In collaboration with professor Jinwen Zhang of Washington State University (WSU) in Pullman, Liu and ARS-WSU colleagues developed a biodegradable thermoplastic (meaning plastic that becomes soft when heated) that could be used in disposable food containers.
The bioplastic is manufactured from both sugarbeet pulp and a bio-degradable polymer called polylactic acid, or PLA, using a twin screw extruder. PLA is a commercially available polymer derived from the sugars in corn, sugarbeet, sugarcane, switchgrass and other plants/renewable feedstocks. Extrusion is a cost-effective manufacturing process that is popularly used in large-scale production of food, plastics and composite materials. Many biopolymers and their composite materials with petroleum-based polymers also can be extruded.
The scientists showed that up to 50% sugarbeet pulp can be incorporated with PLA, and the resulting thermoplastic composites retain mechanical properties similar to those of polystyrene and polypropylene — the compounds used to make white, spongy food packages. The new thermoplastic is cost competitive with commonly used petrochemical plastics. The study was published in Industrial & Engineering Chemistry Research in 2008.
ARS-WSU researchers also developed other beet pulp materials. Under extrusion compounding, sugarbeet pulp was turned into a thermoplastic-like material with the assistance of water and/or glycerol. This material can be subsequently processed by extrusion or injection molding to produce neat (meaning pure) sugarbeet pulp products.
The resulting thermoplastic sugarbeet pulp possesses mechanical properties that are similar to those of low-density polyethylene — the commonly produced materials used for opaque plastic containers, bags and film coverings. It can also be blended with PLA and other biodegradable polymers for enhanced water resistance. The composite could function as a lightweight-bearing material comprising up to 98% sugarbeet pulp.
This continued development of the sugarbeet pulp plastic (for example, as yogurt cups, cottage cheese tubs or other thin, opaque plastic containers) could benefit sugarbeet growers and beet sugar processors. (More findings were reported in the Journal of Polymers and the Environment and Industrial Engineering Chemistry Research in 2011.)
The new composite plastics containing sugarbeet pulp are cost competitive when compared to materials that are made solely of PLA, according to Liu and Hotchkiss. “The technology is promising and provides a ‘green’ material for food packaging,” says Hotchkiss. — Rosalie Marion Bliss, ARS Information Staff