Polylactide (PLA) is a versatile polymer produced by Cargill Dow. The Minnesota-based company says that it is the first supplier to offer a family of commercially available polymers derived 100percent from annually renewable resources with the cost and performance to compete with petroleum-based packaging materials and fibres.
The company has achieved this breakthrough by applying its novel technology to the processing of natural plant sugars to create a proprietary polylactide polymer, which is marketed under the NatureWorks PLA and Ingeo fibre brand names.
PLA is made from lactic acid, which in turn is made from dextrose by fermentation. Dextrose is made from cornstarch and cornstarch is made from carbon dioxide and water.
According to Cargill Dow, the amount of corn needed to produce 1kg of PLA depends on several variables including average starch content and the respective yields of starch/dextrose conversion in the corn wet mill. Also important is the dextrose/lactic acid conversion during fermentation and lactic acid/lactide/polymer conversion during polymerisation.
On average, however, the company says that approximately 2.5kg of corn with a moisture content of 15percent is required to produce one kilogramme of PLA. It is worth noting that the remaining 1.5kg is not all waste. Part of it is simply water, part of it ends up in other corn wet mill products such as germ oil, corn gluten meal and corn gluten feed, and part compensates for the yield losses in the different processes.
Today Cargill Dow uses dextrose, a natural sugar derived from the starch in kernels of corn or maize, as the primary raw material for PLA. However, other agricultural raw materials, such as rice, sugar beets, sugar cane, wheat and sweet potatoes, can also serve as sources for the starch or sugars used to make PLA. So the future the polymer could be made from the dominant locally available crops.
The company's latest innovation is a compostible drinking water bottle made for BIOTA Brands of America which supplies Colorado spring water (Fig.1). For this project, Cargill Dow worked closely with both BIOTA and Husky, a leading supplier of bottle preform production equipment and services. The result is a bottle that is compatible with all municipal and industrial composting facilities.
Husky worked hand-in-hand with these companies to develop what we feel is a breakthrough application Mike Urquhart, Husky's vice president, PET, said. One of our core values is proactive environmental responsibilitywhich is why we're thrilled to be involved in such a project. This is a great example of how it's possible to combine commercial success with environmental sustainability." Husky supplied BITA with the preform production equipment -- a 24-cavity HyPET 120 system that is currently producing preforms for 12 ouncehalf litre and one litre water bottles (Fig.2). Husky's HyPET machine offers faster cyclesreduced mold wearbetter repeatabilitylower acetaldehyde generation and better energy efficiencyleading to higher output-per-capital and high-quality preforms. Looking aheadCargill Dow is also working to develop technologies to facilitate the use of lignocellulosic biomass feedstockssuch as corn stoverwheat and rice strawand bagasse.
When it reaches full capacitythe company's production facility in BlairNebraskaUSAwill produce 136080t/y of PLA using 340200t of corn as raw material.
Chinese hail corn process
Meanwhile DuPont's first biologically derived polymerSoronahas been recognised by the China State Intellectual Property Office and China Central Television as amost visionary innovation' at a recent award ceremony. Fabrics made with Sorona for active wearapparel and sportswear are commercially available through Chinese fibre and fabric manufacturers.
The judging panel commentedChemical fibres can now be made with natural ingredients. This will reduce the dependency of traditional chemical fibre products on oil resources. It will be another bold attempt in the innovative use of renewable resources. Crops and plants are becoming the most reliable backup power for the resource consumption of humans and will serve to further protect the environment.
According to DuPontSorona offers a number of beneficial qualities as a fabricincluding exceptional softnesseasy careand UV- and chlorine-resistance. Mills and manufacturers appreciate its easy dyeability and handling. In additionproducts made with Sorona are naturally stain resistantrequiring no additional chemical treatment to prevent stains. It can be used in a variety of applications including soft floor coveringtextiles for apparel and interiorsengineering resins and packaging.
DuPont scientists recently developed a way to make Bio-PDOthe key Sorona ingredientfrom corn using a new biological process that requires over 40percent less total energy than the traditional petrochemical feedstock. It will be commercially available in 2006.