The Sustainability of Natureworks Polylactide Polymers and Ingeo
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Essay 551 The Sustainability of NatureWorksTM Polylactide Polymers and IngeoTM Polylactide Fibersa: an Update of the Future Initiated by the 1st International Conference on Bio-based Polymers (ICBP 2003), November 12–14 2003, Saitama, Japan Received on February 6, 2004; DOI: 10.1002/mabi.200400023 Keywords: biopolymers; PLA; polylactide; renewable resources; sustainability Introduction corn, wheat, sugar beets) and other grown biomass materials. It is in this new and renewed reality of renewable raw- Cargill Dow LLC produces a new packaging and fiber materials reliance that Cargill Dow LLC emerges. material – polylactide (PLA) – from annually renewable The objective of this paper is to answer the question: resources. The presence of the company and the PLA ‘‘What makes NatureWorksTM PLA a more sustainable polymer on the industrial scene signals the emergence of a polymer?’’ To answer this question the article addresses new model for industrial development in the twenty-first applications and marketing of PLA, costs, today’s and century. During the nineteenth century people relied pre- future renewable raw material resources, reduction of fossil dominantly on a wide range of natural materials, such as fuels and the associated emissions of green house gases, wood, hides, wool and starch, to provide the essentials of waste management options, and manufacturing processes. then-modern life. This picture changed significantly during the twentieth century, when people in developed countries experiencing the industrial revolution became almost totally dependent on fossil materials to produce the fuels, About Cargill Dow polymers and chemicals required for modern life. With exponential growth in the demand for fossil raw materials in Cargill Dow LLC is leading the world in its effort to convert, both developing and developed countries today, the ques- through the application of new science and technology, tion increasingly posed is how we will derive the materials annually renewable plant matter into a full range of useful we will need in the twenty-first century. An increasingly products such as food packaging materials, films and fibers. broad range of experts and analysts have concluded that Cargill Dow LLC was founded in 1997 as a joint venture new – or in some very important ways, ‘‘old’’ – raw mate- between Cargill Incorporated and The Dow Chemical rials will become the foundation of packaging materials and Company. It is a new business dedicated to building a plat- fibers in a world challenged by the interrelated problems of form of sustainable polymers and chemicals with compe- depletion of fossil resources and of proliferation of global titive performance and entirely made from annually climate changing emissions, pollutants and solid wastes. A renewable resources. The company’s efforts focus on using consensus remains that fossil resources will be required and and optimizing a combination of agriculture (crop grow- used for quite some time, but it is also hardly doubted that ing), biological processes (fermentation), and chemical maintaining and enhancing quality of life for a growing technologies (polymerization). Cargill Dow has its head- populationaroundtheglobe compelsthedevelopmentofnew quarters in Minneapolis, Minnesota, USA. It also operates technologies to produce packaging materials and fibers from offices in Naarden, The Netherlands, and Tokyo, Japan. new ‘‘old’’ resources like traditional agricultural crops (e.g., Today Cargill Dow is a stand-alone organization employing more than 250 people worldwide. To date, more than US$750 million has been invested in the development of the a NatureWorksTM and IngeoTM are trademarks of Cargill Dow technology, as well as in the construction and commission- LLC. ing of the world’s first commercial scale production facility Macromol. Biosci. 2004, 4, 551–564 DOI: 10.1002/mabi.200400023 ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 552 E. T. H. Vink et al. for a polymer with broad practical application derived the corn kernel (proteins, fats, fibers, sugars and water) and entirely from annually renewable resources. Squarely based converted via enzymatic hydrolysis into dextrose. Cargill on a foundation of research and development spanning Dow ferments dextrose into lactic acid at almost neutral pH. many years, Cargill Dow researchers are titled in hundreds Via acidulation and a series of purification steps, the lactate of patents worldwide. salt fermentation broth is then purified to yield lactic acid. Cargill Dow has increased its manufacturing capacity for Cargill Dow uses ring-opening polymerization through PLA polymer from 4 000 to 140 000 metric tons per year the lactide intermediate. In the first step of the process, with the completion of its Blair, Nebraska polylactide water is removed under mild conditions (and without the manufacturing facility. This facility began operating in use of a solvent) to produce a low-molecular-weight pre- November 2001, was producing prime material by the end polymer. This prepolymer is then catalytically depolymer- of December 2001 and had gone through a complete ized to form a cyclic intermediate dimer, referred to as product production cycle by February 2002. The associated lactide, which is then purified to polymer grade using lactic acid facility, with a capacity of 180,000 metric tons, is distillation. The purified lactide is polymerized in a solvent- located adjacent to the polymer facility and was started up free ring-opening polymerization and processed into PLA in October 2002. Both plants are situated near a corn wet pellets. By controlling the purity of the lactide it is possible mill where the starchy component of corn kernels is to produce a wide range of molecular weights. Because converted into dextrose that Cargill Dow uses as a raw there are four unique groups attached to the central carbon material for its lactic acid fermentation process. All these atom, lactic acid is a chiral molecule. Chiral molecules exist facilities are situated at one industrial ‘‘park’’ on the eastern as ‘mirror images’ or stereoisomers. The optically active edge of the state of Nebraska, one of the largest U.S. lactic acid has both left-handed (‘‘L’’ or ‘‘S’’) and right- producers of corn. The proximate location of the facilities handed (‘‘D’’ or ‘‘R’’) stereoisomers. Chemically synthe- and the production of corn make it possible to build a very sized lactic acid gives the racemic mixture (50% D and efficient integrated production operation. 50% L). Fermentation-derived lactic acid typically consists of99.5%ofthe L-isomerand0.5%ofthe D-isomer.Production of the cyclic lactide dimer results in three potential forms: the NatureWorksTM Polylactide Production Process D,D-lactide (called D-lactide), L,L-lactide (called L-Lactide) and L,D or D,L lactide called meso lactide. Meso lactide has Cargill Dow’s PLA is a versatile new compostable polymer different properties from D and L lactide. The D and L lactide that is made from 100% annually renewable resources. are optically active, but the meso is not. Before polymer- Today, the PLA life cycle starts with corn. The various steps ization, the lactide stream is split into a low D lactide in the production process, beginning with corn production stream and a high D/meso lactide stream. Ring-opening and culminating in the production of PLA, are illustrated in polymerization of the optically active types of lactide Figure 1. can yield a ‘family’ of polymers characterized by the The basic building blocks for the PLA polymer chain are molecular weight distribution and by the amount and carbon dioxide and water. Both components are formed into the sequence of the D-lactide in the polymer backbone. sugars through photosynthesis driven by solar energy and Polymers with high L-lactide levels can be used to produce occurring inside growing plants. Hundreds of years of crystalline polymers while the higher D-lactide materials hybridization and crop improvement have yielded modern are more amorphous. More details about the PLA varieties of corn that result in some 30% of the plant mass production process are given by Gruber[1] and Vink.[2] developing as sugars stored as starch in the kernels of the cob. After harvest, the corn is transported to a corn wet mill where the starch is separated from the other components of Today’s and Future Products from NatureWorksTM Polylactide NatureWorksTM Packaging NatureWorksTM PLA is the foundation of a new, versatile, bulk polymer family and can be used in a wide range of applications. An overview of Cargill Dow’s business segment opportunities and examples of commercially available products is provided in Table 1. Some specific final product examples merit further discussion, and are illustrated in Figure 2–4. Figure 2 shows a rigid thermoformed food container. Figure 1. PLA Manufacturing overview. These food containers have various valuable attributes. Macromol. Biosci. 2004, 4, 551–564 www.mbs-journal.de ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The Sustainability of NatureWorksTM Polylactide Polymers and IngeoTM Polylactide Fibers: an Update of the Future 553 Table 1. Business segments for products based on NatureWorksTM PLA. Business segment Commercially available applications Rigid thermoforms – Clear fresh fruit and vegetable clamshells – Deli meat trays – Opaque dairy (yogurt) containers – Bakery, fresh herb and candy containers – Consumer displays & electronics packaging – Disposable articles and cold drink cups Biaxially-oriented – Candy twist and flow wrap films – Envelope and display carton windows – Lamination film Figure 3. ‘‘Disposable’’ cold drink cups. – Product (gift basket) overwrap – Lidding stock – Die cut labels . Figure 4 depicts transparent bread bag windows made – Floral wrap from PLA. Some typical valuable attributes of this – Tapes application include the low barrier for moisture – so the – Shrink sleeves warm bread can be put in the bag and the moisture leaves – Stand-up pouches through the film and high gloss and clarity – so customers – Cake mix, cereal and bread bags Bottles – Short shelf-life milk can view the product. Again, the product is made of – Edible oils renewable resources and can be composted at the end of – Bottled water its useful life.