weight percentage less than 7.5. These include for instance aluminium and silicon oxides AlOx , SiOx, and Ethylene Vinyl Alcohol (EVOH). The research objective is to improve the Oxygen barrier level of monomaterial PP films based on film thickness enhancement, modulating cast film and biaxial stretching parameter, and additives. The methodology is based on full factorial design and Pearson correlation to systematically investigate distinct and synergetic sensitivity of BOPP processing parameters to barrier properties. The optimum BOPP barrier performance is realised in 40-50 µm thickness range with further 50% increase 50% at 100-120 µm range beyond which there is no major improvement. The BOPP crystallinity and barrier properties is highly sensitive and dependant on synergetic effect of stretch ratio and processing history controlled by chill roll temperature. Regression fitting between transmission rate and inverse film thickness at distinct chill roll temperatures is provided to predict permeation of BOPP produced with over 30 processing scenarios. This shows dominant role of BOPP film thickness and crystallinity in Swiss partner funded by Funded by the European Union. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or REA. Neither the European Union nor REA can be held responsible for them. Oxygen transmission rate. The addition of nucleating agents promotes BOPP crystallinity and barrier performance by 6-8% and up to 8-10% by further thermal annealing for 10 seconds at 20-40 °C bellow polymer peak melting temperature. Simultaneous addition of nucleating agent and plate-like talc at 4 wt% improves the BOPP Oxygen barrier by 14.5%. Addition of ethylene elastomeric impact modifiers can supress film crystallinity and barrier properties up to 10% and therefore it is not preferred. Overall, this research shows that Oxygen permeability of BOPP films can be reduced to 25.9 ± 1.2 (cc.mm/m2.day) and Oxygen transmission rate of 319 ± 12 (cc/m2.day) by modulating processing parameters and additives used here. The realised Oxygen barrier performance of BOPP is 80% better than commercial coextruded PP-PE films and 80% lower than PET-PE commercial multilayer film used for e.g., fresh salads. It is foreseen that insights and systematic results reported here on sensitivity of BOPP processing scenarios on barrier properties and optimum design window will enhance the technology readiness level (TRL) of monomaterial from two to four. The data can be valuable for both biaxial stretching and blow moulding processes. Furthe research is needed on compounding different grades of the same base polymer and continuous barrier layer such EVOH. Swiss partner funded by Funded by the European Union. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or REA. Neither the European Union nor REA can be held responsible for them.