BioCycle May 2006, Vol. 47, No. 5, p. 50
A leading manufacturer of carpet and textile examines in-vessel composting of PLA feedstocks.
Connie Hensler

THERE has been a recent surge in development of commercial biobased plastics including PLA (polylactic acid), PHB (polyhydroxybutyrate), PHV (polyhydroxyvalerate), starch-based polymers, and soy based polymers. The U.S. Department of Agriculture’s establishment of the Federal Biobased Products Purchasing Program in January 2005 certainly added extra incentives to this new direction. The goal is to stop using petroleum and to start using agricultural products as raw materials for plastics manufacturing – and the industry is responding positively.
One of the added values of these developments is that many bio-based polymers are now biodegradable. Early versions of some so-called “biodegradable” plastics didn’t actually biodegrade, but simply dissolved or fragmented into smaller pieces of plastic. The biobased polymers being introduced today are biodegradable back to elemental carbon. The key to taking advantage of these properties – and to close the loop completely – is to get the materials back into the carbon cycle. New disposal methods must be developed to address this important challenge.
One company trying to close that loop is Interface, Inc., a leading global manufacturer of carpet and textile products. Interface is incorporating the biobased polymer PLA, from Cargill Dow, into its products in an effort to reduce its environmental footprint and become more environmentally sustainable. Interface is also looking to close the loop by composting the products at the end of their useful lives.
PLA is currently used in Interface’s modular carpets and commercial fabrics. The fibers, marketed by Cargill Dow under the Ingeo™ fiber brand name, are used to produce the fabrics. Interface markets the fabrics as part of its Terratex® brand. “Panel fabrics manufactured with the PLA were first introduced with furniture manufacturers Herman Miller, Allsteel and Teknion, and fabric distributors Carnegie and Designtex,” says Paul Bennotti, Director of Marketing Strategy at Interface Fabrics. “More recently, Interface Fabrics has brought PLA panel products to the marketplace through mid-market customers, including companies such as Davies and IntraSpec. In addition to their renewable resource content, the fabrics must also meet Interface Fabrics’ Dye and Chemical Protocol – a rigorous, systematic method of evaluating all the ingredients in all the materials used to manufacture the fabrics.”
CLOSING THE LOOP WITH COMPOSTING
As part of its initiatives to “close the loop completely” with its panel and upholstery fabrics for commercial interiors, Interface is working with its customer, Herman Miller, Inc. (HMI), to keep cutting room scraps out of the landfill. With assistance from the Sustainable Research Group (SRG), the two companies are developing a method for composting the fabric scraps along with waste sawdust from the furniture manufacturing process. With input from Michigan State University Extension (MSUE) and the Michigan Department of Environmental Quality (MDEQ), Willie Beattie and the Design For Environment team at HMI were instrumental in developing baseline requirements. Mike Bronkema of Shady Side Farm in Holland, Michigan, who already has been composting sawdust from HMI, is providing straw, poultry manure and his pilot scale rotary-drum compost vessel for the development of a commercial PLA composting process. Interface has initiated the development of an in-vessel process to biodegrade PLA fabric quickly under thermophilic conditions.
Since the fabric comes from the cutting room of a chair manufacturing facility, we chose 8-inch by 8-inch squares for the composting trials. One of the optimum feedstock ratios used was as follows (percentage on a wet weight basis): Pullet manure – 72%; Industrial sawdust from furniture manufacture – 24%; Straw – 1%; Fabric squares – 3%.
A number of parameters were measured – temperature, moisture and pH – during the in-vessel stage; and temperature, moisture, pH, stability (Solvita Compost Maturity Index), total organic carbon, total nitrogen, nitrification (ammonia, nitrites, nitrates), C:N ratio, phytotoxicity, and Michigan Type B chemicals during the curing phase. Other parameters measured included bulk density, foreign matter, specific conductance, water holding capacity, free carbonates (CO3), phosphorus, sodium, potassium, calcium, magnesium, chloride, and sulfate. The feedstocks remained in the vessel for eight days. The curing time tested was 84 days, but the compost was stable (based on Solvita test) at day 29.
To ensure that the commercial compost is free of any toxic chemicals, Interface has set up a monitoring program for its products and processes, beginning with the yarn handling stage. The PLA yarns are dyed and treated using Interface Fabrics’ Dye and Chemical Protocol (noted above), which helps avoid the incorporation of any toxic materials into the finished fabric. Working with SRG, the fabric and the finished compost are tested for the presence of any of Michigan’s 225 “Type B” chemicals. Furthermore, testing of the compost is conducted to ensure that none of the listed chemicals are produced in the decomposition process. In addition to eliminating landfill waste, Interface continues to evaluate the market possibilities for compost derived from PLA. Initial results have shown the compost to be suitable as a high quality soil amendment.
PRODUCT RECOVERY
So far, the results have been promising for developing a viable composting process for reclaimed PLA products. Rapid composting has been accomplished with little modification to the standard process, which is still being studied and optimized. Conventional compost parameters were scientifically monitored to assess the effect of the fabric on the efficiency of the composting process and the quality of the final compost product. Verification of the complete degradation of the polymer and evaluation of alternative raw materials, including food residuals, are important parts of the development process.
Developing a means for composting from a point source supply, like a furniture manufacturer, is the easy part. Setting up an infrastructure to recover postconsumer biodegradable plastics is a greater challenge. Product reclamation programs designed to return used polymers to recycling and composting sites are few. Interface Fabrics has a program in place called ReSKU™ to recover fabric waste and Interface’s flooring businesses feature the ReEntry® program that takes back postconsumer carpet (regardless of manufacturer) for recycling. Both programs are focused on delivering the highest possible level of reuse for reclaimed products and both are being expanded to incorporate the recovery of biobased polymer products. Interface, though, is well aware of the major hurdles, including widespread issues of collection and educational gaps as well as the need for consistency of polymer manufacturing processes and a consistent market availability of biobased feedstocks. All of these things will be necessary for this technology to become fully integrated into the current structure of the commercial composting industry.
“Interface continues to develop the best combination of inputs and conditions to optimize PLA fabric composting and evaluate various feedstocks,” explains Bill Foley, market development director for Interface Fabrics. “Based on research, we believe it is worth pursuing the idea of alternative carbon sources including food waste.” Developing systems that make economic sense and reclassifying materials that were once considered industrial wastes to compost feedstocks will reduce the strain on landfills and increase the production of quality compost.
Connie Hensler is Director of Sustainable Research at Interface Research & Development in LaGrange, Georgia. For more information on Interface’s biobased product initiatives and product reclamation programs, visit: www.interfacesustainability.com/biobased.html; www.interfacesustainability.com/redesign.html; and www.resku.net.