THE KEY PRINCIPLES GOVERNING MATERIAL FLOWS IN CRADLE TO CRADLE DESIGN WERE FIRST SYSTEMATICALLY OUTLINED IN 1993 THE "INTELLIGENT PRODUCT SYSTEM" (IPS), DEVELOPED AND ARTICULATED BY MICHAEL BRAUNGART AND HIS COLLEAGUES AT EPEA. THE DEVELOPMENT OF THIS MODEL DRAWS ON ADVANCES IN MANY RELATED FIELDS OF SCIENCE, INCLUDING INDUSTRIAL ECOLOGY, TOXICOLOGY, CHEMISTRY, MATERIALS SCIENCE, AND ENVIRONMENTAL SCIENCE.
Just as in natural systems one organism's 'waste' becomes nutrients for another, the cradle-to-cradle model utilizes effective nutrient cycles in the realm of human industry. The cradle-to-cradle model recognizes two metabolisms within which materials flow as healthy nutrients.
Biological Metabolism
Materials that flow optimally through the biological metabolism are called biological nutrients (e.g. the nitrogen cycle). As defined for cradle-to-cradle products, biological nutrients are biodegradable (or otherwise naturally degradable) materials posing no immediate or eventual hazard to living systems that can be used for human purposes and be safely returned to the environment to feed ecological processes.
Products conceived as biological nutrients are called products of consumption. They are designed for safe and complete return to the environment to become nutrients for healthy living systems.
Example: Upholstery Fabric
Upholstery fabrics, which wear out with use, can be comprised of biological nutrients that can be returned to ecosystems after use. Climatex? Lifecycle? fabric is an example of this type of product. The fabric is a blend of pesticide-residue-free wool and organically grown ramie, dyed and processed entirely with non-toxic chemicals. All of its product and process inputs were defined and selected for their human and ecological safety within the context of a biological metabolism. Currently, the fabric trimmings (process "waste") is made into felt and used by garden clubs as mulch for growing fruit and vegetables, returning the textile's biological nutrients to the soil, to feed new growth.
The return of Climatex Lifecycle's nutrients to the biological metabolism depends on the fabric's appropriate use and post-use handling. The application of the fabric to furniture must facilitate its ultimate, clean separation from materials that cannot function as biological nutrients, such as synthetic foams. Substances used to treat and clean the fabric also should be compatible with the biological metabolism. Finally, the post-use cycling of the fabric's nutrients probably will rely on a well-run composting system.
Technical Metabolism
A technical nutrient is a material, frequently synthetic or mineral, that remains safely in a closed-loop system of manufacture, recovery, and reuse (the technical metabolism), maintaining its highest value through many product life cycles.
Technical nutrients are used in products of service, which are durable goods that render a service to customers. The product is used by the customer but owned by the manufacturer, either formally or in effect. The product of service strategy is mutually beneficial to the manufacturer and the customer. The manufacturer maintains ownership of valuable material assets for continual reuse while customers receive the service of the product without assuming its material liability (an "eco-lease"). The manufacturer or commercial representative of the product also fosters long-term relationships with returning customers through many product life cycles.
Example: Batteries
The well-developed system for lead-acid battery recovery provides a model for the development of technical metabolisms through the product of service strategy. Car batteries are valuable to customers for storing and providing electricity by design, but incidentally pose a risk to customers and the environment as a result of the hazardous materials that they contain. To reduce the risk of releasing hazardous materials, economic incentives have been built in to encourage the return of old batteries to authorized locations with credit towards a new battery. Old batteries are sent to secondary lead smelters where the material value of the lead, plastic and the acid is recovered for use in new batteries. Over 95% of all lead and plastic from recovered car batteries is recycled, making them the most recycled consumer product in the U.S.
Because technical metabolisms exist within the natural world and material releases to ecosystems are inevitable, technical nutrients ideally should pose little or no hazard to the biological metabolism. Lead is universally recognized as being so toxic that even minor releases damage human and ecological health. For car batteries, since there are safer alternatives (e.g., lithium; zinc) that provide comparable performance, a cradle-to-cradle strategy suggests replacing lead with these alternative materials and optimizing the technical metabolism for material recovery.
