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01 | 2008

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Foam PLA foams for

Foam PLA foams for packaging applications Article contributed by Cesare Vannini, Packaging System R&D Coopbox Europe SpA, Reggio Emilia, Italy Foams are very common material structures. Wood has a foam structure, bones are also foams, bread is a foam, and many other natural materials are foams. Why? The reason is clear: a foam is a simple way to obtain a structure with good mechanical properties and low weight. The prime property of foam is weight reduction. This characteristic is very important in packaging applications where foams are used to produce trays, cups, containers, boxes, etc. In all of these products the weight reduction is between 30 and 50% compared with alternative rigid materials. Many retailers have stated their intention to reduce the total amount of packaging used in their stores, and so a foam seems the right solution for rigid food packaging applications, independently of the plastic material selected. Coopbox is a major producer of foam food packaging, and has developed this activity within the growing retail industry as a privileged partner at national and European level for the production of polystyrene trays. Today Coopbox, by focusing on the clients‘ needs and on service and product innovation, has developed a deep understanding of fresh food packaging systems with different materials: PS, PET, and recently PLA. Each of these different polymers permits us to produce packaging systems with specific characteristics: • NATURALBOX ® with PLA: packaging systems using only renewable resource that comply with European standard EN13432 for compostable packaging. • DRYMAX ® PS: an open cell foam structure for absorbing liquid in fresh meat and fish packaging • AERPACK ® PS: foam barrier trays for fresh meat and fish • DOT ® : crystallised PET foam for heat resistant containers in ready meals packaging All of these different materials are processed on a tandem extruder using different physical foaming gases such as nitrogen or butane, depending on the required behaviour of the final package. Specific tooling design and modifications are necessary, especially for low melt strength materials such as PET or PLA where the semicrystalline properties require perfect temperature control to avoid the formation of gels during the extrusion process. 14 bioplastics MAGAZINE [01/08] Vol. 3

Foam An interesting additional performance characteristic of ‘open-cell‘ foamed trays is the possibility to absorb liquids. The open-cell structure allows the foam to absorb the liquids released by certain foods such as meat or fish, thus maintaining the pack in a clean condition and increasing the aesthetics and freshness of the food. This innovation, introduced at the beginning of the 1990s, completely changed fresh meat packaging because a tray with absorbent properties avoids the use of traditional absorption pads. Coopbox is working to improve the performance of the Naturalbox PLA tray to obtain an absorption performance comparable with traditional XPS absorbent trays. The barrier properties of PLA are somewhere between PET and PP, two of the standard materials used to pack fresh meat in a protective atmosphere. The most recent innovation from Coopbox is foamed Naturalbox PLA trays, top-sealed with PLA-film. This is another example of the successful application of biodegradable materials for fresh meat packaging in a protective atmosphere. Naturalbox trays are made of foamed Nature- Works ® PLA, laminated with PLA film to guarantee airtight sealing. The top film is standard PLA, or is coated with SiOx to guarantee a better barrier performance. The complete packaging system is perfectly water and humidity resistant, with good mechanical properties. The top film is highly transparent and (unless coated with SiOx) offers natural antifog properties. If the packaged meat has a significant drip loss a biodegradable absorbent pad can be placed inside the trays to absorb the liquid that is released and maintain the pack in a clean condition. www.coopbox.it bioplastics MAGAZINE [01/08] Vol. 3 15

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