Rigid Packaging PLA for
Rigid Packaging PLA for thermoforming More functionality by sustainable thermoforming films By Larissa Zirkel Huhtamaki Films Forchheim, Germany Fig. 1: Die-cutting test with Huhtamaki standard (right side, Q. 4007) and flexibilised (left side, Q. 4010) PLA grades Under the brand-name BioWare Huhtamaki offers a sustainable material concept, where all products are biodegradable, compostable and preferably bio-based, i.e. derived from renewable resources. Since 2004 Huhtamaki Films has been developing innovative PLA films for thermoforming purposes showing outstanding performance during processing and application. In general, the films have coextruded structures consisting of up to nine layers and are available in thicknesses between 180 and 800 µm. Rigid packaging Standard PLA thick films for thermoforming are highly transparent and glossy. They exhibit a high tear strength, which is comparable to that of PS. Due to its intrinsic high value of surface tension of 36 to 38 mN/m, PLA is easily printable. Moreover, trays from PLA show an excellent sealability at temperatures much lower than required to process common polymer materials. Besides, special combinations of different biodegradable polymers offer the opportunity to create packings with easy opening properties by introducing a peel layer to either the lid film or the tray. The very high oxygen and water vapour transmission rates often make an additional perforation step redundant as spare humidity from the product can easily evaporate through the PLA trays or lid films, thus, protecting e.g. food from moulding. As PLA has a very good flavour and aroma barrier, it is very qualified for packing food with a distinctive smell as e.g. cheese or goods, that require a protection of their specific aroma, like e.g. herbs. Furthermore, it could be shown, that the climatic conditions inside a PLA packaging due to the gas exchange from inside the package to the environment, related to its pronounced permeation ability, is beneficial for the maturing of cheese without influencing its unique taste. Another advantage of PLA trays for packing food is its high resistance to grease and oil. Flexibilised films Although the application of pure PLA is preferred in many cases due to its 100% origin from renewable resources, these standard grades exhibit some disadvantages in terms of their mechanical properties. Thus, pure PLA has a high rigidity, which causes e.g. splintering when the films are die-cut (cf. fig. 1, right side, grade 4007). Additionally, trays and blisters especially for packing food but also other goods in general have to withstand drop tests. When dropping a package from a shelf at the point of sale, it should neither break nor splinter for giving a good protection to the products inside. This kind of damage is usually observed when using a standard pure PLA. Therefore, the material has to be modified to obtain a certain 18 bioplastics MAGAZINE [02/12] Vol. 7
Rigid Packaging flexibility as it is known e.g. from the PET widely spread in this market. Adding special modifiers to PLA, which are also completely biodegradable, its mechanical properties can be improved to values close to the ones of PET (cf. fig. 2). Compared to standard PLA, the flexibilised version shows a significantly reduced elastic modulus in the range of PET and a relatively high impact strength, which could be increased to the 100-fold of the poor original value. These improved mechanical properties allow the PLA film to be diecut without splintering (cf. fig. 1, left side, grade 4010) and enable the trays and blisters produced thereof to withstand the required drop tests. As the flexibiliser is biodegradable, too, these modified films are certified according to the DIN EN 13432 for biodegradability. Apart from the mechanical properties, the modifier does not affect the unique characteristics of PLA like transparency, gloss, printability, sealability, and aroma barrier. As there is no migration of the flexibiliser used, Huhtamaki PLA films comply with the FDA and, therefore, are appropriate for packing all kind of food. By introducing different amounts of modifier to the PLA, the flexibilisation can be adjusted to the degree required by the specific application, enabling custommade solutions, which are offered by Huhtamaki in form of a wide variety of films. Golden PLA A very new product in the range of Huhtamaki BioWare films for thermoforming is a golden PLA developed for e.g. luxury packaging or the confectionary industry. First results of production trials were presented already at the Interpack 2011 and the ProSweets 2012, where they attracted a broad interest (cf. fig. 3). The golden trays from coloured and metalized PLA are also fully biodegradable and comply with the DIN EN 13432. Just like the transparent versions, Huhtamaki offers them with different degrees of flexibilisation to meet the specific application requirements. PLA standard | PLA flexibilised | PET 3500 350 3000 300 2500 250 2000 200 1500 150 1000 100 500 50 0 md td md td E-Modulus in MPa Impact Strength in kJ/m ≤ Fig. 2: Comparison of mechanical properties of Huhtamaki standard and flexibilised PLA films with PET Fig. 3: Golden trays for confectionary from Huhtamaki flexibilised PLA films; thermoformed by Falomo Termoplastici S.r.l., Italy 0 Barrier For some applications, mainly in the food packaging market, the high oxygen and water vapour transmission rates of PLA are of disadvantage. Especially the infiltration of oxygen into the package significantly reduces the shelf life of fresh products. The coextruded structure of Huhtamaki PLA films allows the introduction of additional functionalities as e.g. barrier properties. Figure 4 shows the oxygen bioplastics MAGAZINE [02/12] Vol. 7 19
