DuPont is poised to switch production of a key polymer feedstock from a petrochemical to a maize-based process as part of its strategy to derive 25% of revenues from non-depletable resources by 2010.
If the switch goes ahead, it will become the second US chemical company to mass produce a "bio-polymer" for a range of products.
Since early last year, its rival Dow, in partnership with agricultural commodities company Cargill, has used maize to produce the biopolymer polylactic acid (PLA) for its Ingeo fibre range and NatureWorks packaging materials (ENDS Report 338, pp 33-34 ). Japanese electronics manufacturers such as Sony and Fujitsu have also used PLA to make components for products such as Walkmans and laptop computers (ENDS Report 336, p 36 ).
PLA could soon be joined by a second biopolymer, polytrimethylene terephthalate (PTT), which is also aimed at the carpeting, packaging and clothing sectors. Under the trade name Sorona, DuPont already makes PTT from petrochemical feedstock at its Kinston site in North Carolina, but intends to start full-scale production of a version derived from maize in the next few months.
The key building block - 1,3 propanediol (PDO) - is already produced from maize in a pilot facility at Tate & Lyle's works in Decatur, Illinois, in the heart of the US corn belt. The process, developed by DuPont and biotechnology company Genencor, produces PDO using a genetically modified version of the micro organism E coli to convert dextrose sugar derived from the maize.
Sorona is the first product developed by DuPont's bio-based materials business and is described as "one of the most significant new polymers developed by the company in recent years." The company says it is the first in what will become a family of materials derived from crops such as maize.
Both Cargill Dow and DuPont use claims of reduced environmental impact in their marketing campaigns. Cargill Dow says that PLA represents a "giant step towards sustainability" and that its manufacture results in lower greenhouse gas emissions than those from petrochemical polymers.
Similarly, DuPont claims that the maize-based version of PTT has environmental advantages because it "uses less energy, reduces emissions and employs renewable resources compared to traditional petrochemical processes." Like PLA, PTT is technically recyclable.
Not surprisingly, neither company highlights the environmental impacts associated with intensive agriculture. Nor do they flag up the contribution of landfilled biopolymers to the generation of methane - a powerful greenhouse gas.
Although life-cycle assessments have been published comparing the performance of PLA and conventional plastics on certain issues such as fossil fuel and water consumption, there does not appear to be a study which takes all the relevant environmental issues into account.
ENDS asked DuPont if it had conducted LCAs comparing maize-derived PTT with the petrochemical-based version or with other plastics, but got no response.
Despite the green marketing, it is clear that the development of biopolymers in the US is being driven as much by concern about dependence on imported oil as any real or perceived environmental benefits.
In October, DuPont announced a partnership with the US Government's National Renewable Energy Laboratory to work towards building "the world's first" integrated bio-refinery. The facility would produce biofuels such as ethanol and "value-added chemicals" such as PDO from maize or other commodity crops.
"New technologies that produce fuels, chemicals and energy from biomass will allow the US to reduce its reliance on foreign sources of fossil fuels, while creating new markets for domestic grains and crop residues," said Michael Pacheco, director of the NREL's National Bioenergy Centre.
The partnership is part of the larger $38 million DuPont-led consortium known as the integrated corn-based bioproducts refinery project, which was awarded $19 million in match funding from the US Energy Department last year to design and demonstrate the feasibility of such a facility. As well as the NREL, the consortium includes genomic technology company Diversa, agricultural equipment manufacturer Deere & Co and Michigan State University.
However, the first signs are emerging in the US of a more sophisticated analysis of the environmental impacts of plant-derived products.
Earlier this year, the University of Oklahoma organised a workshop on assessing the sustainability of bio-based products. Its aim was to "begin building a consensus about appropriate methods for assessing the impacts and sustainability of products, such as fuels and chemicals, made from biomass."
A review of the workshop warns that while the use of biomass for energy and bio-based products "is often touted as a means of achieving greater sustainability...this is by no means a universal view and questions have been raised about the benefits of bio-based products."1Focusing on what happens to bio-based products when they become waste, Professor Ramani Narayan of Michigan State University noted that landfilling is problematic due to methane emissions. While "biodegradability is an advantage for products that are directly distributed in the environment, such as agricultural films or chainsaw lubricants, bio-based products cannot always claim biodegradability and compostability, nor environmental superiority."
Workshop participants agreed that assessment over the full life cycle is crucial in assessing the impact of bio-based products - as it is for all products. Sustainability indicators could include land use, soil conservation and nutrient cycles, as well as established indicators such as greenhouse gas emissions and energy flows.
To help establish a common assessment methodology, the workshop agreed that a common case study should be conducted using different assessment techniques to identify the critical sustainability issues.
If this is achieved, important questions could be asked such as: what kind of crops and which products make best use of the limited land available for agriculture and present the highest environmental, social and economic benefits when compared to conventional products?
Another issue for companies producing materials derived from commodity crops such as maize is the hostility of European consumers towards genetically modified crops. Cargill Dow argues that processed PLA pellets do not contain GM DNA - and it has also devised a system which allows customers to request the use of non-GM maize. DuPont failed to respond to ENDS' questions on the issue.