Films | Flexibles | Bags
Films | Flexibles | Bags Article contributed by Dr. Christian Bonten and Patrick Zimmermann, FKuR Kunststoff GmbH, Willich, Germany New Bioplastics For Multilayer Systems Advantages of multilayer systems Approximately one third of worldwide plastics production is used for the production of film, making film extrusion one of the most important processing procedures for plastics. The requirements placed on plastic films, especially those used predominantly in food packaging, have been constantly rising over recent years and have now reached a level that can only be achieved by means of a variety of procedures. Fig. 1.: Three layer film tool Source: Burmann, G.; Wortberg, J. „Grundlagen und Strategie für die Auslegung von Extrusionswerkzeugen“ - an IKV seminar on the basics and techniques of tool design Fig. 2: Bioplastic Bio-Flex F 2110 used, for example, in deep freeze packaging Whilst in the beginning three-layer systems, and later on fivelayer systems, were sufficient (fig. 1) to meet the specific criteria of the packaging task, nowadays films with seven or even nine layers are needed. Only with this multiple layer matrix is it possible to guarantee all of the desired features, such as protection against sunlight and oxygen, preservation of flavour and aroma, effective barrier properties, and also sealability and printability. The demand for bioplastics is continuously rising! Growth over the last few years has clearly been due to the demand for bioplastics to be used for packaging goods with a short shelf-life (e. g. food packaging, waste bags, diaper backing sheets, and also mulch film etc.). Here the biodegradability and the associated alternative disposal route are especially beneficial for the consumer. The content of material from renewable resources is increasingly coming to the fore as a selling point. Bioplastics – the challenge is processing on conventional machinery Hitherto existing biofilms have been produced mainly as monolayer films, since until recently it was assumed that bioplastics could not be used for multilayer systems because of their limited processibility. In cooperation with the Fraunhofer UMSICHT Institute, FKuR Kunststoff GmbH has developed a wide range of biodegradable plastics primarily made from renewable raw materials and which enable straightforward processing on conventional extrusion lines without any kind of additional additives. Many of the bio raw materials used nowadays (PLA, cellulose actetate, starch, PHA, etc.) only partially meet the processability requirements: they are not ready made for the conversion process. By manufacturing bio-compounds it is possible to optimise the processability, the mechanical characteristics and the barrier properties of these bio raw materials. This processing of biodegradable raw materials requires special knowledge of both the selection of additives and a smooth compounding process. Multilayer films made from bioplastics can significantly expand the range of applications for the bio-compounds; e. g. by developing a combination in order to optimise the barrier properties as well as the mechanical characteristics. 16 bioplastics MAGAZINE [06/08] Vol. 3
Films | Flexibles | Bags Based on the pressure to optimise the use of bio raw materials FKuR has developed different bio-compounds with the brand name Bio-Flex ® , which can be converted to blown film. • Bio-Flex F 1130 is particularly elastic and ductile. This product is predominantly used for the production of mulch film, T-shirt bags and waste bags. The product is comparable to LDPE. • Bio-Flex F 2110 is a more rigid, but very low temperature impact resistant, and with a translucent quality. It is used, for example, in deep freeze packaging (fig. 2), bags, air pillows, and is especially useful in co-extrusion. With regard to the mechanical characteristics it is very much comparable to HDPE. • Bio-Flex VA 4100 CL represents a speciality amongst bioplastics. It is the first transparent PLA blend which can be converted to an excellent blown film. In addition its content of material from renewable resources is outstandingly high and the film is especially transparent. (fig. 3). Bio-Flex VA 4100 CL is a rather rigid film and the mechanical characteristics are comparable to those of PP. This material is often used in packaging of fruit, vegetables and flowers, as well as in co-extrusion. An obvious advantage of the Bio-Flex range is the excellent compatibility of the different types. This is at the same time a precondition for an outstandingly adherent multilayer system that combines the different advantages required in a semifinished film product. The entire multilayer system made from Bio-Flex is, of course, biodegradable. Multilayer systems now also possible with bioplastics The following three practical examples will clarify the expansion of the range of applications for bioplastics by means of skilled utilisation in multilayer systems: • The three layer combination made from Bio-Flex VA 4100 CL / Bio-Flex F 2110 / Bio-Flex VA 4100 CL in a layer ratio of 30/40/30 allows for the production of a very tough film with high tear resistance and good barrier properties for a bioplastic. • A three layer system made from Bio-Flex F 1130 / Bio-Flex F 2110 / Bio-Flex F 1130 allows for a very flexible and tough film with very good bubble stability. It is also possible to process the film at high throughputs of about 350 kg/h and attain film thicknesses of 8 µm, the film is perfectly suitable for the production of T-shirt bags and waste bags. • It is likewise possible to produce films with a good oxygen barrier. Merely as example we state here a five layer system, made from Bio-Flex VA 4100 CL / tie layer / X / tie layer/ Bio-Flex VA 4100 CL. Bioplastics are technically mature and do not represent an obstacle in the conversion process! The processing of multilayer films using bioplastics from FKuR offers new application possibilities! Vapour [g/(m² • d)] Elongation at break [%] www.fkur.de 350 300 250 200 150 100 50 0,0 PLA EVAP Multilayer Film including Bio-Flex ® VA 4100 CL Bio-Flex ® VA 4100 CL 250 500 550 600 2500 3000 3500 Oxygen [cm³/(m² • d • bar)] Testing conditions: H 2 O: 23°C/ 85% r.F. O 2 : 23°C / 50% r.F. Fig. 4: Barrier data of a five-layer system with Bio-Flex VA 4100 CL in comparison with pure PLA and pure Bio-Flex VA 4100 CL. 700 600 500 400 300 200 100 0,0 Fig. 3: Bioplastic Bio-Flex VA 4100 CL with high transparency EVAP Multilayer including Bio-Flex ® VA 4100 CL Bio-Flex® VA 4100 CL 500 1000 1500 2000 2500 3000 3500 Tensile Modulus [MPa] PLA Fig. 5: Mechanical characteristics of a five-layer system with Bio-Flex VA 4100 CL in comparison with pure PLA and pure Bio-Flex VA 4100 CL. bioplastics MAGAZINE [06/08] Vol. 3 17
