Processing PLA –
Processing PLA – Environmental protection is getting more and more important, at the same time crude oil prices are highly volatile and raw material costs are as high as never before. Therefore, the future of packaging materials relies on environmentally friendly resources. Sample applications for cast PLA film (all packaging pictures: Natureworks) Article contributed by Volker Siebott, Brückner Formtec, Siegsdorf, Germany PLA Casting Unit with Pinning Technology (photo: Brückner) As there are a couple of biodegradable materials like Cellophane, Cellulose Acetate, starch based PVOH and PHB/PHA, PLA (Poly Lactic Acid) is the most cost competitive material to be used in commodity applications. PLA is made from annually renewable resources, preferably corn, and 100% biodegradable. It offers best material properties, that are comparable to PET and better than PS and thus is perfectly suitable to replace these materials in a wide range of applications. Outstanding properties like high stiffness and tensile strength and even higher transparency and exceptional surface gloss (haze less than 5 %) as well as good chemical resistance against greases, fats and oils are arguments for the market success of PLA. Excellent barrier properties, especially of aroma and flavour, the high water vapour transmission rate (WVTR) as well as FDA approval for food contact make it perfectly suitable for packaging of organically grown „green“ foodstuff and thus provide good shelf impact, while demonstrating environment responsibility when disposing. Regarding converting features it can be said that it is fully thermoformable with existing equipment, provides low sealing temperature and high seal strength and can be thermolaminated to paper or cardboard. Furthermore it offers an inherent dyne level of 38 and thus is easily printable and offers good lay flat properties. As economical reasons the independency of crude oil prices and the ability to reduce material consumption by down-gauging due to the high stiffness can be named. But also marketing reasons like the growing environmental awareness and the trend towards „green“ food (bio-food in biopackaging) as well as governmental subsidies will heat up the demand and need for rigid PLA packaging. Natureworks LLC is the world leader in producing such materials with an annual production capacity of 140,000 tons of Poly Lactic Acid per annum, and plans to further extend this production capacity to 210,000 tons. Brückner Formtec GmbH from 28 bioplastics MAGAZINE [01/07] Vol. 2
Processing The Future of Rigid Packaging? Brückner Formtec develops line concept tailored to PLA Siegsdorf, Germany, has developed a process to produce PLA film and sheet in a very cost effective way. This technology has been presented to public for the first time on the 3rd CEE Film and Sheet conference in Budapest, Hungary in April 2006. Processing of PLA sheet and film The main requirements for the new process were best product properties and, at the same time low production costs. The best way to cut production costs per unit is to increase productivity through higher output volume and higher line speed. Due to process limitations, the regular calandering process is only capable of a maximum diameter of about 800 mm for the first cooling roller and thus the cooling capacity is limited. Considering the state of the art roll stack widths and speeds, result in a maximum output of around 900 kg/h. The reason for such a low output is to be found in the very low heat transfer coefficient of PLA and the tendency of PLA to stick at the polishing roller. These reasons limit the production speed even further. Due to the vast experience in biaxial orienting technology and excellent results in producing such biaxially oriented PLA (BOPLA) films on the Brückner Group laboratory line, Brückner Formtec decided to go for the proven and reliable cast film technology with pinning as the basis to develop a new concept. Furthermore Bückner’s engineers took a closer look at the material and found out that the overall energy consumption can be reduced drastically by using a twin screw extruder, avoiding the slow and energy intensive predrying of the hygroscopic raw material. A further benefit of the twin screw technology is that problems with sticky regrind are omitted and the equipment for predrying and crystallizing is not necessary. To avoid degradation due to long residence time and high shearing, Brückner developed a new, shorter extruder with special, smooth screw design. Compared to other materials, PLA can be processed at a temperature of 220°C. Brückner Formtec expects a rapid growth of PLA applications in rigid packaging. Especially in the area of disposable convenience packaging for fresh food with a short shelf life significant growth rates are expected. A further argument for the use in agricultural packaging is that the high stiffness suggests freshness. Furthermore packaging of bread and other bakery goods that are packed warm are promising due to the antifog properties of PLA. In the area of cheese and salami packaging, PLA enables riping and thus enhances shelf life. Brückner Formtec PLA Cast lines key features: • Twin screw extrusion for highest efficiency • High efficiency cast film technology • Output up to 2,000 kg/h, speed up to 75 m/min. • Thickness range from 250 µm up to 1,200 µm • Proven pinning technology • Unchallenged cost per unit Brückner Formtec, member of the German Brückner Group, was founded in 2001 and is a global supplier of flat film extrusion systems. The range of machinery covers cast film and sheet extrusion, focussing on the rapidly growing CPP, LLDPE and PET markets. Twin screw technology is an important feature for PET extrusion, eliminating the need for raw material pre-drying. www.brueckner.com Twinscrew (photo: Brückner) bioplastics MAGAZINE [01/07] Vol. 2 29
