ARS | Publication request: Green composites of poly(lactic acid) and sugar beet pulp. II. Structural and mechanical property analysis.

Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2006
Publication Date: December 1, 2007
Citation: Liu, L.S., Finkenstadt, V.L., Liu, C., Coffin, D.R., Willett, J.L., Fishman, M., Hicks, K.B. 2007. Green composites of poly(lactic acid) and sugar beet pulp. II. Structural and mechanical property analysis. Journal of Biobased Materials and Bioenergy. 1:323-330.

Interpretive Summary: Polymer composite materials may be used in non-durable and short-term applications. Green composite use agricultural-based polymers and biodegradable plant-based fillers. Poly(lactic acid )(PLA) is a hydrophobic polymer prepared from renewable agriculture-based feed stocks which are fermented to lactic acid and then polymerized. PLA is biodegradable in soil, compost or water, and the degradation products of PLA are non-toxic to the environment. PLA has comparable mechanical properties to petroleum-based plastics, but is more expensive. The use of renewable and biodegradable fillers is desirable to provide cost-competitive polymer composites. Sugar beet (Beta vulgaris) is grown as a commercial crop and is the source of about one-third of the world supply of sugar. The U.S. sugar beet industry is estimated at $1.27 billion annually and over 400 million metric tons of wet pulp is generated each year. Sugar beet pulp (SBP) is usually used as low value animal feed or disposed of at additional cost. We report on the mechanical properties of PLA-SBP composite materials.

Technical Abstract: Poly(lactic acid) and sugar beet pulp were compounded by twin-screw extrusion and injection molded into composite forms. Specific mechanical energy decreased with the addition of SBP during processing. PLA-SBP composites retained more tensile strength than expected based on the Nicolais-Narkis model especially at high levels of SBP suggesting adhesion between SBP and PLA. The thermal characteristics of PLA were not affected by thermo-mechanical processing or by the incorporation of SBP up to 30% weight basis. PLA and PLA-SBP composites had similar tensile properties to other thermoplastic resins and may be used as a cost-competitive replacement.