PLA Recycling Chemically
PLA Recycling Chemically recycling post-consumer PLA A research project at the University of Wisconsin-Stevens Point over the past two years has instituted what is believed to be the first concerted effort in the USA to collect and recycle post-consumer PLA. Today, PLA is technically recyclable but infrastructure is not in place for recycling post-consumer PLA. The Wisconsin Institute for Sustainable Technology (WIST) at UW-Stevens Point inaugurated a plan to create the recycling infrastructure on a small scale to determine the practical feasibility of chemical recycling of post-consumer PLA. UW-Stevens Point dining services began buying food service ware of PLA plastic in 2009 as an initiative in sustainability. However, no system for collecting and composting or recycling the material was in place at the university. In fact, the switch to PLA from the polystyrene foam products the university had been using had been intended in part as a way to kick-start a compostability service on campus. But that didn’t happen, either. The FRESH Project In an effort to more fully take advantage of the PLA attributes, WIST created a research project to collect and recycle post-consumer PLA. A graduate student in soil and waste resources, Waneta Kratz, was recruited to take on the project in conjunction with her graduate research. The project had several aspects. The primary research goal was to determine how much processing – rinsing and washing – was required in order to successfully recycle post-consumer PLA, turning waste back into lactic acid from which new, non-food products again could be made. A secondary goal was to test awareness on campus about PLA and its sustainability attributes, and to learn to what degree a publicity campaign could influence knowledge about PLA and improve recycling success. As part of the public relations aspect, Kratz hired several assistants to create a campaign. The campaign was called the FRESH project, for Focused Research Effort for Sustainable Habits. It is believed to be the first such recycling campaign at any university in the U.S. and the first attempt at recycling post-consumer PLA. Publicity included informational kiosks and displays, surveys, social media and poster campaigns to educate the campus community about PLA environmental benefits and end-of-useful-life options for the bioplastics. Additional recycling containers specifically labeled for PLA food service ware disposal were placed in dining areas for source separation of the PLA waste where consumers were most likely to be using and disposing of the items. FRESH project student employees collected material from the recycling bins and sorted the material to separate PLA from other materials. Although the bins were clearly labeled, there was inevitably other material deposited. The postconsumer PLA was washed, dried and stored before being transported to a chemicals’ re-processor elsewhere in the state that chemically recycles post-industrial and off-grade PLA resin, but had not recycled post-consumer PLA. Level Time, min Temp, °C NaOH, wt % Surfactant, wt % Low
PLA Recycling by Paul Fowler Waneta Kratz Ron Tschida Wisconsin Institute for Sustainable Technology University of Wisconsin-Stevens Point Stevens Point, Wisconsin, USA Chemical recycling analysis Recycling post-consumer PLA presents an additional problem in that it is contaminated by food. Prior to the WIST research no studies had been done nor any procedures established in the USA for cleaning post-consumer PLA for chemical recycling. The WIST project designed two different rinsing protocols to test whether a light rinse or more intensive washing was required for effective chemical recycling. The procedure for an intensive wash was adapted from a standard washing procedure [1] for post-consumer PET containers such as beverage bottles. A low-level treatment was designed by Kratz for the FRESH project. (See washing parameters summarized in Table 1, adapted from Kratz thesis, unpublished, used with permission.) Chemical recycling of PLA is done by hydrolysis, with pressure and heat added to speed the process. To test the rinse processing methods, laboratory hydrolysis in sealed flasks was performed on PLA that had received a high-level treatment, PLA receiving a low-level treatment, and on preconsumer PLA as a control. The PLA products tested were clear plastic cups made from NatureWorks Ingeo. Total acid recovery in all treatments and controls exceeded the client specification and ranged from 89.5 to 96.0% for total acid (see Table 2, adapted from Kratz thesis, unpublished, used with permission). The difference in acid recovery was insignificant between samples receiving a low-level treatment and those receiving the more intensive treatment. The results indicated that even a low level rinse of post-consumer PLA is adequate for chemical recycling. The intensive wash procedures used for PET may not be necessary to chemically recycle postconsumer PLA. Further research is needed on this topic, and experiments on a larger scale would be useful toward developing practical infrastructure. Meanwhile the FRESH project is ongoing at UW-Stevens Point. [1] Chariyachotilert, C., Selke, S., Auras, R.A., and Joshi, S. 2012. Assessment of the properties of poly(L-lactic Acid) sheets produced with differing amounts of post-consumer recycled poly(L-lactic Acid). Journal of Plastic Film and Sheeting 28: 314–335. Recovery through chemical recycling was evaluated in terms of the amount of free acid and total acid in the hydrolyzed lactic acid product. There is currently no industry standard published for successful lactic acid recovery. However, a potential client had specified that recovered material should contain 68.5-74.5% free acid and 80-91% total acid. WIST used those numbers for comparison purposes. Treatment Sample Starting mass (g) Recovery (g) Recovery % Recovery Average % Preconsumer PLA 1 2 3 113.59 113.60 112.24 108.57 109.42 106.91 95.58 96.32 95.25 4 113.60 103.13 90.79 Low-level 5 113.60 105.10 92.52 6 113.60 105.32 92.71 High-level 1 8 113.62 104.19 91.71 7 113.60 101.84 89.64 9 113.62 102.61 90.31 95.71 92.01 90.55 Table 2. Recovery of lactic acid product from chemical recycling of polylactic acid (PLA) cups. Lowlevel indicates FRESH wash only; high-level indicates adapted industrial PET recycling wash [1] bioplastics MAGAZINE [03/13] Vol. 8 53
