|Rice Waste Conversion to Biodegradable Plastics - 2010
Project Leader and Principal Investigators
Joseph Greene,professor, Dept of Mechanical Engineering & Manufacturing Technology, CSU Chico
A project by scientists at Chico State University continued work on
converting rice straw and hulls into biodegradable plastics.
Using selective fermentation bacteria, the sugars in plants can be converted into lactic acid and then polymerized into the most common form of biodegradable plastic called polylactic acid (PLA). An efficient and economical method of doing so would bode well for an environmentally sound and profitable use for rice harvesting byproducts such as straw and hulls.
Hulls and straw from M-206 rice were collected from a local farmer for this research. Scientists significantly improved the conversion of rice hulls into lactic acid from 10% in previous years to 40% in 2010. Approximately 40% of the rice straw was converted to glucose. The maximum amount of hulls or straw that can be converted to glucose and then lactic acid is 40%, the amount of available cellulose.
The improvement in conversion of rice hulls to lactic acid was due primarily to improved sulfuric acid and sodium hydroxide treatments. Improved pretreatment methods included isolating rice hulls with acid treatments, heating waste materials in an autoclave, and then treating the effluent with enzymes for increased conversion of rice waste to glucose and production of lactic acid using one bacterium.
The conversion of glucose to lactic acid from hulls or straw ranged between 95% and 100%. The lactic acid was then purified with an ion-exchange process and then polymerized into PLA. Improved purification and polymerization processes for straw included grinding and pulverizing in a mortar and a “super critical” carbon dioxide process.
Although the bacterial conversion of rice waste to glucose and lactic acid proved technically feasible, faster conversion times are necessary for it to become economically feasible. Further research will focus on low-cost materials and faster conversion methods.